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Population regulation and distribution.pdf

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BIOL 1070
Shoshanah Jacobs

Population regulation and distribution February-25-14 6:40 PM Population Regulation: Density Dependence: Magnitude of effect depends on population density. For example, the effects of a sickness willbe morepronounced in areas with higherdensity. Sicknesswould be a density dependent factor. More effect in areas with more density. These factors usuallyused to regulate populations through births and deaths. Density Independence:Effect isthe same regardlessof population density. For example, an ice age would wipeout every species regardlessof how dense their populations are. An examplewould be a major freeze. This isdensity independent as it affects all populations equally, but it would intensify density dependent factors like food supply as areas with higher density willbe more affected. Population Distribution Spatial: Clumped,even or random. • Clumpeddistribution: Some sort of causation for all the species staying in this area. Could be food, water, shelter. Possible mechanisms for species location 1) Endemism: Evolvedhere and is only found in this region. Example: Polar bears are endemic to Arctic regions. • Bio geographical exampleof biotic similaritieson different continents: Not explainedby endemism. 2) Dispersal- A. Rangeexpansion: Evolved elsewhereand then expanded its range to alsoinclude this area. Natal: Movement of young from their birthplace prior to reproducing. Breeding:Movement of reproductivelyactive adults B. Range Shift:Evolved elsewhereand used to be found elsewhere,but its range shifted to include ONLY the current distribution and NOT the former distribution C. Long-RangeDispersal : Invasivespecies usually. Arrivedfrom somewherefar away. Wind Assisted Dispersal:Gliders,parachutes, helicopters, cottony seeds, flutters are all structures that cause wind dispersal of seeds Animal-assisted:Sticky top (burrs for example)to stick to animals. Some seedsor berriesget eaten and travel in the digestivetract to be releasedelsewhere. 3) ContinentalDrift and Vicariance: Continents used to all be joinedas Pangaea. Evolved elsewherebut physical landscape changed. Explains geographical species distributions along Wallace'sLine. Biogeography,Vicariance and Dispersal • Species are distributed in clear patterns geographicallyand not just by habitat • Major patterns are now known to correspond to Earth history • Similarbiotas on very distant continents: Connected by lineknown as Wallace'sLine. WhyARE
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