Homework answers / question archive / Need complete within 5 to 6 hours DUE TODAY WILL PROVIDE STUDY GUIDES Directions : In this unit, you learned that the characteristics of a population at a given time can be represented graphically using birth and death rate data, among many other parameters

Need complete within 5 to 6 hours DUE TODAY WILL PROVIDE STUDY GUIDES Directions : In this unit, you learned that the characteristics of a population at a given time can be represented graphically using birth and death rate data, among many other parameters

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Need complete within 5 to 6 hours

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WILL PROVIDE STUDY GUIDES

Directions : In this unit, you learned that the characteristics of a population at a given time can be represented graphically using birth and death rate data, among many other parameters. In Part I of this activity, you will work with a simple data set to create a human survivorship curve and answer questions about the results and the data itself. In Part II, you will work with interactive age structure diagrams in an online simulator to analyze population growth trends for both China and the United States. For an example of an age structure diagram, see the presentations for the Unit II Lesson.

Name: Population Ecology Activity Introduction In Unit II, you learned that the characteristics of a population at a given time can be represented graphically using birth and death rate data, among many other parameters. In Part I of this activity, you will work with a simple data set to create a human survivorship curve and answer questions about the results and the data itself. In Part II, you will work with interactive age structure diagrams (see unit lesson part II, Slide 22, Figure 3 for an example) in an online simulator to analyze population growth trends for both China and the United States. Part I: Constructing a Survivorship Curve Survivorship curves are created by estimating the age of an organism at the time of its death and the number of deaths within each age bracket inside of a given population of organisms. Once constructed, survivorship curves create a general picture of the life history of that organism. The two biggest influences on the shape of a survivorship curve are predation and disease. There are three general survivorship curve types: Type III: Indicates a high mortality rate of the young. Type II: Indicates a constant mortality rate throughout the life span of the organism. Type I: Reflects a low mortality rate among the young with individuals dying at the end of their life span. Activity In the United States, the current average life span of a human female is about 83 years of age, and the average life span of a human male is about 77 years. For this activity, we will assume that the average life span is 80 years of age. For Table 2a below, age brackets in five-year increments were created. Age data was collected randomly from 100 newspaper obituaries from around the United States and entered into the age bracket Table 2a. Using this data, you will complete the survivorship information in Table 2b and construct a survivorship curve using an Excel spreadsheet table. You will create a graph from the data and import it later in this assignment. Completing the Survivorship Data Table Procedure (Table 2b) (10 points) 1. Enter the data from “Number of Deaths” column for each age bracket in Table 2a into the “Number of Deaths” column in Table 2b. 2. To calculate the data for the “Number of Survivors” column in Table 2b, start by subtracting the number of deaths in age bracket 1-5 from the number of survivors in age bracket 0. This number will be 100, of course. Continue subtracting the number of deaths in each age bracket from the number of survivors in the preceding age bracket. (Hint: The number of survivors will be 100 until you get to age bracket 21-25, where you will subtract 2, making the number for that bracket 98. Continue the process through the last age bracket. The number of survivors in age bracket 91-100 should be 0). 3. Create a line graph using Microsoft Excel and the data from Table 2b. The X-axis should reflect the Percent Life Span (%) and the Y-axis data should reflect the number of survivors data that you calculated. Table 2a Age Bracket Number of Deaths 0 0 1-5 0 6-10 0 11-15 0 16-20 0 21-25 2 26-30 0 31-35 6 36-40 4 41-45 0 46-50 2 51-55 2 56-60 8 61-65 2 66-70 8 71-75 10 76-80 16 81-85 8 86-90 22 91-100 10 Total 100 Table 2b Age Bracket (Age of Death) 0 Percent of Life Span (%) Number of Deaths (from Table 2a) 0 0 1-5 3.1 0 6-10 9.4 0 11-15 16 0 16-20 22 0 21-25 28 2 26-30 34 31-35 41 36-40 47 41-45 53 46-50 59 51-55 66 56-60 72 61-65 78 66-70 84 71-75 91 76-80 97 81-85 100 86-90 100 91-100 100 Number of Survivors 100 Complete The Graph (12 points) Right click on the graph below, choose either edit data or edit data→edit data in Excel, and complete using the Number of Survivors data from table 2b. The graph will update automatically as data is entered. Simply close the data entry window once complete. Number of Survivors 1.2 Number of Survivors 1 0.8 0.6 0.4 0.2 0 0 3.1 9.4 16 22 28 34 41 47 53 59 66 72 78 84 91 97 100 100 100 % of Life Span (Questions: 6pts each) 1. What type of survivorship curve do modern humans possess? Resize as needed. 2. Would you expect that there is a difference in the survivorship of men and women? Explain why, or why not? Resize as needed. 3. Why do humans exhibit this type of survivorship curve? What factors are involved? Resize as needed. 4. Why might obituaries be a poor source of data for determining a human survivorship curve? Resize as needed. 5. The data for this exercise was collected from the United States. Would you expect to see the same curve from data collected in a developing (i.e., under-developed) country? What might the differences be, if any? Resize as needed. Part II: Where To Go: Go to the Demographics Lab at Annenberg Learner: https://www.learner.org/courses/envsci/interactives/demographics/ Instructions Review the section on Age Structure, Population Growth, and Economic Development in the reading for Unit II. Familiarize yourself with the age structure diagrams and know what the general shapes represent (rapid growth, slow growth, stabilized growth, and negative growth) Open the Annenberg Demographics Lab page (click the OPEN SIMULATOR link). On the Annenberg Demographics Lab page, you will see a pyramid-shaped age structure diagram in the middle of your screen and a population curve to the left of your screen. At the top of the page, the “Lesson” may need to be changed to “Population Momentum” and the default “Country” should be “Nigeria: 182 M.” The population curve to the left is constructed with population (in millions) on the Y-axis and year on the X-axis. The black diamond denotes where the population is as of 2015. The age structure diagram in center screen is constructed with population (in millions) along the X-axis and age brackets along the Y-axis. The red bars to the right represent female individuals and blue bars represent males. Familiarize yourself with both the graph and the chart before you continue. Answer each questions in complete sentences in as much detail as possible. Activity and Questions China Instruction: Go to “Country,” and select “China: 1.36 B.” The gray “Vital Rates” box will show the birth rate (1.52 per woman) and death rate (1.05% per year) for the year 2015. (Questions: 6pts each) 6. Based on what you know about the different shapes of the age structure diagrams, what kind of growth is China’s population is experiencing? Resize as needed. 7. In 2015, which two age brackets have the highest number of individuals? Resize as needed. Instruction: Now click the green “Run” button, and watch the changes that happen through the year 2050 (the simulator will stop at 2050 automatically). 8. In 1979, China implemented the well-known One Child Policy in an effort to slow an exploding population. Looking at the population curve and the changes in the age structure diagram through 2050, what were the results of the policy? Did it work? How do you know? Resize as needed. Instruction: Click the green “Run” button again, and watch the changes that happen through the year 2100 (the simulator will stop at 2100 automatically). 9. If the One Child Policy is kept in place through 2100 and birth and death rates stay the same, how does the age structure of the population change? Why might this become a problem in an industrialized society? Resize as needed. Instruction: Click ”Reset” and then click the “Birth” tab, and click the “up 5%” button seven times to where the birth rate is about 2.12-2.15 per woman. Click apply, and run the simulator through the year 2200. 10. All other parameters being consistent what does the age structure diagram’s pattern tell us about China’s population if birth rates are raised to 2.15 per woman through the year 2200? Resize as needed. USA Instruction: Let’s change countries now. Go to “Country” at the top of the page, and click “USA: 321 M.” Click “Run” twice to cycle forward to the year 2100. 11. Given the current birth rate of 1.98 per woman in the U.S. and a 1.36% per year death rate, what kind of pattern do we see in the age structure diagram through the year 2100? Is our population declining or increasing? Is it generally stable? Resize as needed. Instruction: Click “Reset” and increase the birth rate by 5% to 2.08 per woman (Do not forget to click “Apply”). Run the simulator through 2100. 12. What does this slight change do to the U.S. population? Is it generally stable or unstable by 2100? Resize as needed. Instruction: Lastly, click on each country in the drop-down menu at the top of the page, and look at the 2015 default age structure diagram for each. 13. Which two countries’ default diagrams for 2015 best represent rapid population growth? Resize as needed. For Your Own Enrichment: Feel free to play with the simulator after you have finished this assignment. There are other parameters that can be adjusted to cause changes in the population age structure diagrams. The data that drives the simulator is mostly accurate, and it is fun to make adjustments and view the outcomes over time. Adobe Captivate Slide 1 Text Captions: Unit II: Part 1 Population Ecology: Population Growth and Regulation (Geralt, 2017) Page 1 of 29 Adobe Captivate Slide 2 Text Captions: Unit II: Population Ecology: Population Growth and Regulation Course Learning Outcome 2. Describe the various factors that affect population growth regulation. Unit Learning Outcomes 2.1 Examine the concept of population demography and the methods by which population demographics are researched and described. 2.2 Compare reproductive strategies and population growth models. 2.3 Identify and describe factors that limit population growth. (DeMers, 2012) (Tpsdave, 2017) (Hans, 2011) Page 2 of 29 Adobe Captivate Slide 3 Text Captions: Unit Lesson The European starling is a familiar bird across the United States and Canada. This ubiquitous avian’s success across its North American range might give the impression that its history on the continent goes back eons. However, in fact, European starlings are a relative newcomer. In the early 1890s, drug manufacturer, bird enthusiast, and Shakespeare fanatic, Eugene Scheiffelin, had the romantic idea of introducing the birds from the works of Shakespeare to Central Park in New York City. Scheiffelin introduced skylarks, bullfinches, nightingales, and chaffinches, all of which died in the harsh conditions of an unfamiliar habitat. However, one of Scheiffelin’s introductions was successful: the European starling (Zielinski, 2011). Over the course of two years, roughly 100 of these birds were released in Central Park. The birds not only survived but were able to reproduce and colonize areas outside of Central Park. Eventually, the birds found their way outside of the state of New York and moved North, South, and West. Today, these birds are estimated to number more than 200 million across North America (Zielinski, 2011). European starlings flock in massive numbers, damaging crops; spreading disease to native birds, livestock, and people; and out-competing native birds for food and nesting sites (OpenStax, 2017). In this unit, you will explore population ecology, which is the study of how populations of organisms change over time and space and the factors that influence those changes. Two of the most important pieces of information included in a population study are population size and population density. As you watch nature programs or listen to the news, you may hear statistics on a topic, such as depleting salmon populations, and you may ask yourself, “How do researchers know?” Mark and recapture is a commonly used technique to estimate the population size of a wide variety of organisms that are highly mobile. Other organisms such as plants and coral tend to stay in place so their populations can be studied via the use of a quadrat. These methods will be discussed in more detail (OpenStax, 2017). European starling (Sturnus vulgaris) (Kieschnick, 2015) The European starling is a medium-sized passerine bird in the starling family, Sturnidae. Page 3 of 29 Adobe Captivate Slide 4 Text Captions: Knowledge Check Population ecology is the study of how populations of organisms change over time and space and the factors that influence those changes. A) True B) False Page 4 of 29 Adobe Captivate Slide 5 Text Captions: Unit Lesson Single species are often distributed over an area in patterns that may be generally described as uniform, random, or clumped. There is a variety of reasons for these patterns, and as you read about these distributions, think about some of the organisms you are most familiar with and how they are distributed in the landscape. Demography is the statistical study of the changing characteristics of a population. You may already be familiar with this word as it relates to human sociology. However, it can apply to any population of organisms. Some of the commonly collected demographic data can include population characteristics such as birth rates, death rates, and life expectancies. This type of data can be used to predict the growth or decline of a population or how to best manage a population. Life tables and survivorship curves can be constructed to visualize population structure by age and determine the likelihood of mortality by a given age. Life history information may include how that organism obtains and uses resources, how it endures the environmental conditions of its habitat, and how it reproduces. An organism’s energy budget is how that organism manages its energy intake in order to maintain its metabolism, reproduce, feed and care for its young, and store energy (OpenStax, 2017). Population ecologists use mathematical models to describe population growth and predict future changes in a population of organisms. Two very common growth curves show us how organisms reproduce in the presence of unlimited or limited resources. A J-shaped curve demonstrates what happens to a population when resources are unlimited. This is known as exponential growth. When resources are finite and competition for those resources results in slowed or zero population growth, an S-shaped curve is the result. This is known as logistic growth. While useful, these two growth pattern models are simplified pictures of population growth changes actually seen in nature. There are numerous factors controlling the ebb and flow of population growth. In nature, population growth can be controlled in numerous ways. These controls are broadly divided into two categories, density-dependent and density-independent factors. Density-dependent factors are usually biological in nature and include things such as diseases (e.g., bacteria, viruses, parasites), competition among species (both inter- and intra-specific), or the build-up of biologic waste. When a given space is densely populated, diseases are easily and more rapidly transmitted from one individual species to another as opposed to individual species being spaced farther apart and interacting with one another less frequently. Crowding can also increase stress and lower an individual’s reproductive capability (OpenStax, 2017). (Geralt, 2017) The life history of an organism is a description of how that organism maintains and reproduces itself from its birth until its death. Page 5 of 29 Adobe Captivate Slide 6 Text Captions: Knowledge Check (Geralt, 2017) In nature, population growth can be controlled in numerous ways. These controls are broadly divided into what two categories? A) Dispersion-dependent and dispersion-independent factors B) Density-dependent and density-independent factors C) Population size and population density D) Exponential growth and logistic growth Correct - Click anywhere or press ‘y’ to continue. Page 6 of 29 Adobe Captivate Slide 7 Text Captions: Unit Lesson Density-independent factors are typically abiotic, meaning that they are not of biological origin. These can affect a population regardless of density. An example of this would be a natural disaster such as a large flood. As all areas are inundated, all individuals are affected, even if the population of the flooded area is sparse. Life histories relative to habitat and reproductive behavior can be described by the concepts of K-selected and r-selected species. K-selected species tend to live in a stable and predictable environment. These organisms tend to have few offspring and devote considerable long-term care to those offspring. Elephants would be a good example of K-selected species. On the other hand, r-selected species produce large numbers of offspring and provide little, if any, care. The goal with this strategy is to produce enough offspring that a few might survive exposure to the environment or predation, living long enough to reproduce. Oysters or house flies would be examples of r-selected strategists. Unit II finishes with a look at human population growth in relation to the population ecology concepts that we have learned. Humans have developed ways to manipulate the environment to increase its carrying capacity. This has resulted in exponential human population growth worldwide. From one region to another, human populations exhibit varying age structure, which is often visualized using age structure diagrams. Age structure patterns can indicate rapid growth, slow growth, or stable growth of a population. Page 7 of 29 Adobe Captivate Slide 8 Text Captions: Knowledge Check A(n) __________ species tends to live in a stable and predictable environment. Organisms in this category tend to have few offspring and devote considerable long-term care to those offspring. A) r-selected B) K-selected Page 8 of 29 Adobe Captivate Slide 9 Text Captions: Unit Lesson Population Demography Populations are dynamic entities. Populations consist all of the species living within a specific area, and populations fluctuate based on a number of factors: seasonal and yearly changes in the environment, natural disasters such as forest fires and volcanic eruptions, and competition for resources between and within species. The statistical study of population dynamics, demography, uses a series of mathematical tools to investigate how populations respond to changes in their biotic and abiotic environments. Many of these tools were originally designed to study human populations. For example, life tables, which detail the life expectancy of individuals within a population, were initially developed by life insurance companies to set insurance rates. In fact, while the term “demographics” is commonly used when discussing humans, all living populations can be studied using this approach (OpenStax, 2017). Population Size and Density The study of any population usually begins by determining how many individuals of a particular species exist, and how closely associated they are with each other. Within a particular habitat, a population can be characterized by its population Page 9 of 29 Adobe Captivate size (N), the total number of individuals, and its population density, the number of individuals within a specific area or volume. Population size and density are the two main characteristics used to describe and understand populations. For example, populations with more individuals may be more stable than smaller populations based on their genetic variability, and thus their potential to adapt to the environment. Alternatively, a member of a population with low population density (more spread out in the habitat), might have more difficulty finding a mate to reproduce compared to a population of higher density. As is shown in Figure 1, tend to be more densely distributed than larger organisms. smaller organisms Population Research Methods The most accurate way to determine population size is to simply count all of the individuals within the habitat. However, this method is often not logistically or economically feasible, especially when studying large habitats. Thus, scientists usually study populations by sampling a representative portion of each habitat and using this data to make inferences about the habitat as a whole. A variety of methods can be used to sample populations to determine their size and density. For Page 10 of 29 Adobe Captivate immobile organisms such as plants, or for very small and slow-moving organisms, a quadrat may be used (Figure 2). A quadrat is a way of marking off square areas within a habitat, either by staking out an area with sticks and string, or by the use of a wood, plastic, or metal square placed on the ground. After setting the quadrats, researchers then count the number of individuals that lie within their boundaries. Multiple quadrat samples are performed throughout the habitat at several random locations. All of this data can then be used to estimate the population size and population density within the entire habitat (OpenStax, 2017). Download for free at http://cnx.org/contents/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.99 (Geralt, 2017) Page 11 of 29 Adobe Captivate Slide 10 Text Captions: Unit Lesson The number and size of quadrat samples depends on the type of organisms under study and other factors, including the density of the organism. For example, if sampling daffodils, a 1 m2 quadrat might be used whereas with giant redwoods, which are larger and live much farther apart from each other, a larger quadrat of 100 m2 might be employed. This ensures that enough of the species are counted to get an accurate sample that correlates with the habitat, including areas not sampled. For mobile organisms, such as mammals, birds, or fish, a technique called mark and recapture is often used. This method involves marking a sample of captured animals in some way (such as tags, bands, paint, or other body markings), and then releasing them back into the environment to allow them to mix with the rest of the population; later, a new sample is Page 12 of 29 Adobe Captivate collected, including some individuals that are marked (recaptures) and some individuals that are unmarked (Figure 3) (OpenStax, 2017). Using the ratio of marked and unmarked individuals, scientists determine how many individuals are in the sample. From this, calculations are used to estimate the total population size. This method assumes that the larger the population, the lower the percentage of tagged organisms being recaptured since they will have mixed with more untagged individuals. For example, if 80 deer are captured, tagged, and released into the forest, and later 100 deer are captured and 20 of them are already marked, we can determine the population size (N) using the following equation: (number of marked first catch x total number of second catch) =N number of marked second catch Using our example, the population size would be estimated at 400. (80 x 100) = 400 20 Therefore, there are an estimated 400 total individuals in the original population. There are some limitations to the mark and recapture method. Some animals from the first catch may learn to avoid capture in the second round, thus inflating population estimates. Alternatively, animals may preferentially be retrapped (especially if a food reward is offered), resulting in an underestimate of population size. Also, some species may be harmed by the marking technique, reducing their survival. A variety of other techniques have been developed, including the electronic tracking of animals tagged with radio transmitters and the use of data from commercial fishing and trapping operations to estimate the size and health of populations and communities (OpenStax, 2017). Page 13 of 29 Adobe Captivate Slide 11 Text Captions: Knowledge Check Select all that apply. Which of the following method(s) will tell an ecologist about both the size and density of a population? A) Mark and recapture B) Mark and release C) Quadrat D) Life table Correct - Click anywhere or press ‘y’ to continue. Page 14 of 29 Adobe Captivate Slide 12 Text Captions: Unit Lesson Species Distribution In addition to measuring simple density, further information about a population can be obtained by looking at the distribution of the individuals. Species dispersion patterns (or distribution patterns) show the spatial relationship between members of a population within a habitat at a particular point in time. In other words, they show whether members of the species live close together or far apart and what patterns are evident when they are spaced apart (OpenStax, 2017). Individuals in a population can be more or less equally spaced apart, dispersed randomly with no predictable pattern, or clustered in groups. These are known as uniform, random, and clumped dispersion patterns, respectively (Figure 4). Page 15 of 29 Adobe Captivate Uniform dispersion is observed in plants that secrete substances inhibiting the growth of nearby individuals (such as the release of toxic chemicals by the sage plant Salvia leucophylla, a phenomenon called allelopathy) and in animals such as the penguin that maintains a defined territory. An example of random dispersion occurs with dandelions and other plants that have wind-dispersed seeds that germinate wherever they happen to fall in a favorable environment. A clumped dispersion may be seen in plants that drop their seeds straight to the ground, such as oak trees, or animals that live in groups (schools of fish or herds of elephants). Clumped dispersions may also be a function of habitat heterogeneity. Thus, the dispersion of the individuals within a population provides more information about how they interact with each other than does a simple density measurement. Just as lower density species might have more difficulty finding a mate, solitary species with a random distribution might have a similar difficulty when compared to social species clumped together in groups. Demography While population size and density describe a population at one particular point in time, scientists must use demography to study the dynamics of a population. Demography is the statistical study of population changes over time: birth rates, death rates, and life expectancies. Each of these measures, especially birth rates, may be affected by the population characteristics described above. For example, a large population size results in a higher birth rate because more potentially reproductive individuals are present. In contrast, a large population size can also result in a higher death rate because of competition, disease, and the accumulation of waste. Similarly, a higher population density or a clumped dispersion pattern results in more potential reproductive encounters between individuals, which can increase birth rate. Lastly, a female-biased sex ratio (the ratio of males to females) or age structure (the proportion of population members at specific age ranges) composed of many individuals of reproductive age can increase birth rates (OpenStax, 2017). Page 16 of 29 Adobe Captivate Slide 13 Text Captions: Unit Lesson In addition, the demographic characteristics of a population can influence how the population grows or declines over time. If birth and death rates are equal, the population remains stable. However, the population size will increase if birth rates exceed death rates; the population will decrease if birth rates are less than death rates. Life expectancy is another important factor; the length of time individuals remain in the population impacts local resources, reproduction, and the overall health of the population. These demographic characteristics are often displayed in the form of a life table (OpenStax, 2017). Life Tables Life tables provide important information about the life history of an organism. Life tables divide the population into age groups and often sexes, and show how long a member of that group is likely to live. They are modeled after actuarial tables used by the insurance industry for estimating human life expectancy. Life tables may include the probability of individuals dying before their next birthday (i.e., their mortality rate), the percentage of surviving individuals dying at a particular age interval, and their life expectancy at each interval. An example of a life table is shown in a table on the following slide using a study of Dall mountain sheep, a species native to northwestern North America. Notice that the population is divided into age intervals (column A). The mortality rate (per 1,000), shown in column D, is based on the number of individuals dying during Page 17 of 29 Adobe Captivate the age interval (column B) divided by the number of individuals surviving at the beginning of the interval (Column C), multiplied by 1,000. mortality rate = number of individuals dying x 1000 number of individuals surviving For example, between ages three and four, 12 individuals die out of the 776 that were remaining from the original 1,000 sheep. This number is then multiplied by 1,000 to get the mortality rate per thousand. mortality rate = 12 / 776 x 1000 ≈ 15.5 Page 18 of 29 Adobe Captivate Slide 14 Text Captions: Unit Lesson As can be seen from the mortality rate data, a high death rate occurred when the sheep were between six and 12 months old, and then increased even more from eight to 12 years old, after which there were few survivors. The data indicate that if a sheep in this population were to survive to age one, it could be expected to live another 7.7 years on average, as shown by the life expectancy numbers in the last column (OpenStax, 2017). Page 19 of 29 Adobe Captivate Slide 15 Text Captions: Knowledge Check Which of the following is best at showing the life expectancy of an individual within a population? A) Quadrat B) Mark and recapture C) Survivorship curve D) Life table Page 20 of 29 Adobe Captivate Slide 16 Text Captions: Unit Lesson Survivorship Curves Another tool used by population ecologists is a survivorship curve, which is a graph of the number of individuals surviving at each age interval plotted versus time (usually with data compiled from a life table). These curves allow us to compare the life histories of different populations (Figure 5). Humans and most primates exhibit a Type I survivorship curve because a high percentage of offspring survive their early and middle years—death occurs predominantly in older individuals. These types of species usually have small numbers of offspring at one time, and they give a high amount of parental care to them to ensure their survival. Birds are an example of an intermediate or Type II survivorship curve because birds die more or less equally at each age interval. These organisms also may have relatively few offspring and provide significant parental care. Trees, marine invertebrates, and most fishes exhibit a Type III survivorship curve because very few of these organisms survive their younger years; however, those that make it to an old age are more likely to survive for a relatively long period of time. Organisms in this category usually have a very large number of offspring, but once they are born, little parental care is provided. Thus these offspring are “on their own” and vulnerable to predation, but their sheer numbers assure the survival of enough individuals to perpetuate the species (OpenStax, 2017). Section Summary Page 21 of 29 Adobe Captivate Populations are individuals of a species that live in a particular habitat. Ecologists measure characteristics of populations: size, density, dispersion pattern, age structure, and sex ratio. Life tables are useful to calculate life expectancies of individual population members. Survivorship curves show the number of individuals surviving at each age interval plotted versus time. Life Histories and Natural Selection A species’ life history describes the series of events over its lifetime, such as how resources are allocated for growth, maintenance, and reproduction. Life history traits affect the life table of an organism. A species’ life history is genetically determined and shaped by the environment and natural selection (OpenStax, 2017). Page 22 of 29 Adobe Captivate Slide 17 Text Captions: Knowledge Check Humans have which type of survivorship curve? A) Type I B) Type II C) Type III D) Type IV Page 23 of 29 Adobe Captivate Slide 18 Text Captions: Unit Lesson Life History Patterns and Energy Budgets Energy is required by all living organisms for their growth, maintenance, and reproduction; at the same time, energy is often a major limiting factor in determining an organism’s survival. Plants, for example, acquire energy from the sun via photosynthesis, but must expend this energy to grow, maintain health, and produce energy-rich seeds to produce the next generation. Animals have the additional burden of using some of their energy reserves to acquire food. Furthermore, some animals must expend energy caring for their offspring. Thus, all species have an energy budget: they must balance energy intake with their use of energy for metabolism, reproduction, parental care, and energy storage (such as bears building up body fat for winter hibernation) (OpenStax, 2017). Parental Care and Fecundity Fecundity is the potential reproductive capacity of an individual within a population. In other words, fecundity describes how many offspring could ideally be produced if an individual has as many offspring as possible, repeating the reproductive cycle as soon as possible after the birth of the offspring. In animals, fecundity is inversely related to the amount of parental care given to an individual offspring. Species, such as many marine invertebrates, that produce many offspring usually provide Page 24 of 29 Adobe Captivate little if any care for the offspring (they would not have the energy or the ability to do so anyway). Most of their energy budget is used to produce many tiny offspring. Animals with this strategy are often self-sufficient at a very early age. This is because of the energy tradeoff these organisms have made to maximize their evolutionary fitness. Because their energy is used for producing offspring instead of parental care, it makes sense that these offspring have some ability to be able to move within their environment and find food and perhaps shelter. Even with these abilities, their small size makes them extremely vulnerable to predation, so the production of many offspring allows enough of them to survive to maintain the species. Animal species that have few offspring during a reproductive event usually give extensive parental care, devoting much of their energy budget to these activities, sometimes at the expense of their own health. This is the case with many mammals, such as humans, kangaroos, and pandas. The offspring of these species are relatively helpless at birth and need to develop before they achieve self-sufficiency. Plants with low fecundity produce few energy-rich seeds (such as coconuts and chestnuts) with each having a good chance to germinate into a new organism; plants with high fecundity usually have many small, energy-poor seeds (like orchids) that have a relatively poor chance of surviving. Although it may seem that coconuts and chestnuts have a better chance of surviving, the energy tradeoff of the orchid is also very effective. It is a matter of where the energy is used, for large numbers of seeds or for fewer seeds with more energy (OpenStax, 2017). Page 25 of 29 Adobe Captivate Slide 19 Text Captions: Unit Lesson Early Versus Late Reproduction The timing of reproduction in a life history also affects species survival. Organisms that reproduce at an early age have a greater chance of producing offspring, but this is usually at the expense of their growth and the maintenance of their health. Conversely, organisms that start reproducing later in life often have greater fecundity or are better able to provide parental care, but they risk that they will not survive to reproductive age. Examples of this can be seen in fishes. Small fish like guppies use their energy to reproduce rapidly, but never attain the size that would give them defense against some predators. Larger fish, like the bluegill or shark, use their energy to attain a large size, but do so with the risk that they will die before they can reproduce or at least reproduce to their maximum. These different energy strategies and tradeoffs are key to understanding the evolution of each species as it maximizes its fitness and fills its niche. In terms of energy budgeting, some species “blow it all” and use up most of their energy reserves to reproduce early before they die. Other species delay having reproduction to become stronger, more experienced individuals and to make sure that they are strong enough to provide parental care if necessary (OpenStax, 2017). Shark in aquarium (PublicDomainPictures, 2010) Page 26 of 29 Adobe Captivate Slide 20 Text Captions: Knowledge Check Which of the following is associated with long-term parental care? A) Few offspring B) Many offspring C) Semelparity D) Fecundity Page 27 of 29 Adobe Captivate Slide 21 Text Captions: Unit Lesson References DeMers, J. [JamesDeMers]. (2012). Six-spotted tiger beetle [Photograph]. Retrieved from https://pixabay.com/en/sixspotted-tiger-beetle-56924/ Geralt. (2017). Sunset [Image]. Retrieved from https://pixabay.com/en/sunset-sunrise-continents-personal-1938198/ Hans. (2011). Sumatran tiger [Photograph]. Retrieved from https://pixabay.com/en/tiger-sumatran-tiger-cat-predator-8057/ Kieschnick, S. (2015). European starling (sturnus vulgaris). [Photograph]. Retrieved from http://www.inaturalist.org/observations/2315609 OpenStax. (2017). Biology. Retrieved from http://cnx.org/contents/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.99 PublicDomainPictures. (2010). Shark in aquarium [Photograph]. Retrieved from https://pixabay.com/en/animal-aquariumcreature-deep-fish-21731/ Tpsdave. (2017). Peacock [Photograph]. Retrieved from https://pixabay.com/en/peacock-bird-plumage-exotic-bright1973546/ Zielinski, S. (2011, October). The invasive species we can blame on Shakespeare: There are 200 million European starlings in North America, and they are a menace. Smithsonian Magazine. Retrieved from http://www.smithsonianmag.com/sciencenature/the-invasive-species-we-can-blame-on-shakespeare-95506437/ Page 28 of 29 Adobe Captivate Slide 22 Text Captions: Unit Lesson This concludes Unit II: Part 1. Congratulations! Page 29 of 29 1. Identify the three main types of computer software that were discussed in your unit lesson. Within the three main categories, give examples of each and a brief explanation of each. Each explanation/description category must be answered with at least 100 words. You must cite your sources within your answers. MAIN TYPES OF COMPUTER SOFTWARE Application Software EXAMPLES EXPLANATION/DESCRIPTION Examples of Application Software include -Calculator, calendars, word processors, spreadsheet programs, database management systems, compression software, accounting packages, photo editors, and more (study guide) Application software systems are often called productivity programs or enduser programs because they enable the user to complete tasks. The user can complete tasks such as creating documents, spreadsheets, databases, and publications, doing online research, sending email, designing graphics, running businesses, playing games and more. Application software is specific to the task it is designed for and can be as simple as a calculator application or as complex as a word processing application. Application software is a helpful tool as it provides a one in all platforms for various tasks. Application software assists the user in compiling, organizing, recording, and calculating data, creating work presentations, writing documents and reports, developing websites, editing graphics, communicating using the internet, and a variety of other tasks / activities (Mukherjee, 2020). Techterms.com explains that “System software refers to the files and programs that make up your computer's operating system files include libraries of functions, system services, drivers for printers and other hardware, system preferences, and other configuration files. The most common operating system being Microsoft Windows. System software is not designed to be used by the end user like application software is. The programs that are part of the system software include assemblers, compilers, file Examples of System Software include the following operating systems. System Software • • • • • • • Android CentOS iOS Linux Mac OS MS Windows Ubuntu • Unix (Different Types of Software with Examples n.d.). Device Driver examples associated with system software include: • • • • • • • BIOS Driver Display Drivers Motherboard Drivers Printer Drivers ROM Drivers Sound card Driver USB Drivers and more (Different Types of Software with Examples n.d.). Some examples of software Development tools are the Development Tools following: • Text editors • Assemblers/compilers • Simulators • High-level language simulators • Integrated development environments (IDEs) (Development Tool n.d.) management tools, system utilities, and debuggers. System software is installed into a computer after the operating system installation occurs. The system software can be updated by running a “Windows Update”. After system software is programmed, it runs in the background continuously using user interference, permitting the operating system coordinate with the hardware (System Software n.d.). Development tools are used for developing software applications, websites, operating systems, and utilities. Development tools are used in hypertext markup language, more commonly known as HTML, and other computing languages such as C++. 2. Write a 150-word essay on the importance of operating systems (OSs). Locate at least one article in the CSU Online Library and one article from an Internet search. You may also use the required readings to support your essay. You must cite your sources within your essay. As technology continuously evolves, operating systems (OSs) are an essential part of the evolution. Computer hardware cannot perform any task without the presence of software. Software gives instructions to the computer hardware to perform desired actions. The operating system is software that provides an environment for the user to perform tasks on the computer system (Garg, R., & Verma, G. (2017). Operating Systems: An Introduction. Mercury Learning & Information). An operating system utilizes the computer in a cost-effective manner, keeping a memory log of the applications and functions that the computer features. An operating system has three main goals: Optimum and efficient use of the computer system hardware, to provide a convenient, user friendly experience, and to hide the complexity of the computer hardware. Operating systems communicates a link between user and the system and helps the user to run application programs properly and get the required output. Also, operating systems help the user manage files, in the making of directions, and saving files in them, organizes data, etc. all in effort to help the user. Multiprogramming is a vital function of operating system. It schedules and controls the running of several programs at once and provides program editors that help the user to modify and update the program lines. Debugging aids provided by the operating system help the user to detect and rename errors (Operating System Definition Types of Functions Importance 2020). In conclusion, an Operating system are important because it is what makes a computer run. Currently, computers are what is used in various, essential manners around the world; however, without an OS a computer would be useless. 3. Identify three mobile OSs and three personal computer OSs. Explain advantages and disadvantages of each one. Describe each OS. The total wording for each OS description/advantages/disadvantages should be no less than 100 words. You must cite your sources. OPERATING SYSTEMS 1.Android 2.IOS DESCRIPTION Android runs on smartphones and tablets. Touchscreen input is a plus for Android, which also supports voice input. Android also provides access to a file system. This OS powers Macs and is used for desktops and laptops. This OS has been through as many revisions as Windows. OS X is said to be userfriendly. It is also known to be reliable and more secure than Windows. The OS is based on UNIX. UNIX has protection memory features that ADVANTAGES DISADVANTAGES limit glitches. UNIX is very secure and has very few security holes. Hackers have developed fewer viruses for Mac users because of the size of the user base. Even though OS X is very secure. 3.Windows RT 4.Microsoft Windows 5.OS X by Apple 6.Chrome OS References Mukherjee, S. (2020, August 16). Types of Application Software Examples We Use All the Time. Ranker Online. https://rankeronline.com/types-of-applicationsoftware/#:%7E:text=Application%20software%20include%20programs%20like%20wor d%20processors%2C%20web,Windows%20Media%20Player%2C%20Adobe%20Photos hop%2C%20Google%20Chrome%2C%20etc. System Software. System Software Definition. (n.d.). https://techterms.com/definition/systemsoftware Different Types of Software with Examples. Squareboat. (n.d.). https://www.squareboat.com/blog/different-types-of-software-with-examples Operating System Definition Types Functions Importance. Study Lecture Notes. (2020, September 17). http://studylecturenotes.com/operating-system-definition-types-functionsimportance/#:~:text=Importance%201%20Operating%20system%20behaves%20as%20a% 20resource,and%20get%20the%20required%20output.%20More%20items...%20 Garg, R., & Verma, G. (2017). Operating Systems : An Introduction. Mercury Learning & Information. Adobe Captivate Slide 1 Text Captions: Unit II: Part 2 Population Ecology: Population Growth and Regulation (Geralt, 2017) Page 1 of 37 Adobe Captivate Slide 2 Text Captions: Unit II: Population Ecology: Population Growth and Regulation Course Learning Outcome 2. Describe the various factors that affect population growth regulation. Unit Learning Outcomes 2.1 Examine the concept of population demography and the methods by which population demographics are researched and described. 2.2 Compare reproductive strategies and population growth models. 2.3 Identify and describe factors that limit population growth. (Tpsdave, 2017) (Hans, 2011) (DeMers, 2012) Page 2 of 37 Adobe Captivate Slide 3 Text Captions: Unit Lesson Single Versus Multiple Reproductive Events Some life history traits, such as fecundity, timing of reproduction, and parental care, can be grouped together into general strategies that are used by multiple species. Semelparity occurs when a species reproduces only once during its lifetime and then dies. Such species use most of their resource budget during a single reproductive event, sacrificing their health to the point that they do not survive. Examples of semelparity are bamboo, which flowers once and then dies, and the Chinook salmon (Figure a), which uses most of its energy reserves to migrate from the ocean to its freshwater nesting area, where it reproduces and then dies. Scientists have posited alternate explanations for the evolutionary advantage of the Chinook’s post-reproduction death: a programmed suicide caused by a massive release of corticosteroid hormones, presumably so the parents can become food for the offspring, or simple exhaustion caused by the energy demands of reproduction; these are still being debated (OpenStax, 2017). Iteroparity describes species that reproduce repeatedly during their lives. Some animals are able to mate only once per year, but survive multiple mating seasons. The pronghorn antelope is an example of an animal that goes into a seasonal estrus cycle (“heat”): a hormonally induced physiological condition preparing the body for successful mating (Figure b). Females of these species mate only during the estrus phase of the cycle. A different pattern is observed in primates, including humans Page 3 of 37 Adobe Captivate and chimpanzees, which may attempt reproduction at any time during their reproductive years, even though their menstrual cycles make pregnancy likely only a few days per month during ovulation (Figure c) (OpenStax, 2017). The (a) Chinook salmon mates once and dies. The (b) pronghorn antelope mates during specific times of the year during its reproductive life. Primates, such as humans and (c) chimpanzees, may mate on any day, independent of ovulation. (credit a: modification of work by Roger Tabor, USFWS; credit b: modification of work by Mark Gocke, USDA; credit c: modification of work by “Shiny Things”/Flick (OpenStax, 2017). Page 4 of 37 Adobe Captivate Slide 4 Text Captions: Knowledge Check Which of the following is associated with multiple reproductive episodes during a species’ lifetime? A) Semiparity B) Iteroparity C) Semelparity D) Fecundity Page 5 of 37 Adobe Captivate Slide 5 Text Captions: Unit Lesson Environmental Limits to Population Growth Although life histories describe the way many characteristics of a population (such as their age structure) change over time in a general way, population ecologists make use of a variety of methods to model population dynamics mathematically. These more precise models can then be used to accurately describe changes occurring in a population and better predict future changes. Certain models that have been accepted for decades are now being modified or even abandoned due to their lack of predictive ability, and scholars strive to create effective new models (OpenStax, 2017). Exponential Growth Charles Darwin, in his theory of natural selection, was greatly influenced by the English clergyman Thomas Malthus. Malthus published a book in 1798 stating that populations with unlimited natural resources grow very rapidly, and then population growth decreases as resources become depleted. This accelerating pattern of increasing population size is called exponential growth. Page 6 of 37 Adobe Captivate The best example of exponential growth is seen in bacteria. Bacteria are prokaryotes that reproduce by prokaryotic fission. This division takes about an hour for many bacterial species. If 1000 bacteria are placed in a large flask with an unlimited supply of nutrients (so the nutrients will not become depleted), after an hour, there is one round of division and each organism divides, resulting in 2000 organisms—an increase of 1000. In another hour, each of the 2000 organisms will double, producing 4000, an increase of 2000 organisms. After the third hour, there should be 8000 bacteria in the flask, an increase of 4000 organisms. The important concept of exponential growth is that the population growth rate—the number of organisms added in each reproductive generation—is accelerating; that is, it is increasing at a greater and greater rate. After 1 day and 24 of these cycles, the population would have increased from 1000 to more than 16 billion. When the population size, N, is plotted over time, a J-shaped growth curve is produced (Figure) (OpenStax, 2017). The bacteria example is not representative of the real world where resources are limited. Furthermore, some bacteria will die during the experiment and thus not reproduce, lowering the growth rate. Therefore, when calculating the growth rate of a population, the death rate (D) (number organisms that die during a particular time interval) is subtracted from the birth rate (B) (number organisms that are born during that interval). This is shown in the following formula: Page 7 of 37 Adobe Captivate Slide 6 Text Captions: Unit Lesson The birth rate is usually expressed on a per capita (for each individual) basis. Thus, B (birth rate) = bN (the per capita birth rate “b” multiplied by the number of individuals “N”) and D (death rate) =dN (the per capita death rate “d” multiplied by the number of individuals “N”). Additionally, ecologists are interested in the population at a particular point in time, an infinitely small time interval. For this reason, the terminology of differential calculus is used to obtain the “instantaneous” growth rate, replacing the change in number and time with an instant-specific measurement of number and time (OpenStax, 2017). Notice that the “d” associated with the first term refers to the derivative (as the term is used in calculus) and is different from the death rate, also called “d.” The difference between birth and death rates is further simplified by substituting the term “r” (intrinsic rate of increase) for the relationship between birth and death rates The value “r” can be positive, meaning the population is increasing in size; or negative, meaning the population is decreasing in size; or zero, where the population’s size is unchanging, a condition known as zero population growth. A further refinement of the formula recognizes that different species have inherent differences in their intrinsic rate of increase (often thought of as the potential for reproduction), even under ideal conditions. Obviously, a bacterium can reproduce more rapidly and have a higher intrinsic rate of growth than a human. The maximal growth rate for a species is its biotic potential, or rmax, thus changing the equation to as shown below (OpenStax, 2017): Page 8 of 37 Adobe Captivate Slide 7 Text Captions: Knowledge Check The maximal growth rate for a species is called its __________. A) limit B) carrying capacity C) biotic potential D) exponential growth pattern Page 9 of 37 Adobe Captivate Slide 8 Text Captions: Unit Lesson Logistic Growth Exponential growth is possible only when infinite natural resources are available; this is not the case in the real world. Charles Darwin recognized this fact in his description of the “struggle for existence,” which states that individuals will compete (with members of their own or other species) for limited resources. The successful ones will survive to pass on their own characteristics and traits (which we know now are transferred by genes) to the next generation at a greater rate (natural selection). To model the reality of limited resources, population ecologists developed the logistic growth model (OpenStax, 2017). Charles Darwin circa 1838 (Lecen, 2012) Page 10 of 37 Adobe Captivate Page 11 of 37 Adobe Captivate Slide 9 Text Captions: Unit Lesson Carrying Capacity and the Logistic Model In the real world, with its limited resources, exponential growth cannot continue indefinitely. Exponential growth may occur in environments where there are few individuals and plentiful resources, but when the number of individuals gets large enough, resources will be depleted, slowing the growth rate. Eventually, the growth rate will plateau or level off (Figure). This population size, which represents the maximum population size that a particular environment can support, is called the carrying capacity, or K (OpenStax, 2017). The formula we use to calculate logistic growth adds the carrying capacity as a moderating force in the growth rate. The expression “K – N” is indicative of how many individuals may be added to a population at a given stage, and “K – N” divided by “K” is the fraction of the carrying capacity available for further growth. Thus, the exponential growth model is restricted by this factor to generate the logistic growth equation: Notice that when N is very small, (K-N)/K becomes close to K/K or 1, and the right side of the equation reduces to rmaxN, which means the population is growing exponentially and is not influenced by carrying capacity. On the other hand, when N is large, (K-N)/K come close to zero, which means that population growth will be slowed greatly or even stopped. Thus, population growth is greatly slowed in large populations by the carrying capacity K. This model also allows for the population of a negative population growth, or a population decline. This occurs when the number of individuals in the population exceeds the carrying capacity (because the value of (K-N)/K is negative). A graph of this equation yields an S-shaped curve (Figure), and it is a more realistic model of population growth than exponential growth. There are three different sections to an S-shaped curve. Initially, growth is exponential because there are few individuals and ample resources available. Then, as resources begin to become limited, the growth rate decreases. Finally, growth levels off at the carrying capacity of the environment, with little change in population size over time (OpenStax, 2017). Page 12 of 37 Adobe Captivate Slide 10 Text Captions: Knowledge Check The population size of a species capable of being supported by the environment is called its __________. A) limit B) carrying capacity C) biotic potential Page 13 of 37 Adobe Captivate Slide 11 Text Captions: Unit Lesson Role of Intraspecific Competition The logistic model assumes that every individual within a population will have equal access to resources and, thus, an equal chance for survival. For plants, the amount of water, sunlight, nutrients, and the space to grow are the important resources, whereas in animals, important resources include food, water, shelter, nesting space, and mates (OpenStax, 2017). In the real world, phenotypic variation among individuals within a population means that some individuals will be better adapted to their environment than others. The resulting competition between population members of the same species for resources is termed intraspecific competition (intra- = “within”; -specific = “species”). Intraspecific competition for resources may not affect populations that are well below their carrying capacity—resources are plentiful and all individuals can obtain what they need. However, as population size increases, this competition intensifies. In addition, the accumulation of waste products can reduce an environment’s carrying capacity. Examples of Logistic Growth Page 14 of 37 Adobe Captivate Yeast, a microscopic fungus used to make bread and alcoholic beverages, exhibits the classical S-shaped curve when grown in a test tube (Figure a). Its growth levels off as the population depletes the nutrients that are necessary for its growth. In the real world, however, there are variations to this idealized curve. Examples in wild populations include sheep and harbor seals (Figure b). In both examples, the population size exceeds the carrying capacity for short periods of time and then falls below the carrying capacity afterwards. This fluctuation in population size continues to occur as the population oscillates around its carrying capacity. Still, even with this oscillation, the logistic model is confirmed (OpenStax, 2017). Page 15 of 37 Adobe Captivate Slide 12 Text Captions: Knowledge Check Species with limited resources usually exhibit a(n) __________ growth curve. A) logistic B) logical C) experimental D) exponential Try again Correct - Click anywhere or press ‘y’ to continue. Page 16 of 37 Adobe Captivate Slide 13 Text Captions: Unit Lesson Population Dynamics and Regulation The logistic model of population growth, while valid in many natural populations and a useful model, is a simplification of real-world population dynamics. Implicit in the model is that the carrying capacity of the environment does not change, which is not the case. The carrying capacity varies annually: for example, some summers are hot and dry whereas others are cold and wet. In many areas, the carrying capacity during the winter is much lower than it is during the summer. Also, natural events such as earthquakes, volcanoes, and fires can alter an environment and hence its carrying capacity. Additionally, populations do not usually exist in isolation. They engage in interspecific competition: that is, they share the environment with other species, competing with them for the same resources. These factors are also important to understanding how a specific population will grow. Nature regulates population growth in a variety of ways. These are grouped into density-dependent factors, in which the density of the population at a given time affects growth rate and mortality, and density-independent factors, which influence mortality in a population regardless of population density. Note that in the former, the effect of the factor on the population depends on the density of the population at onset. Conservation biologists want to understand both types because this helps them manage populations and prevent extinction or overpopulation (OpenStax, 2017). Page 17 of 37 Adobe Captivate Density-Dependent Regulation Most density-dependent factors are biological in nature (biotic), and include predation, inter- and intraspecific competition, accumulation of waste, and diseases such as those caused by parasites. Usually, the denser a population is, the greater its mortality rate. For example, during intra- and interspecific competition, the reproductive rates of the individuals will usually be lower, reducing their population’s rate of growth. In addition, low prey density increases the mortality of its predator because it has more difficulty locating its food source. An example of density-dependent regulation is shown in this figure with results from a study focusing on the giant intestinal roundworm (Ascaris lumbricoides), a parasite of humans and other mammals.1 Denser populations of the parasite exhibited lower fecundity: they contained fewer eggs. One possible explanation for this is that females would be smaller in more dense populations (due to limited resources) and that smaller females would have fewer eggs. This hypothesis was tested and disproved in a 2009 study which showed that female weight had no influence.2 The actual cause of the density-dependence of fecundity in this organism is still unclear and awaiting further investigation (OpenStax, 2017). Page 18 of 37 Adobe Captivate Slide 14 Text Captions: Knowledge Check A forest fire is an example of __________ regulation. A) density-dependent B) density-independent C) r-selected D) K-selected Page 19 of 37 Adobe Captivate Slide 15 Text Captions: Unit Lesson Density-independent Regulation and Interaction with Density-Dependent Factors Many factors, typically physical or chemical in nature (abiotic), influence the mortality of a population regardless of its density, including weather, natural disasters, and pollution. An individual deer may be killed in a forest fire regardless of how many deer happen to be in that area. Its chances of survival are the same whether the population density is high or low. The same holds true for cold winter weather. In real-life situations, population regulation is very complicated and density-dependent and independent factors can interact. A dense population that is reduced in a density-independent manner by some environmental factor(s) will be able to recover differently than a sparse population. For example, a population of deer affected by a harsh winter will recover faster if there are more deer remaining to reproduce (OpenStax, 2017). Life Histories of K-selected and r-selected Species Page 20 of 37 Adobe Captivate While reproductive strategies play a key role in life histories, they do not account for important factors like limited resources and competition. The regulation of population growth by these factors can be used to introduce a classical concept in population biology, that of K-selected versus r-selected species. Early Theories about Life History: K-Selected and r-Selected Species By the second half of the twentieth century, the concept of K- and r-selected species was used extensively and successfully to study populations. The concept relates not only reproductive strategies, but also to a species’ habitat and behavior, especially in the way that they obtain resources and care for their young. It includes length of life and survivorship factors as well. For this analysis, population biologists have grouped species into the two large categories: K-selected and r-selected—although they are really two ends of a continuum. K-selected species are species selected by stable, predictable environments. Populations of K-selected species tend to exist close to their carrying capacity (hence the term K-selected) where intraspecific competition is high. These species have few, large offspring, a long gestation period, and often give long-term care to their offspring (Table B). While larger in size when born, the offspring are relatively helpless and immature at birth. By the time they reach adulthood, they must develop skills to compete for natural resources. In plants, scientists think of parental care more broadly: how long fruit takes to develop or how long it remains on the plant are determining factors in the time to the next reproductive event. Examples of K-selected species are primates including humans), elephants, and plants such as oak trees (Figure a) Page 21 of 37 Adobe Captivate Slide 16 Text Captions: Knowledge Check Species that have many offspring at one time are usually: A) r-selected. B) K-selected. C) both r- and K-selected. D) not selected. Page 22 of 37 Adobe Captivate Slide 17 Text Captions: Unit Lesson Modern Theories of Life History The r- and K-selection theory, although accepted for decades and used for much groundbreaking research, has now been reconsidered, and many population biologists have abandoned or modified it. Over the years, several studies attempted to confirm the theory, but these attempts have largely failed. Many species were identified that did not follow the theory’s predictions. Furthermore, the theory ignored the age-specific mortality of the populations which scientists now know is very important. New demographic-based models of life history evolution have been developed which incorporate many ecological concepts included in r- and K-selection theory as well as population age structure and mortality factors. Section Summary Populations are regulated by a variety of density-dependent and density-independent factors. Species are divided into two categories based on a variety of features of their life history patterns: r-selected species, which have large numbers of offspring, and K-selected species, which have few offspring. The r- and K-selection theory has fallen out of use; however, many of its key features are still used in newer, demographically-based models of population dynamics. Page 23 of 37 Adobe Captivate Page 24 of 37 Adobe Captivate Slide 18 Text Captions: Knowledge Check Primates are examples of __________. A) density-dependent species B) density-independent species C) r-selected species D) K-selected species Page 25 of 37 Adobe Captivate Slide 19 Text Captions: Unit Lesson Human Population Growth Concepts of animal population dynamics can be applied to human population growth. Humans are not unique in their ability to alter their environment. For example, beaver dams alter the stream environment where they are built. Humans, however, have the ability to alter their environment to increase its carrying capacity sometimes to the detriment of other species (e.g., via artificial selection for crops that have a higher yield). Earth’s human population is growing rapidly, to the extent that some worry about the ability of the earth’s environment to sustain this population, as long-term exponential growth carries the potential risks of famine, disease, and large-scale death. Although humans have increased the carrying capacity of their environment, the technologies used to achieve this transformation have caused unprecedented changes to Earth’s environment, altering ecosystems to the point where some may be in danger of collapse. The depletion of the ozone layer, erosion due to acid rain, and damage from global climate change are caused by human activities. The ultimate effect of these changes on our carrying capacity is unknown. As some point out, it is likely that the negative effects of increasing carrying capacity will outweigh the positive ones—the carrying capacity of the world for human beings might actually decrease (OpenStax, 2017). Page 26 of 37 Adobe Captivate The world’s human population is currently experiencing exponential growth even though human reproduction is far below its biotic potential (Figure 1). To reach its biotic potential, all females would have to become pregnant every nine months or so during their reproductive years. Also, resources would have to be such that the environment would support such growth. Neither of these two conditions exists. In spite of this fact, human population is still growing exponentially. A consequence of exponential human population growth is the time that it takes to add a particular number of humans to the Earth is becoming shorter. Figure 2 shows that 123 years were Page 27 of 37 Adobe Captivate necessary to add 1 billion humans in 1930, but it only took 24 years to add two billion people between 1975 and 1999. As already discussed, at some point it would appear that our ability to increase our carrying capacity indefinitely on a finite world is uncertain. Without new technological advances, the human growth rate has been predicted to slow in the coming decades. However, the population will still be increasing and the threat of overpopulation remains. Overcoming Density-Dependent Regulation Humans are unique in their ability to alter their environment with the conscious purpose of increasing its carrying capacity. This ability is a major factor responsible for human population growth and a way of overcoming density-dependent growth regulation. Much of this ability is related to human intelligence, society, and communication. Humans can construct shelter to protect them from the elements and have developed agriculture and domesticated animals to increase their food supplies. In addition, humans use language to communicate this technology to new generations, allowing them to improve upon previous accomplishments (OpenStax, 2017). Page 28 of 37 Adobe Captivate Slide 20 Text Captions: Knowledge Check A country with zero population growth is likely to be __________. A) in Africa B) in Asia C) economically developed D) economically underdeveloped Page 29 of 37 Adobe Captivate Slide 21 Text Captions: Knowledge Check How many years did it take for the world population to go from 6 billion to 7 billion people? A) 12 B) 13 C) 16 D) 26 Page 30 of 37 Adobe Captivate Slide 22 Text Captions: Unit Lesson Other factors in human population growth are migration and public health. Humans originated in Africa, but have since migrated to nearly all inhabitable land on the Earth. Public health, sanitation, and the use of antibiotics and vaccines have decreased the ability of infectious disease to limit human population growth. In the past, diseases such as the bubonic plaque of the fourteenth century killed between 30 and 60 percent of Europe’s population and reduced the overall world population by as many as 100 million people. Today, the threat of infectious disease, while not gone, is certainly less severe. According to the World Health Organization, global death from infectious disease declined from 16.4 million in 1993 to 14.7 million in 1992. To compare to some of the epidemics of the past, the percentage of the world's population killed between 1993 and 2002 decreased from 0.30 percent of the world's population to 0.24 percent. Thus, it appears that the influence of infectious disease on human population growth is becoming less significant (OpenStax, 2017). Age Structure, Population Growth, and Economic Development The age structure of a population is an important factor in population dynamics. Age structure is the proportion of a population at different age ranges. Age structure allows better prediction of population growth, plus the ability to associate this growth with the level of economic development in the region. Countries with rapid growth have a pyramidal shape in their age structure diagrams, showing a preponderance of younger individuals, many of whom are of reproductive age or will Page 31 of 37 Adobe Captivate be soon (Figure 3). This pattern is most often observed in underdeveloped countries where individuals do not live to old age because of less-thanoptimal living conditions. Age structures of areas with slow growth, including developed countries such as the United States, still have a pyramidal structure, but with many fewer young and reproductive-aged individuals and a greater proportion of older individuals. Other developed countries, such as Italy, have zero population growth. The age structure of these populations is more conical, with an even greater percentage of middle-aged and older individuals. The actual growth rates in different countries are shown in Figure 4, with the highest rates tending to be in the less economically developed countries of Africa and Asia. Long-Term Consequences of Exponential Human Population Growth Many dire predictions have been made about the world’s population leading to a major crisis called the “population explosion.” In the 1968 book The Population Bomb, biologist Dr. Paul R. Ehrlich wrote, “The battle to feed all of humanity is over. In the 1970s hundreds of millions of people will starve to death in spite of any crash programs embarked upon now. At this late date nothing can prevent a substantial increase in the world death rate.”1 While many critics view this statement as an exaggeration, the laws of exponential population growth are still in effect, and unchecked human population growth cannot continue indefinitely (OpenStax, 2017). Page 32 of 37 Adobe Captivate Page 33 of 37 Adobe Captivate Slide 23 Text Captions: Knowledge Check Which type of country has the greatest proportion of young individuals? A) Economically developed B) Economically underdeveloped C) Countries with zero population growth D) Countries in Europe Page 34 of 37 Adobe Captivate Slide 24 Text Captions: Unit Lesson Another result of population growth is the endangerment of the natural environment. Many countries have attempted to reduce the human impact on climate change by reducing their emission of the greenhouse gas carbon dioxide. However, these treaties have not been ratified by every country, and many underdeveloped countries trying to improve their economic condition may be less likely to agree with such provisions if it means slower economic development. Furthermore, the role of human activity in causing climate change has become a hotly debated socio-political issue in some developed countries, including the United States. Thus, we enter the future with considerable uncertainty about our ability to curb human population growth and protect our environment. Section Summary The world’s human population is growing at an exponential rate. Humans have increased the world’s carrying capacity through migration, agriculture, medical advances, and communication. The age structure of a population allows us to predict population growth. Unchecked human population growth could have dire long-term effects on our environment (OpenStax, 2017). Aerial view of crowed urban lanscape congestion (Unsplash, 2016) Page 35 of 37 Adobe Captivate Slide 25 Text Captions: Knowledge Check Which of the following is not a way that humans have increased the carrying capacity of the environment? A) agriculture B) using large amounts of natural resources C) domestication of animals D) use of language Page 36 of 37 Adobe Captivate Slide 26 Text Captions: Unit Lesson References DeMers, J. [JamesDeMers]. (2012). Six-spotted tiger beetle [Photograph]. Retrieved from https://pixabay.com/en/sixspotted-tiger-beetle-56924/ Geralt. (2017). Sunset [Image]. Retrieved from https://pixabay.com/en/sunset-sunrise-continents-personal-1938198/ Hans. (2011). Sumatran tiger [Photograph]. Retrieved from https://pixabay.com/en/tiger-sumatran-tiger-cat-predator-8057/ Lecen. (2012). Charles Darwin by G. Richmond circa 1838 [Painting]. Retrieved from https://commons.wikimedia.org/wiki/File:Charles_Darwin_by_G._Richmond.jpg OpenStax. (2017). Biology. Retrieved from http://cnx.org/contents/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.99 Tpsdave. (2017). Peacock [Photograph]. Retrieved from https://pixabay.com/en/peacock-bird-plumage-exotic-bright1973546/ Unsplash. (2016). Aerial view urban landscape congestion [Photograph]. Retreived from https://pixabay.com/en/aerialview-crowded-urban-landscape-1209065/ Page 37 of 37 Adobe Captivate Slide 1 Text Captions: Unit II: Part 1 Population Ecology: Population Growth and Regulation (Geralt, 2017) Page 1 of 29 Adobe Captivate Slide 2 Text Captions: Unit II: Population Ecology: Population Growth and Regulation Course Learning Outcome 2. Describe the various factors that affect population growth regulation. Unit Learning Outcomes 2.1 Examine the concept of population demography and the methods by which population demographics are researched and described. 2.2 Compare reproductive strategies and population growth models. 2.3 Identify and describe factors that limit population growth. (DeMers, 2012) (Tpsdave, 2017) (Hans, 2011) Page 2 of 29 Adobe Captivate Slide 3 Text Captions: Unit Lesson The European starling is a familiar bird across the United States and Canada. This ubiquitous avian’s success across its North American range might give the impression that its history on the continent goes back eons. However, in fact, European starlings are a relative newcomer. In the early 1890s, drug manufacturer, bird enthusiast, and Shakespeare fanatic, Eugene Scheiffelin, had the romantic idea of introducing the birds from the works of Shakespeare to Central Park in New York City. Scheiffelin introduced skylarks, bullfinches, nightingales, and chaffinches, all of which died in the harsh conditions of an unfamiliar habitat. However, one of Scheiffelin’s introductions was successful: the European starling (Zielinski, 2011). Over the course of two years, roughly 100 of these birds were released in Central Park. The birds not only survived but were able to reproduce and colonize areas outside of Central Park. Eventually, the birds found their way outside of the state of New York and moved North, South, and West. Today, these birds are estimated to number more than 200 million across North America (Zielinski, 2011). European starlings flock in massive numbers, damaging crops; spreading disease to native birds, livestock, and people; and out-competing native birds for food and nesting sites (OpenStax, 2017). In this unit, you will explore population ecology, which is the study of how populations of organisms change over time and space and the factors that influence those changes. Two of the most important pieces of information included in a population study are population size and population density. As you watch nature programs or listen to the news, you may hear statistics on a topic, such as depleting salmon populations, and you may ask yourself, “How do researchers know?” Mark and recapture is a commonly used technique to estimate the population size of a wide variety of organisms that are highly mobile. Other organisms such as plants and coral tend to stay in place so their populations can be studied via the use of a quadrat. These methods will be discussed in more detail (OpenStax, 2017). European starling (Sturnus vulgaris) (Kieschnick, 2015) The European starling is a medium-sized passerine bird in the starling family, Sturnidae. Page 3 of 29 Adobe Captivate Slide 4 Text Captions: Knowledge Check Population ecology is the study of how populations of organisms change over time and space and the factors that influence those changes. A) True B) False Page 4 of 29 Adobe Captivate Slide 5 Text Captions: Unit Lesson Single species are often distributed over an area in patterns that may be generally described as uniform, random, or clumped. There is a variety of reasons for these patterns, and as you read about these distributions, think about some of the organisms you are most familiar with and how they are distributed in the landscape. Demography is the statistical study of the changing characteristics of a population. You may already be familiar with this word as it relates to human sociology. However, it can apply to any population of organisms. Some of the commonly collected demographic data can include population characteristics such as birth rates, death rates, and life expectancies. This type of data can be used to predict the growth or decline of a population or how to best manage a population. Life tables and survivorship curves can be constructed to visualize population structure by age and determine the likelihood of mortality by a given age. Life history information may include how that organism obtains and uses resources, how it endures the environmental conditions of its habitat, and how it reproduces. An organism’s energy budget is how that organism manages its energy intake in order to maintain its metabolism, reproduce, feed and care for its young, and store energy (OpenStax, 2017). Population ecologists use mathematical models to describe population growth and predict future changes in a population of organisms. Two very common growth curves show us how organisms reproduce in the presence of unlimited or limited resources. A J-shaped curve demonstrates what happens to a population when resources are unlimited. This is known as exponential growth. When resources are finite and competition for those resources results in slowed or zero population growth, an S-shaped curve is the result. This is known as logistic growth. While useful, these two growth pattern models are simplified pictures of population growth changes actually seen in nature. There are numerous factors controlling the ebb and flow of population growth. In nature, population growth can be controlled in numerous ways. These controls are broadly divided into two categories, density-dependent and density-independent factors. Density-dependent factors are usually biological in nature and include things such as diseases (e.g., bacteria, viruses, parasites), competition among species (both inter- and intra-specific), or the build-up of biologic waste. When a given space is densely populated, diseases are easily and more rapidly transmitted from one individual species to another as opposed to individual species being spaced farther apart and interacting with one another less frequently. Crowding can also increase stress and lower an individual’s reproductive capability (OpenStax, 2017). (Geralt, 2017) The life history of an organism is a description of how that organism maintains and reproduces itself from its birth until its death. Page 5 of 29 Adobe Captivate Slide 6 Text Captions: Knowledge Check (Geralt, 2017) In nature, population growth can be controlled in numerous ways. These controls are broadly divided into what two categories? A) Dispersion-dependent and dispersion-independent factors B) Density-dependent and density-independent factors C) Population size and population density D) Exponential growth and logistic growth Correct - Click anywhere or press ‘y’ to continue. Page 6 of 29 Adobe Captivate Slide 7 Text Captions: Unit Lesson Density-independent factors are typically abiotic, meaning that they are not of biological origin. These can affect a population regardless of density. An example of this would be a natural disaster such as a large flood. As all areas are inundated, all individuals are affected, even if the population of the flooded area is sparse. Life histories relative to habitat and reproductive behavior can be described by the concepts of K-selected and r-selected species. K-selected species tend to live in a stable and predictable environment. These organisms tend to have few offspring and devote considerable long-term care to those offspring. Elephants would be a good example of K-selected species. On the other hand, r-selected species produce large numbers of offspring and provide little, if any, care. The goal with this strategy is to produce enough offspring that a few might survive exposure to the environment or predation, living long enough to reproduce. Oysters or house flies would be examples of r-selected strategists. Unit II finishes with a look at human population growth in relation to the population ecology concepts that we have learned. Humans have developed ways to manipulate the environment to increase its carrying capacity. This has resulted in exponential human population growth worldwide. From one region to another, human populations exhibit varying age structure, which is often visualized using age structure diagrams. Age structure patterns can indicate rapid growth, slow growth, or stable growth of a population. Page 7 of 29 Adobe Captivate Slide 8 Text Captions: Knowledge Check A(n) __________ species tends to live in a stable and predictable environment. Organisms in this category tend to have few offspring and devote considerable long-term care to those offspring. A) r-selected B) K-selected Page 8 of 29 Adobe Captivate Slide 9 Text Captions: Unit Lesson Population Demography Populations are dynamic entities. Populations consist all of the species living within a specific area, and populations fluctuate based on a number of factors: seasonal and yearly changes in the environment, natural disasters such as forest fires and volcanic eruptions, and competition for resources between and within species. The statistical study of population dynamics, demography, uses a series of mathematical tools to investigate how populations respond to changes in their biotic and abiotic environments. Many of these tools were originally designed to study human populations. For example, life tables, which detail the life expectancy of individuals within a population, were initially developed by life insurance companies to set insurance rates. In fact, while the term “demographics” is commonly used when discussing humans, all living populations can be studied using this approach (OpenStax, 2017). Population Size and Density The study of any population usually begins by determining how many individuals of a particular species exist, and how closely associated they are with each other. Within a particular habitat, a population can be characterized by its population Page 9 of 29 Adobe Captivate size (N), the total number of individuals, and its population density, the number of individuals within a specific area or volume. Population size and density are the two main characteristics used to describe and understand populations. For example, populations with more individuals may be more stable than smaller populations based on their genetic variability, and thus their potential to adapt to the environment. Alternatively, a member of a population with low population density (more spread out in the habitat), might have more difficulty finding a mate to reproduce compared to a population of higher density. As is shown in Figure 1, tend to be more densely distributed than larger organisms. smaller organisms Population Research Methods The most accurate way to determine population size is to simply count all of the individuals within the habitat. However, this method is often not logistically or economically feasible, especially when studying large habitats. Thus, scientists usually study populations by sampling a representative portion of each habitat and using this data to make inferences about the habitat as a whole. A variety of methods can be used to sample populations to determine their size and density. For Page 10 of 29 Adobe Captivate immobile organisms such as plants, or for very small and slow-moving organisms, a quadrat may be used (Figure 2). A quadrat is a way of marking off square areas within a habitat, either by staking out an area with sticks and string, or by the use of a wood, plastic, or metal square placed on the ground. After setting the quadrats, researchers then count the number of individuals that lie within their boundaries. Multiple quadrat samples are performed throughout the habitat at several random locations. All of this data can then be used to estimate the population size and population density within the entire habitat (OpenStax, 2017). Download for free at http://cnx.org/contents/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.99 (Geralt, 2017) Page 11 of 29 Adobe Captivate Slide 10 Text Captions: Unit Lesson The number and size of quadrat samples depends on the type of organisms under study and other factors, including the density of the organism. For example, if sampling daffodils, a 1 m2 quadrat might be used whereas with giant redwoods, which are larger and live much farther apart from each other, a larger quadrat of 100 m2 might be employed. This ensures that enough of the species are counted to get an accurate sample that correlates with the habitat, including areas not sampled. For mobile organisms, such as mammals, birds, or fish, a technique called mark and recapture is often used. This method involves marking a sample of captured animals in some way (such as tags, bands, paint, or other body markings), and then releasing them back into the environment to allow them to mix with the rest of the population; later, a new sample is Page 12 of 29 Adobe Captivate collected, including some individuals that are marked (recaptures) and some individuals that are unmarked (Figure 3) (OpenStax, 2017). Using the ratio of marked and unmarked individuals, scientists determine how many individuals are in the sample. From this, calculations are used to estimate the total population size. This method assumes that the larger the population, the lower the percentage of tagged organisms being recaptured since they will have mixed with more untagged individuals. For example, if 80 deer are captured, tagged, and released into the forest, and later 100 deer are captured and 20 of them are already marked, we can determine the population size (N) using the following equation: (number of marked first catch x total number of second catch) =N number of marked second catch Using our example, the population size would be estimated at 400. (80 x 100) = 400 20 Therefore, there are an estimated 400 total individuals in the original population. There are some limitations to the mark and recapture method. Some animals from the first catch may learn to avoid capture in the second round, thus inflating population estimates. Alternatively, animals may preferentially be retrapped (especially if a food reward is offered), resulting in an underestimate of population size. Also, some species may be harmed by the marking technique, reducing their survival. A variety of other techniques have been developed, including the electronic tracking of animals tagged with radio transmitters and the use of data from commercial fishing and trapping operations to estimate the size and health of populations and communities (OpenStax, 2017). Page 13 of 29 Adobe Captivate Slide 11 Text Captions: Knowledge Check Select all that apply. Which of the following method(s) will tell an ecologist about both the size and density of a population? A) Mark and recapture B) Mark and release C) Quadrat D) Life table Correct - Click anywhere or press ‘y’ to continue. Page 14 of 29 Adobe Captivate Slide 12 Text Captions: Unit Lesson Species Distribution In addition to measuring simple density, further information about a population can be obtained by looking at the distribution of the individuals. Species dispersion patterns (or distribution patterns) show the spatial relationship between members of a population within a habitat at a particular point in time. In other words, they show whether members of the species live close together or far apart and what patterns are evident when they are spaced apart (OpenStax, 2017). Individuals in a population can be more or less equally spaced apart, dispersed randomly with no predictable pattern, or clustered in groups. These are known as uniform, random, and clumped dispersion patterns, respectively (Figure 4). Page 15 of 29 Adobe Captivate Uniform dispersion is observed in plants that secrete substances inhibiting the growth of nearby individuals (such as the release of toxic chemicals by the sage plant Salvia leucophylla, a phenomenon called allelopathy) and in animals such as the penguin that maintains a defined territory. An example of random dispersion occurs with dandelions and other plants that have wind-dispersed seeds that germinate wherever they happen to fall in a favorable environment. A clumped dispersion may be seen in plants that drop their seeds straight to the ground, such as oak trees, or animals that live in groups (schools of fish or herds of elephants). Clumped dispersions may also be a function of habitat heterogeneity. Thus, the dispersion of the individuals within a population provides more information about how they interact with each other than does a simple density measurement. Just as lower density species might have more difficulty finding a mate, solitary species with a random distribution might have a similar difficulty when compared to social species clumped together in groups. Demography While population size and density describe a population at one particular point in time, scientists must use demography to study the dynamics of a population. Demography is the statistical study of population changes over time: birth rates, death rates, and life expectancies. Each of these measures, especially birth rates, may be affected by the population characteristics described above. For example, a large population size results in a higher birth rate because more potentially reproductive individuals are present. In contrast, a large population size can also result in a higher death rate because of competition, disease, and the accumulation of waste. Similarly, a higher population density or a clumped dispersion pattern results in more potential reproductive encounters between individuals, which can increase birth rate. Lastly, a female-biased sex ratio (the ratio of males to females) or age structure (the proportion of population members at specific age ranges) composed of many individuals of reproductive age can increase birth rates (OpenStax, 2017). Page 16 of 29 Adobe Captivate Slide 13 Text Captions: Unit Lesson In addition, the demographic characteristics of a population can influence how the population grows or declines over time. If birth and death rates are equal, the population remains stable. However, the population size will increase if birth rates exceed death rates; the population will decrease if birth rates are less than death rates. Life expectancy is another important factor; the length of time individuals remain in the population impacts local resources, reproduction, and the overall health of the population. These demographic characteristics are often displayed in the form of a life table (OpenStax, 2017). Life Tables Life tables provide important information about the life history of an organism. Life tables divide the population into age groups and often sexes, and show how long a member of that group is likely to live. They are modeled after actuarial tables used by the insurance industry for estimating human life expectancy. Life tables may include the probability of individuals dying before their next birthday (i.e., their mortality rate), the percentage of surviving individuals dying at a particular age interval, and their life expectancy at each interval. An example of a life table is shown in a table on the following slide using a study of Dall mountain sheep, a species native to northwestern North America. Notice that the population is divided into age intervals (column A). The mortality rate (per 1,000), shown in column D, is based on the number of individuals dying during Page 17 of 29 Adobe Captivate the age interval (column B) divided by the number of individuals surviving at the beginning of the interval (Column C), multiplied by 1,000. mortality rate = number of individuals dying x 1000 number of individuals surviving For example, between ages three and four, 12 individuals die out of the 776 that were remaining from the original 1,000 sheep. This number is then multiplied by 1,000 to get the mortality rate per thousand. mortality rate = 12 / 776 x 1000 ≈ 15.5 Page 18 of 29 Adobe Captivate Slide 14 Text Captions: Unit Lesson As can be seen from the mortality rate data, a high death rate occurred when the sheep were between six and 12 months old, and then increased even more from eight to 12 years old, after which there were few survivors. The data indicate that if a sheep in this population were to survive to age one, it could be expected to live another 7.7 years on average, as shown by the life expectancy numbers in the last column (OpenStax, 2017). Page 19 of 29 Adobe Captivate Slide 15 Text Captions: Knowledge Check Which of the following is best at showing the life expectancy of an individual within a population? A) Quadrat B) Mark and recapture C) Survivorship curve D) Life table Page 20 of 29 Adobe Captivate Slide 16 Text Captions: Unit Lesson Survivorship Curves Another tool used by population ecologists is a survivorship curve, which is a graph of the number of individuals surviving at each age interval plotted versus time (usually with data compiled from a life table). These curves allow us to compare the life histories of different populations (Figure 5). Humans and most primates exhibit a Type I survivorship curve because a high percentage of offspring survive their early and middle years—death occurs predominantly in older individuals. These types of species usually have small numbers of offspring at one time, and they give a high amount of parental care to them to ensure their survival. Birds are an example of an intermediate or Type II survivorship curve because birds die more or less equally at each age interval. These organisms also may have relatively few offspring and provide significant parental care. Trees, marine invertebrates, and most fishes exhibit a Type III survivorship curve because very few of these organisms survive their younger years; however, those that make it to an old age are more likely to survive for a relatively long period of time. Organisms in this category usually have a very large number of offspring, but once they are born, little parental care is provided. Thus these offspring are “on their own” and vulnerable to predation, but their sheer numbers assure the survival of enough individuals to perpetuate the species (OpenStax, 2017). Section Summary Page 21 of 29 Adobe Captivate Populations are individuals of a species that live in a particular habitat. Ecologists measure characteristics of populations: size, density, dispersion pattern, age structure, and sex ratio. Life tables are useful to calculate life expectancies of individual population members. Survivorship curves show the number of individuals surviving at each age interval plotted versus time. Life Histories and Natural Selection A species’ life history describes the series of events over its lifetime, such as how resources are allocated for gro...