Intraspecific Competition

1. 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

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

3. 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 a=density independent; b=undercompensating density dependance; c=overcompensating density dependent

5. Exactly compensating density-dependent mortality

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

7. Total yield Root wt. Shoot wt. 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

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

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

10. Results of Intraspecific competition • Stress • Dispersal • Social interactions • dominance • territoriality

11. Territories • Type of territory • general - breaks down after breeding season • nesting - (feeding is done elsewhere) • food resource • Means of “defending” • Sound • Visual • Scent marking

12. 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

13. Red grouse breeding & survival

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

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

16. Territory size vs. animal size