community ecology

• Community Ecology


  Populations are linked by interspecific interactions that impact the survival & reproduction of the species involved
• Autecology


  The study of the interaction between individual species with their environment
• Synecology


  The study of interactions among two or more species or a population with their environment
• Community


  An assemblage of populations living close enough together for potential interaction
• Dominant Species


  Most abundant, highest biomass, powerful control over occurrence and distribution of other species
• Keystone Species


  Not necessarily most abundant, exert strong control due to their ecological roles or niches
• Richness


  Number of species & abundance
• Communities with higher diversity

  • More productive and more stable regarding their productivity
  • Better able to withstand and recover from environmental stresses
  • More resistant to invasive species, organisms that become established outside their native range
• Species Richness


  Number of different species
• Observation Of Sea Otter Populations And Their Predation

  1. Food chain before killer whale involvement in chain

  2. Food chain after killer whales started preying on otters
• Keystone species


  One that has a strong effect on the composition of the community
• Removal of keystone species causes a decrease in species richness
• Stability


  Population sizes and number of species remain constant over time (Equilibrium)
• Community Stability


  • Stability Increases (The ecosystem can withstand disturbances)
• Disturbances


  Events that change communities, remove organisms, or alter resource availability
• Components of Stability

  • Resistance - force needed to change the community
  • Resilience - ability of the community to return to prior state (equilibrium) after perturbation
  • Elasticity - how quickly community returns to equilibrium
  • Amplitude - how much disturbance community can tolerate, and still return to some kind of equilibrium
• A community in equilibrium is generally stable and balanced
• Disturbances or changes in the environment can throw a community into disequilibrium
• Severe disturbances can cause permanent change to environment
• Human activities


  Cause more disturbance than natural events but usually reduce species diversity in communities because they do not allow recovery after disturbance but keep communities constantly disturbed, and hence in an early colonization
• Climax Community


  A mature stable community that is the final stage of ecological succession
• Climax Community


  A stable group of plants and animals which is the end result of succession process
• Island


  Areas of land that are bordered by water
• Islands can serve almost as a laboratory for the study of biogeography
• Types of islands


  • Islands that were originally part of a nearby continent, but were separated by rising sea levels (land-bridge islands)
  • Islands that are part of a volcanic island arc
  • Seamount chains which formed over geological "hotspots"
• Island Biogeography


  The geographical analysis of the biodiversity of the plant and animal species on islands
• Theory of island biogeography

  Relates the number of species on an island to the land area of the island and the degree of isolation of the island
• Target effect


  A species will have a greater success rate immigrating, or establishing a new home, to a larger island than on a smaller island
• Principle of Island Biogeography

  • Two significant factors that contributes to the rate of species change are: the area of the island (size) and its distance from the mainland (Isolation)
• Extinction


  The dying out of a species
• Immigration


  The establishment of a home by a species in a new habitat
• Emigration


  The departure of a species from its established habitat
• Island populations are more likely to go extinct than those on mainland, for several reasons
• Equilibrium


  The balance of extinction and immigration of species on an island
• Succession


  The steady and gradual change in a species of a given area with respect to the changing environment
• The ultimate aim of this process is to reach equilibrium in the ecosystem
• Types of Ecological Succession

  • Primary Succession
  • Secondary Succession
  • Cyclic succession
• Primary Succession


  Occurs when there are no traces of the original community remaining, including vegetation and soil
• Secondary Succession


  Occurs when a disturbance dramatically alters a community but does not completely destroy it
• Cyclic Succession


  The change in the structure of an ecosystem on a cyclic basis