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1

an assemblage of species living together in an area

community

2

Community zonation also occurs in

aquatic communities.

3

Communities are often categorized by their

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

4

Aquatic systems are often categorized by

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

5

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

focus on a subset of species that live in an area

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.

Ecotone

7

Some species move between

adjacent communities

8

most species live in

one of the communities and spread into the ecotone.

9


Ecotones support a large number of species

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

10

communities in which species depend on each other to exist.

Interdependent communities

11

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

Independent communities

12

If species are interdependent, removing a species should cause

other species to decline

13

if species are independent, removing a species should cause

neutral or positive changes in other species’ fitness

14

the # of species in a community.

Species richness

15

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

Relative abundance

16

In a typical community, only a few species have

low or high abundance

17

most species have intermediate

abundance

18

if a species has intermediate abundance they follow a

log normal distribution

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.

Rank-abundance curves

20

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

Species evenness

21

The species richness of a community can be affected by

the amount of available resources.

22

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

productivity and species richness.

23

observed patterns across aquatic and terrestrial environments

u shaped
negative
neutral
positive
hump shaped

24

what is the most commonly observed relationship between diversity and productivity

hump shaped curve

25

Experiments have manipulated productivity by

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

26

Added fertility commonly causes a decline in the species richness of

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

27

The reason species richness declines with increased habitat fertility

is unclear.

28

For plant communities, increased fertility may cause

dominant plants to cast more shade on competitively inferior plants.

29

Communities with a higher diversity of habitats should offer

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

30

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

Keystone species