Community Ecology Chapter 54 Eric Ribbens Western Illinois University Questions prepared by Eric Ribbens Western Illinois University John Zarnetske Hoosick Falls Central Schools

Two-species interactions are classified by the impact each species has on the other. Thus, a competitive interaction is one where the populations of each species are hurt by the presence of the other species, usually because each species uses the same resources. Niche partitioning enables species to coexist by avoiding direct competition. encouraging mutualistic interactions. enabling prey to hide from predators. creating new resources. allowing abiotic factors, such as climate or nutrient availability, to influence the community. Answer: a

Which of the following best describes resource partitioning? Two species can coevolve to share identical niches. Competitive exclusion results in the success of the superior species. A climax community is reached when no new niches are available. Slight variations in niche allow similar species to coexist. Differential resource utilization results in the decrease in community species diversity. Answer: d

What is one difference between the fundamental niche and the realized niche? The realized niche is larger. The fundamental niche is determined by competitors. The realized niche is determined by abiotic resources. Individuals will be found only in the realized niche. The difference is called the occupied niche. Answer: d

The common spiny mouse (Acomys cahirinus) and the golden spiny mouse (A. russatus) can occupy essentially the same ecological niche. They accomplish this by a) character displacement. b) temporal niche partitioning. c) eating different foods. d) mating at different times of year. e) each occupying their functional niche. Answer: b

Look at the figure in the next slide Look at the figure in the next slide. Joseph Connell showed that when Balanus are removed from the intertidal zone, Chthamalus expanded to occupy the space formerly occupied by Balanus. What would you predict if he removed Chthamalus? Since Balanus is the superior competitor, it probably would move up into the space Chthamalus occupied. Since Chthamalus is the superior competitor, it probably would move down into the space Balanus occupied. Since Balanus is the superior competitor, it probably cannot live in the high intertidal zone. Balanus would disappear as well, since it preys on Chthamalus. Because of the mutualistic association, the range of Balanus would shrink. Answer: c

When Connell removed Balanus from the lower strata, the Chthamalus population spread into that area. RESULTS Ecologist Joseph Connell studied two barnacle species—Balanus balanoides and Chthamalus stellatus —that have a stratified distribution on rocks along the coast of Scotland. EXPERIMENT

The figure shows that when two species of finch coexist, their beak sizes diverge, which is character displacement. If the two species colonized an island on which there were seeds of only one size, what would Gause’s principle of competitive exclusion predict? The finches would hybridize and become one species. b) G. fuliginosa would evolve small beaks, and G. fortis would evolve large beaks. c) One of the finch species would probably disappear from the island. d) The plants would evolve seeds of different sizes. It is impossible to predict the outcome. Answer: c

An obligate mutualism is an interaction in which at least one species cannot survive without the presence of the other species; a facultative mutualism is an interaction that benefits both species but is not required by either species. One reason facultative mutualism is more common is that in an obligate mutualism, if the partner becomes extinct, the obligate mutualist will also become extinct. in a facultative mutualism, if the partner becomes extinct, the obligate mutualist will also become extinct. in an obligate mutualism, the obligate mutualist is obliged to support its partner. in a facultative mutualism, neither partner can depend on the other partner. facultative mutualisms require longer periods of time to evolve. Answer: a

This graph shows the effect of soil pH on microbial diversity This graph shows the effect of soil pH on microbial diversity. One conclusion you should draw from this figure is the higher the soil pH, the higher the microbial diversity. the lower the soil pH, the higher the microbial diversity. microbes eat pH. the scientists couldn’t find any acidic or basic soils. there appears to be an optimal pH value for maximizing microbial diversity. Answer: e

Look at the following figure, which shows a partial Chesapeake Bay food web. If sea nettles disappeared, there would be fewer fish eggs. there would be more striped bass. there would be fewer zooplankton. striped bass would have less food to eat. sea nettles would reinvade from the ocean. Answer: b

In rocky intertidal communities of western North America, Robert Paine removed Pisaster, an uncommon starfish, and measured species diversity. He found species diversity dropped dramatically when Pisaster was not present. From this, we can conclude that uncommon species are more vital to the community than common species. predators are more vital to the community than prey. Pisaster likely consumed the dominant competitors. Robert Paine’s experiment was poorly designed. removing one species always hurts the community. Answer: c

Disturbance is an important component of succession because it removes keystone species. changes the biome from one kind to another. introduces invasive species. is associated with humans. tends to promote earlier successional stages. Answer: e

The intermediate disturbance hypothesis predicts that most disturbances are intermediate in intensity. species richness is highest when disturbances are intermediate. most communities are at an intermediate stage of succession. intermediate disturbances maximize competitive exclusion. because species richness corresponds to geographic area, intermediate disturbances increase species richness. Answer: b

Ecologists are studying the potential spread of the H1N1 virus by quarantining domestic birds. trapping and testing migrating and resident birds. hunting infected migratory species. comparing the virulence of H1N1 to various avian species. e) cleaning up commercial poultry operations. Answer: b