Filling gaps on the diversity and biogeography of Chilean millipedes (Myriapoda: Diplopoda)

Research on the diversity and biogeography of Chilean millipedes (Diplopoda) represents a severe gap in knowledge. To reduce this gap we conducted a study to: (1) investigate the state of knowledge of millipede diversity, and (2) assess the pattern and causes underlying the latitudinal diversity gradient in Chilean millipedes. After combining the number of described species with those that have not yet been formally described, we concluded that there are 95 native millipede species in Chile. A diversity estimate suggested that in the future this number could increase to 125 or 197 species. However, this estimate is based on limited data. Therefore, the number of millipede species inhabiting Chile probably exceeds our estimate. Consistently, rarefaction-extrapolation curves revealed that we have not yet recorded a substantial fraction of millipede diversity and that increased sampling effort will reveal the presence of a greater number of millipede species in Chile. Most millipede species exhibited narrow geographic ranges in Chile. The north-south distribution of their species richness followed a bell-shaped latitudinal gradient of diversity, i.e. diversity peaked at the temperate climate of central Chile and then decreases towards the arid and polar climates of northern and southern Chile, respectively. The causes underlying this biogeographical pattern were water availability, ambient energy input and climate stability. This finding provided support for two of the five biogeographic hypotheses we tested: water-energy balance and climate stability. Thus, Chilean millipedes were more diverse at sites that exhibit warm and humid (temperate) climates for much of the year.