Community ecology Ch 53 U114PP

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Community ecology- Ch 53 U114PP
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Competition
Recall

• Interspecific competition
• Occurs when species compete for a particular
  resource that is in short supply

• Competition can result in four outcomes
• ongoing competition
• competitive exclusion (local extinction)
• resource partitioning
• character displacement

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Character Displacement

• 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

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Predation

• Predation refers to an interaction
• Where one species, the predator, kills and eats
  the other, the prey
• A /- interaction

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• Feeding adaptations of predators include
• Claws, teeth, fangs, stingers, and poison
• Animals also display
• A great variety of defensive adaptations

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Prey Defenses

• Cryptic coloration, or camouflage
• Makes prey difficult to spot

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Prey Defenses

• Aposematic coloration
• Warns predators to stay away from prey

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Prey Defenses

• In some cases, one prey species
• May gain significant protection by mimicking the
  appearance of another

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

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• In Müllerian mimicry
• Two or more unpalatable species resemble each
  other

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Herbivory

• Herbivory, the process in which an herbivore eats
  parts of a plant
• Has led to the evolution of plant mechanical
  (e.g. thorns) and chemical defenses and
  consequent adaptations by herbivores

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Parasitism

• In parasitism, one organism, the parasite
• Derives its nourishment from another organism,
  its host, which is harmed in the process
• Not always a feedinge.g., brood parasitism
• A /- interaction

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Disease

• The effects of disease on populations and
  communities
• Is similar to that of parasites

• Pathogens, disease-causing agents
• Are typically bacteria, viruses, or protists

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Mutualism

• Mutualistic symbiosis, or mutualism
• Is an interspecific interaction that benefits
  both species
• A / interaction

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Commensalism

• In commensalism
• One species benefits and the other is not
  affected
• A /0 interaction (?)

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• Commensal interactions have been difficult to
  document in nature
• Because any close association between species
  likely affects both species

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Interspecific Interactions and Adaptation

• Evidence for coevolution
• Which involves reciprocal genetic change by
  interacting populations, is scarce

• However, generalized adaptation of organisms to
  other organisms in their environment
• Is a fundamental feature of life

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• Concept 53.3 Disturbance influences species
  diversity and composition
• Decades ago, most ecologists favored the
  traditional view
• That communities are in a state of equilibrium

• However, a recent emphasis on change has led to a
  nonequilibrium model
• Which describes communities as constantly
  changing after being buffeted by disturbances
• Promotes diversity, because small scale
  disturbances enhance patchiness

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What Is Disturbance?

• A disturbance
• Is an event that changes a community
• Removes organisms from a community
• Alters resource availability

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• Fire
• Is a significant disturbance in most terrestrial
  ecosystems
• Is often a necessity in some communities

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• The intermediate disturbance hypothesis
• Suggests that moderate levels of disturbance can
  foster higher species diversity than low levels
  of disturbance
• For most communities, disturbance is not bad-
  it is the norm

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• The large-scale fire in Yellowstone National Park
  in 1988
• Demonstrated that communities can often respond
  very rapidly to a massive disturbance

Figure 53.22a, b
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Human Disturbance

• Humans
• Are the most widespread agents of disturbance

This is not productive disturbance it is so
severe, species loss results.
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• Human disturbance to communities
• Usually reduces species diversity
• Humans also prevent some naturally occurring
  disturbances
• Which can be important to community structure

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Ecological Succession

• Ecological succession
• Is the predictable sequence of community and
  ecosystem changes after a disturbance

Why does succession occur? Some species are
adapted to initial abiotic conditions (foundation
species). They gradually alter the environment
and facilitate other species to come in. Shifts
from r-selected to K-selected species
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• Primary succession
• Occurs where no soil exists when succession
  begins
• Secondary succession
• Begins in an area where soil remains after a
  disturbance

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• Early-arriving species
• May facilitate the appearance of later species by
  making the environment more favorable
• May inhibit establishment of later species
• May tolerate later species but have no impact on
  their establishment

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• Succession on the moraines in Glacier Bay, Alaska
• Follows a predictable pattern of change in
  vegetation and soil characteristics

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Climax community?

• Eventually there are no more big transitions of
  species types- supposedly the community is
  full
• Myth! Always microhabitat changes, so a given
  area may have a variety of succession stages in it

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• Concept 53.4 Biogeographic factors affect
  community diversity
• Two key factors correlated with a communitys
  species diversity
• Are its geographic location and its size

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Equatorial-Polar Gradients

• The two key factors in equatorial-polar gradients
  of species richness
• Are probably evolutionary history and climate

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• Species richness generally declines along an
  equatorial-polar gradient
• And is especially great in the tropics
• The greater age of tropical environments
• May account for the greater species richness
• Higher productivity, longer growing season
• Spatial heterogeneity- more microhabitats

700 species of birds in Central America fewer
than 50 toward the poles 711 tree species in
Malaysia 10-15 in Michigan 200 ant species in
Brazil 7 in Alaska

• Climate
• Is likely the primary cause of the latitudinal
  gradient in biodiversity
• What components make up climate?

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• The two main climatic factors correlated with
  biodiversity
• Are solar energy input and water availability

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Area Effects

• The species-area curve quantifies the idea that
• All other factors being equal, the larger the
  geographic area of a community, the greater the
  number of species

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• A species-area curve of North American breeding
  birds
• Supports this idea

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Island Equilibrium Model

• Species richness on islands
• Depends on island size, distance from the
  mainland, immigration, and extinction

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• The equilibrium model of island biogeography
  maintains that
• Species richness on an ecological island levels
  off at some dynamic equilibrium point

Figure 53.27ac
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• Studies of species richness on the Galápagos
  Islands
• Support the prediction that species richness
  increases with island size