Community Ecology The study of the interactions

between the species in an area.

Community Hypothesis

1. Individualistic2. 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. Parasitism2. Commensalism3. 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. Primary2. 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 Factors2. 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 Weeds2. Triple-Awn Grass3. Bunch Grass4. 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.

Productivity Lab Report

Graph and data are on BlackBoard.

Graph - Analysis of results: 7 questions

DO Readings – Analysis of results: - 2 questions

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.