Answers to Review Questions
1. Most carnivores have a broad diet in that they eat a wide range of prey species. Although a substantial number of herbivores can eat many different plant species, the majority of herbivores are insects, most of which feed on just one or a few plant species.
This difference is hypothesized to be due to the differences carnivores and herbivores experience related to encountering and handling their food. Carnivores are mostly generalists because their encounter rates are low for mobile prey, and thus they should not be too narrow in their prey choices. Herbivores are specialists because they have relatively high encounter rates with their immobile prey, but their handling times are longer because plants are less nutritious food.2. A prey individual that cannot evade a carnivore is killed and eaten. While herbivores do not typically kill their food plants, they do have powerful negative effects on the plants on which they feed. As a result of this strong selection pressure that carnivores and herbivores exert on their food organisms, prey species have evolved a wide range of defensive mechanisms that increase the chance that they will not be eaten. Animals must eat if they are to survive, so there is also strong selection pressure on them to overcome the defenses of their prey. These effects are pervasive because all organisms must obtain food— setting in motion the conflicts just described. The effects are pronounced because there is such strong selection for both defensive and counterdefensive mechanisms.
3.
a. Evidence described in this and preceding chapters indicates that predation can have a powerful effect on the abundance and distribution of prey species, and this can affect communities in dramatic ways.
b. The scientific evidence strongly supports this claim. As described in this chapter, in many cases the effects of carnivory and herbivory have been so pronounced that they have altered ecological communities greatly, in some cases causing a shift from one community type to another. For example, arctic foxes feeding on seabirds, lesser snow geese feeding on marsh grasses, and aquatic snails feeding on large aquatic plants had such effects.