Ecology: Lecture 13

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Ecology Lecture 13

• Interspecific Competition (finish)
• October 31, 2005

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What evidence is required to show that
competition is responsible for a particular
pattern of distribution?

• The distribution of the two species is inversely
  correlated.
• The two species have been demonstrated to require
  the same limited resource and/or one interferes
  with the others ability to acquire resources
• Removal of the superior competitor results in
  movement of the inferior competitor into the
  now unoccupied region.
• It is really the presumed competitor that is
  responsible for the exclusion and not some
  correlated factor.

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Definition of a nicheTheodore Giesel

• And NUH is the letter I use to spell Nutches,
  Who live in small caves, known as Niches, for
  hutches.
• These Nutches have troubles, the biggest of which
  is The fact there are many more Nutches than
  Niches.
• Each Nutch in a Nich knows that some other Nutch
  Would like to move into his Nich very much.
• So each Nutch in a Nich has to watch that small
  Nich Or Nutches who haven't got Niches will
  snitch.
•            
•   -On Beyond Zebra (1955)

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Definition of a niche(from Hutchinson and
Shelford)

• For each environmental variable it faces in its
  world, an organism has a range of values for
  which it can grow and multiply

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A space of n-dimensions

• Fig. 14.15

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Defining and mapping niches (based on key
characteristics)

• Fig. 14.17

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Define niche overlap between species

• Fig. 14.19

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Niche relationships among species
Fig. 14.19

• x-axis state of a particular resource (size of
  prey, for example)
• y-axis species response/fitness (much as for
  Shelfords law of tolerance)

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Niche overlap mapping gt1 variable

• Fig. 14.21

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Fundamental vs. realized niche

• Fig. 14.16

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Competitive exclusion principle

• Gause As a result of competition, two similar
  species scarcely ever occupy similar niches, but
  displace each other in such a manner that each
  takes possession of certainly particular kinds of
  food and modes of life in which it has an
  advantage over its competitor.
• Hardin Complete competitors cannot coexist.

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Resource partitioning

• Fig. 14.9

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Resource partitioningMojave desert plants

• Fig. 14.10

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Resource partitioningChristmas Island terns
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Other responses to competition (spatial rather
than resource-based)

• Niche compression
• Example Doves in New Guinea
• Niche shift
• Example Sunfish in artificial ponds
• Ecological release

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Character displacement Darwins finches

• Fig. 14.23