01:119:115 Lecture Notes - Lecture 21: Trophic Cascade, Keystone Species, Radiant Energy

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Dr torres december 13 10:20 am to 11:40 noon arc 103. Communities can be characterized based on their species diversity and trophic structure. Species diversity is the variety of organisms that make up a community. Trophic structure: feeding relationships between organisms in communities. Certain species can have very large impacts on community structure. Dominant species: most abundant or have highest biomass: ex: sugar maple is dominant species in north america. Keystone species: not most abundant species but have strong control in community. Bottom-up model: unidirectional influence from lower to higher trophic levels: nutrients producers consumers. Top-down model: (trophic cascade): control comes from trophic levels above: 1ry consumers producers nutrients, 2ry consumers 1ry consumers producers nutrients. Most communities are constantly changing, particularly after a disturbance. Up to 1900s ecologist thought any given community was at equilibrium (was like super organism) Challenged with new ideas that disturbances kept communities from reaching equilibrium.

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