Chap 17: Change in Communities

A mudslide kills a large fraction of a population of a flower species. The reduction in this flower population allows for an increase in the population size of a fern that competes with the flower. This is an example of:

 a. stress

 b. facilitation

 c. disturbance

 d. inihibition

disturbance

A region that is experiencing very frequent disturbances of intermediate intensity will most likely exhibit _______.

 a. extinction

 b. Primary succession

 c. none of these

 d. Secondary succession

Secondary succession

Suppose that a late succession plant that is surrounded by early succession plants will grow at a rate of 0.7 cm per day. If the early succession plants are removed experimentally, the late succession plants are observed to grow at a rate of 0.6 cm per day. This experiment shows that the early succession plants have a _______ effect on the late succession plants, and this observation is most consistent with the _______ model of succession.

 a. positive; inhibition

 b. negative; facilitation

 c. positive; facilitation

 d. positive; tolerance

positive; facilitation

The inability of a system to shift back to the original community state, even after the original conditions have been restored, is called:

 a. hysteresis

 b. the photic state

 c. the climax stage

 d. an ecological valley

hysteresis

Which of the following statements best describes Henry Gleason’s view of succession?

 a. Plant communities act like “superorganisms”

 b. Succession results in a predictable, stable end point

 c. Communities are a random product of fluctuating environmental conditions

 d. Early colonizers facilitate later successional stages

Communities are a random product of fluctuating environmental conditions

Ecologists are concerned about the establishment of invasive species in new areas because invasive species

 a. can have large ecological effects in their new communities.

 b. always cause a decline in biological diversity of the communities they invade.

 c. often become established are easy to control.

 d. are often toxic.

can have large ecological effects in their new communities.

When wolves were returned to Yellowstone National Park in 1995, some of the effects noted were increasing levels of berries available to black bears, stabilization of stream banks, increased nesting habitat for birds, and increasing beaver numbers as a result of rejuvenating aspen trees. These were later determined to be the results of reduced numbers and altered feeding behavior of elk as they were preyed upon by the wolves. Given this information, which of the following best describes wolves in Yellowstone National Park?

 a. They are an ecosystem engineer.

 b. They are a primary consumer.

 c. They are a keystone species.

 d. They are a foundation species.

They are a keystone species.

Which of the following would be considered a community stress?

 a. Acidity in the water that is limiting the reproduction of certain fish species

 b. A beaver population that is causing trees to fall

 c. A fire that destroys nearly all the trees in an area

 d. Predation by a new predator

Acidity in the water that is limiting the reproduction of certain fish species

Which of the following is a biotic factor that can be an agent of change?

 a. A forest fire

b. Rought

c. Competition

 d. A hurricane

Competition

Alternative stable states most often arise

 a. in intertidal zones.

 b. in terrestrial ecosystems.

 c. under the tolerance model of succession.

 d. when there are strong interactions among species.

when there are strong interactions among species.