Chapter 54 Community Ecology

Community Ecology

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

Community Hypothesis

1. Individualistic

2. Interactive

Individualistic Hypothesis

H.A. Gleason Community as a chance

assemblage of species because of similar abiotic requirements.

Interactive Hypothesis

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

Predation

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 Types

1. 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. Primary

2. Secondary

Primary Succession

Building a community from a lifeless area.

Ex: volcanic islands glaciated areas road cuts

Comment 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

2. Allogenic Factors

Autogenic Factors

Changes introduced by the organisms themselves.

Ex: toxins acids

Allogenic Factors

Outside disturbances

Ex: Fire Floods

Prairie Succession in Oklahoma - Stages

1. Annual Weeds

2. Triple-Awn Grass

3. Bunch Grass

4. Climax: Tall-grass Prairie

Annual Weed Stage

Lasts 2-3 years. Very robust growth (1-2 m). Species: Sunflower

Pigweed Lamb's Quarter

Annual Weed Stage

Annual Weed Stage

Annual Weed Stage

Annual Weed Stage

Triple-Awn Stage

Lasts 10 - 50 years. Very poor growth (5-12 cm). Species: Triple-Awn Grass

Triple Awn Stage

Question

How can Triple-Awn replace the more robust annual weeds?

Allelopathy

The release of chemical inhibitors into the environment.

Sunflower: autotoxic Triple Awn: tolerant

Triple-Awn

Inhibits Nitrogen fixing bacteria species

Result: soil N stays low which stalls succession.

Bunch Grass Stage

Lasts 20 - 100 years. Good growth (30-50 cm). Species: Little Bluestem

Bunch Grass Stage

Succession Causes

Bunchgrass eventually shades out Triple-Awn, releasing the inhibition of the nitrogen fixers.

Result: soil fertility increases, allowing the next group of species to invade.

Climax Prairie Stage

Lasts centuries if maintained by fire.

High growth (up to 2 meters). Species: Big Bluestem,

Indiana Grass, Switch Grass, Little Bluestem

Tall Grass Prairie

Tall Grass Prairie

Question

Stages 3 and 4 are the best for cattle grazing.

Normal succession takes 20 - 50+ years.

Can the time needed for restoring the prairie be decreased?

Solution

Add more N to soil (NH4+)

Seed climax species Result: prairie in 3-10 years. Maintain the prairie by

burning.

Upland, IN Prairie

Upland, IN Prairie

Upland, IN Prairie

Point

If you understand the causes and controlling factors of succession, you can manipulate them.

Biogeography

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

Range Limitations

1. 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

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.

Summary

Know some examples and causes of succession.

Know how island communities are shaped.