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Community Ecology Chapter 56. Biological Communities. Community: all the organisms that live together in a specific place Evolve together Forage together Compete Cooperate. Biological Communities.

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biological communities
Biological Communities
  • Community: all the organisms that live together in a specific place
    • Evolve together
    • Forage together
    • Compete
    • Cooperate
biological communities1
Biological Communities
  • Individualistic concept: a community is a group of species that happen to occur together at one place
    • species respond independently to changing environmental conditions
    • The composition of a Community can change
ecological niche
Ecological Niche
  • Niche: An Organism’s way of life
    • Habitat
    • Food
    • Temp. range
    • Reproduction
ecological niche1
Ecological Niche
  • Fundamental niche: the entire niche that a species is capable of using.
  • Realized niche: actual niche in which the species can establish a stable population
ecological niche2
Ecological Niche

study of barnacles

ecological niche3



Ecological Niche
  • causes of niche restriction
    • Competition
    • Predators
    • Absence of pollinators
    • Presence of herbivores
ecological niche4
Ecological Niche
  • Principle of competitive exclusion: no two species can occupy the same niche when resources are limited
    • Species may divide up the resources, (resource partitioning)
    • natural selection can then lead to adaptive radiation
ecological niche5
Ecological Niche

Character displacement in Darwin’s finches

predator prey
  • Predation and coevolution
    • Predation provides strong selective pressure on the prey population
    • Features that decrease the probability of capture are strongly favored
    • Predator populations counteradapt to continue eating the prey

Coevolution race


Examples of prey adaptations:

  • Chemical defenses
  • Camouflage
  • Warning coloration
  • mimicry
species interactions
Species Interactions
  • Symbiosis: two or more kinds of organisms interact in more-or-less permanent relationships
  • All symbiotic relationships carry the potential for coevolution
  • Three major types of symbiosis
    • Commensalism (Win-Neutral)
    • Mutualism(Win-Win)
    • Parasitism(Win-Lose)
species interactions1
Species Interactions
  • Commensalism benefits one species and is neutral to the other
    • Spanish moss: an epiphyte hangs from trees
species interactions2
Species Interactions
  • Mutualism benefits both species
  • Coevolution: flowering plants and insects

Ants and acacias

    • Acacias provide hollow thorns and food
    • Ants provide protection from herbivores
species interactions3
Species Interactions
  • Parasitism benefits one species at the expense of another
  • Can be external or internal parasites
species interactions4
Species Interactions

External parasite: the yellow vines are the flowering plant dodder, it is a parasite that obtains its food from the host plant it grows on

species interactions5
Species Interactions
  • Ecological processes can interact
    • Predation reduces competition
      • Superior competitors become more numerous and attract predators
      • This allows other species to survive when they could have been out competed
species interactions6
Species Interactions

Starfish eat barnacles, allowing other species to thrive instead of being crowded out by the explosive population of barnacles

species interactions7
Species Interactions
  • Keystone species: species whose effects are greater than expected
  • Examples:
    • Sea star predation on barnacles
    • Beaver ponds
    • Top predators
    • Krill
species interactions8
Species Interactions

Beavers construct dams and transform flowing streams into ponds, creating new habitats for many plants and animals