Community Ecology. Community interactions: Community Ecology.
Community Ecology
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Transcript of Community Ecology
Community Ecology
Chapter 53
•Community - group of species living close enough for interaction.
•Species richness – # of species a community contains; relative abundance - # of members of each species.
• 2 theories on community development:
• 1Individualistic hypothesis - species arrive in community by chance because of abiotic needs.
• 2Interactive hypothesis - species are in community because of similar biotic needs and interactions between species.
Relationships
• Interspecific interactions - relationships between species in community.
• Defined by how they affect other species.
• 1Interspecific (between species) competition - resources are limited.
• Organisms own ecological niche (specific role in environment).
• If two organisms have same niche, cannot coexist (competitive exclusion principle)
• Resource partitioning allows two similar species to coexist.
• Done by differentiating species’ niches.
Same genus of lizards, but the differentspecies occupy different areas in the treesto allow the resources to be shared.
• 2Predation - 1 species hunts, kills, eats other (the prey).
• AParasitism - 1 species lives off other species (may/may not kill host)
• Predators and prey have own survival adaptations.
• Predators - claws, fangs, etc.
• Plants – toxic chemical compounds - protect against herbivores.
• Prey - defenses (i.e. blending in to environment)
• Cryptic coloration - prey uses coloration to deceive predators.
• aAposematic coloring - present as warning sign to predators.
• Prey - odors and toxins as defense against predators.
• bMimicry - organism resembles another species.
• 1Batesian mimicry - harmless organism mimics harmful one.
• 2Mullerian mimicry – 2+ species resemble each other (both species are not tasteful)
• Parasites - live on host (ectoparasite) or in host (endoparasite).
• Parasitoidism - parasite eventually kills host.
• 3Mutualism - both species benefit.
• 4Commensalism - 1 species benefits, other is unharmed but does not benefit (barnacles that attach to side of whales)
Acacia tree and ants – the ants feed off the tree and receive shelter; in return, the ants protect the tree from any harmful insects that may kill the tree.
• Coevolution - 1 species evolves, puts pressure on another species to evolve.
• 2nd species relies on 1st species; must adapt to continue to benefit (selective pressure)
• Trophic structure - based on feeding patterns in community.
• Food chain - flow of energy from producers up to carnivores.
• Trophic level shows where organism fits in food chain.
• Food web - more accurate way to look at feeding.
• Feeding relationships shown in interrelated way.
• Food chains have limits on length (2 hypotheses):
• 1Energetic hypothesis - length of food chain limited by inefficiency of energy transfer along chain.
• 2Dynamic stability hypothesis - long food chains less stable than short chains.
• Dominant species - most abundant or highest biomass.
• Biomass - sum weight of all individuals in population.
• Keystone species - species that have regulating effect on entire community.
• If removed, can affect entire community.
• 2 models at how food chain is controlled.
• 1Bottom-up model - producers are the controlling factor of the population.
• 2Top-bottom model - consumers are controlling factor of population.
Disturbances
• Stability - ability of community to persist through disturbances.
• Fire, weather, or human activities can alter communities.
• Some disturbances necessary for community to thrive.
Succession
• Succession - sequence of community changes after disturbance.
• 1Primary succession- no life, soil not formed yet.
• Mosses and lichens first; cause development of soil.
• Example - after glacier retreats.
• 2Secondary succession - after major disturbance.
• Soil left intact.• Grasses first, then trees and
other organisms.
• Community’s diversity (biodiversity) controlled by two factors; size and biogeography.
• Remember: species richness - different species living in a community; relative abundance - # of those species living in the area.