Community Ecology BIO2207

• Biological community

  A group of different species living close enough together for potential interaction
• Interspecific interactions

  • Competition
  • Predation
  • Herbivory
  • Symbiosis (including parasitism, mutualism, and commensalism)
• Interspecific interactions

  Classified by whether they help, harm, or have no effect on the species involved
• 0


  Indicates that a population is not affected by the interaction in any known way
• Interspecific competition

  Occurs when species compete for a resource that limits their growth and survival
• When two species engage in interspecific competition for a limiting resource

  The result is detrimental to one or both species (-/-)
• Competitive exclusion

  Strong competition between two species can lead to the local elimination of one of the two competing species
• Gause concluded that two species competing for the same limiting resources cannot coexist in the same place
• One species will always use the resources more efficiently, gaining a reproductive advantage that will eventually lead to local elimination of the inferior competitor
• Ecological niche

  The sum total of an organism's use of abiotic and biotic resources in its environment
• Niche


  An organism's "profession" or ecological role - how it "fits into" an ecosystem
• Niche of a tropical tree lizard


  • Temperature range it tolerates
  • Size of the branches it perches on
  • Time of day when it is active
  • Sizes and Types of insects
• The competitive exclusion principle can be restated to say that two species cannot coexist permanently in a community if their niches are identical
• Ecologically similar species can coexist in a community if their niches differ in one or more significant ways
• Resource partitioning


  The differentiation of niches that enables two similar species to coexist in a community
• Fundamental niche


  The niche potentially occupied by a species
• Realized niche


  The niche a species actually occupies in a particular environment
• Testing whether a potential competitor limits a species' realized niche


  Removing the competitor and seeing whether the first species expands into the newly available space
• Experiment in the rocky intertidal zone of Scotland

  • Competition from one barnacle species kept a second barnacle species from occupying part of its fundamental niche
• Character displacement


  The tendency for characteristics to be more divergent in sympatric populations of two species than in allopatric populations of the same two species
• Character displacement


  • Variation in beak size between different populations of the Galápagos finches Geospiza fuliginosa and Geospiza fortis
• Predators


  • Have acute senses and weaponry (claws, teeth, fangs, stingers, or poison) to help them catch and subdue prey
  • Predators that pursue prey are generally fast and agile
  • Predators that lie in ambush are often camouflaged
• Prey animals


  • Have evolved adaptations that help them avoid being eaten (fleeing, hiding, forming herds and schools, active self-defense, alarm calls)
  • Have adaptive coloration (camouflage, cryptic coloration, bright warning aposematic coloration, Batesian and Müllerian mimicry)
  • Have mechanical or chemical defenses
• Herbivory


  A +/- interaction in which an herbivore eats parts of a plant or alga
• Herbivores


  • Have chemical sensors on their feet to recognize appropriate food plants
  • Have specialized dentition and digestive systems to process vegetation
• Plants


  • Produce chemical toxins, spines, and thorns to prevent herbivory
• Symbiosis


  All direct and intimate relationships between species, whether harmful, helpful, or neutral
• Parasitism


  A +/- symbiotic interaction in which a parasite derives its nourishment from a host, which is harmed in the process
• Endoparasites

  Live within the body of the host
• Ectoparasites

  Live and feed on the external surface of the host
• a parasite that lays eggs on or in living hosts, with the larvae feeding on the body of the host, eventually killing it
• Parasites


  • Have complex life cycles involving a number of hosts
  • Can change the behavior of their hosts in ways that increase the probability of the parasite being transferred from one host to another
• Presence of parasitic acanthocephalan (spiny-headed) worms


  Leads their crustacean hosts to move into the open, where they have a greater chance of being eaten by the birds that are the second host in the parasitic worm's life cycle
• Parasites


  Can have significant direct and indirect effects on the survival, reproduction, and density of their host populations
• Effects of parasites on moose

  • Ticks that live as ectoparasites on moose weaken their hosts by withdrawing blood and causing hair breakage and loss, thus increasing the chance that the moose will die from cold, stress, or predation by wolves
• Mutualism


  An interspecific symbiosis in which two species benefit from their interaction (+/+)
• Mutualism


  • Nitrogen fixation by bacteria in the root nodules of legumes
  • Digestion of cellulose by microorganisms in the guts of ruminant mammals
  • Exchange of nutrients in mycorrhizae, the association of fungi and plant roots
• Obligate mutualism

  At least one species has lost the ability to survive without its partner
• Facultative mutualism

  Both species can survive alone
• Mutualistic interactions

  May result in the evolution of related adaptations in both species