1. How could you experimentally test whether herds of African antelope affect the
abundance of plants on which they graze?
2. Explain why an herbivore that consumes many different species of plant might be less
successful at regulating the abundance of a well-defended plant species compared to
an herbivore that specializes on eating a single species of plant.
3. In the classic experiments of C. F. Huffaker with mites and oranges, what
mechanisms allowed the predator and prey populations to persist?
4. Which factors determine the duration of population cycles and which determine the
magnitude of change in population sizes?
5. Explain in words the equations of the Lotka-Volterra model for the change in the
population sizes of prey and predators.
6. According to the Lotka-Volterra model of predator–prey interactions, why do
predator and prey populations cycle?
7. How do search image formation and prey switching behavior lead to a type III
functional response in predators?
8. Compare and contrast a predator’s numerical response and functional response.
9. How might a type II functional response prevent a predator from controlling a large
10. Explain the causes of an evolutionary arms race between consumers and the species
that they consume.
SUMMARY OF CHAPTER CONCEPTS
Predators and herbivores can limit the abundance of populations. Using observations in
nature and manipulative experiments, ecologists have found that predators commonly
limit the abundance of prey and herbivores commonly limit the abundance of producers.
Populations of consumers and consumed populations fluctuate in regular cycles.
Cycling populations have been observed frequently in nature and recreated in laboratory
experiments. Lags in the response times of predator movement and reproduction linked to
changes in the abundance of prey cause these cycles. Mathematical models have been
developed to mimic the cycling behavior of predator and prey populations.
Predation and herbivory favor the evolution of defenses. Prey have evolved a wide
variety of defenses including behavioral defenses, mechanical defenses, chemical
defenses, crypsis, and mimicry. Producers have evolved defenses against herbivores
including mechanical defenses, chemical defenses, and tolerance. Evolved defenses are
commonly costly and can sometimes be countered by subsequent adaptations in
Predators and herbivores can limit the
abundance of populations
Figure 14.1 Lizard predation on spiders. (a) In the Bahamas, researchers introduced a total of 20
spiders to each of five small islands with predatory lizards and to five small islands without
lizards. (b) Spiders were introduced to each island on two dates, indicated by the red arrows. The
spiders remained rare or absent on islands with lizards but increased 10-fold on islands without
lizards. Error bars are standard errors.
When a species is introduced to a region of the world where it has not
historically existed, we say that the species is introduced, exotic, or non-
native. If the introduced species spreads rapidly and negatively affects other
species, we say that the species is invasive.
Figure 14.3 Effects of a parasitoid on populations of red scale insects. (a) The California
red scale, a tiny insect with a hard shell, feeds on the sap of citrus trees and other plants.
The parasitoid wasp lays its eggs under the hard shell of the scale insect. When the eggs
hatch, the larvae slowly consume the scale insect. (b) After introducing large numbers of
scale insects to trees—during the months indicated by yellow shading on the x axis—the
scale insect population grew rapidly. Soon after the addition of the scale insects, the
number of juvenile and adult parasitoid wasps began to rapidly increase. This increase in
parasitoid wasps caused a subsequent rapid decline in scale insects.
parasitoid |ˈpar"siˌtoid, -ˌsī-|Entomology
an insect (e.g., the ichneumon wasp) whose larvae live as parasites that eventually kill their hosts (typically other insects).
Two levels of predators often exist in ecological communities:
mesopredators and top predators.
Mesopredators: Relatively small carnivores that consume herbivores.
Mesopredators such as coyotes, weasels, and feral cats are relatively small carnivores that