Chapter 18: Factors Influencing the Structure of Communities

Question 1

Fundamental niches along an environmental gradient can be represented by which type of curve?

Answer 1

Bell curves

Question 2

This model assumes that the presence and abundance of the individual species found in a given community are solely a result of the independent responses of each species to the prevailing physical environment.

Answer 2

Null model

Question 3

True or false: the null model assumes that interactions among species have no significant influence on community structure.

Answer 3

True

Question 4

True or false: according to the null model, if we remove one species and examine the population response of the other and find that it does not differ from that observed previously in the presence of the removed species, the removed species’ interaction has no influence on the remaining one’s abundance.

Answer 4

True

Question 5

What does it mean to say that species interactions are diffuse?

Answer 5

They involve a number of species.

Question 6

Why do studies of the null model underestimate the importance of species interactions?

Answer 6

They often look at only two species within the community.

Question 7

In this form of competition, direct interactions between any two species may be weak, making it difficult to determine the effect of any given species on the other.

Answer 7

Diffuse competition

Question 8

Food webs illustrate ___ and ___ interactions within the community.

Answer 8

Diffuse, indirect

Question 9

A lynx eats all the snowshoe hares, which feed on white spruce. This is an example of ___ between the lynx and the white spruce.

Answer 9

Indirect interaction

Question 10

These types of interactions can potentially arise throughout the entire community because of a single direct interaction between only two component species.

Answer 10

Indirect interactions

Question 11

This refers to the average number of feeding links per species in a food web.

Answer 11

Linkage density

Question 12

This is a type of indirect interaction in which the predator enhances one or more inferior predators by reducing the abundance of the superior competitor.

Answer 12

Keystone predation

Question 13

This type of competition occurs when a single species of predator feeds on two prey species.

Answer 13

Apparent competition

Question 14

In this type of competition, when the predator is absent, the population of the two prey species is regulated by purely infraspecific, density dependent mechanisms, and neither species competes with each other.

Answer 14

Apparent competition.

Question 15

What can happen to prey populations if a predator depends on both of them?

Answer 15

Together, the prey populations can be lower than they would be if there was just one, because having both species of prey around means the predator does well. More predators means the prey gets eaten more often. If one species of prey disappears the predator suffers, and the other prey does better.

Question 16

This type of indirect interaction is beneficial to one species while neutral to another.

Answer 16

Indirect commensalism

Question 17

This type of indirect interaction is beneficial to both species involved.

Answer 17

Indirect mutualism

Question 18

This is when productivity and abundance of populations at any given trophic level are controlled by the productivity and abundance of populations in the trophic level below them.

Answer 18

Bottom-up control

Question 19

Plant population densities controlling herbivore population abundance is an example of ___ control.

Answer 19

Bottom-up

Question 20

This is when predator populations control the abundance of prey species.

Answer 20

Top-down control

Question 21

Plants in harsh environment are determined by ___, while species in less stressful environments are determined by ___.

Answer 21

Physical stress tolerance; competition

Question 22

True or false: environmental heterogeneity does not influence community diversity.

Answer 22

False

Question 23

The height of vegetation impacting the diversity of bird life within the community is an example of ___ influencing diversity in the community.

Answer 23

Environmental heterogeneity

Question 24

The relationship between nutrient availability and plant diversity is an ___ one.

Answer 24

Inverse

Question 25

How does the inverse relationship between nutrient availability and plant diversity affect plant populations?

Answer 25

As more nutrients become available, plants shift their competition from below ground to their leaves. Taller, faster growing plants will win this competition, leading to less plant diversity.

Question 26

True or false: in general, there’s a tradeoff between a species’ stress tolerance and its competitive ability along a gradient of resource ability.

Answer 26

True