Chapter 54

The feeding relationships among the species in a community determine the community's (A) secondary succession. (B) ecological niche. (C) species richness. (D) trophic structure.

The principle of competitive exclusion states that (A) two species cannot coexist in the same habitat. (B) competition between two species always causes extinction or emigration of one species. (C) two species that have exactly the same niche cannot coexist in a community. (D) two species will stop reproducing until one species leaves the habitat.

Based on the intermediate disturbance hypothesis, a community's species diversity is increased by (A) frequent massive disturbance. (B) stable conditions with no disturbance. (C) moderate levels of disturbance. (D) human intervention to eliminate disturbance.

According to the island equilibrium model, species richness would be greatest on an island that is (A) large and remote. (B) small and remote. (C) large and close to a mainland. (D) small and close to a mainland.

Predators that are keystone species can maintain species diversity in a community if they (A) competitively exclude other predators. (B) prey on the community's dominant competitors. (C) reduce the number of disruptions in the community. (D) prey on the least abundant species in the community.

Food chains tend to be short because (A) only a single species of herbivore feeds on each plant species. (B) local extinction of a species causes extinction of the other species in its food chain. (C) most of the energy in a trophic level is lost as energy passes to the next higher level. (D) most producers are inedible.

Which of the following could qualify as a top-down control on a grassland community? (A) limitation of plant biomass by rainfall amount (B) influence of temperature on competition among plants (C) influence of soil nutrients on the abundance of grasses versus wildflowers (D) effect of grazing by bison on plant species diversity

The most plausible hypothesis to explain why species richness is higher in tropical than in temperate regions is that (A) tropical communities are younger. (B) tropical regions generally have more available water and higher levels of solar radiation. (C) higher temperatures cause more rapid speciation. (D) diversity increases as evapotranspiration decreases.

Community 1 contains 100 individuals distributed among four species: \(5 \mathrm{~A}, 5 \mathrm{~B}, 85 \mathrm{C},\) and \(5 \mathrm{D}\). Community 2 contains 100 individuals distributed among three species: \(30 \mathrm{~A}, 40 \mathrm{~B}\) and \(30 \mathrm{C}\). Calculate the Shannon diversity index \((H)\) for each community. Which community is more diverse?

In the Chesapeake Bay estuary, the blue crab is an omnivore that eats eelgrass and other primary producers as well as clams. It is also a cannibal. In turn, the crabs are eaten by humans and by the endangered Kemp's Ridley sea turtle. Based on this information, draw a food web that includes the blue crab. Assuming that top-down control occurs in this system, describe what would happen to the abundance of eelgrass if humans stopped eating blue crabs.

Explain why adaptations of particular organisms to competition may not necessarily represent instances of character displacement. What would a researcher have to demonstrate about two competing species to make a convincing case for character displacement?

An ecologist studying desert plants performed the following experiment. She staked out two identical plots, containing sagebrush plants and small annual wildflowers. She found the same five wildflower species in roughly equal numbers on both plots. She then enclosed one plot with a fence to keep out kangaroo rats, the most common grain-eaters of the area. After two years, four of the wildflower species were no longer present in the fenced plot, but one species had become much more abundant. The control plot had not changed in species diversity. Using the principles of community ecology, propose a hypothesis to explain her results. What additional evidence would support your hypothesis?

In Batesian mimicry, a palatable species gains protection by mimicking an unpalatable one. Imagine that individuals of a palatable, brightly colored fly species are blown to three remote islands. The first island has no predators of that species; the second has predators but no similarly colored, unpalatable species; and the third has both predators and a similarly colored, unpalatable species. In a short essay (100-150 words), predict what might happen to the coloration of the palatable species on each island through time if coloration is a genetically controlled trait. Explain your predictions.