Population Ecology

• Ecology


  Scientific study of relationships between living organisms/groups of organisms in relation to their environment
• Ecology


  • Allows scientists to manage ecosystems, grow food, manage pests, deal with natural + biological disasters
• Environment


  All external factors/influences which directly/indirectly affect the life of an individual/community
• Biosphere


  Part of Earth + it's atmosphere in which living organisms exist / which can support life
• Biome


  Major regional ecological complex of communities extending over large natural areas + characterised by distinctive vegetation + climate
• Bioregion


  Region defined by characteristics of natural environment rather than man-made divisions
• Ecosystem


  Community of organisms interacting with one another + with their abiotic (physical + chemical) environment
• Community


  Consists of different populations (species) living in a defined area + interacting with each other
• Population


  Group of organisms of SAME SPECIES living in the SAME AREA at the SAME TIME
• Habitat


  Ecological environment where population/community lives
• Microhabitat


  Smaller habitat within a larger one
• Species


  Subgroup of a Genus, group of interbreeding natural populations that are reproductively isolated from other such groups + share physical/physiological/behavioural characteristics
• Taxonomy


  Unit of biological diversity as used in species richness, Simpson's index
• Types of Species


  • Indigenous
  • Endemic
  • Alien/Exotic
  • Invader
  • Keystone
• Indigenous


  Naturally-occurring in region in which it is currently found + was present BEFORE arrival of humans
• Archaeophyte


  Not indigenous, but present before human arrival
• Endemic


  Species restricted to a particular region
• Alien/Exotic


  Species which does not form part of original biodiversity of a defined geographical region
• Invader


  Alien species which once introduced, reproduces + spreads into areas where not wanted, poses serious threat to endemic/indigenous species
• Invaders


  • Lack natural predators, have high reproductive rate, good dispersal, adapt quickly to new environment
• Keystone species


  Species with important role + disproportionally large effect on its ecosystem relative to its abundance - if it dies out, whole ecosystem will collapse without backup species
• African elephant


  • Uproots small trees which would otherwise overtake savanna (grassland → forest /shrub), ensures survival of grazing antelopes + their predators
• Factors affecting population growth

  • Mortality / death rate
  • Natality / birth rate
  • Emigration
  • Immigration
• Population growth


  (Births + Immigrants) - (Deaths + Emigrants)
• Recruitment


  Proportion of offspring in population which attain sexual maturity, i.e. breeding age can contribute to natality
• Recruitment rate


  No. of young females in population in autumn / No. of young females in population in spring
• Patterns of population growth


  • Sigmoid growth curve
  • Exponential growth curve
• Sigmoid growth curve

  S-shaped, with lag phase, log/exponential phase, deceleration phase, stationary phase
• Lag phase


  • Low rate of growth, initial small no. of individuals, acclimatisation, synthesis of appropriate enzymes
• Log / Exponential growth phase


  • Population growing at continuously increasing rate, maximum growth rate/biotic potential, ideal environmental conditions
• Deceleration phase


  • Competition for food / space sets in, accumulation of toxins, environmental resistance sets in
• Stationary phase


  • Population stops growing, maximum size reached/carrying capacity, no net change in population
• Carrying capacity


  Maximum no. of individuals of a population which the resources in a given area can support
• Biotic potential (r)


  Highest possible growth rate at which a population could increase under ideal conditions
• Biotic potential


  • Depends on avg. no. of offspring per reproduction, chances of survival to reproductive age, how often organism reproduces, age of 1st reproduction, reproductive life span, gestation period, death rate under ideal conditions
• Environmental resistance


  Environmental limiting factors which prevent biotic potential of organism from being reached, prevent population from continuing to increase exponentially
• Environmental limiting factors


  • Density-dependent
  • Density-independent
• Density-independent factors


  Factors which reduce reproduction OR increase mortality independently/irrespective of population density, e.g. weather, climate, geological disturbances, natural disasters, physical characteristics, human activities, behaviour of organisms
• Density-dependent factors


  Factors which have an increasing effect on population the more closely spaced individuals become / the higher the population density, e.g. competition, predation, disease, parasitism, behavioral problems
• Sigmoid growth curve


  Density-dependent /logistic growth, rate of growth depends on density-dependent factors