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Unformatted text preview: Biology 1B, Ecology Lecture 5, Page 1 *Assigned readings, 8th Edition pp. 1198-1203 7th Edition pp. 1083-1093, 1159-1171 Organism Interactions and Competition Outline of Lecture 5 A. Competition 1. Competitive exclusion 2. Competition between two species B. Limiting resources C. Competition 1. Exploitative competition 2. Interference competition D. Demonstrations of interspecific competition 1. Tribolium beetles 2. Barnacles Professor Resh • Spring 2010 A. Competition: the use or attempted use of a limited environment resource by two or more populations (interspecific) or by members of the same population (intraspecific). 1. Competitive exclusion: if two species are competing for the same limited resource, one species will be able to use that resource more efficiently than the other and the former species will be able to eliminate the latter species locally. 2. Competition between two species is likely to be more intense, the more similar their ecological requirements; species occupying similar niches will tend to evolve in ways to minimize competition. Niche: sum total of all ecological needs and tolerances. Biology 1B, Ecology Lecture 5, Page 2 *Assigned readings, 8th Edition pp. 1198-1203 7th Edition pp. 1083-1093, 1159-1171 Organism Interactions and Competition Professor Resh • Spring 2010 B. Limiting resources 1. Energy 2. Nutrients 3. Water space 4. Nesting sites 5. Refugia C. Competition (N1 and N2 populations) dN1 dt also, dN2 dt = N2r2 K – N2 – (β x N1) K = N1r1 K – N1 – (α x N2) K Competition cont’d when N1 is the size of competing population 1, N2, is competing population 2, α is the proportional effect on species 2 on the population size of species 1 relative to resource K, and β is the effect of species 1 on species 2. α and β tend (but not always) to be reciprocal. For example:
Cockroaches Gorillas Elephants α= 0.001 1.0 100.0 β=100 1.0 0.001 Competition Species 1 Species 2 intraspecific intraspecific Interspecific Biology 1B, Ecology Lecture 5, Page 3 *Assigned readings, 8th Edition pp. 1198-1203 7th Edition pp. 1083-1093, 1159-1171 Organism Interactions and Competition Professor Resh • Spring 2010 1. Exploitative competition: two individuals are using the same limited resource in the same way but have different efficiencies in using that resource. There are no direct interactions. 2. Interference competition: competition results from direct behavioral interactions. E. Demonstrations of interspecific competition 1. Tribolium flour beetles (hot and damp, T. castaneum thrives; cool and dry, T. confusum thrives). 2. Barnacles: species A lives in shallow water, often exposed to air; species B lives in deeper water, rarely exposed to air.
a. In deeper water, species B out competes species A; but if species B is removed, species A moves into deeper zone. In shallow water, remove species A but species B cannot tolerate shallow water conditions. Hence they are only competing in deeper waters. b. c. ...
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- Spring '07