Drivers of taxonomic, functional and phylogenetic diversities in dominant ground-dwelling arthropods of coastal heathlands

Although functional and phylogenetic diversities are increasingly used in ecology for a large variety of purposes, their relationships remain unclear and likely vary presumably over taxa, yet most recent studies focused on plant communities. Different concepts predict that a community becomes functionally more diverse by adding phylogenetic lineages, subtracting lineages, adding species, reducing or increasing environmental constraints. In this study, we investigated ground-dwelling spider, ground beetle and ant assemblages in coastal heathlands (>11 000 individuals, 216 species), and their estimated functional and phylogenetic diversities as minimum spanning trees using several traits related to the morphology, feeding habits and dispersal of species, and phylogenetic trees, respectively. Correlations were overall positive and high between functional and phylogenetic diversities. Accounting for taxonomic diversities and environments made disappear this relationship in ants, but maintained them in spiders and ground beetles, where taxonomic diversity related to functional diversity only via increasing phylogenetic diversity. Environmental constraints reduced functional diversity in ants, but affected functional diversity only indirectly via phylogenetic diversity (ground beetles) and taxonomic and then phylogenetic diversity (spiders and ground beetles). Results are consistent with phylogenetic conservatism in traits in spiders and ground beetles, while in ants traits appear more neutral with any new species potentially representing a new trait state. Lineage diversities mostly increased with taxonomic diversities, possibly reflecting un-measured environmental conditions.