Chapter 53:Community Ecology

Community Ecology

The study of the interactions between the species in an area.

Community Hypothesis

1. Individualistic H.A. Gleason Community as a chance assemblage of

species because of similar abiotic requirements.

2. Interactive F.E. Clements Community as a linked assemblage of

species that function as an integrated whole.

Predictions

Individualistic - fuzzy borders Interactive - sharp borders Robert Whittaker – tested the two ideas

against each other.

Results

If abiotic factors form a continuum, then borders are fuzzy.

Individualistic Hypothesis is correct. Comment

Abiotic factors may form sharp borders. Ex: soil types

Result – the Community may look very much like the Interactive Hypothesis.

Interspecific Interactions

Interaction between species. May be positive, negative, or neutral. Ex:

1. Coevolution2. Predation3. Mimicry4. Competition5. Symbiosis

Coevolution

When two species have reciprocal evolution to each other.

Ex: Flowers and their

pollinators.

Predation (+/-)

Predator and prey relationships.

Ex – Lynx and Hares Often results in

interesting defenses or adaptations.

Ex: Plant defenses Cryptic coloration Aposematic coloration

Cryptic Coloration

A passive defense where the prey is camouflaged against its environment.

Aposematic Coloration

The use of conspicuous colors in toxic or unpalatable organisms

to warn off predators.

poison arrow frogs

Mimicry

Defense mechanism where the mimic has a resemblance to another species, the model.

Types: Batesian Mullerian

Batesian Mimicry

Palatable species mimics an unpalatable model.

Hawk moth larva Snake

Mullerian Mimicry

Two unpalatable species resemble each other.

Cuckoo Bee Yellow Jacket

Competition

When two species rely on the same limiting resource. Intraspecific competition usually more severe than

Interspecific competition. Why? Competitive Exclusion Principle

Predicts that two species with the same requirement can not co-exist in the same community.

One species will survive and the second will go extinct.

Ecological Niche

The n-hyperspace of requirements for a species. How a species “fits into” an ecosystem. Species can not have niche overlap, the

Competitive Exclusion Principle Niche Types1. Fundamental - what a species is theoretically

capable of using.2. Realized - what a species can actually use.

Resource Partitioning

A way that species avoid niche overlap by splitting up the available resources.

Ex: Anolis lizards

A. distichus A. insolitus

Symbiosis

When two different species live together in direct contact.

Types:1. Parasitism

2. Commensalism

3. Mutualism

Parasitism (+/-)

Parasite harms the host. Parasites may be external or internal. Well adapted parasites don't kill the host.

Parasitic behavior: A female Nasonia vitripennis laying a clutch of eggs into the pupa of a blowfly (Phormia regina)

Commensalism (+/o)

One partner benefits while the other is unchanged.

Ex. – Cattle and Egrets

Mutualism (+/+)

Both partners benefit from the interaction.

Ex: Pollinators and flowers

Acacia Tree and Ants

Succession

Changes in species composition over time.

Succession Stages

Sere: unstable stage usually replaced by another community.

Climax: stable stage, self-reproducing. Succession Types:

1. 1. Primary

2. 2. Secondary

Primary Succession

1. Primary Building a community from a lifeless area. Ex: volcanic islands

glaciated areas road cuts

The first example of primary succession was worked out on the Indiana Dunes.

Stages: Open Beach Beach Grasses Conifers (Junipers and Pines) Oaks Beech-Maple forest (Climax)

Secondary Succession

Where a community has been disturbed and the soil is mostly intact.

Ex: Cutting down a forest Blow-outs on the Dunes

Causes of Succession

1. Autogenic Factors Changes introduced by the organisms

themselves. Ex: toxins

acids

2. Allogenic Factors Outside disturbances Ex: Fire

FloodsPrairie Restoration Project

Upland, IN

Biogeography

Study of the past and present distributions of individual species and communities.

Range Limitations1. Lack of dispersion.2. Failure to survive in new areas.3. Retraction from former range area. Proof

Fossil Evidence Pollen Studies Transplant Experiments

Islands

Special cases in Biogeography. Must be colonized from other areas. Island Species Factors

Island size. Distance from mainland.

Island Size and Distance

Small islands hold few species. Why?

Fewer niches available for species to occupy. Distance from Mainland

Closer islands have more species. Why?

Easier for colonization.

Comment

Islands tend to have high numbers of Endemic species

Why? Adaptive Radiation and Evolution of new

species.

Summary

Know the two hypothesis of community structure.

Know the various types of interspecific interactions.

Know the Competitive Exclusion Principle and Niche Concept.

Know some examples and causes of succession.

Know how island communities are shaped.