Communities - Structure Flashcards
How are communities organized?
Communities can be organized by a variety of concepts that categorize according to the interactions between a community’s populations
Use conceptual models to describe communities
Communities can be structured according to interdependent and independent models
Link concepts from physical environment to populations to explain communities
Community
A group of organisms living together in
space & time that interact directly/indirectly
How is a community defined?
A community is defined by the area’s dominant vegetation type and its biogeoclimatic zones
Ecotone
Area of transition (sharp or gradual) between communities
Organismal (interdependent) community concept
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
Individualistic (independent) community concept
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
Functional orgaization
Groups of species processing resources to provide specific functions
Guild
Groups of species sharing a resource
Equilibrium
Allows community to reach stable point because competing influences are balanced
Non-equilibrium
Communities are dynamic and unpredictable because local conditions vary temporally & spatially. Competition influences the dynamic.
Species richness
How many species are present
Species evenness
Relative abundance of each species
Species diversity
Product of both richness and evenness of each species
Dominant species
The most abundant and obvious species
Keystone species
Has a disproportionate impact on community structure given its abundance
What is a niche?
The sum of all environmental factors that limit growth, reproduction, and distribution
Fundamental niche
The environmental conditions a species could occupy is there is no competition
Realized niche
The environmental conditions a species does occupy given competitive interactions
Can two species occupy the exact same niche?
No, but overlap is possible
How do abiotic elements influence the presence abundance of species?
How does this in turn affect community structure & function?
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.
How does herbivory influence the presence abundance of species?
How does this in turn affect community structure & function?
Plant individuals and/or communities may be threatened if overconsumed. This affects the community by changing light levels, habitat, and nutrient availability.
How does predation influence the presence abundance of species?
How does this in turn affect community structure & function?
Prey numbers are greatly affected by predation, and prey numbers directly affect the amount of vegetation that makes up a community’s structure.
How does competition influence the presence abundance of species?
How does this in turn affect community structure & function?
Competition works on individuals, but effects will move up the line to populations and communities. Successful competitors will proliferate, while unsuccessful competitors are reduced.
How does disease influence the presence abundance of species?
How does this in turn affect community structure & function?
Disease makes individuals less competitive and will control population growth. It will also change competition dynamics.
How do symbiotic relationships influence the presence abundance of species?
How does this in turn affect community structure & function?
Symbiotic relationships may increase or decrease fitness, leading to changes in competition.
Competitive exclusion
Creates an unstable equilibrium because of two species overlapping ecological needs
How does competitive release influence the presence abundance of species?
How does this in turn affect community structure & function?
A species will occupy more of its fundamental niche because it is no longer hindered by competition.
Asymmetric competition
When one species has a larger fundamental niche than another. This makes it better able to tolerate conditions.
Resource partitioning
When species divide limited resources in order to reduce competition.
Facilitation
When one species has a beneficial effect on another species, but it is not intentional (altruistic).
What is the intermediate disturbance hypothesis?
The highest diversity is maintained at intermediate disturbance because competitive species and not competitive species can establish themselves.
Alternative stable states
In response to a disturbance, a community may be stable, resilient, change, or reach a new stable state.
Types of trophic transfers
Food chain: linear representation of feeding interactions
Food web: complex representation of multiple feeding interactions.
Entropy increases whenever there is a transfer of energy
What is the top down regulation concept?
An ecological system is regulated by consumers who limit populations. Doesn’t account for over predation making the system collapse.
What is the bottom up regulation concept?
Resources control an ecological system by limiting populations. Doesn’t account for how not all plants are edible.
Trophic cascade
A change at the top of a food web will trickle down and affect all levels
