Community Ecology

Question 1

Community def

Answer 1

An assemblage of individuals of different species in a certain area at a certain time

Question 2

How do ecologists distinguish between communities

Answer 2

-composition: species composition (which species), species richness (how many), diversity (number and evenness)

-structure: trophic structure (food web), plant growth forms

Question 3

Vertical structure of communities

Answer 3

Heights of canopies in which species live

Question 4

Communities have distinct or gradual boundaries called….

Answer 4

Ectotones

Gradual

Question 5

Gradual boundaries

Answer 5

Usually follow gradients
-latitude
-altitude
-humidity
-salinity
-exposure

Question 6

Eco tones

Answer 6

Rather sharp transition from one community to a different, adjacent one.

Sharp changes in environmental condition Over short distances leading to a major change in the composition of species

Question 7

Species richness is greater where?

Answer 7

I’m the ecotone

Question 8

Interdependent vs independent views of communities

Answer 8

Interdependent or organismic view: highly organized systems with tight associations among species
Approach to study: classification

Independent or individualistic view: haphazard collection of individuals with little integration together because they have similar environmental requirements
Approach to study: dynamics, functional organization

Independent is better approach

Question 9

What can be used to measure species diversity and richness

Answer 9

Simpsons index

Shannon-wiener index

Question 10

Rank abundance curves

Answer 10

-greater evenness seen by smaller slope
-more species richness seen by longer line

Question 11

What has happened to plant diversity since long term fertilization?

Answer 11

-diversity has declined

Question 12

Natural patterns of productivity and species richness

Answer 12

-U shaped
-negative
-none
-positive
-hump shaped (common)

Question 13

Keystone species

Answer 13

Species that, despite low biomass, exert strong effects on the structure of the communities they inhabit

A species who’s removal produces a significant effect on other species

Effects spread through food Web

Question 14

Pisaster keystone species example

Answer 14

Starfish are keystone predators on shores

Pisaster clams in absence of star fish take over the shore and decrease biodiversity

More starfish=more diversity

Question 15

Top down and bottom up effects of food webs

Answer 15

Reduction of a producer, will result in less primary consumers, then less secondary consumers and then less tertiary consumers.

Reduction in tertiary consumer, will result in more secondary consumers, will result in less primary consumers, and more producers

Question 16

Stability

Answer 16

Ability of community to maintain structure

Question 17

Resilience

Answer 17

Measures as the time it takes after disturbances for a community to return to original state

Question 18

Resistance

Answer 18

Amount of change in a community after disturbances (more change=lower resistance)

Question 19

Low disturbance means what generally?

Answer 19

1 species overt takes the others and species richness decreases

Question 20

Is there more or less stability with more species

Answer 20

More

Question 21

Species richness

Answer 21

Number of species in a community

Question 22

Species evenness

Answer 22

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

Question 23

Intermediate disturbance hypothesis

Answer 23

More species are present in a community that experiences occasional disturbances than in a community that experiences frequent or rare disturbances

Question 24

Direct effect

Indirect effect

Answer 24

When two species interact without involving other species

When two species interact and invoke one or more intermediate species

Question 25

Trophic cascade

Answer 25

Indirect effects in a community that are initiated by a predator

Question 26

Density-mediated indirect effect

Answer 26

An indirect effect caused by changes in the denature of an intermediate species

Question 27

Trait-mediated indirect effects

Answer 27

An indirect effect caused by changes in the transits of an intermediate species

-when a predator causes its prey to change its feeding behaviour which in turn alters the amount of food consumed by the prey

Question 28

Bottom up control

Top down control

Answer 28

When the abundance of trophic groups in nature are determined by the amount of energy available from the producers in a community

When the abundance of trophic groups is determined by the existence of predators at the top of the food web