COMMUNITY ECOLOGY

• Community


  An assemblage of populations of various species living close enough for potential interaction
• Interspecific interactions


  • Competition
  • Predation
  • Herbivory
  • Symbiosis
  • Disease
• Interspecific interactions


  Affect the survival and reproduction of the species engaged in the interaction
• Effects of interspecific interactions

  • Positive
  • Negative
  • Neutral
• Interspecific competition


  Occurs when species compete for a particular resource that is in short supply
• Competitive exclusion


  The local elimination of one of the two competing species
• Competitive exclusion principle


  Two species competing for the same limiting resources cannot coexist in the same place
• Ecological niche


  The total of an organism's use of the biotic and abiotic resources in its environment
• Two species cannot coexist in a community if their niches are identical</b>
• Ecologically similar species can coexist in a community if there are one or more significant differences in their niches
• A species' fundamental niche may be different from its realized niche as a result of competition
• Resource partitioning


  The differentiation of niches that enables similar species to coexist in a community
• In character displacement, there is a tendency for characteristics to be more divergent in sympatric populations of two species than in allopatric populations of the same two species
• Predation


  An interaction where one species, the predator, kills and eats the other, the prey
• Feeding adaptations of predators

  • Claws
  • Teeth
  • Fangs
  • Stingers
  • Poison
• Cryptic coloration


  Makes prey difficult to spot
• Aposematic coloration


  Warns predators to stay away from prey
• Batesian mimicry


  A palatable or harmless species mimics an unpalatable or harmful model
• Müllerian mimicry


  Two or more unpalatable species resemble each other
• Herbivory


  The process in which an herbivore eats parts of a plant
• Parasitism


  One organism, the parasite, derives its nourishment from another organism, its host, which is harmed in the process
• Pathogens


  Disease-causing agents, typically bacteria, viruses, or protists
• Mutualism


  An interspecific interaction that benefits both species
• Commensalism


  One species benefits and the other is not affected
• Commensal interactions have been difficult to document in nature because any close association between species likely affects both species
• Generalized adaptation of organisms to other organisms in their environment is a fundamental feature of life
• Dominant species


  Species in a community that are most abundant or have the highest biomass and exert powerful control over the occurrence and distribution of other species
• Keystone species


  Species that are not necessarily abundant in a community but exert strong control on a community by their ecological roles or niches
• Beaver dams can transform landscapes on a very large scale
• Foundation species


  Organisms that exert their influence by causing physical changes in the environment that affect community structure
• Facilitators


  Foundation species that have positive effects on the survival and reproduction of some of the other species in the community
• Bottom-up model of community organization

  Proposes a unidirectional influence from lower to higher trophic levels, where the presence or absence of abiotic nutrients determines community structure
• Top-down model of community organization

  Proposes that control comes from the trophic level above, where predators control herbivores which in turn control primary producers
• Foundation species


  • Act as facilitators
  • Have positive effects on the survival and reproduction of some of the other species in the community
• Salt marsh with Juncus

  • With Juncus
  • Without Juncus
• Bottom-up model of community organization

  Proposes a unidirectional influence from lower to higher trophic levels
• Top-down model of community organization

  Proposes that control comes from the trophic level above
• Presence or absence of abiotic nutrients

  Determines community structure, including the abundance of primary producers
• Predators


  Control herbivores
• Herbivores


  Control primary producers