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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
Two types of competition
• Scramble (exploitative) competition
* no direct interaction
• Contest (direct or interference) competition
* some type of confrontation
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
Density dependent mortality
a=density independent; b=undercompensating density dependance; c=overcompensating density dependent
Exactly compensating density-dependent mortality
Mortality/fecundity equilibrium
Reality means there is a broader range in which an equilibrium can be found
Results of Intraspecific competition
• Stress
• Dispersal
• Social interactions
* dominance
* territoriality
Territories• Type of territory
* general - breaks down after breeding season* nesting - (feeding is done elsewhere)* food resource
• Means of “defending”* Sound* Visual* Scent marking
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
Red grouse breeding & survivalTime Event
August
September
October
November
January
April
Strife - family breakup
Displaced birds
Nonterritorial transientsClass 3
Class 3 birds do not breed
Most Class 3 birds dead
Territorial behavior(young and old) Successful territorial
defenders
Territorial ownersClass 1High survivalreplacement
Resident surplus birdsClass 2
Move to marginal habitat
Fail to breedSurvival poor
Family groups(territorial behavior byold cocks at dawn)
Breeding stock
When is defense profitable? • When competition exists
• When enough resources exist
• When costs do not outweigh benefits
Territory size vs. animal size
Timing and Size
Plants emerging later grow less than predicted by average wt. gain/day
Dactylis