Question 1

Which of the following best describes a keystone species in a community?

Accepted Answer

A species with low abundance but a disproportionately large effect on community structure.

Question 2

In the Pacific Northwest, the shift from western hemlock to Douglas fir as the dominant tree species was primarily due to:

Accepted Answer

Active logging of western hemlock, which allowed Douglas fir seedlings to thrive in increased light conditions.

Question 3

Which of the following scenarios best illustrates a bottom-up control in a community?

Accepted Answer

A decrease in primary producer biomass leads to declines in both herbivore and carnivore populations.

Question 4

The introduction of the brown tree snake to Guam resulted in which of the following cascading effects?

Accepted Answer

A decline in native bird and bat species, leading to increased insect populations and agricultural problems.

Question 5

Which of the following is an example of an indirect positive effect in a trophic cascade?

Accepted Answer

Sea otters preying on sea urchins, which reduces grazing pressure on kelp, allowing kelp forests to recover.

Question 6

In the Yellowstone ecosystem, what was the primary reason for the decline of aspen and cottonwood trees before wolf reintroduction?

Accepted Answer

Overgrazing by elk populations that were no longer kept in check by wolves.

Question 7

Which of the following best explains why dominant species often achieve their status in a community?

Accepted Answer

They are able to competitively exclude other species for resources such as space, nutrients, or light.

Question 8

A fig tree that provides the only fruit available during certain times of the year is an example of which type of keystone species?

Accepted Answer

Key food resource keystone species

Question 9

If the egret (cleaner) is removed from the rhino-tick-egret system, what is the most likely outcome for the rhino population?

Accepted Answer

Rhino population will decrease due to increased tick loads and disease transmission.

Question 10

Which of the following equations best represents the concept of competitive exclusion between two species competing for the same resource?

Accepted Answer

$$N_1(t+1$$) = $$N_1(t$$) + $$r_1$$ $$N_1(t$$) \left(1 - \frac{$$N_1(t$$) + \alpha_{12} $$N_2(t$$)}{$$K_1$$}\right)$$

Question 11

Which of the following is NOT a possible role for a keystone species?

Accepted Answer

A dominant competitor that excludes all other species.

Question 12

In a bottom-up controlled aquatic ecosystem, what would be the expected effect of a significant decrease in primary productivity?

Accepted Answer

Decrease in both herbivore and carnivore biomass.

Question 13

Which of the following best describes a trophic cascade?

Accepted Answer

A process where changes at one trophic level cause reciprocal changes at adjacent trophic levels, often initiated by predators.

Question 14

After the reintroduction of wolves to Yellowstone, which of the following sequences best describes the indirect effects observed?

Accepted Answer

Wolves increase → Elk decrease → Aspen and willow increase → Songbirds and beavers increase

Question 15

Which of the following is a real-world example of a top-down effect in a community?

Accepted Answer

Sea otters controlling sea urchin populations, which in turn allows kelp forests to thrive.

Question 16

Why is it important for ecologists to study species with high interaction strength?

Accepted Answer

Because their addition or removal can dramatically alter community structure.

Question 17

Which of the following best explains why the removal of sea otters led to 'urchin barrens' along the west coast of the US?

Accepted Answer

Without sea otters, sea urchin populations exploded and overgrazed kelp forests.

Question 18

Which of the following is an example of a habitat modifier keystone species?

Accepted Answer

Beavers building dams that alter water flow and landscape structure.

Question 19

Competitive exclusion is most likely to occur when:

Accepted Answer

Two species occupy the same niche and compete for identical resources.

Question 20

Which of the following statements about dominant and keystone species is correct?

Accepted Answer

Keystone species can have a large effect on community structure despite low abundance.

7.2 Community Ecology: Species Interactions and Trophic Dynamics

Study Guide - Practice Questions