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Ch. 26 Community Ecology (Diversity (Diversity and Latitude (geographical…

- - - - larger areas more diverse than smaller ones
        
        larger areas have more variation
        
        types of soil
        
        topography
        
        geology
        
        larger populations
        
        less likely to die out in disturbances
      - levels of scales
        
        local
        
        small area less than a few km
        
        region
        
        larger than a few km
        
        less than a continent
        
        all members of many species
        
        biome
        
        large region
        
        characterized by the dominant plants
        
        ex: temperate rain forest, salt marsh, desert
        
        biographical region
        
        extremely large region
        
        usually coincides w/a continent or other very large region bounded by a geographical or climate barrier
        
        ex: ocean, mountains, deserts
        
        prevents dispersal of organisms
        
        measuring diversity
        
        alpha diversity
        
        number of species or growth forms that occur @ a local/small site
        
        beta diversity
        
        compares differences between several small sites w/in a larger region
        
        region should be the larger community being studied
        
        gamma diversity
        
        number of species w/in a region
    - - between area and species richness
      - S+cA^z
        
        S is number of species
        
        A is the area
        
        c and z are constants
  - - - little sunlight and warmth
      - bitterly cold
      - little energy available
    - - temps always warm
      - freezing conditions rare
        
        except in mountains
      - rainfall abundant
    - - Antarctica covered in ice
      - temperate southern hemisphere is ocean
      - region between Tropic of Cancer and Capricorn contains extensive land mass
      - tropic regions have more land available
- - - - fish
      - deer
      - lumber
    - - herbivore consumes more of plant
        
        plant pop decreases
        
        difficult for herbivore to find food
      - predator may consume so much of prey that numbers become low/extinct
      - other factors may limit pop of predator
        
        cannot over consume
        
        both species stable pop
    - - predator's feeding rate
        
        how quickly predator find a new prey individual
        
        faster if more prey available
      - handling time
      - functional response is the combination of these two
        
        dependent on prey density
    - - dN/dt=rN-aNP
        
        r is intrinsic rate of increase for the prey species
        
        N is number of prey individuals in the community
        
        a is predator's capita attack rate
        
        dN/dt is rate of change w/time of prey pop
      - prey pop stable
        
        rN-aNP=0
        
        rN=aNP
        
        r=aP
        
        r/a=P
    - - dP/dt=faNP-qP
        
        dP/dt is rate of change w/time of predator pop
        
        f is a constant indicating predator's efficiency @ converting prey it has eaten into new predators
        
        q is predator's capita mortality rate
      - predator pop stable
        
        faNP-qP=0
        
        faNp=qP
        
        N=q/fa
    - - line indicates population stability
      - point where intersects indicates the pop sizes of both that can coexist stably
      - more curves rather than straight lines
      - stable & unstable pops are more complicated
        
        improved conditions, more prey may lead to predator to overploit they prey
        
        both species will be lost
        
        paradox of enrichment
        
        important factor in the loss of species diversity
        
        ex: eutrophication
  - - - probability of encountering prey
        
        rare species consumed less
        
        cryptic may escape detection
      - decision to attack
        
        poisonous or spiny
        
        worth the trouble
      - probability that attacked prey will be successfully eaten
        
        ex: fruit hard to crack
      - optimal foraging theory
        
        examine the interactions between these factors
        
        optimal diet model
        
        predators prefer prey yields the most energy per unit of handling time
        
        high yield prey becomes sufficiently scarce
        
        predator more successful broadening its diet to include prey that are lower in energy and abundant
        
        some prey always eaten if encountered, others not even if easy to obtain
        
        probability particular plant will be eaten depends on abundance of other plants that are easier to handle and have higher value
  - - - interspecies competition
        
        exploitation competition
        
        one or both grows more poorly than would if had habitat to self
        
        interference competition
        
        one organism restricts another organism's access to resources even though the first might not be using it
      - ex: water, light, and minerals
      - many niches overlap
      - two competing species can coexist
        
        if each species has a greater neg effect on its own per capita growth rate than competitor
      - invasive species
        
        can increase from low pop density even with competitor present
      - resource
        
        any substance or factor that can lead to increased growth rates as availability is increased & is consumed
- - - - relationship not free
        
        both require work
      - natural selection favors relationships that reduce costs
  - - - plants that alter a small area of habitat immediately below themselves such that it is more favorable to the survival of seedlings of other plants
    - - primary succession
        
        organisms become attached to newly created substance
        
        pioneers
        
        tolerate low levels of nutrients
        
        mutualitstic association w/nitrogen fixing bacteria
- - - - 1.) a region of the environment is composed of many discrete patches in which the species can live
        
        source habitat
        
        high-quality patch
        
        sink habitat
        
        low-quality habitat
      - 2.) some patches are occupied by the species whereas other suitable patches are not
        
        empty patches are not a surplus or spare or unneeded
      - 3.) empty patches will become colonized by migration from occupied patches
        
        migration corridors important
      - 4.) populations w/in individual patches have a probability of going extinct w/in that patch
        
        fugitive species
        
        survives by colonizing new patches
        
        flourishes temporarily
        
        colonizes more patches b4 dies out in old ones
- - - - plants
      - algae
      - cynobacteria
    - - herbivores
    - - carnivores
  - - - direct line of consumption
    - - network of numerous interrelationships
      - keystones species
        
        affects the structure of their community
        
        impact out of proportion to its size
        
        ex: sea otters and sea urchins
    - - how energy flows through the community
      - extremely difficult to construct