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Lecture 23.docx

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Biology 1001A
Tom Haffie

Community Ecology Continued (Lecture 23) • One of the major factors that shapes communities, that affects which organisms are going to be distributed where in niche space (ecological space), or which organisms is going to inhabit which particular habitats, one of the main factors driving all this is COMPETITION • 2 species of barnacle • Normally smaller species found on shallow portion of rocks and larger only on deeper rock • Experimentally, get rid of deep water barnacle; shallow barnacles expand • Reverse the experiment and deep barnacles do not change • This tells us that competition is affecting the community (the distribution of barnacles in space) Species Diversity • Is a composite of: o Species richness- total number of different species in the community o Species evenness- relative abundance of each of those different species in the community Trophic Levels (Food Web) • In any community different organisms/species occupy what is known as different trophic levels • Based on where they get there food from and what, if anything, eats them • The levels are classed as primary producers, primary consumers, secondary, tertiary, etc… • Not all of the energy makes it into the food web. Some goes in to waste. o There’s decomposers in the food web Diversity and Keystone Species • Some ecological communities (not all) have a particular species contained in them that we call the keystone species o Something that has disproportionate effects on the rest of the community. i.e. effects that are greater than we would predict based on how abundant that species is/biomass o Keystone species are often keystone predators (at the top of the food web) o Keystone predators usually increase species richness (number of species) Patterns on species Diversity • Latitude o The closer you are to the equator, the more species you’ll find (lower in latitude) o Communities are more diverse (rich) near the equator (tropics) than closer to the north or south pole • Equilibrium Theory of island biography o The number of species on an island is going to reflect a balance (equilibrium) between the rates at which new species colonize the island and the rate at which
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