chapter 18

Question 1

an assemblage of species living together in an area

Answer 1

community

Question 2

Community zonation also occurs in

Answer 2

aquatic communities.

Question 3

Communities are often categorized by their

Answer 3

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

Question 4

Aquatic systems are often categorized by

Answer 4

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

Question 5

Ecologists rarely study every species in a community; rather, they

Answer 5

focus on a subset of species that live in an area

Question 6

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

Answer 6

Ecotone

Question 7

Some species move between

Answer 7

adjacent communities

Question 8

most species live in

Answer 8

one of the communities and spread into the ecotone.

Question 9

Ecotones support a large number of species

Answer 9

including those from adjoining habitats, and species specifically adapted to the ecotone

Question 10

communities in which species depend on each other to exist.

Answer 10

Interdependent communities

Question 11

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

Answer 11

Independent communities

Question 12

If species are interdependent, removing a species should cause

Answer 12

other species to decline

Question 13

if species are independent, removing a species should cause

Answer 13

neutral or positive changes in other species’ fitness

Question 14

the # of species in a community.

Answer 14

Species richness

Question 15

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

Answer 15

Relative abundance

Question 16

In a typical community, only a few species have

Answer 16

low or high abundance

Question 17

most species have intermediate

Answer 17

abundance

Question 18

if a species has intermediate abundance they follow a

Answer 18

log normal distribution

Question 19

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.

Answer 19

Rank-abundance curves

Question 20

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

Answer 20

Species evenness

Question 21

The species richness of a community can be affected by

Answer 21

the amount of available resources.

Question 22

To understand the influence of resources, ecologists have examined the relationship between

Answer 22

productivity and species richness.

Question 23

observed patterns across aquatic and terrestrial environments

Answer 23

u shaped 
negative 
neutral 
positive
hump shaped

Question 24

what is the most commonly observed relationship between diversity and productivity

Answer 24

hump shaped curve

Question 25

Experiments have manipulated productivity by

Answer 25

adding nutrients (e.g., nitrogen) to an ecosystem.

Question 26

Added fertility commonly causes a decline in the species richness of

Answer 26

producers (e.g., plants and algae).

Question 27

The reason species richness declines with increased habitat fertility

Answer 27

is unclear.

Question 28

For plant communities, increased fertility may cause

Answer 28

dominant plants to cast more shade on competitively inferior plants.

Question 29

Communities with a higher diversity of habitats should offer

Answer 29

more potential niches (e.g., places to feed and breed) and a higher diversity of species.

Question 30

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

Answer 30

Keystone species

Question 31

Removal of a keystone species can cause

Answer 31

a community to collapse

Question 32

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

Answer 32

Ecosystem engineers

Question 33

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

Answer 33

Intermediate disturbance hypothesis

Question 34

When disturbances are rare, populations

Answer 34

grow until resources are scarce, and competitively superior species become dominant

Question 35

When disturbances are frequent, habitats

Answer 35

typically support a small number of species that are adapted to disturbances.

Question 36

When disturbances occur at an intermediate frequency,

Answer 36

both types of species can persist

Question 37

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

Answer 37

Food chain

Question 38

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

Answer 38

Food web

Question 39

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

Answer 39

Trophic level

Question 40

the autotrophs that convert light energy and CO2 into carbohydrates through photosynthesis.

Answer 40

Producers

Question 41

a species that eats producers.

Answer 41

Primary consumer

Question 42

a species that eats primary consumers

Answer 42

Secondary consumer

Question 43

a species that eats secondary consumers

Answer 43

Tertiary consumer

Question 44

a species that feeds at several trophic levels.

Answer 44

Omnivore

Question 45

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

Answer 45

Guild

Question 46

an interaction between two species that does not involve other species

Answer 46

Direct effect

Question 47

The direct effect of one species often sets off a chain of events that

Answer 47

affect other species in the community

Question 48

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

Answer 48

Indirect effect

Question 49

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

Answer 49

Trophic cascade

Question 50

Indirect effects can occur

Answer 50

between communities.

Question 51

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

Answer 51

Bottom-up control

Question 52

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

Answer 52

Top-down control

Question 53

If food webs have three trophic levels, top-down control by predators would

Answer 53

reduce the abundance of herbivores, leading to an increase in vegetation.

Question 54

researchers (Hairston, Slobodkin, and Smith) suggested that since communities contain an abundance of vegetation

Answer 54

food webs must be controlled from the top-down.