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Reproduction and Niches ES 100 August 20, 2007 Opportunists vs. Competitors • • • • • • Do well in variable climate or with disturbance Population boom and bust cycles Rapid development Early reproduction Small body size Single reproductive effort • • • • • • Do well in stable climate Population carrying capacity Slow development Late reproduction Large body size Repeated reproduction Practical Aspects of r vs. K Robin Eagle Why different life strategies? • More ways to live in an environment and use its resources. • Another way to say this: filling niches • • Fundamental vs. Realized niche Principle of competitive exclusion What is a niche? • A niche is the total of all biotic and abiotic factors that determine how an organism fits into its environment. • Where and how does an organism live and function? • • habitat role in community Fundamental vs. Realized niche Fundamental niche: All possible environmental (biotic and abiotic) conditions in which an organism can live. Realized niche: The actual environmental conditions in which an organism lives. Success potential survival, but stressed intolerant potential survival, but stressed optimum intolerant Environmental variable (Temperature, for example) Niche in n-variable hyperspace Fundamental vs. Realized Niche Fundamental niche: where a species could live Realized niche: with competition from other species, where a species does live Principle of Competitive Exclusion Two species can’t occupy the same niche… one would out-compete other and drive it to extinction Niche Partitioning in Animals Species divide up an apparent niche Selection minimizes competition Two species living separately. In a guild, natural selection minimizes competition Disease prevention via C.E. Convergent Evolution •Organisms adapt to fill open niches •Niches that are separated by geographic barriers may be filled by different species (1 species, 1 niche, 1 location) •Unrelated species who fill a similar niche and display similar form or function exemplify convergent evolution Summary of Today Life History: Reproductive Strategies opportunists vs. competitors Insight into ecosystem management Life tables Insights into population dynamics Vulnerable age stages Fitness Generation time Population trajectories Niches Fundamental vs. realized niche Competitive exclusion principle Convergent evolution