Exam 56: Communities

A forest is clear-cut and then abandoned.Over the next 100 years, it changes.First, fast-growing weedy annuals move in.These are replaced by perennial grasses and forbs, and eventually by shrubs.At some point, tree seedlings take root, and over time, a forest similar to the original forest appears.This region is undergoing the process of _______.

Refer to the table. A community contains four species of birds in the following numbers of individuals: 30, 10, 5, 5.The table gives most of the information required to determine the Shannon index of diversity.Complete the table by choosing the correct values: The proportion for species B is _______; the total value for p_i ln(p_i)is _______.

The ability of species to disperse to a community is determined by which of the "filters" that help determine community membership?

In 1963, an oceanic volcanic eruption off the southern coast of Iceland formed the island of Surtsey.If the Surtsey volcano erupted again and a new layer of lava completely covered the island, would the resulting succession be considered primary or secondary succession?

A food web is generally used to describe connections or interactions in an ecological community that are related to which factor?

After the 1980 eruption of Mount St.Helens, populations of small mammals and other organisms recovered much more quickly in the zones of secondary succession than in the Pumice Plain, where primary succession occurred.This more rapid recovery was aided by all of the following factors except

The text shows a large, complex area of desert and a single pitcher plant with water that contains microorganisms as two examples of communities.What do both have that allows them to be defined as communities?

Ecologists sometimes have difficulty defining and separating communities in nature because most communities have

One reason agricultural communities are often unstable is the practice of planting only a single species, which is called _______.

Bluegills in a pond prefer to feed on large zooplankton, such as copepods.The zooplankton in turn feed on algae.The pond has a few bass, which feed on the bluegills.A farmer introduces a large number of additional bass, which decimate the bluegill population.Quickly, algal blooms threaten to overwhelm the pond.The control of algae in this pond is an illustration of a(n)

A new community is forming in a region devastated by a years-long drought.Rain has recently returned to the area; in some cases, the rain has been severe enough to cause flooding and rapid runoff.Seeds from a number of plant species enter from the surrounding region and begin to grow.However, periodic storms erode the soil, and many species have difficulty becoming established.This series of events suggests that which factor is most important in determining membership in the new community?

In the Eel River of Northern California, the food web includes the following set of interactions: Assuming this set of interactions is controlled by a trophic cascade, what changes would be expected if the predatory fish were removed?

Managers sow seeds for a new non-native grass species in a field and allow the grass to become established.Later, they introduce cattle to graze there.The new grass becomes the cattle's favorite food, and the new species is grazed to extinction.This might be considered an example of which process at work?

Charles Crisafulli and his colleagues studied populations of small mammals on Mount St.Helens over 20 years following the volcanic eruption.They studied mammals in the Pumice Plain (primary succession) and in the Blowdown Zone and Tephra-fall Zone (secondary succession) and compared them with an unaffected reference area.What was the result of this study?

A hurricane devastates a region of the Gulf Coast.Its winds destroy many trees and damage other natural environments.This situation would be described ecologically as a(n)

A semiarid ecosystem is dominated by a mixture of shortgrass prairies and chaparral.Prairie primary producers include grasses and other herbaceous flowering plants (forbs).The chaparral is dominated by shrubs, including mesquite and yucca intermixed with grasses and forbs.Herbivores (jackrabbits and cottontails) in turn are eaten by "mesopredators," including badgers, bobcats, skunks, and gray foxes.The top-level predator is the coyote.How many trophic levels are described in this ecosystem?

A small fish species is accidentally introduced into a large lake.It adapts easily to the lake environment and reproduces rapidly.However, a large native fish species finds it easy prey, and within a few generations, the introduced fish is essentially wiped out.The species was prevented from remaining in the community by the process of _______.

The establishment of a non-native species in a new community would most likely be considered unsuccessful if

The Shannon index of species diversity is calculated using this equation: The data for a community of four species is given in the table.Use the table and the equation to determine the diversity value (H) for this community.

The rocky intertidal zone on the Washington coast supports a community including a bivalve mussel, Mytilus, which is preyed upon by the sea star Pisaster.If sea stars are removed, the mussel becomes dominant and other space-occupying species, including algae, decline.This suggests that the sea star Pisaster in this community serves as a