Ecology

• Ecology


  Study of relationships of organisms with each other and their environment
• Population


  A group of organisms belonging to the same species occupying a defined area at the same time and usually isolated to some degree from other similar species
• Community


  Any group of organisms belonging to a number of different species that coexist in the same habitat or area and interact through trophic and spatial relationships
• Ecosystem


  A complex, self-sustaining natural system of which living organisms are part, together with the non-living component
• Subdivisions of the biosphere

  • Lithosphere
  • Hydrosphere
  • Atmosphere
• Biotic factors


  The living component of the ecosystem: producers, consumers and decomposers
• Abiotic factors


  The non-living component of the ecosystem, including climatic factors and edaphic factors
• Habitat


  A specific locality of a place each with an adapted community of organisms
• Niche


  An animal's place in the biotic environment, that is, what it does and its relation to its food and its enemies
• Biological Species


  Two organisms that are able to reproduce naturally to produce fertile offspring of both genders
• Ecological Species


  A set of organisms adapted to a particular set of resources, called a niche, in the environment
• Biome


  A major biotic unit bearing characteristic and easily recognized array of plants, identified by its dominant plant formation
• Factors governing population size

  • Births (natality)
  • Deaths (mortality)
  • Migration (emigration and immigration)
• Biotic potential


  The inherent capacity of an organism to reproduce at a given rate and replace itself many times over during its lifetime
• Environmental resistance


  Factors which decrease the birth rate and increase death rate
• Recruitment


  The proportion of offspring that attained sexual maturity in the population
• Carrying Capacity (K)


  The maximum population size that can be sustained in the long term under the prevailing conditions
• Population density


  The number of individuals per unit area
• Population frequency


  The number of samples in which the species occurs
• Factors affecting population growth

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


  Factors which increase with increase in population density, e.g. predation, competition, grazing, parasitism
• Density-independent factors


  Factors unrelated to density of population, arising due to a sudden change in abiotic factors like light, temperature, water, humidity, wind
• 1. shaped Growth Curves


  • Population shows exponential growth that eventually slows down and stabilizes due to density-dependent factors
  • Population stabilizes at or slightly below the carrying capacity (K)
• 1. shaped Growth Curves


  • Population density increases rapidly in an exponential or logarithmic form, but then stops abruptly as environmental resistance or other factors become effective
  • Growth is limited only intrinsically through factors influencing the biotic potential/intrinsic rate of increase
• Boom and bust Curves

  • Populations go through repeated and regular periods of exponential growth - boom followed by a drastic decline - bust
• 1. strategists (opportunist species)


  Have high biotic potential, reproduce quickly, are pioneers of disturbed habitats, show J-shaped growth, exceed carrying capacity, disperse widely, invest in many small offspring
• 1. strategists (equilibrium species)


  Have low numbers, reproduce slowly, occupy stable habitats, maintain population size close to K, disperse slowly, invest in few large offspring
• Intraspecific competition


  Competition for resources between members of the same species, tends to have a stabilising influence on population size
• Overcrowding


  Results in reduced fecundity, failure to copulate, infertility, natural abortions, cannibalism of the young, decrease in parental care, and increased aggressive behaviour
• Overcrowding


  • Reduced fecundity due to hormonal changes which affect reproductive behaviour
  • Failure to copulate
  • Infertility
  • Natural abortions
  • Cannibalism of the young
  • Decrease in parental care
  • Aggressive behaviour increases
• Intraspecific competition is the driving force behind natural selection, since the individuals with the "best" genes are more likely to win the competition and pass on their genes
• Some species use aggressive behaviour to minimise real competition
• Ritual fights, displays, threat postures are used to allow some individuals (the "best") to reproduce and exclude others (the "weakest")
• This avoids real fights or shortages, and results in an optimum size for a population
• Aphids of both sexes have winged and wing-less morphs; winged morphs are produced during overcrowding
• Ecological community


  Organisms that live together in a small area and interact with one another
• Interacting species have a tremendous influence on the size of each other's populations
• Symbiosis


  Living together in close association of two or more organisms of different species
• Types of symbiotic relationships

  • Predation
  • Parasitism
  • Amensalism
  • Commensalism
  • Mutualism
• Predator-Prey Relationships


  • The populations of predators and their prey depend on each other
  • They tend to show cyclical changes