Geographic scaling of diversity
Species richness across the entire landscape increased with the cumulative amount of habitat (as all patches were sequentially summed; Fig. 5A). However, small patches contributed disproportionately to this increase because they typically added distinct sets of species to the regional pool (high beta-diversity; steep increase in the left region of Fig. 5A and 5B). Landscape diversity resulted mostly from heterogeneity in species composition among patches, rather than from the local diversity observed within individual patches (Fig. 5B-D; compare blue and green circles in Fig. 5D). Although local diversity in small fragments was lower than that in larger fragments (Fig. 5B), small patches greatly differed in composition and added new species to the regional pool (Fig. 5C). Beta-diversity rapidly increased with additional habitat at low values of overall habitat amount in the landscape (Fig. 5C). When the number of species added by beta-diversity reached an asymptote, additional species could still be added to the landscape by adding large fragments with high local-diversity (Fig. 5A). However, this increase was relatively small compared to gains due to the beta-diversity among small fragments. Beta-diversity was therefore the main component of regional diversity in virtually all possible scenarios (Fig. 5D).
When comparing the SAR with the expectation based on an unitary community, we estimated an R value of 3.44, indicating that smaller patches contributed a significantly higher number of species to the regional diversity than what would be expected based on area alone.