Chapter 7. Chapter 7: Population Ecology
What role do predators play in regulating populations...?
Guiding Question 7.5
What role do predators play in regulating populations, and how can the presence or absence of predators affect entire communities?
Why You Should Care
Chances are that you or someone you know has dealt with the problem of too few predators. In eastern North America, white-tailed deer are becoming overpopulated and are a major nuisance to homeowners. In the Rockies, elk numbers are rising, too. In both cases, this increase in population is the result of not having enough predators. The high density of deer is having a negative impact on ecosystems because the higher populations are eating too much of the local vegetation, some of which contains endangered or threatened plants. Deer may also inhibit the regeneration of forests when they browse too heavily on tree seedlings, leaving no young trees to replace older ones.
Question 7.1
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Predict what will happen after the following event:
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Predict what will happen after the following event:
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Short-Answer Questions
Populations of hares and lynx (a small wild cat species) in Canada demonstrate the same bust and boom cycles that wolves and moose do on Isle Royale. As hares increase in number, so do lynx; once lynx numbers increase, hare numbers will decrease. However, scientists have determined that the cycles are not dependent only on the lynx and hares. In winter, the hares live off the young shoots of trees and shrubs. When the trees and shrubs are eaten heavily, they produce toxic and unpalatable compounds in their twigs. This effectively reduces the hares’ food supply and therefore their population size.
2) As lynx populations increase, hare populations will decrease, and the toxicity should decrease as well.
3) With the information provided to you, this is a challenging question to answer. A good first step would be to eliminate any species that couldn't be a keystone species. In this case, the plants are not good candidates for keystone species. First off, there is actually a group of different species here, so it would be impossible with the information provided to zero in on one species, and chances are good that, if one plant species were removed, the hares could survive on the other species. So, that leaves the lynx and hares. You could easily make the case that both of these species not only influence the abundance of the other, but also the abundance of the vegetation, and hence either would be a good candidate for keystone species.