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Biol 121 225 Freeman 1209-1217 (Ch. 53)

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BIOL 121
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Biol 121 225 th Freeman 1209-1217 (Ch. 53) Jan 15 , 10 Limits on research on species -usually focuses on two at a time, but biological communities can contain interactions thousands of species -to understand how communities work, biologists must broaden the scope of research and explore how combinations of many species interact -if community destroyed by disturbance and allowed to recover, diversity and abundance of species should be identical when recovery complete -but if communities can be made up of many diff combo of species, depending on which arrive earlier/later, then community composition will be difficult to predict Climax community (Frederick -proposed by Frederick Clements Clements) -Clements argued that communities develop by passing through a series of predictable stages dictated by extensive interactions among species and that this development culminates in a stable final stage known as a climax community Henry Gleason -contended that community in an area is neither stable nor predictable -claimed that plant and animal communities just happen to share similar climatic requirements -largely a matter of chance whether similar community develops in the same area after a disturbance occurs Factors that determine community -Gleason’s view is closer to being correct makeup -although both biotic interactions and climate are important in determining which species exist at a certain site, chance and history also play a large role Keystone species -a species that has a much greater impact on the surrounding species than its abundance and total biomass would suggest -for example, introducing wolves can reduce elk pop due to predation, and the food that elks eat (aspen, willow, cottonwood) increase, which increases number of beavers that competed with elks for these resources -also, wolves might not tolerate presence of coyotes, so decline of coyotes which increases mouse pop which then increases hawk pop Disturbance -any event that removes some individuals or biomass from a community (biomass is the total mass of living organisms) (What do disturbances affect in -e.g. fires, windstorms, floods, fall of large canopy tree, disease epidemics, short- general?) term explosions in herbivore numbers -these events are important because they alter light levels, nutrients, unoccupied space, etc. What factors determine the impact 1. Type of disturbance of disturbance? (3) 2. Frequency 3. Severity (e.g. speed/duration of flood, intensity of heat during fire, earthquake magnitude) -most communities experience a characteristic type of disturbance, and in most cases, disturbances occur with a predictable frequency and severity Disturbance regime - a disturbance’s impact on a community (or the range of the impact) -it can be predicted b/c disturbances usually occur with a predictable frequency and severity Succession -the recovery that follows a disturbance -name was inspired by observation that certain species succeed others over time Primary succession
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