Exam 56: Communities

Several members of a mouse species living in a weedy edge environment migrate into a nearby crop field.They find plenty of fallen seeds to eat, so they dig tunnels and begin to colonize.The soil often receives inputs of concentrated chemicals, including pesticides.The mice begin to die, and after a few generations the survivors move back into the edge environment.The mice have failed to colonize the new community because of

Peas, beans, clover, and peanuts are all legumes, which are nitrogen-fixing plants.Ecologically, these plants can all be placed in the same _______.

Which statement describes an important difference between a keystone species and a foundation species?

Which of these is not an environmental factor that might prevent a species of mollusk from becoming established in a shallow-water marine community?

A wetland is drained, filled, and planted with corn.After 20 years, the farmer decides to restore the wetland and works with a local conservation agency to return the habitat to its original conditions.After some time, it becomes obvious that the species composition is very different from that of the original wetland.What is the most likely explanation for what has happened to the wetland?

Two species eat the same prey, which is a limiting resource, and both their populations remain stable.Species A is removed, and the population of species B begins to increase rapidly.This suggests that the two species are _______ and the interaction is _______.

Corals affect their communities by producing elaborate limestone skeletons (coral reefs) that provide habitat for thousands of species and by helping to concentrate resources on the reef.Sea otters affect their communities by acting as top predators that generate trophic cascades, helping to maintain species richness, abundance, and composition.Are these animals considered keystone species or foundation species?

Seagrass beds extend along much of the Atlantic coast of the United States.A group of scientists is studying an estuary that contains seagrass beds.They arbitrarily set a boundary around their study community such that it includes a 100-yard length of seagrass plus the next 100 feet of water extending from it in all directions.Are the scientists defining their community in theoretical or practical terms?

Lottery (neutral) models of species diversity in a community are most likely to operate when

Which statement best explains the difference between primary and secondary succession?

Species composition was analyzed for fish communities in two Brazilian rivers.The higher (headwaters), middle, and lower (floodplain) sections of both the Iguatemi River and the Jogui River were sampled.The Iguatemi had 34 species and the Jogui had 31.In both rivers, some species occurred only in the headwaters, others only in the floodplains.Water velocity decreased and turbidity increased from the headwaters to the floodplains.Neither river had rooted vegetation, and the communities did not differ significantly from season to season.The factor most important in determining species composition in the two rivers was most likely

Plant species A has only one pollinator; if the pollinator disappears, the plant is not pollinated and its numbers decline.Plant species B has multiple pollinators; if a single pollinator disappears, the remaining pollinators ensure that species B is still pollinated and its numbers remain stable.Which species shows the greatest interaction strength with its pollinators?

The type of succession most often resulting from human activities such as deforestation is _______ succession.

Tropical rainforests have hundreds of tree species.It has been hypothesized that the model that best describes the causes of species richness in these tree communities is the neutral, or lottery, model.This is because rainforest trees likely

In a salt marsh habitat, snails feed on marsh grasses, and blue crabs feed on snails.A high population of snails can graze the marsh so intensely that it becomes a mudflat.When blue crabs are present, the levels of all three species remain balanced and the marsh is healthy.What change in the salt marsh would be expected if blue crabs were removed?

Which example of trophic interactions represents an indirect interaction in a community?

Bison were introduced to a small fenced-in prairie region and allowed to reproduce.The bison soon overpopulated the area and overgrazed the native prairie grasses.After several years of overpopulation and overgrazing, managers removed the bison.However, after 10 years, the prairie has still not returned to its original species composition.This suggests it has undergone the process of _______.

Which of these species or groups of species would be considered both foundation species and ecosystem engineering species?

A freak cold spell in October 2009 in the northeastern United States dramatically reduced the survival of several small mammal species.In this situation, the cold spell was acting as a(n) _______.

There are several meanings of the word "community" and several ways to subdivide a community.Three are shown in the figure.Distinguish among these three subdivisions and explain why the members of a subdivision can be considered a community.