Is biotic diversity a function of climatic equability? One explanation for the latitudinal gradient of species diversity is that stable environmental parameters in the tropics allow for finer gradation of niches and therefore greater speciation than in higher latitudes, where greater swings of seasonality promotes fewer, more generalist taxa.
This hypothesis may be tested by examining patterns of insect diversity in the Eocene, a time of highly equable climate (low temperature seasonality). The study region was a temperate (low mean annual temperature) upland which today bear rich fossil insect deposits. It was then both equable (like the modern tropics) and temperate (like modern mid latitudes). If climatic stability promotes diversity, then we should see increased numbers of insect taxa in the Eocene Okanagan Highlands relative to regions of similar mean annual temperature today.
Is the temperate/tropical-identified character of modern biota a function of cold month mean temperature? Preliminary results (Archibald & Mathewes 2000) show insect taxa that today are exclusively associated with warm climates were present in the temperate Okanagan Highland. In a world of warmer winters in a temperate region than today, what community assemblages and associations resulted?
These fossil insect-bearing Early to Middle Eocene lacustrine shale deposits (and amber) extend from Northern Washington State through about 1000 kilometers into central British Columbia. Precise radiometric dating, paleobotanical community characterization and paleoclimate determination combined with insect systematics will allow these sites to be stacked in time, characterized as to climate, community, and insect diversity, and therefore changes in diversity and association may be determined and interpreted.
The ESA 2001 Annual Meeting - 2001: An Entomological Odyssey of ESA