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Chapter 26: Community Ecology, Cross Connection: Diversity of a species…

- - - - Predator feeding time
        
        How quickly predator finds new prey individual
      - Predator handling time
        
        Amount of time needed to consume prey
      - Both together constitute predator’s functional response
        
        This is prey-dependent
    - - Known as Lotka-Volterra model
      - Models net rate of change in prey numbers
      - dN/dt is rate of change with time of the prey population
        
        Prey population stable when =0
      - r is intrinsic rate of increase for prey species
      - N is number of individuals of prey species in the community
      - a is predator’s per capita attack rate
        
        Number of prey eaten per prey per predator per unit of time
        
        Prey-dependant
      - P is number of predator individuals present
      - Equation for net rate of change of predator numbers is dP/dt=faNP-qP
        
        dP/dt is rate of change with time of predator population
        
        Predator population stable when 0
        
        f is constant indicating efficiency at converting prey eaten to new predators
        
        q is predator’s per capita mortality rate
      - A zero growth isocline is a line that indicates population stability
      - Criticized for being too simplistic
    - - Adds more factors that affect predator and prey in real communities
      - Equations slightly more complex
      - Zero growth isoclines are curves
      - Relationship between stable and unstable populations more complicated
      - Paradox of enrichment
        
        Improving conditions for prey
        
        Predator overexploits prey
        
        Both species lost
        
        May be important factor in loss of species diversity
      - Maximum sustained yield
        
        Harvest just enough of a species to keep population density at maximum per capita productivity
        
        Species would be stable
      - Fixed effort harvesting
        
        Population health determined by amount of species that can be harvested with particular amount of effort
        
        Harvest
        
        Abundant=Healthy population
        
        Poor=Sparse populations
        
        Must be stopped after particular amount of time or effort
      - Fixed quota harvesting
        
        Allowed to harvest a particular amount of a species
        
        Amount of time or effort does not matter
  - - - Probability particular prey individual will be encountered
      - Decision by predator to attack an individual once encountered
      - Probability attacked prey item will be successfully eaten
    - - Examine interactions between factors
      - Attempts to understand why herbivores eat some plants while ignoring others
      - Produced optimal diet model that makes four predictions
        
        Predators should prefer whichever prey yields the most energy per unit of handle if time
        
        If high yield prey become scarce predator would be more successful by broadening diet
        
        Some prey items will always be eaten if encountered, others will never be eaten even if easy to obtain
        
        Probability that particular plant will be eaten partially depends on abundance of other plants that are easy to handle and have higher value
  - - - Organisms consume a shared resource
      - Makes respires less available for other organisms
    - - One organism restricts another’s access to resources
      - First organism does not have to be using the resource
    - - Any substance or factor that can lead to increased growth rates as availability is increased and that is consumed by organism
    - - Species can increase from very low population density
      - Even with competitor present
- - - - Old and widely taught theory states
        
        Tropical regions near equator have relatively benign environments
        
        Higher latitudes have more severe conditions
        
        Satisfying but is not the entire explanation
    - - Hundreds of millions of years to adapt to tropical conditions
      - Tens of millions of years to adapt to temperate conditions
  - - - Important to studying communities
      - Larger areas more diverse than smaller areas
    - - Relationship between area a species richness
      - Expressed by formula S = cA^z
        
        A is area
        
        c and z are constants discovered by studying individual communities
        
        Once known can be used to compare diversity
        
        S is number of species
    - - Beta diversity
        
        Compares differences of several small sites within larger region
        
        Region should be larger than community studied
      - Gamma diversity
        
        Number of species within a region
      - Alpha diversity
        
        Number of species or growth forms
        
        Uses local small sites
    - - Plot of the number of species in each abundance class
      - Most communities have
        
        Few species that dominate
        
        Most species that are sparse
        
        Several species that are rare
- - - - More or less predictable sequence of changes
      - Disturbed patches undergoes this until climax community is reached
    - - Act of restoring communities from
        
        Habitat loss
        
        Habitat fragmentation
- - - - Region of environment composed of many discrete patches in which the species can live
      - Some patches occupied by species whereas other suitable patches are not
        
        Postulates that some patches are occupied by species others are not
        
        Population size varies with time due to predators, competition, and disturbances
      - Empty patches become colonized by migration from occupied patches
        
        Emphasizes need for colonization of new patches by migration
        
        Plants migrate by means of spores or seeds
        
        Assisted dispersal proposed to help migration where there is human disruption
      - Populations within individual patches have a probability of going extinct within the patch
        
        Postulates that populations within a patch have probability of going extinct locally
        
        Fugitive species survive by
        
        Colonizing new patches
        
        Flourishing temporarily
        
        Colonizing more patches before dying out in old ones
    - - High quality patch
    - - Low quality patch
- - - - Which herbivores consume most energy
      - Which herbivores are eaten the most
- - - - Alter a small area of habitat below themselves
      - Habitat becomes more favorable for survival of seedlings
    - - Organisms become established on newly created substrates