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Competition

Competition. Chapter 13. Modes of Competition. Interference/Contest : Direct aggressive interaction between individuals. Intraspecific : Competition with members of own species; includes exploitative competition Interspecific :

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Competition

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  1. Competition Chapter 13

  2. Modes of Competition • Interference/Contest: • Direct aggressive interaction between individuals. • Intraspecific: • Competition with members of own species; includes exploitative competition • Interspecific: • Competition between individuals of two species - reduces fitness of both.

  3. Interspecific Competition in Sunfishes • Pumpkinseed • alone-broad feeding niche (fundamental feeding niche) • when bluegills present, feed heavily on snails (narrower realized niche) • recall MacArthur’s warblers

  4. Intraspecific Competition Among Herbaceous Plants • Plant growth rates and weights have been found to increase in low density populations. • Competition for resources is more intense at higher population densities. • Usually leads to mortality among competing plants. • Self-Thinning

  5. Niches • Niche: Summarizes environmental factors that influence growth, survival, and reproduction of a species. • Gause: Principle of Competitive Exclusion • Two species with identical niches cannot coexist indefinitely. • One will be a better competitor and thus have higher fitness and eventually exclude the other.

  6. Niches • Hutchinson defined niche as: • n-dimensional hyper-volume • n equates the number of environmental factors important to survival and reproduction of a species. • Fundamental niche - hypervolume • Realized niche includes interactions such as competition that may restrict environments where a species may live.

  7. Feeding Niches of Galapagos Finches • Grant found differences in beak size among ground finches translates directly into diet. • Size of seeds eaten can be estimated by measuring beak depths. • Individuals with deepest beaks fed on hardest seeds. • After 1977 drought, the remaining seeds were very hard. Thus, mortality was most heavy in birds with smaller beaks.

  8. Feeding Niches of Galapagos Finches

  9. Lotka Volterra • Effect of interspecific competition on population growth of each species: • dN1 / dt = rm1N1 ((K1-N1-12N2) / K1) • dN2 / dt = rm2N2 ((K2-N2-21N1) / K2) • 12: Effect of individual of species 2 on rate of pop. growth of species 1. • 21: Effect of individual of species 1 on rate of pop. growth of species 2.

  10. Lotka Volterra • In general, LV predicts coexistence of two species when, for both species, interspecific competition is weaker than intraspecific competition.

  11. Paramecia Lab Experiments • Gause demonstrated resource limitation with Paramecium caudatum and Paramecium aurelia in presence of two different concentrations of Bacillus pyocyaneus. • When grown alone, carrying capacity determined by intraspecific competition. • When grown together, P. caudatum quickly declined. • Reduced resource supplies increased competition.

  12. Paramecia Lab Experiments

  13. Competition and Niches • Competition can restrict species to their realized niches. • But if competitive interactions are strong and pervasive enough, they may produce an evolutionary response in the competitor population. • Changes fundamental niche.

  14. Niche Overlap and Competition Between Barnacles • Connell discovered interspecific competition in barnacles. Balanus plays a role in determining lower limit of Chthamalus within intertidal zone. • Did not account for all observed patterns.

  15. Character Displacement

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