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Lecture 18

BIO205 Lecture 18 (Nov 7, 2012).docx

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Christoph Richter

BIO205 Lecture 18 - Lecture 18: community change through time - The story of two squirrel species o Native European red squirrel o Introduction of eastern grey squirrel in Europe and this leads to the decrease of the red squirrel; why?  Competition? Predation? Food? Virus?  The grey squirrel has squirrel pox virus that is not lethal for their species but it is lethal for the red squirrel species  It wasn’t direct competition but some other factor o Look at populations as dynamic - Krakatau explodes in 1883 o Island with 3 volcanoes - Krakatau explodes in 1883 o Catastrophic o 2/3 of the island disappeared o A new volcano growing year to year on the remaining island o Amount of ash blown into the atmosphere caused low global temperature - How would the first organisms arrive on what was left of the island? o Dispersals of seeds from animal, wind, sea - Picture o Mount Helen volcano - The damage was catastrophic o Before volcano o Pyroclastic flow that races down the mountain and very little survive o Acidic water - Clearly things have changed after four years o Fireweed growing on the edge of the lake o Within a few years, you can go fishing in the lake again o Development of a community - Communities change through time o Disturbance to succession o How do communities change through time? - Succession is marked by a sequence of communities o Sere: sequence of communities on a given site o Seral stage: each change from one community to the next  Changes happen continuously  Each stage is defined by distinct community o Happens through time - Primary succession describes the establishment of a community o site that has never supported
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