Chapter 18

Question 1

Communities are often categorized by…

Answer 1

their dominant organisms or by physical conditions that affect the distribution of species.

Question 2

Ecotone

Answer 2

a boundary created by sharp changes in environmental conditions over a relatively short distance, accompanied by a major change in the composition of species.

Ecotones support a large number of species, including those from adjoining habitats, and species specifically adapted to the ecotone.

Question 3

Aquatic systems are often categorized by

Answer 3

physical characteristics (e.g., stream or lake communities) or by dominant organisms (e.g., coral reef communities).

Question 4

Communities are often categorized by

Answer 4

their dominant organisms or by physical conditions that affect the distribution of species.

Question 5

Line-transect surveys

Answer 5

can demonstrate the existence of an ecotone.

Sharp changes in the distribution of species should occur across the ecotone.

Question 6

Interdependent communities

Answer 6

communities in which species depend on each other to exist.

Question 7

Independent communities

Answer 7

communities in which species do not depend on each other to exist.

Question 8

Plant biologist Frederic Clements proposed

Answer 8

most communities are interdependent and act as superorganisms.

Question 9

Plant biologist Henry Gleason proposed

Answer 9

that most communities consist of species with independent distributions.

Question 10

If species distributions are independent, they should depend only on __________ _________ _______; there should be gradual changes in species along a line transect.

Answer 10

individual habitat requirements

Question 11

If species are interdependent, removing a species should cause other species to ___________

Answer 11

decline

Question 12

if species are independent, removing a species should cause _________ or _________ changes in other species’ fitness.

Answer 12

neutral or positive

Question 13

Species living under harsh environmental conditions (e.g., high elevation) frequently exhibit ______________.

Answer 13

interdependence

Question 14

Species richness

Answer 14

the number of species in a community.

Question 15

Relative abundance

Answer 15

the proportion of individuals in a community represented by each species.

Question 16

Log-normal distribution

Answer 16

a normal, or bell-shaped, distribution that uses a logarithmic scale on the x-axis.

Question 17

Rank-abundance curves

Answer 17

a curve that plots the relative abundance of each species in a community in rank order from the most abundant species to the least abundant species.

To plot a rank-abundance curve, rank each species in terms of its abundance; the most abundant species receives a rank of 1, the next most abundant species receives a rank of 2, etc.

Question 18

Species evenness

Answer 18

a comparison of the relative abundance of each species in a community.

Question 19

most commonly observed relationship between diversity and productivity

Answer 19

Across studies of vertebrates and invertebrates in aquatic and terrestrial systems, a hump-shaped curve.

his indicates that a site with medium productivity has a higher species richness than sites with either low or high productivity.

Question 20

This suggests that light limitation by dominant plant species _________ ________ _________ in fertilized plant communities.

Answer 20

reduces species richness

Question 21

Keystone species

Answer 21

a species that substantially affects the structure of communities, although species might not be particularly numerous.

Removal of a keystone species can cause a community to collapse.

Question 22

Ecosystem engineers

Answer 22

are keystones species that affect communities by influencing the structure of a habitat.

Question 23

Intermediate disturbance hypothesis

Answer 23

the hypothesis that more species are present in a community that experiences occasional disturbances than in a community with either frequent or rare disturbances.

Question 24

Food chain

Answer 24

a linear representation of how different species in a community feed on each other.

Question 25

Food web

Answer 25

a complex and realistic representation of how species feed on each other in a community.

Question 26

Arrows in a food web indicate

Answer 26

consumption and the movement of energy and nutrients.

Question 27

Trophic level

Answer 27

a level in a food chain or food web of an ecosystem.

Question 28

Primary consumer

Answer 28

a species that eats producers.

Question 29

Secondary consumer

Answer 29

a species that eats primary consumers.

Question 30

Tertiary consumer

Answer 30

a species that eats secondary consumers.

Question 31

Omnivore

Answer 31

a species that feeds at several trophic levels.

Question 32

Guild

Answer 32

within a given trophic level, a group of species that feeds on similar items (e.g., guilds of leaf eaters); members of the group are not necessarily related.

Question 33

Direct effect

Answer 33

an interaction between two species that does not involve other species.

The direct effect of one species often sets off a chain of events that affect other species in the community.

Question 34

Indirect effect

Answer 34

an interaction between two species that involves one or more intermediate species.

Question 35

Trophic cascade

Answer 35

indirect effects in a community that are initiated by a predator.

Question 36

Density-mediated indirect effect

Answer 36

an indirect effect caused by changes in the density of an intermediate species.

Question 37

Trait-mediated indirect effect

Answer 37

an indirect effect caused by changes in the traits of an intermediate species.

Trait-mediated indirect effects commonly occur when a predator causes its prey to change its feeding behavior, which alters the amount of food consumed by the prey.

Question 38

Bottom-up control

Answer 38

when the abundances of trophic groups are determined by the amount of energy available from producers.

Question 39

Top-down control

Answer 39

when the abundances of trophic groups are determined by the existence of predators at the top of the food web.

Question 40

Community stability

Answer 40

the ability of a community to maintain a par=cular structure.

Question 41

Community resistance

Answer 41

the amount a community changes when acted upon by a disturbance (e.g., addition or removal of a species).

Question 42

Community resilience

Answer 42

the time it takes after a disturbance for a community to return to its original state.

Question 43

Alternative stable state

Answer 43

when a community is disturbed so much that species composition and relative abundance change, and the new community structure is resistant to further change.