Patterns of regional endemism among New Zealand invertebrates

Biodiversity is unevenly distributed worldwide in terms of both species diversity and species endemism. Although centres of endemism are a conservation priority, both patterns and drivers of endemism are poorly understood in New Zealand. Here we explore whether invertebrate species distribution records in New Zealand represent the complete geographic range of species. We use distribution records of 2,322 invertebrate species to survey variation in range size and regional-endemism among 28 New Zealand regions, and explore the correlates of diversity and regional-endemism. Our data suggest patterns of regional-endemism in New Zealand invertebrates are not artefacts of sampling effort and the majority of species are not widespread. We found that endemism-score (which is a measure that corrects for species diversity) correlates positively with the relative size of the region three million years ago. Five variables (and their interactions) contributed to the relative level of invertebrate species endemism within a region (in a generalised linear model). Level of endemism tends to be lower in regions with greater geographic connectivity. This suggests that high levels of regional-endemism are not simply the product of the accumulation of species over time, but depends on the ability of a region to retain local species.