Communities - Structure

Question 1

How are communities organized?

Answer 1

Communities can be organized by a variety of concepts that categorize according to the interactions between a community’s populations

Question 2

Use conceptual models to describe communities

Answer 2

Communities can be structured according to interdependent and independent models

Question 3

Link concepts from physical environment to populations to explain communities

Question 4

Community

Answer 4

A group of organisms living together in
space & time that interact directly/indirectly

Question 5

How is a community defined?

Answer 5

A community is defined by the area’s dominant vegetation type and its biogeoclimatic zones

Question 6

Ecotone

Answer 6

Area of transition (sharp or gradual) between communities

Question 7

Organismal (interdependent) community concept

Answer 7

Created by Frederick Clements.
A community is a mutually interdependent superorganism.

Species have overlapping habitat requirements and are divided by only narrow boundaries

Predictable succession towards a climax

Fails to account for competition and disturbance

Question 8

Individualistic (independent) community concept

Answer 8

Created by Henry Gleason.
Species act selfishly & independently. Local environment drives community.

There is no predictable end point to succession because there is continuous variation.

Does not account for facilitation, predictable patterns, and symbiotic relationships

Question 9

Functional orgaization

Answer 9

Groups of species processing resources to provide specific functions

Question 10

Guild

Answer 10

Groups of species sharing a resource

Question 11

Equilibrium

Answer 11

Allows community to reach stable point because competing influences are balanced

Question 12

Non-equilibrium

Answer 12

Communities are dynamic and unpredictable because local conditions vary temporally & spatially. Competition influences the dynamic.

Question 13

Species richness

Answer 13

How many species are present

Question 14

Species evenness

Answer 14

Relative abundance of each species

Question 15

Species diversity

Answer 15

Product of both richness and evenness of each species

Question 16

Dominant species

Answer 16

The most abundant and obvious species

Question 17

Keystone species

Answer 17

Has a disproportionate impact on community structure given its abundance

Question 18

What is a niche?

Answer 18

The sum of all environmental factors that limit growth, reproduction, and distribution

Question 19

Fundamental niche

Answer 19

The environmental conditions a species could occupy is there is no competition

Question 20

Realized niche

Answer 20

The environmental conditions a species does occupy given competitive interactions

Question 21

Can two species occupy the exact same niche?

Answer 21

No, but overlap is possible

Question 22

How do abiotic elements influence the presence abundance of species?
How does this in turn affect community structure & function?

Answer 22

Competition for light between plants affects vertical profile/structure which creates more or less habitat for animals

Fire disturbance affects structure by destroying the vertical profile and underbrush that provide habitats for animals.

Question 23

How does herbivory influence the presence abundance of species?
How does this in turn affect community structure & function?

Answer 23

Plant individuals and/or communities may be threatened if overconsumed. This affects the community by changing light levels, habitat, and nutrient availability.

Question 24

How does predation influence the presence abundance of species?
How does this in turn affect community structure & function?

Answer 24

Prey numbers are greatly affected by predation, and prey numbers directly affect the amount of vegetation that makes up a community’s structure.

Question 25

How does competition influence the presence abundance of species? How does this in turn affect community structure & function?

Answer 25

Competition works on individuals, but effects will move up the line to populations and communities. Successful competitors will proliferate, while unsuccessful competitors are reduced.

Question 26

How does disease influence the presence abundance of species? How does this in turn affect community structure & function?

Answer 26

Disease makes individuals less competitive and will control population growth. It will also change competition dynamics.

Question 27

How do symbiotic relationships influence the presence abundance of species? How does this in turn affect community structure & function?

Answer 27

Symbiotic relationships may increase or decrease fitness, leading to changes in competition.

Question 28

Competitive exclusion

Answer 28

Creates an unstable equilibrium because of two species overlapping ecological needs

Question 29

How does competitive release influence the presence abundance of species? How does this in turn affect community structure & function?

Answer 29

A species will occupy more of its fundamental niche because it is no longer hindered by competition.

Question 30

Asymmetric competition

Answer 30

When one species has a larger fundamental niche than another. This makes it better able to tolerate conditions.

Question 31

Resource partitioning

Answer 31

When species divide limited resources in order to reduce competition.

Question 32

Facilitation

Answer 32

When one species has a beneficial effect on another species, but it is not intentional (altruistic).

Question 33

What is the intermediate disturbance hypothesis?

Answer 33

The highest diversity is maintained at intermediate disturbance because competitive species and not competitive species can establish themselves.

Question 34

Alternative stable states

Answer 34

In response to a disturbance, a community may be stable, resilient, change, or reach a new stable state.

Question 35

Types of trophic transfers

Answer 35

Food chain: linear representation of feeding interactions Food web: complex representation of multiple feeding interactions. Entropy increases whenever there is a transfer of energy

Question 36

What is the top down regulation concept?

Answer 36

An ecological system is regulated by consumers who limit populations. Doesn't account for over predation making the system collapse.

Question 37

What is the bottom up regulation concept?

Answer 37

Resources control an ecological system by limiting populations. Doesn't account for how not all plants are edible.

Question 38

Trophic cascade

Answer 38

A change at the top of a food web will trickle down and affect all levels