Biodiversity and WorldMap

• Patterns of regional structure in the distribution of organisms
• Measuring variation in the strength & breadth of transition zones between biotic regions
• Distinguishing transition zones dominated by species replacements from zones dominated by species richness gradients

Current work is exploring other kinds of patterns in distribution of organisms, including the tendency for species to be associated at different spatial scales. One familiar procedure is to classify areas into regions with similar biotas. In this example, equal-area grid cells are grouped into faunal regions (numbered 1-10) by their bumble bee faunas using Mark Hill's TWINSPAN software (ref 9) (below):

Measuring variation in the strength and breadth of transition zones between biotic regions
New approaches to measuring spatial turnover in species among neighbourhoods of adjacent grid cells on maps can be used to locate many of the boundaries detected by classification (see above) between different faunas. But in addition, these turnover measures allow exploration of variation in the strength and breadth of the transition zones along the biogeographic boundaries (high scores are not constrained to occur together in lines, and need not completely encircle biotic regions). The example shows the application of one of these measures ('beta-3', based on Whittaker's measure of beta diversity) to the same bumble bee data (ref 9). Orange cells occur in neighbourhoods of high species turnover (i.e. the transition zones) and blue cells are in neighbourhoods of low species turnover (below):

Descriminating species replacements from richness gradients in transition zones

The measure of species turnover with the simplest interpretation is the density of range edges. The pattern can be considered to have two components: simple gradients in the numbers of species; and replacements between pairs of species.

A paper in the Journal of Biogeography (1999, 26: 459-474) shows simple measures of these components and the patterns they find within data for birds in sub-Saharan Africa.

Current work is exploring this approach at finer spatial scales and using a broad range of pattern measures. This work relates not only to questions in academic biogeography, but also has potential applications in conservation biology and research into environmental change through changing ecotones.