Community Ecology

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Community Ecology

• Chapter 53

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• Community - group of species living close enough
  for interaction.
• Species richness of species a community
  contains relative abundance - of members of
  each species.

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• 2 theories on community development
• 1Individualistic hypothesis - species arrive in
  community by chance because of abiotic needs.
• 2Interactive hypothesis - species are in
  community because of similar biotic needs and
  interactions between species.

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Fluctuations are independent of one another and
constantly changing.
INDIVIDUALISTIC HYPOTHESIS
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Fluctuations are dependent upon one another.
INTERACTIVE HYPOTHESIS
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Relationships

• Interspecific interactions - relationships
  between species in community.
• Defined by how they affect other species.

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• 1Interspecific (between species) competition -
  resources are limited.
• Organisms own ecological niche (specific role in
  environment).
• If two organisms have same niche, cannot coexist
  (competitive exclusion principle)

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Both species occupy different niches because they
require the same biotic needs.
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• Resource partitioning allows two similar species
  to coexist.
• Done by differentiating species niches.

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Same genus of lizards, but the different species
occupy different areas in the trees to allow the
resources to be shared.
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• 2Predation - 1 species hunts, kills, eats other
  (the prey).
• AParasitism - 1 species lives off other species
  (may/may not kill host)
• Predators and prey have own survival adaptations.
• Predators - claws, fangs, etc.

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http//janoelofsesafaris.com/images/update11-01/ch
eetah1.jpg
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• Plants toxic chemical compounds - protect
  against herbivores.
• Prey - defenses (i.e. blending in to environment)
• Cryptic coloration - prey uses coloration to
  deceive predators.

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• aAposematic coloring - present as warning sign to
  predators.
• Prey - odors and toxins as defense against
  predators.

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Frog shows toxicity by presenting with bright
colors.
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• bMimicry - organism resembles another species.
• 1Batesian mimicry - harmless organism mimics
  harmful one.
• 2Mullerian mimicry 2 species resemble each
  other (both species are not tasteful)

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Batesian mimicry
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Mullerian mimicry
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• Parasites - live on host (ectoparasite) or in
  host (endoparasite).
• Parasitoidism - parasite eventually kills host.

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http//www.sierrapotomac.org/W_Needham/Pictures/Wo
od_Tick_040307.jpg
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• 3Mutualism - both species benefit.
• 4Commensalism - 1 species benefits, other is
  unharmed but does not benefit (barnacles that
  attach to side of whales)

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Acacia tree and ants the ants feed off the
tree and receive shelter in return, the ants
protect the tree from any harmful insects that
may kill the tree.
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• Coevolution - 1 species evolves, puts pressure on
  another species to evolve.
• 2nd species relies on 1st species must adapt to
  continue to benefit (selective pressure)

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http//www.fs.fed.us/wildflowers/pollinators/polli
nator-of-the-month/images/rubythroat/ruby-throated
_hummingbird_lg.jpg
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• Trophic structure - based on feeding patterns in
  community.
• Food chain - flow of energy from producers up to
  carnivores.
• Trophic level shows where organism fits in food
  chain.

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• Food web - more accurate way to look at feeding.
• Feeding relationships shown in interrelated way.

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• Food chains have limits on length (2 hypotheses)
• 1Energetic hypothesis - length of food chain
  limited by inefficiency of energy transfer along
  chain.
• 2Dynamic stability hypothesis - long food chains
  less stable than short chains.

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• Dominant species - most abundant or highest
  biomass.
• Biomass - sum weight of all individuals in
  population.
• Keystone species - species that have regulating
  effect on entire community.
• If removed, can affect entire community.

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• 2 models at how food chain is controlled.
• 1Bottom-up model - producers are the controlling
  factor of the population.
• 2Top-bottom model - consumers are controlling
  factor of population.

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http//www.iarc.uaf.edu/highlights/2005/coupled_ma
rine_ecosystem/food_web.jpg
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Disturbances

• Stability - ability of community to persist
  through disturbances.
• Fire, weather, or human activities can alter
  communities.

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After disturbance
Before disturbance
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Disturbance in marine community
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• Some disturbances necessary for community to
  thrive.

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Fire is necessary for this community to bring new
wildlife.
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Succession

• Succession - sequence of community changes after
  disturbance.
• 1Primary succession- no life, soil not formed
  yet.
• Mosses and lichens first cause development of
  soil.
• Example - after glacier retreats.

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• 2Secondary succession - after major disturbance.
• Soil left intact.
• Grasses first, then trees and other organisms.

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• Communitys diversity (biodiversity) controlled
  by two factors size and biogeography.
• Remember species richness - different species
  living in a community relative abundance - of
  those species living in the area.

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Community 1 has higher species richness
Community 2 has higher relative abundance
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• Species - richer towards equator, poorer towards
  the poles. (due to climate and evolutionary
  history of species)
• Greater the geographic area, more abundant the
  number of species.