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Lec 23.docx

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Western University
Biology 1001A
Tom Haffie

Lec 23- Community Ecology • text 46.4a, 46.6abc, 46.7, 46.8, 46.9abc, 46.10ab • Community Ecology 2 • Species Diversity, trophic levels (food webs), complexity • Patterns in diversity • Succession, ecological disturbance, more diversity! Species richness, evenness, diversity Diversity- composite of 2 things 1. Species richness (total number of species that live in the community) 2. Species evenness (abundance of each species) - 2 of these forests (left and center) have the same richness but different eveness - Right: species richness is lower but evenness is the same - Middle is most diverse Trophic Levels - Trophic levels defined by how a group of organisms get there energy, and what eats them. - Photoplankton takes in energy from the sun Primary producers - Primary consumers eat the photoplankton Trophic Levels Complex community = many species per trophic level, and many trophic levels - Terrestrial community- energy comes in almost all the time (powered by the sun) - Solar energy produced by primary producers (trees) and then are eaten by primary consumers ect. - Not all energy makes it through the food web, some is lost as heat, but most of energy and biomass from the grazing food web is transferred to the decomposing food web. - Waste products become part of the decomposing food web - Some communities are more complex then others- this community isnt as complex as the marine example - Complexity of a community involves how many tropic levels are in that community and the total number of species - Diversity is different then complexity. - Complex communities are sometimes more stable. Diversity and keystone species • keystone species have major effects (relative to abundance or total biomass) on an ecological community • keystone species often keystone predators • keystone predators usually increase species richness • One reason why communities are more species rich is because some contain • keystone species that have major effects despite their low abundance. If it is removed from the community, it changed the community drastically. • Keystone species often keystone predators (often at the top of the foodweb) Patterns in species diversity • Latitude (tropics vs poles) • The farther you go from the equator, the fewer species you will see around you • Species richness is much more higher around the equator • Global pattern in species diversity Patterns in species diversity • Equilibrium theory of island biogeography: why are some islands much more species rich than others? - Distribution of species on islands- Higher number of species on bigger island, More species on islands closer to the mainland. - On any island, the number of species of that island is going to have a balance of immigration and extinction. Patterns in species diversity Big islands have more species, because ... - If we use the idea that species richness/ diversity on an island is a function of immigration and extinction, this can
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