Community Ecology

  • Intro
    • Community: association of pop. living/interacting in same place @ same time (many species)
    • Resource: anything from environment meeting needs of particular species
    • Limiting resource: resource in scarce supply (around carrying capacity)
    • Habitat: location where species lives 
    • Ecological niche: sum of species’ use of biotic/abiotic resources = organism’s ecological rule
    • Habitat is address and niche is profession/what you do 
    • Fundamental niche: potentially occupied by species-broad
    • Realized niche: actually occupied by species (more narrow) -> most animals actually live here
  • Competition: need same resources
    • Can occur between same species (intraspecific) or different species (interspecific) 
    • When both species fill same ecological niche, will compete
    • Identical eco. Niches competing same limiting resources can’t coexist (competition exclusion)
    • One can be extirpated (go locally extinct)
    • Raised separately: each pop. reached K (paramecium)
    • Grown together: compete for same resources -> one went extinct (locally)
    • Conclusion: can’t coexist permanently
    • Resource partitioning: divide up resources by habitat/time of day or use
    • 1 species excludes other sp. From parts of fundamental niche (forest), uses realized niche (trees)
    • Lizards: same resources except for perching area (habitats differ -> less direct competition for food)
    • Can also get better @ using specific resources (character displacement: more dramatic when sp. In direct competition) 
  • Predation: one species, predator, kills/eats prey; +/- interaction (win/lose)
    • Coevolution: results in evol. “Arms race,” evolves in response to each other
    • Predator: evolves better prey catching strategies
    • Prey: evolves better predator avoidance strategies
    • Adaptations by predators for finding/capturing prey: claws, fangs, venom, speed, camouflage/mimicking (thermoreception in rattlesnake) 
    • Adaptations by prey for protection
    • Mechanical defense (quills), chemical defense (spray), aposematic coloration (warning coloration: frogs store poison in skin), cryptic coloration: camouflage (colors/marking blending into phys. environ.)
    • Batesian mimicry: harmless species mimics harmful one (hawk moth mimics parrot snake) 
    • Mullerian mimicry: 2 harmful species mimic each other (more of the same) -> wasp and bee
    • Fleeing: run and hide (lynx and hare)
    • Living in groups: > chance that someone will notice a predator (herds, murmurations in birds/falcons) 
    • Herbivory: plant predatory organism eats part of plant/algae (+/- interaction)
    • Plants can’t escape, have adaptations for lower chance of being etan 
    • physical/chemical adaptations 
  • Symbiosis (intimate, long-term relationship) 
    • Parasitism: parasite benefits, host harmed (rarely killed) -> +/- interaction
    • Mutualism: both benefit and depend on each other ( mitochondria/some fungi) -> +/+ interaction
    • Commensalism: 1 species benefits and other is neither harmed/helped (egrets and buffalo) -> +/0 interaction 
  • Species diversity in a community
    • Species richness: number doesn’t equal species in community (how many different species)
    • Way to measure health of a region/habitat
    • Relative abundance: makeup of abundance, how many of 1 species represented compared to another
    • Diversity has effect on stability (monoculture could wipe out entire pop. and affect community) 
    • Communities with > diversity are more productive/stable/resistant to invasive species, withstand/recover from stresses
  • Food web: arrow represents transfer of energy; feeding relationships between organisms in community (about energy)
  • Limits on trophic structure: all food webs have limits to # links
    • Energetic hypothesis: suggests food chain length limited by inefficiency of E transfer along chain 
    • All food webs have limits to # of links; > photosynthesis = > energy = longer chains; only 10% of E from each trophic levels travels to next trophic level
  • Species with a large impact
    • Dominant species: those that are most abundant/have highest biomass
    • Keystone species: exert strong control on community by eco. roles/niches (not necessarily abundant) 
  • Primary succession: occurs where no soil exists (uncommon on earth) -> no life previously 
    • Ecological succession: seq. Of community/ecosystem changes after disturbance
    • Colonized by life for first time 
  • Secondary succession: begins in area where soil remains (previously inhabited); disturbance and recolonized