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Lecture 2

BIOC63Fall2013 Lecture 2 Notes.docx

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University of Toronto Scarborough
Biological Sciences
Karen Williams

BIOC63Fall2013 Lecture 2 Notes: Global biodiversity: pattern and processes II Global pattern of biodiversity o Biodiversity is distribute non-randomly o Most species are around the Equator  away from there, either way , biodiversity drops o More habitats? More sun? more space? o Diversity of fruit eating bats, N/S America o diversity of fruit-eating bats decreases as you go away from the equator, North and South o o Graph: as latitude increases North and South, diversity decreases Mammalian Diversity o Going South  there is almost a linear decrease in diversity o Going North from Equator  there is still a decrease, but not as linear of a pattern o Vascular Plant Diversity o red and purple = highest diversity o coastal areas around the equator are the highes in vascular plant diversity o the lowest are the areas very high north and very high south o 1 Tropical Rain Forest Diversity o about 6% of land surface area is occupied by tropical rain forest o but it makes up more than 50% of the earth’s plant and animal species o also found around the equator  small fraction of land mass harbours a large mass of biodiversity o Latitudinal gradient of biodiversity o explaining the latitudinal gradient of species diversity .. has long been and still remains the Holy Grail of ecology and evolutionary biology Causes for biodiversity gradients 1. Rapoport’s rule o seasonal variation at higher latitude > seasonal variation at low latitude o so species at higher latitude have to be equipped to survive more climates  they have to have broader climatic tolerance o because they have a broader climatic tolerance  they can occupy a larger range o further away from the equator, the larger the tolerance range of a species is  the more it can spread (the more habitats it can occupy) so it will crowd our every other species o so more habitat niches taken by just one species o less species at high latitudes  since species can occupy a larger niche there is less room for other species and therefore we have less species the further away we go from the equator o o graphs: organisms at higher latitudes have greater latitudinal ranges 2. Glacial history o North American glaciation vs. tropical ‘stability’  there was no glaciation in the equator which means that there will be higher diversity because more time for species to speciate and etc. o Less evolutionary time for speciation in higher latitudes o Slow recolonization after deglaciation  no saturation yet? o So higher latitude places then have not yet reached their most saturated level of diversity o Pleistocene ice age  occurred 2.5 million years to approx. 14000 years ago o o not all the area that contains forest today, always contained forest 2 o during the ice age, the forest was fragmented (embedded in a sea of savannah), but there was still no ice, so species could evolve o North America then was ice free starting about 14000 years ago  little evolutionary time for speciation to occur, therefore less species diversity than at equator where glaciation did not occur o Another example: plant species endemic per US state o The northern part of the US was covered by ice sheet, the southern part was not o The number of endemic species decreases going north
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