Mechanisms underlying biological diversities at different scales have received significant attention over the last decades. The hypothesis whether local abiotic factors, driving functional and phylogenetic diversities, can differ among taxa of arthropods remains under-investigated. In this study, we compared correlations and drivers of functional (FD) and phylogenetic (PD) diversities between spiders and carabids, two dominant taxa of ground-dwelling arthropods in salt marshes. Both taxa exhibited high correlation between FD and PD; the correlation was even higher in carabids, probably due to their lower species richness.  Analyses highlight that FD and PD were positively linked to taxonomic diversity in both taxa; however, abiotic factors driving the FD and PD differed between spiders and carabid. Salinity particularly drove the taxonomic diversity of carabids, but not that of spiders, suggesting that spiders are phenotypically more plastic and less selected by this factor. Conversely, phylogenetic diversity was influenced by salinity in spiders, but not in carabids. This result can be attributed to the different evolutionary history and colonisation process of salt marshes between the two model taxa. Finally, our study highlights that, in taxa occupying the same niche in a constrained habitat, functional and phylogenetic diversities can have different drivers, showing different filtering mechanisms.

The data was collected by pitfall traps (2019 charrante maritime) in 2 natural reserves (Moëze Oléron and Fiers d'Ars).