Why are ecological interactions important?

1. Why are ecological interactions important? Interactions can affect distribution and abundance. Interactions can influence evolution.

2. Competition – two species share a requirement for a limited resource  reduces fitness of one or both species

3. Ecological effects of competition Intraspecific competition – between individuals of the SAME species contributes to K (carrying capacity) Interspecific competition – between individuals of DIFFERENT species How does interspecific competition affect N?

4. k rats excluded control 0 .2 .4 .6 .8 1 # deer mice captured 1978-801988-90 (Heske, E. J., J. H. Brown, and S. Mistry 1994) What is the effect of kangaroo rat competition on deer mice?

5. competitive exclusion principle If two species have the same niche, the stronger competitor will eliminate the other competitor. “Complete competitors cannot coexist.”

6. Why do kangaroo rats exclude deer mice? What if you put more seeds in the environment? What if you added another resource to the environment?

7. Complete competitors cannot coexist. Competitive exclusion is reached more slowly with higher resource abundances. Stable coexistence requires niche differentiation, such that members of each species compete more strongly among themselves than with members of the other species.  (intraspecific > interspecific)

8. α12 – effect of an indv of species 2 on an indv of species 1 α21 – effect of an indv of species 1 on an indv of species 2 α21 & α21 = competition coefficients How does interspecific competition affect N? dN1 dt r1N1 K1-N1 K1 species 1 = dN2 dt r2N2 K2-N2 K2 species 2 =

9. intraspecific competition interspecific competition How does interspecific competition affect N? Lotka-Volterra equations dN1 dt r1N1 K1-N1 - α12N2 K1 species 1 = dN2 dt r2N2 K2-N2- α21N1 K2 species 2 = What does it mean ifα12= 1? What ifα12= 0.5?

10. Competitors can coexist: if intraspecific competition is stronger than interspecific competition, for both species Translate this intoα12andα21. for coexistence, α12< 1 andα21< 1 Predict α12andα21for k rats and mice.

11. Lotka-Volterra competition equations = including interspecific competition in the logistic model. Competition coefficients (’s) show per capita competitive effect of each species on the other. When ’s are less than 1, stable coexistence is possible.  implies that niches don’t completely overlap

12. A classic interspecific competition experiment two species of Paramecium predict the outcome of interspecific competition P. aurelia P. caudata ac = 0.8 ca = 1.1 Gause (1934)

13. What is the niche? set of conditions within which an organism can maintain a viable population multi-dimensional with as many dimensions as their are limiting conditions ecological niche light intensity okay temperature salinity

14. Fundamental niche depends on physical (abiotic) conditions. Realized niche depends on biotic as well as abiotic conditions. What is the realized niche of each barnacle? What is the fundamental niche of each?

15. How can we determine the realized niche of each barnacle? Where do they grow when allowed to compete? Balanus and Chthamalus growth rate Balanus realized niche Chthamalus realized niche low middle high Location in intertidal zone

16. How can we determine the fundamental niche of each barnacle? Removal experiments – remove each species and see where the other grows Balanus alone Balanus fundamental niche growth rate Chthamalus alone Chthamalus fundamental niche low middle high Location in intertidal zone

17. The niche of a species may contract in the presence of a competitor species. This phenomenon leads to resource (niche) partitioning and coexistence among functionally similar species. The narrower niche resulting from competition is called the realized niche. What happens if the competitor is removed?

18. competitive release – niche of the competitively-inferior species expands in the absence of the competitively-superior species competitive release growth rate Chthamalus with Balanus Chthamalus alone realized niche fundamental niche low middle high Location in intertidal zone

19. Streams with only Planaria species A Streams with only Planaria species B Streams with both Planaria species What are the fundamental and realized niches for each species?

20. The niche of a species may contract in the presence of a competitor species. This phenomenon leads to resource (niche) partitioning and coexistence among functionally similar species. The narrower niche resulting from competition is called the realized niche. When the dominant competitor is removed, the niche of the inferior competitor can expand by competitive release.