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• Chapter 53 ~ Community Ecology

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Community structure• Community

– Richness & Abundance…….

• Species diversity• Hypotheses: Contrasting

views• •Individualistic

~independently distributed along gradient, similar abiotic needs b/w species

•Interactive: species closely interdependent and nearly always occur together.

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Interactions• Interspecific (interactions between

populations of different species within a

community):

• Competition

• Predation

• Mutualism

• Commensalism

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Competition for Resources• Interspecific Competition:

• Grasshoppers vs. Bison for grass

• Lynx vs. fox for hares

– Competition for same resource

• Competitive Exclusion Priniciple– Reproductive advantage of one over another causes????

• Eventually elimination of weaker/inferior

• Ecological Niche:– “ecological role”: no two species can have same niche

• Resource Partitioning– Extinction or evolution to different resource of weaker

• Character Displacement– Allopatric and Sympatric speciation

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Predation• Lion Killing prey

• Bison eating plants (herbivory)

• Parasite on host organism (parasitism)

• Predator Adaptation– Acute senses– Claws, teeth, fangs, poisons

• Plant Defenses

• Animal Defenses against predators

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Animal Predation defense

• Cryptic coloration (camouflage)

• Aposematic coloration (warning) may have effective chemical defense also.

• Mimicry~ superficial resemblance to another species

– Batesian~ palatable/ harmless species mimics an unpalatable/ harmful model

– Mullerian~ 2 or more unpalatable, aposematically colored species resemble each other

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IndoMalayan OctopusMimicry Octopus

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Mutualism Commensalism

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Trophic Structures

• Feeding relationships b/w organisms of the community

• Food Chain: Transfer of energy from its source in plants through herbivores, carnivores finally to decomposers.

• Trophic Levels: length of food chain limit to 4-5 levels/links.

• Food Web: Not linear chain, but interactive.

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Limit of Food Chain• Food chain only 4-5 levels or smaller• WHY?

• Energetic Hypothesis:– Inefficiency of energy transfer (10%)– 100kg10kg1kg

• Dynamic Stability hypothesis– Long food chains less stable than short– Fluctuations at bottom magnified at top (predator adaptation)

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Dominant Species

• Highest abundance in a community• Highest Biomass (sum weight of all individuals in a pop)

Sugar Maple dominant in eastern N. America

What happens when dominant species is lost??

•American Chestnut Dominant in deciduous forest (canopy tree)•Chestnut Blight fungus brought over from China (1910)

•Killed all chestnuts•Over all very little impact ………except

•56 species of insect fed on Chestnut tree•7 became extinct (sole food source)

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Keystone Species

• Not abundant in community

• Exert a strong control on community structure

• Best ways to recognize Keystone is to remove it in a controlled area

•Sea Otter abundance depends on

•Sea urchin biomass•Kelp density

•Food chain illustrates hypothetical changes due to killer whale predation

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Disturbance of the Community

• Stability: state of equilibrium

• Non-equilibrium Model:– Constant change

– Role of disturbances• Natural Occurrence

• Human Interference

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Succession

• Ecological succession~ transition in species composition over ecological time

• Primary~ begun in lifeless area; no soil, perhaps volcanic activity or retreating glacier

• Secondary~ an existing community has been cleared by some disturbance that leaves the soil intact