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Chapter 26 Community Ecology (Metapopulations in Patchy Environments…

- - - - occur together at
        
        same time and place
    - - boundaries in both
        
        time
        
        come into being then
        
        ceasen to exist
        
        place
    - - predictable sequence of changes
      - occurs in many communities
    - - when stability of
        
        a habitat is reached
    - - patchworks of coexisting species
      - maintained by processes
        
        disturbance
        
        competition
        
        mutualism
        
        predation
        
        commensalism
    - - bringing nature back to
        
        its natural order
      - examples
        
        reintroducing animal species
        
        removing dams
        
        reintroduce plant species
  - - - we are members in
        
        most communities
        
        impacting nature
        
        need to farm
        
        can lead to
        
        habitat loss
        
        1 more item...
        
        habitat fragmentation
        
        1 more item...
        
        build towns
        
        mine for minerals
- - - - larger areas
        
        more diverse
        
        than smaller ones
        
        reasons
        
        more soil variations
        
        various topography
        
        various geology
        
        advantages
        
        host larger populations
        
        less likely to
        
        die out during
        
        disturbance
    - - relationship between
        
        area and species richness
      - expressed as formula
        
        S=cA^z
        
        S=species
        
        c and z
        
        are constants
        
        discovered when studying
        
        individual communities
        
        used to compare
        
        diversity of individual communities
        
        A=area
    - - measuring diversity at specific scales
        
        Alpha diversity
        
        number of species or
        
        growth forms that occur
        
        at a local, small site
        
        Beta diversity
        
        compares differences between
        
        several small sites
        
        within a larger region
        
        region should be the
        
        larger community being studied
        
        Gamma diversity
        
        number of species
        
        within a region
    - - plotting the number of
        
        species in each abundance class
        
        to obtain
  - - - with latitude
        
        early naturalists saw
        
        more northern equals
        
        fewer species
        
        also with
        
        geographical
        
        geological
        
        components
    - - tropical regions near equator
        
        have relatively benign environments
        
        whereas
        
        higher altitudes
        
        have more severe conditions
      - oldest and most widely taught
    - - temperatures always warm
      - abundance of rainfall
      - plants do not need
        
        adaptions for
        
        freezing temperatures
        
        water stress
- - - - prey population decreases
        
        and vice versa
    - - prey go locally extinct
    - - prey-predator populations remain stable
    - - predator's
        
        feeding rate
        
        amount of time it takes
        
        to find prey individual
        
        predator's functional response
        
        handling time
        
        amount of time needed to
        
        consume prey
    - - models the net rate of
        
        change in prey numbers
        
        change in predator numbers
        
        equation
        
        dP/dt=faNP-qP
        
        dP/dt represents
        
        rate of change with time
        
        1 more item...
        
        f represents
        
        a constant
        
        1 more item...
        
        q represents
        
        predator's per capita mortality rate
      - equation
        
        dN/dt=rN-aNP
        
        dN/dt represents
        
        rate of change with
        
        prey population
        
        r represents
        
        intrinsic rate of
        
        increase for prey species
        
        N represents
        
        number of individuals of
        
        prey species in community
        
        a represents
        
        predator's per capita attack rate
        
        P represents
        
        number of predators present
      - has been criticized for being
        
        too simplistic
        
        Rosenzeig-MacArthur model
        
        more realistic
        
        adds more factors that affect
        
        predators
        
        in real communities
        
        prey
      - Humans as predators
        
        maximum sustained yield
        
        harvest just enough to
        
        maintain population density
        
        hard to determine
        
        population density
        
        fixed effort harvesting
        
        population health determined by
        
        amount harvested with
        
        particular amount of effort
        
        healthy population
        
        abundant harvest
        
        sparse population
        
        poor harvest
        
        fixed quota harvesting
        
        harvesters only allowed to
        
        harvest certain amount per season
  - - - resource competition occurs when
        
        organisms actually consume shared resource
        
        making it less available
        
        for other organisms
    - - one organism restricts another
        
        organism's access to resource
        
        although first organism
        
        does not need it
      - example
        
        bracken ferns
        
        lay over shrubs in autumn/ winter
        
        not allowing sunlight to pass
        
        although brackens do not need it
    - - when species can increase
        
        from very low population density
        
        even when competitor is present
    - - any substance or factor
        
        that can lead to
        
        increased growth rates
        
        as availability is increased
        
        and consumption increases
- - - - and both benefit
        
        but still incur cost
        
        can reduce cost
        
        may involve "cheating"
        
        example
        
        nectar robbing bees
        
        1 more item...
    - - pollinators and plants
    - - evolved from
        
        predation
        
        example
        
        ancestral predation
  - - - without any benefit
    - - the presence of the other
    - - plants that alter
        
        small area of habitat
        
        immediately below themselves
        
        more favorable to
        
        the survival of seedlings
        
        of other plants
        
        2 more items...
    - - especially primary succession
        
        organisms become established
        
        on newly created substrates
        
        examples
        
        volcanoes produce new substrate
        
        in form of
        
        lava flows
        
        ash fields
        
        completely sterile
        
        1 more item...
        
        moving glacier
        
        frees soil from
        
        organisms
        
        pioneer species inhabit areas
- - - - interconnected by migration and gene flow
        
        between patches
  - - - composed of many discreet patches
        
        in which species live
    - - occupied by species
        
        whereas other suitable patches
        
        are not
    - - will become colonized by
        
        migration from occupied patches
    - - have a probability of
        
        going extinct within that patch
  - - - colonizing new patches
        
        flourishing temporarily
        
        then colonizing more patches
        
        before it dies out of
        
        old ones
  - - - possible solution
        
        assisted dispersal
        
        animals are captured
        
        and released into new area
- - - - full story
    - - have small number
        
        of strong food chains
  - - - to understanding environment
    - - trace how energy flows through community
  - - - absence or presence can
        
        dramatically affect community
    - - sea otters
        
        help limit sea urchins
        
        which in turn allow
        
        kelp forests to grow
        
        keystone species
    - - they limit herbivores
        
        so plant diversity can flourish