Ecology 7th Edition by Manuel Molles

Exercise 20

In chapter 14 we have seen how a herbivorous stream insect controls the density of its food organisms, how a herbivorous moth larva and pathogenic microbes combine to control an introduced cactus population, and how decimation of a red fox population led to increases in the populations of the foxes' prey. We do not know the specific environmental factors controlling most populations. Explain why such factors must exist. (Hint: Think back to our discussions of geometric and exponential growth in chapter 11.)