Fig. 3. Butterfly species richness and land cover variation as measured by the number of land cover types per quadrat. Land cover is derived from the classification by DeFries et al. (1998) of global AVHRR data at 8-km resolution. This measure of habitat heterogeneity, which is a simple count of the number of land cover types occurring within each quadrat, is strongly correlated with richness (R² = 0.67).