1. Interspecific Competition Chapter 6

2. Interspecific Competition Individuals of one species suffer reduction in fecundity, survivorship, or growth as a result of exploitation of resources or interference by individuals from another species

3. Interspecific Competition May exclude one another from particular habitats (no coexistence) Or may coexist (utilize slightly different habitats)

4. Interspecific Competition Exploitation or interference

5. Exploitation - diatoms OK when alone, but one disappears when together More effective exploiters exclude less effective ones Depresses resources so low other species can’t survive

6. Interference - barnacles One species pushes other off rock surfaces

8. Highly Assymetric Consequences not same for both species One harmed greatly, other less so or not much at all

9. More Effects Competition for one resource affects competition for other resources E.g., plants competing for light have ability to compete for nutrients affected

10. Competition Models Lotka-Volterra model Examines changes in abundance of one species while in competition with another species

11. Competition Models

12. 4 possible outcomes

13. Competition Models Species 1 is stronger competitor, so 1 wins Species 2 is stronger competitor, so 2 wins Both species are stronger competitors on each other than on themselves, so may exist in unstable coexistence Both species are weak competitors, so exist in stable coexistence

14. Coexistence Partitioning of resources, differentiation of realized niches Species deprived of realized niche by a competitor is driven to extinction

15. Competitive Exclusion Principle If two competing species coexist in stable environment, then they do so as a result of niche differentiation. If there is no such differentiation, one competing species will eliminate the other.

16. Niche Differentiation How much niche differentiation is necessary for species to coexist?

17. Niche Differentiation Interspecific competition tends to increase separation along gradient (reduce overlap) to reduce the effects of the competition

18. Niche Differentiation Intraspecific competition tends to decrease separation along gradient by expanding each species’ use of the gradient

19. Niche Differentiation Niche differentiation results from interaction of the effects of intra- and interspecific competition

20. End result? Environment may not be constant enough for effects of competition to reach final conclusion Environment may change before one competitor wins

21. Evidence for interspecific comp. Laboratory experiments Controlled conditions Simple environment, unlike natural

22. Evidence for interspecific comp. Manipulative field experiments Reduce density of one, see how other responds Best for sessile organisms

23. Evidence for interspecific comp. Natural experiments Competitive release - expansion of niche in absence of competitor compared to size in presence of competitor

24. Evidence for interspecific comp. Natural experiments Character displacement - morphological difference between allopatric (species alone) and sympatric (species together) populations