Chapter 53 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. Coevolution 2. Predation 3. Mimicry 4. Competition 5. Symbiosis
When two species have reciprocal evolution to each other. Ex: Flowers and their pollinators. Coevolution
Predator and prey relationships. Ex – Lynx and Hares Predation (+/-)
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.
The use of conspicuous colors in toxic or unpalatable organisms to warn off predators. poison arrow frogs Aposematic Coloration
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. Yellow Jacket Cuckoo Bee
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.
Homework • Read – Chapter 55, 53 • Chapter 52 - today • Productivity lab – next lab period • Lab – Animal Behavior
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)
One partner benefits while the other is unchanged. Ex. – Cattle and Egrets Commensalism (+/o)
Both partners benefit from the interaction. Ex: Pollinators and flowers Mutualism (+/+) Acacia Tree and Ants
Changes in species composition over time. Succession
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
Outside disturbances Ex: Fire Floods Allogenic Factors
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
Triple-Awn Stage • Lasts 10 - 50 years. • Very poor growth (5-12 cm). • Species: Triple-Awn Grass
Question • How can Triple-Awn replace the more robust annual weeds?