17. (extra credit) We did not study density-dependent processes in age-structure
ID: 302720 • Letter: 1
Question
17. (extra credit) We did not study density-dependent processes in age-structured populations, but you could guess behavior of such models from the simpler models. Imagine a species with several years before first reproduction, no senescence (i.e., after attainment of maturity, fecundity is >0 for all ages), and where older age classes eat newborns (i.e., cannibalism), with the rate of cannibalism increasing with both the number of newborns and number of older adults (the last clause adds density-dependence to population growth). For each of the following aspects of population growth, would you expect it (.5 points each) and provide a brief justification (1.5 points each) (for c and d, it may help to think about a perturbation such as added mortality of the oldest age class): Exponential population growth at a lower rate than in a corresponding population without cannibalism a. b. Growth (or decrease) to an equilibrium population size; c. Attainment of a stable age distribution; More extreme fluctuations of age distribution following a disturbance which changes age distribution than in the corresponding population without cannibalism; d.Explanation / Answer
A. Fecundity is the ability of organism to produce numerous number of offsprings. Exponential growth will be at lower rate than the corresponding population without cannibalism because the number of organisms which reach the maturity start producing offsprings. But in that case explained above as these mature organisms grow old some of the offsprings will be in mature state and they produce new offsprings and some of the offsprings will be eaten by the older age classes. So the exponential growth rate will be lower.
B. As the population density of old aged organisms increases the intrinsic rate of increase will start to fall because of limited resources (new borns) for living. Now the population size will be in a state of equilibrium. This is also true to decrease to an equilibrium to maintain the population size.
C. Attainment of stable age distribution- Now as I explained the mature ones grow older and the offsprings start to mature, and the offsprings produces by these new matured ones will be eaten by the older ones. These all create a kind of age distribution. To keep up the species the old ones don't eat all the offsprings because some of the offsprings need to mature to produce new offsprings. If the number of offsprings fall short then there will be competition in the older ones. Some survives. And it's create age distribution: offsprings-young-old.
D. Extreme fluctuation of age distribution can be occured by a disturbance and this can be the old age classes' mortality. If the old ones start dying more and more, there will be more offsprings survived and the number of young ones fall short, and the number of old ones fall shorter than the actual age distribution.
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