Intraspecific Competition competition is an interaction between individuals

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 densitydependent mortality

Mortality/fecundity equilibrium Reality means there is a broader range in which an equilibrium can be found

L, M, N = nutrient levels Carrot Density and Yield Total yield Root wt. Shoot wt. Law of Constant Final Yield • At low densities yield increases with density • Eventually yield becomes independent of density

Timing and Size Dactylis Plants emerging later grow less than predicted by average wt. gain/day

Asymmetric Competition Density & time of emergence both play a role Flax

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 & survival

When is defense profitable? • When competition exists • When enough resources exist • When costs do not outweigh benefits

Convict Cichlid Fish • As territory size increases: * Chase rate * Growth rate

Territory size vs. animal size