Ecology: Lecture 13

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Ecology Lecture 13

• Interspecific Competition 2
• November 5, 2007

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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 Niche knows that some other Nutch
  Would like to move into his Niche very much.
• So each Nutch in a Niche has to watch that small
  Niche 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
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Defining and mapping niches (based on key
characteristics)
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Niche relationships among species

• 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 1 variable
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Fundamental vs. realized niche
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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
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Resource partitioningMojave desert plants
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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
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So, how is it possible for so many similar
species of tropical fish to exist?
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So, how is it possible for so many similar
species of tropical fish to exist?

• Explanations consistent with the competitive
  exclusion principle
• i.e. resource partitioning, niche compression,
  niche shift
• Essentially, these suggest extreme specialization
• Multiple niche dimensions must be considered
  (see. Fig. 14.21)
• What might some of these dimensions be?

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So, how is it possible for so many similar
species of tropical fish to exist?

• Non-equilibrium conditions
• Factor 1 Transient nature of larvae
• What does this mean?
• How could this prevent competitive exclusion?
• Factor 2 Environmental disturbance (i.e.
  storms)
• Cause mortality
• How could this prevent competitive exclusion?
• Factor 3 Predation!
• Predators may target the species that are most
  abundant, so that less abundant species are able
  to increase.
• How can we relate this back to the Lotka-Volterra
  competition equations?