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Environmental Science: A Global Concern, 7/e

William P. Cunningham, University of Minnesota
Mary Ann Cunningham, Vassar College
Barbara Woodworth Saigo, St. Cloud State University

Biological Communities and Species Interaction

Essay Quiz


1		Explain what is meant by community productivity, and describe how productivity is related to the concept of limiting factors.



2		Explain how a community could have a very large number of individual organisms yet be considered to have low diversity



3		How did elephants come to have such long snouts? Ducks to have webbed feet? Eagles to have such sharp eyesight? The generic answer to all of these questions is the same. It is to outline the process of natural selection. So, how did elephants come to have such long snouts?



4		How does a robin’s niche differ from its habitat?



5		Describe one important way natural selection has acted to reduce intraspecific competition.



6		Why do ecologists prefer that species from one community not be introduced willy-nilly into other communities?



7		A surprising number of pest insect species are currently immune to pesticides that decades ago were lethal in ancestral populations of these same species. Explain how this resistance came about.



8		Agricultural fields and gardens can be considered low-diversity, low- complexity ecosystems. These systems appear particularly easily invaded by numerous weed species, most of which were accidentally introduced into the New World from Europe or Asia. a. What bearing does this observation have on the argument over whether community complexity is correlated with community stability? b. The skeptic might argue that it only appears that these invaders are more trouble in agricultural land systems because we pay more attention to them than the more complex communities around them. How would you go about determining the facts?



9		Males of many bird species establish breeding territories. The territories are defended against other males of the same species, effectively limiting the number of breeding pairs in a particular area. For example, in a 5-hectare marsh, if red-winged blackbirds establish 0.5-hectare territories, there can only be 10 breeding pairs of birds. That would seem to restrict the total number of offspring below what it could have been if there were no territorial behavior and 20 pairs of birds nested in the marsh. Under what circumstances would territorial behavior actually enhance the total number of offspring produced in the marsh, even though it did reduce the number of nesting pairs? (In other words, how could territorial behavior be more adaptive than the absence of such behavior?)



10		After reading so much about predation, competition, natural selection, and species displacing each other in succession, it would be understandable if you concluded that biological communities are dog-eat-dog places. You might wonder if cooperation has any role to play whatsoever. a. Make a list of examples of nonhuman animal cooperation. Which are intraspecific, and which are interspecific? b. Why do you suppose cooperation is so overwhelmingly intraspecific in nature?



11		Visit the Current Global Environmental Issues map on this Web site. Under Wildlife, select the piece Sea otters suddenly disappearing. The theme of ecology surely is the interconnectedness of the web of life. How does the otter story support this view?

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