Exam 56: Communities

Scientists are still experimenting to better understand the relationship between species richness, productivity, and stability.But agriculturists have been experimenting with these concepts for millennia, as they try to determine the most efficient ways to grow food.In which of these situations do farmers show the greatest understanding that greater diversity produces a more stable, productive ecosystem?

Some Native American cultures traditionally practiced "three sisters" agriculture, in which they planted corn, squash, and climbing beans together.Compared with growing each crop separately as a monoculture, this practice likely offers all of the following benefits except

Refer to the diagram, showing changes occurring during succession as the glacier in Glacier Bay, Alaska, melted over the past 200 years. The moraines, or gravel deposits exposed by the retreating glacier, increase in age of exposure from left to right.Which statement best describes how the vegetation changes during succession?

The hypothesis formulated by Joseph Connell, in which he described the likely effect on species diversity of different levels of disturbance in a community, is known as the _______ hypothesis.

In the tropical seasonal forest of central Kenya, exclosures (experimental plots that excluded grazers) were used to study the influence of grazers on this community.Comparing grazed with ungrazed sites, researchers found that elimination of grazing increased the abundance of trees, which in turn increased the number of beetles and the number of lizards that fed on the beetles.This suggests that grazers

In Yellowstone National Park, elk preferred to browse on specific plants, such as willow and aspen trees.The rapid increase in elk after wolves were removed resulted in what change, if any, to the community structure of the area?

Based on studies of the introduction of exotic plant species into communities, it appears that, in general, biotic resistance posed by native species in the community

The Mount St.Helens volcano erupted in 1980, and scientists have been studying the changes on the mountain ever since.Why are they so interested in studying this site? Name at least two concepts we now know more about as a result of their studies.

The diagram illustrates the intermediate disturbance hypothesis, which correlates the degree of disturbance in a community with the level of species diversity attained by that community.Assume that a dominant plant species is strongly affected by a disturbance and is less able to obtain resources than before the disturbance.Compare the future species diversity of the community under conditions of low, medium, and high levels of disturbance.

Refer to the diagram. In this simplified food web, the gray wolf is classified under "secondary and tertiary consumers." The wolf is a secondary consumer because it feeds on _______ and a tertiary consumer because it feeds on _______.

The Burmese python is native to tropical and subtropical areas of southern Asia.It can grow to 20 feet or more in length.The species was accidentally introduced into Florida's Everglades National Park, and the park now has an estimated 30,000 pythons.It is a voracious predator, feeding on many kinds of birds (many of them endangered) and even on alligators.Native species in its new environment offer little or no competition.How might the Burmese python be affecting community structure in the Everglades, and why?

Which factor represents an "abiotic filter" that may prevent a species from becoming established in a marine community?

After a major disturbance wipes out or seriously damages a community, the community's usual response is to undergo

The branches and canopy of fig trees in tropical rainforests provide habitat for several thousand animal species, including insects, reptiles, birds, and rodents.Their fruit serves as a food source for many species during times of the year when other fruit is scarce.These fruit-eating species in turn provide prey for many different predator species.The benefits provided by fig trees suggest that, in the rainforest, they serve as

Scientists now think some ecosystems undergoing primary succession will not develop into predictable, stable states.Which of these factors might cause an ecosystem to develop into an alternative climax state?

Kelp forests in Alaskan waters support numerous species of fish and invertebrates.Giant kelp, the dominant producer in these communities, can be completely decimated by the grazing of sea urchins, which consume the kelp and create "urchin barrens" devoid of marine life.Urchins are a preferred food of sea otters.By keeping urchin numbers low, otters help ensure the viability of the kelp forest community.The first response to removal of sea otters from this community would likely be

Consider a situation that results in primary succession, such as at Glacier Bay.Imagine that after a fully developed community of organisms exists, the area suffers a major disturbance, such as a storm, and then goes through the process of secondary succession.How would the processes of primary and secondary succession compare?

A plant species in a community grows very rapidly and uses excess amounts of surrounding soil resources.This results in a competitor species being eliminated from the community.The rapidly growing species (interactor) has a (positive/negative) _______ interaction with the eliminated (target) species.

When introduced organisms such as sea squirts are introduced into warm waters, they are able to outcompete native species and become established.They are less able to do this if the water is cooler.This suggests that these species are limited by _______ conditions.

Removal of wolves in Yellowstone National Park caused a rapid increase in the elk population.Return of the wolves caused the population of elk to decline rapidly and stabilize.This response suggests that wolves (the "interactor" species) had what effect on elk (the "target" species)?