Community Ecology

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Community Ecology
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What is Community Ecology?

• A community is an assemblage of species that
  occur together at a particular time in a
  particular place and potentially interact with
  each other.
• In practice we often speak of any grouping of
  several species as being a community and often we
  will treat taxonomic groups as communities if
  they share a habitat - plant community, bird
  community, etc.

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The Ecological Niche

• Ecological niche - the way in which an organism
  interacts with all of the biotic and abiotic
  factors in its environment - often described as
  how the organism makes its living, its functional
  role, but includes the habitat it occupies.
• Habitat is restricted to meaning the environment
  in which individuals of a particular species
  usually exist.

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Two Kinds of Niches

• The fundamental niche - from Hutchinson 1958 -
  the set of resources and conditions that permits
  the survival and reproduction of an organism -
  many resources and conditions interact to form
  the niche.
• The realized niche - the portion of the
  fundamental niche actually occupied by the
  species when restricted by other organisms -
  restricted by competition, predation, parasites,
  disease.

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Fundamental vs. Realized Niche
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Competition
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Competition

• Competition is an interaction between
  individuals, brought about by a shared
  requirement for a resource in a limited supply
  which leads to a reduction in the survivorship,
  growth, and/or reproduction of the competing
  individuals.
• Among the resources competed for are food, water,
  nutrients, light, space for growth, territories,
  mates, etc.
• Two key points
• 1) resource being competed for has to be in
  limited supply - like the amount of grass in a
  meadow
• 2) the interaction is always negative - negative
  because it causes growth, survival, and/or
  reproduction to be lower than maximum potential
  in a world without competition

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Two Kinds of Competition

• Intraspecific competition - competition between
  members of the same species - thought to be
  especially strong because members of the same
  species have the same resource requirements
• Interspecific competition - competition between
  members of different species - can be strong as
  well

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Competition in Paramecium
Observed by Gause in 1934
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Population Growth In Paramecium
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Competition in Paramecium
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Competitive Exclusion Principle from Gause

• "Two competing species cannot coexist in a stable
  environment if both require the same limiting
  resource."
• If two competing species do coexist in a stable
  environment, they do so because of niche
  differentiation - their realized niches are
  slightly different and thus competition between
  them is lessened.

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Competition in Barnacles
Published in 1961
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Joe Connell
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Predation

• autotrophs - organisms which make their own food
• heterotrophs - organisms which consume other
  organisms or their products
• Predators are heterotrophs which consume live
  organisms
• True predators - prey is killed immediately upon
  successful attack
• Partial predators - prey usually not killed but
  many prey organisms affected during predators
  lifetime - grazers, browsers
• Parasitoids - organisms which lay eggs on or in
  prey and then eggs hatch and developing offspring
  consume the prey - mostly insects, many wasps

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True Predators
Great White Shark, Siberian Tiger, Fox Squirrel
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Partial Predators
Giraffe, Bison, Monarch Caterpillar
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Parasitoid
Parasitoid wasp attacking moth caterpillar
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Wolves and Moose on Isle Royale

• 50 of the moose taken by the wolves have a lung
  disease even though only 2 of the total moose
  population have the disease

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Predator-Prey Interactions
Golden eagle and black-footed ferrets prey on
Prairie Dogs consuming many young dispersing
males
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Keystone Predator Pisaster
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Pisaster
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The Mussel Mytilus
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Acorn and Goose Barnacles
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Limpet and Chiton
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Thais the Whelk
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Keystone Predator Pisaster
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Plant Secondary Compounds- Manufactured in a
second round of chemical synthesis, not in the
first round of photosynthesis
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Blue jay eats monarch, barfsdue to cardiac
glycoside from milkweed
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Aposematic or Warning Coloration
Monarch Butterfly and Caterpillar
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Mimicry

• Batesian mimicry in which a palatable species
  mimics a harmful model
• Mullerian mimicry in which several harmful
  species come to resemble each other

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Batesian mimicry several fly species mimicking
bees and wasps
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Batesian mimicry coral and king snakes
Arizona Coral Snake
Central American coral snakes and king snake
mimic coral snake on left or in middle
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Mullerian Mimicry
Monarch Viceroy
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Complex of Batesian and Mullerian Mimics
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Cryptic Coloration
Canyon Tree Frog
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General Defenses the Porcupine
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Symbioses

• Symbiosis means species living in close or
  intimate association
• parasitism ,- one species, the parasite,
  benefits at the expense of the host
• commensalism ,0 or 0,0 here there may be a
  positive effect for one species or neither, but
  neither is harmed
• mutualism , a situation in which two species
  interact with each other and both benefit

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Parasitism

• Parasitism - intimate association between two
  species in which the parasite obtains its
  nutrients from a host - parasite usually causes
  some degree of harm to its host - either reduced
  growth or reproduction
• pathogen - disease causing agent
• disease - abnormal condition of host due to
  infection by a pathogen that impairs
  physiological functioning

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Parasites
Tapeworm, deer liver fluke, medicinal leech, dog
tick
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Evolution of ParasitesRabbits in Australia
Rabbit fence and the wily varmint himself
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Commensalism - ,0 or 0,0 - can have positive
effect for one species or for neither
Shark with remora and water buffalo with cattle
egret