Life processes in the biosphere -POP DYNAMICS

Life processes in the biosphere -POP DYNAMICS

1. Population dynamics

   • understanding factors that influence pop change is important in ...
     • In monitoring species survival
     • Success of conservation strategies
     • Assessing the maximum sustainable yields of a exploited species
   • actual size of pop is controlled by num of births, deaths and migration patterns
     • pop size=starting pop+br+immigration-deaths-emigrants
   • Factors affecting birth rates
     • Number of births=controlled by natural reproductive potential of the species (biotic potential). -Evolved over long time to=sufficient offspring to replace the individualsthat die
       • Must= surplus of young so pop survives in bad years without wasting time+resources that threaten the survival of them all
     • species e.g herring produce many young as chances of dying are high. In contrast, elephants produce few young as chances of dying are low. These species can be particularly vunerable to an increase in DR
   • Factors affecting mortality rates
     • Num of deaths controlled by enviro factors that prevent some individuals from surviving
     • range of enviro factors affect likelihood of organism dying. Density independant factors=draught, flood and volcanic eruption. Density independant factors= food supply and disease
       • Density independant factors- "A factor that is not influenced by the population denisty of the species that may be affected e.g draught"
         • Density dependant facotrs-" A factor whose effect is affected by the density of the population e.g disease"

2. Homeostatic regulation of pop size

   • Carrying capacity
     • "The greatest population that can be supported sustainably in an area"
     • if pop rises above cc density dependant factors become stronger so mortality increases+pop decreases
     • If pop drops below cc density dependent factors=weaker so mortality decreases+pop increases. mortality changes if pop is above or below cc
   • Predator prey pop relationships
     • self regulation. found in habitats where prey species is main food of a predator
       • where there is a few food species available, a reduction in availablilty of one food species+big impact on predator numbers
   • Artificial pop control
     • Culling of a pop may be needed to conserve a species of habitats where natural control mechanism no longer exist
       • e.g Red deer in scotland since wolves no longer exisit
         • Artifically killed by disease, predator introduction, sterilisation and destroying nests

3. Sigmoidal pop growth- "The growth pattern of a pop where abundant resources allow rapid rowth followed by pop stabilisation as the carrying capacity is reached"

   • Lag,log,slow growth, stable phase,death phase.---- discuss environmental resistance

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