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Biology Lecture 23.docx

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Biology 1001A
Tom Haffie

Biology Lecture 23: Community Ecology 23  Species, richness, evenness, diversity o Species diversity or species richness: the total number of different species in a community o Species evenness: the relative abundance of each of those different species in the community  Trophic Levels: o Different species are categorized based on where they get their food from, and what (if anything) eats them o Example: Phytoplankton are the primary consumers (take energy from the sun and convert it to biomass), and whatever eats them are the primary consumers, then whatever eats the primary consumers are secondary consumers, etc…until you reach your tertiary consumers (top carnivore) o Grazing food web: some of the energy fixed by the primary producers flows up these different tropic levels (but not all of it does; majority of energy fixed by the green plants, does not make it up this food web) and some of it goes through the detrital food web (or decomposing food web) o A complex community has many species per trophic level, and many trophic levels  Diversity and Keystone Species: o Keystone species: something that has disproportionate effects (major effects relative to abundance or total biomass) on the community (Example: the sea otter) o Keystone species are often keystone predators because they are at the top of their food web, but this is not always the case o Keystone species tend to increase species richness in a community  Patterns in species diversity: o Communities closer to the equator have higher species richness o Equilibrium theory of island biogeography: the number of species on an island will reflect an equilibrium of immigration and extinction rates o The more species that are already present on a island the less likely it is that any new individual swimming over is member of species that is not already present on the island o The immigration rate decreases, and the rate of extinction increases (due to competition) because there are only so many ecological niches o Larger islands have more species: immigration rate is higher because it is more likely to be found or reached and the extinction rate tends to be lower because it can support more ecological niches o Islands farther away from the mainland have fewer species: immigration rates are lower
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