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

Population size and mortality “Pure competition”

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

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

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