chapter 14 april 18th, 2012. island biogeography loss of dispensability, the development of...
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Chapter 14
April 18th, 2012
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Island Biogeography
• Loss of dispensability,
• the development of gigantism or dwarfism,
• the loss of antipredator defensive features and behaviors,
• the development of woody shrubs and trees from species that occur as soft-stemmed herbs on continents,
• and the development of highly specialized niches
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Theory of Island Biogeography• MacArthur and Wilson 1967
• Constructs linkages between species-area relationships on islands to dispersal and extinction processes
• Large islands support more plants and animals than smaller islands
• Examples: Hawaii and Caribbean
• Nested pattern of insular communities
• Endemics
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• Islands that are closer to continents have higher species richness than those farther away
Theory of Island Biogeography
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Theory of Island Biogeography
• Immigration balanced by extinction
• Species turnover
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• Small Island Effect – islands are too small to impact extinction rates
• Rescue Effect – populations of species on islands on the brink of extinction are rescued by the arrival of new immigrants of the same species
• Target Area Effect – size matters as much as distance
Theory of Island Biogeography
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• Problems with Theory:– Treats all species the same in terms of immigration
and extinction– Doesn’t take into account the impact that plants
and animals might have in facilitating immigration by other species
– Extinction of some species may make immigration for other impossible
– Excludes speciation and evolution
Theory of Island Biogeography
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• Problems with Theory:– Volcanic disturbances, invasive species,
competition, ocean and wind currents, historical land connections, doesn’t account for humans not taken into account
– Doesn't take migratory animals into account
Theory of Island Biogeography
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Island Rule• The smaller the mammal, the larger it gets on
islands; the larger the mammal, the smaller it gets on islands– Massive rodents on islands– Dwarf elephants on Mediterranean Islands