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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.