Lecture 15: Communities: Community Structure

Question 1

basic definition of community

Answer 1

The different species found in one place

Question 2

what is a more detailed definition of community derived from

Answer 2

an understanding of how it is structured

Question 3

Research on how communities are structured is _________, and our knowledge continues to develop and advance.

Answer 3

a highly active area of research

Question 4

Central _____ has revolved around the degree to which cooccurring species are linked in space and time

Answer 4

debate

Question 5

Historical extremes in the debate:

Answer 5

1. interdependent communities
2. independent communities

Question 6

define interdependent communities

Answer 6

The community as a “organism”, evolving as a distinct co-evolving unit

Question 7

define independent communities

Answer 7

A community as fully disassociated populations of species will have similar environmental needs and tolerances, but do not require each other to survive

Question 8

modern view of communities

Answer 8

A community is an association of interacting populations, with the interactions maintained via coevolution to varying degrees across space and time.

Question 9

what is a key pattern in community structure

Answer 9

Species composition changes as we move across the landscape

Question 10

what do community ecologists want to describe

Answer 10

differences in how species composition changes, and understand the underlying processes

Question 11

define ecotone

Answer 11

A region of rapid replacement of species along an ecological gradient (temperature, nutrient, water availability, etc.).

Question 12

the two extreme ecotones

Answer 12

1. closed community
2. open community

Question 13

define closed community

Answer 13

• Clustering, or overlapping of species distributions along an ecological gradient, such that there are distinct transitions in groups of species at ecotones
• zonation is present

Question 14

define open community

Answer 14

• The distribution of any one species does not coincide closely with any other species along an ecological gradient
• weak or no ecotones

Question 15

what is the first key step in understanding the processes that structure communities

Answer 15

Quantifying how the number of species within a communities changes from place to place

Question 16

define species richness

Answer 16

• the number of species in a community
• it is the simplest measure of community structure, but often one of the most revealing

Question 17

how is species richness often the most revealing measure of community structure

Answer 17

substantial variation can exist from place to place that reveals something about the broader processes shaping biodiversity

Question 18

what does greater habitat diversity provide

Answer 18

it provides more niche space and resources
for species to coexist

Question 19

define trophic level

Answer 19

Different points on the food chain of consumer resource feeding relationships.

Question 20

define primary producers

Answer 20

The plants and other autotrophs (self-feeding, photosynthetic organisms) that form the base of the food chain

Question 21

define primary consumers

Answer 21

• Consumers of primary producers
• herbivores/ detritivores.

Question 22

define secondary consumers

Answer 22

• Consumers of primary consumers
• carnivores.

Question 23

Feeding relationships are not really a “food chain”, they are a ________ of interactions

Answer 23

complex web

Question 24

define food web

Answer 24

• The interconnected network of consumer and resource species within a community
• Few consumer species eat only one resource species, so most species have more than one link in the food web

Question 25

define omnivory

Answer 25

Feeding on more than one trophic level

Question 26

_______and more ______ add complexity to a food web

Answer 26

• Omnivory
• trophic levels

Question 27

what can change competitive dynamics and coexistence

Answer 27

When one consumer controls a resource species that would otherwise be competitively dominant, loss of the controlling consumer can change competitive dynamics and coexistence.

Question 28

define keystone consumers

Answer 28

Consumer species that maintain diversity and
coexistence among resource species at lower trophic levels

Question 29

what is the result of the loss of keystone consumers

Answer 29

results in documented “ecological collapse” of communities

Question 30

At the community level, consumers can ________, and producers in a trophic level can ________

Answer 30

• depress trophic level below
• limit the trophic level above

Question 31

define top-down control

Answer 31

when a higher trophic level controls the size of the trophic level below it.

Question 32

define bottom-up control

Answer 32

When the size of a trophic level is determined by the rate of production in the resource species in trophic level below

Question 33

define trophic cascade

Answer 33

When the indirect effects of consumer-resource interactions extend through other trophic levels

Question 34

Cascades can be relatively linear or work via ________ of indirect effects - cascades through the whole food web.

Answer 34

complex network

Question 35

Direct effect

Answer 35

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

Question 36

Indirect effect

Answer 36

An interaction between two species that involves one or more intermediate species