Evol Ecol Res 6: 33-48 (2004)     Full PDF if your library subscribes.

Structure of the North American vegetation gradient during the late Paleocene/early Eocene warm climate

Guy J. Harrington*

Department of Paleobiology, Smithsonian Institution, 10th and Constitution Avenue NW, Washington, DC 20560-0121, USA

e-mail: g.j.harrington@bham.ac.uk


Late Paleocene/early Eocene pollen and spore data taken from the US Gulf Coast (paleolatitude 32°N), western interior basins (Wyoming, North Dakota; paleolatitude 44–47°N) and Canadian Arctic (paleolatitude > 68°N) represent a vegetation proxy for ancient paratropical, subtropical and temperate biomes. These data provide information on the latitudinal diversity gradient of plants during an ancient greenhouse climate with non-freezing winters at polar latitudes. Comparing pollen data from the early Paleogene with a pollen data set compiled at the same latitudes from the late Holocene (3000 years B.P. to present) reveals that the diversity gradient between middle to high latitudes was steeper than today at the same sampling intensity. The gradient is a step-like decrease of about 50% in taxonomic diversity with increasing latitude between regions. The diversity gradient is formed by the ‘spillover’ of paratropical taxa into other regions of North America, which reflects the modern pattern of plant ranges. Taxa present in the Arctic, therefore, have great geographic ranges with endemism greatest in the paratropical biome. Paleogene diversity gradients show that decreasing diversity with increasing latitude is ancient and not dependent upon freezing temperatures.

Keywords: Eocene, latitudinal diversity gradient, North America, Paleocene, palynology, vegetation.

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