Population interactions

1. Population interactions • competition • Types of population interactions: • predation • commenalism • mutualism • parasitism Where have all the sea otters gone?

2. Interspecific competition • Interspecificcompetition = negative interactions between species for limited resources • Classic laboratory experiments demonstrating interspecific competition • Gause (1934): interspecific competition among Paramecium Where have all the sea otters gone?

3. Interspecific competition • Principle of competitive exclusion = if two species compete for a limited resource, the species that uses the resource more efficiently will drive the other species to local extinction Where have all the sea otters gone?

4. Interspecific competition • Species coexist if they do not use resources in exact same way • Gause (1935) found some species could coexist Where have all the sea otters gone?

5. Interspecific competition • interferencecompetition: physical confrontations for resources (e.g. lions and hyenas at a carcass) • Types of interspecific competition: • exploitativecompetition: consumption of shared resources (e.g. Paramecium feeding on bacteria) • Intensity of interspecific competition depends on abundance of resource and niche overlap • Niche = all the ways in which an organism uses resources in its environment Where have all the sea otters gone?

6. Interspecific competition • Fundamental niche: entire niche that a species is capable of using • Two ways to measure the niche of a species: • Realized niche: actual niche occupied because of interspecific interactions such as competition • Measure fundamental and realized niches with removal experiments • Connell (1961): interspecific competition between barnacles on the rocky intertidal zone Where have all the sea otters gone?

7. Larvae of both species settle throughout intertidal, but adults show abrupt vertical distributions (zonation) Interspecific competition • Two species of barnacles in Scotland • Connell’s (1961) classic experiment: • Chthamalus: small size, upper portion of intertidal zone • Semibalanus: large, lower-mid portions of intertidal zone • Connell (1961) removed each species to investigate the reason for vertical zonation between barnacles Where have all the sea otters gone?

8. Interspecific competition • Chthamalus has larger fundamental niche than Semibalanus; only Chthamalus can tolerate upper site • Connell’s (1961) classic experiment: • Semibalanus outcompetes Chthamalus in mid and lower zones Where have all the sea otters gone?

9. Interspecific competition • Observational evidence of interspecific competition: • If two species evolve in competition, selection may favor changes in one or both species that leads to resourcepartitioning (=subdivision of a niche) Where have all the sea otters gone?

10. Interspecific competition • Observational evidence of interspecific competition: • Character displacement = differences in morphology between two species when sympatric but not allopatric Where have all the sea otters gone?

11. Symbiotic relationships • Coevolution = long-term, mutual evolutionary changes between closely interacting species • Coevolution can lead to symbiosis (= two or more species living in a close association) • Types of symbiotic relationships: • Commensalism: one species benefits and the other species neither benefits or is harmed by the association • Mutualism: both species benefit by the association • Parasitism: one species benefits and the other species is harmed by the association • Classifying symbiotic relationships difficult; requires experiments Where have all the sea otters gone?

12. Symbiotic relationships • Clownfish and sea anemones; oxpeckers and grazers • Commensalism Where have all the sea otters gone?

13. Symbiotic relationships • Pollination; Ants and Acacia trees • Mutualism Where have all the sea otters gone?

14. Symbiotic relationships • Ectoparasites, endoparasites, brood parasites • Parasitism Where have all the sea otters gone?