Intraspecific Competition

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Intraspecific Competition

• competition is an interaction between
  individuals, brought about by a shared
  requirement for a resource in limited supply, and
  leading to a reduction in the survivorship,
  growth and/or reproduction of the competing
  individuals concerned
• Begon, et al. Chapter 6

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Two types of competition

• Scramble (exploitative) competition
• no direct interaction
• Contest (direct or interference) competition
• some type of confrontation

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Four characteristics of intraspecific competition

• The ultimate effect decreased contribution of
  individuals to the next generations
• The resource must be in limited supply.
• Competing individuals are all essentially
  equivalent.
• The effect on any individual increases with
  increasing number of competitors

4
Density dependent mortality

• adensity independent bundercompensating
  density dependance covercompensating density
  dependent

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Exactly compensating density-dependent mortality
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Mortality/fecundity equilibrium

• Reality means there is a broader range in which
  an equilibrium can be found

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Population size and mortality

• Pure competition

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Law of Constant Final Yield
Carrot Density and Yield
L, M, N nutrient levels

• At low densities yield increases with density
• Eventually yield becomes independent of density

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Timing and Size
Dactylis

• Plants emerging later grow less than predicted
  by average wt. gain/day

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Asymmetric Competition
Flax

• Density time of emergence both play a role

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Results of Intraspecific competition

• Stress
• Dispersal
• Social interactions
• dominance
• territoriality

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Territories

• Type of territory
• general - breaks down after breeding season
• nesting - (feeding is done elsewhere)
• food resource
• Means of defending
• Sound
• Visual

• Scent marking

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Example Red Grouse

• Three social classes
• territorial cocks with hens
• nonterritorial surplus birds - on periphery
• nonterritorial transient birds
• Fall to Spring - territories defended
• By late winter, all surplus birds removed
• size of territories determined by amount of
  heather N content of foliage

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• Red grouse breeding survival

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When is defense profitable?

• When competition exists
• When enough resources exist
• When costs do not outweigh benefits

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Convict Cichlid Fish

• As territory size increases
• Chase rate
• Growth rate

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Territory size vs. animal size
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