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Homework answers / question archive / In developing the formulas for population growth I made specific assumptions about birth rates and death rates
In developing the formulas for population growth I made specific assumptions about birth rates and death rates. On the graph below draw the line that relates birth rate to population size if the environment were perfect and thus the population is growing at its biotic potential. Also, draw the line that relates birth rate to population size if the environment were real and food is limited and thus the population is growing according to the logistic formula. Be careful, these are NOT population growth curves! Label your lines as "perfect" and "real"! (See graph in attachment)
B. Even though a species is growing logistically, it rarely does so with a smooth growth curve that levels out at the carrying capacity like the formula indicates it should. Instead, the curve fluctuates and looks jagged rather than smooth. Briefly describe two reason why the actual growth curve for such a species is jagged and doesn't smoothly level out at the carrying capacity (look at the curve for questions 1-4).
15. Describe how either a social hierarchy or territoriality can regulate population size in a density-dependent manner.
16. What is the difference in the way data are collected for a cohort life table compared to a static life table?
This question asks you to first draw the birth rate in regards to the population size. (See attached for diagram)
In an ideal situation the birth rate remains the same as the population grows. Without limits on resources or crowding effects there is no detriment to the birth rate. With the constant birth rate the population will grow at an exponential rate. In a real environment external factors such as competition for limited resources and the stress effects of crowding have a negative impact on the birth rate decreasing the number of young born each year as the population increases. See http://courses.washington.edu/anth457/popnecol.htm for more information.
14.b. There are many factors that affect a population's growth rate. Apart from competition and crowd-stress effects, natural disasters, predation rates and cyclic resource levels can dramatically affect a population's growth. These factors cause jagged points in the growth curve of a population and prevent it from reaching carrying capacity.
15. Social hierarchy is the establishment of a pecking order within the community. Individuals at the top of the hierarchy receive the most and the best resources while the lower rungs receive less of these resources. This can limit population density due to the self-preservation instinct of those at the top of the hierarchy. Given limited resources each rung will take the maximum resources they are allowed leaving progressively less for the remainder of the group. At some point the resources are exhausted and individuals that have not received any resources must achieve a higher rung, disperse or face death. Territoriality affects population density in a very similar fashion. There is a limit to territories available and a limit to the number of individuals that can be supported by that territory. New members must fight for an occupied territory or disperse.
16. A static life table samples the individuals in a given population at one time point in order to calculate growth and other population dynamics. A cohort table will sample multiple times and following the progress of individuals born at the same time. See http://www.biology.ualberta.ca/courses/biol208/index.php?Page=1650
