One tool ecologists - but not paleontologists - have traditionally relied on to identify patterns of existing biological diversity is a long-established rule of thumb called the species-area effect: the tendency for species number, or richness, to increase in a predictable way with area. Paleontologists have been unable to account for the species-area effect, or to even know whether it applies, in estimating paleodiversity because of various confounding factors. But, in a new study, published in the premier open access journal PLoS Biology, Anthony Barnosky, Marc Carrasco, and Edward Davis are able to test this assumption and discover that the golden rule of ecology holds for the rock record as well. Just as geographic sampling influences diversity counts in the modern landscape, the species-area effect strongly influences counts in the fossil record. Taking this into account will alter historical estimates of species distributions and extinction.
Barnosky et al. used mapping and imaging systems that generate direct measures of the geography for a given set of fossil species. To get a sense of diversity across time and space, the authors used a recently completed archival database (which they also built) that integrates the geographic data with fossil datasets, called the Miocene Mammal Mapping Project (MIOMAP). MIOMAP includes all western North American mammals from 5-30 million years ago - 3,100 localities and 14,000 occurrences of species in all. The authors then tested the fossil data for species-area effects by plotting fossil species richness against different geographic areas. After correcting for possible biases in sample size that might influence the number of species, Barnosky et al. found a strong
Source:Public Library of Science