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31

Removal of a keystone species can cause

a community to collapse

32

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

Ecosystem engineers

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.

Intermediate disturbance hypothesis

34

When disturbances are rare, populations

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

35

When disturbances are frequent, habitats

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

36

When disturbances occur at an intermediate frequency,

both types of species can persist

37

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

Food chain

38

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

Food web

39

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

Trophic level

40

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

Producers

41

a species that eats producers.

Primary consumer

42

a species that eats primary consumers

Secondary consumer

43

a species that eats secondary consumers

Tertiary consumer

44

a species that feeds at several trophic levels.

Omnivore

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

Guild

46

an interaction between two species that does not involve other species

Direct effect

47


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

affect other species in the community

48

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

Indirect effect

49

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

Trophic cascade

50

Indirect effects can occur

between communities.

51

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

Bottom-up control

52

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

Top-down control

53

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

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

54

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

food webs must be controlled from the top-down.