Abstract
Mechanisms underlying biological diversities at different scales have received significant attention over the last decades. The hypothesis of 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 diversity (FD) and phylogenetic diversity (PD) 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 owing to their lower species richness. Analyses using structural equation modelling highlighted that FD and PD were positively linked to taxonomic diversity (TD) in both taxa; however, abiotic factors driving the FD and PD differed between spiders and carabids. Salinity particularly drove the TD of carabids, but not that of spiders, suggesting that spiders are phenotypically more plastic and less selected by this factor. Conversely, PD was influenced by salinity in spiders, but not in carabids. This result can be attributed to the different evolutionary history and colonization process of salt marshes between the two model taxa. Finally, our study highlights that, in taxa occupying the same niche in a constrained habitat, FD and PD can have different drivers, and thereby different filtering mechanisms.
Highlights
Description of spatial patterns of species assemblages is an objective of community ecology that can be directly used for biological conservation [1,2]
This approach does not consider all facets of biodiversity, such as accumulated evolutionary history traits that can be highlighted through phylogenetic diversity (PD) [3] or the diversity of morphological, physiological and ecological traits of an assemblage that can be revealed by functional diversity (FD) [4,5]
taxonomic diversity (TD) provides information about the species composition of an ecosystem resulting from several processes such as habitat filtering or interspecific competition, PD highlights a part of the processes by providing information on the evolutionary relationships among coexisting species [3], when FD can reflect the differences of traits linking biodiversity, ecosystem functions and environmental constraints [7], as well as the functional response of species assemblages to environmental filtering [8]
Summary
Description of spatial patterns of species assemblages is an objective of community ecology that can be directly used for biological conservation [1,2]. The study of factors driving local diversity is an essential step to understanding these patterns, and has long been performed using taxonomic diversity (TD) only This approach does not consider all facets of biodiversity, such as accumulated evolutionary history traits that can be highlighted through phylogenetic diversity (PD) [3] or the diversity of morphological, physiological and ecological traits of an assemblage that can be revealed by functional diversity (FD) [4,5]. Hypothesis 2: despite the fact that TD influences the strength of the correlation between PD and FD by side effects [9,38,39], we expect a relationship between TD and both PD and FD stronger for carabids owing to the greater sensitivity of carabids to environmental constraints such as salinity [40], resulting in a pool of species with closely functional traits for e.g. resisting salinity, avoiding flooding and/or recolonizing the marsh after tides. Environmental variables affecting FD are expected to differ between taxa, as reported for other ecosystems [46]
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