Phylogenetic diversity of regional beetle faunas at high latitudes: patterns, drivers and chance along ecological gradients

Patterns in phylogenetic diversity are poorly known for many taxonomic groups, including hyperdiverse insect taxa. We contrasted patterns in the species richness and phylogenetic diversity of provincial beetle faunas in northern Europe (54A degrees N to 71A degrees N). We found that species richness and phylogenetic diversity varied rather predictably along ecogeographical gradients, with species richness and a proxy measure of phylogenetic diversity, average taxonomic distinctness (AvTD), decreasing from south to north and being strongly positively related to maximum temperature. A proxy measure of variation in phylogenetic diversity, variation in taxonomic distinctness (VarTD), was also strongly related to maximum temperature, but the relationship was negative. This was a novel finding, showing a reversed latitudinal gradient in biodiversity. In more than half of the provinces, AvTD value was significantly less than expected by chance. Also, more than half of the provinces showed significantly higher VarTD values than expected based on random draws of species. Our results showed that the phylogenetic diversity of beetle faunas is rather strongly associated with climatic gradients at high latitudes. Given that climatic variability and temperature extremes are correlated with phylogenetic diversity, climate change is likely to modify strongly this facet of diversity. Average phylogenetic diversity is likely to increase in the northernmost parts of the study area if climate and vegetation become more suitable for many southern beetle species. Our statistical approach to test chance expectations based on random draws of species from larger-scale species pool is highly flexible in tackling this question when true phylogenies are not available.