Ecology: Ecological Communities

Definition of community

Group of interacting species occurring together in the same place and time

How can a community be defined?

Physical environment (sand dune, stream, desert) and biological environment (kelp forest, bog, coral reef, marsh)

How do ecologists divide up communities?

Taxonomic groups, guilds, functional groups

Example of taxonomic groups

Birds, mammals, reptiles, fungi, bacteria

Definition of guild

Groups of species that use the same resources

Example of guilds

Pollen-feeders, seed-eaters

Example of functional groups

Nitrogen-fixers, insects with piercing mouthparts

What are two aspects of species diversity?

Species richness and species evenness

Definition of species richness

Number of species in a community

Definition of species evenness

Relative abundance of a species; measured as biomass, number of individuals, or percent cover

What dictates how long a researcher is out sampling to get a good idea of the population?

The taxonomic level

How can communities be characterized?

Direct and indirect interactions

Definition of trophic skew

Alterations of the trophic structures within an ecological community through various extinctions and introduction of species

What are different agents of change in a community?

Abiotic vs biotic, stress vs disturbance

What is the difference between stress and disturbance?

Stress is gradual (rise in temperature) while disturbance is abrupt (volcanic eruption)

Definition of succession

Change in species composition over time as a result of both abiotic and biotic interactions

What are the two types of succession?

Primary and secondary

Definition of primary succession

Colonization for the “first” time

Definition of secondary succession

Recolonization following a disturbance

Definition of climax community

Stable endpoint of a community if left undisturbed

What is the general path for the theoretical model of succession?

No life → pioneer stage → intermediate stage (with some life) → Climax stage

What are the three models of succession

Facilitation, tolerance, inhibition

Definition of facilitation

Early species modify the environment in a manner that benefits later species

Definition of tolerance

Early species are r-selected while late species are K-selected

Definition of inhibition

Early species modify the environment in a manner that hinders later species

Are the models of succession mutually exclusive?

No

Is logging primary or secondary succession?

Secondary because not all life is being removed; it removes the larger trees but not the smaller plants

Can there be alternative stable states within a community?

Depends on what’s going on within the community (herbivores, climate)

Definition of a stable community

A community that returns to the same state after a disturbance

What controls which species are found in certain communities?

Regional species pool (availability), abiotic factors (physiological constraints), species interactions (competition, predation, disease)

What traits do stable communities exhibit?

High resistance and/or high resilience

What are the traits of an equilibrium community composition?

Communities are stable, each species occupies a unique niche, diversity maintained by resource partitionin

What are the traits of a non-equilibrium community composition?

Communities are constantly in flux, species may be ecologically equivalent, diversity is maintained by disturbances

Definition of paradox of the plankton

Term where a limited rage of resources (light, nutrients) supports a much wider range of planktonic organisms

Definition of the intermediate disturbance hypothesis

Regular disturbances at the right intervals creates more species diversity in a community