Chapter 53 ~ Community Ecology

Community structure Community Species diversity 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.

Interactions Interspecific (interactions between populations of different species within a community): Competition Predation Mutualism Commensalism

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

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

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

IndoMalayan Octopus Mimicry Octopus

Mutualism Commensalism

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.

Limit of Food Chain Food chain only 4-5 levels or smaller WHY? Energetic Hypothesis: Inefficiency of energy transfer (10%) 100kg10kg1kg Dynamic Stability hypothesis Long food chains less stable than short Fluctuations at bottom magnified at top (predator adaptation)

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)

Keystone Species Not abundant in community Sea Otter abundance depends on Sea urchin biomass Kelp density Food chain illustrates hypothetical changes due to killer whale predation Not abundant in community Exert a strong control on community structure Best ways to recognize Keystone is to remove it in a controlled area

Disturbance of the Community Stability: state of equilibrium Non-equilibrium Model: Constant change Role of disturbances Natural Occurrence Human Interference

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