A network approach to identify bioregions in the distribution of Mediterranean amphipods associated with Posidonia oceanica meadows

Abstract

Although amphipods are key components of the macro-fauna associated with Posidonia oceanica meadows, to date no studies focused on the structure and diversity of their assemblages across the whole Mediterranean Sea. Here, we applied a network approach based on modularity on a dataset mined from literature to identify biogeographic modules and to assess the biogeographic roles of associated localities. We also correlated the patterns evidenced with the biogeographic distribution of amphipod groups by means of a multivariate analysis. Modularity analysis highlighted four biogeographic modules bounded by the main Mediterranean biogeographic divides and evidenced a decrease in species diversity along a NW-SE gradient. Assemblages associated with Central-Western Mediterranean and, to a lesser extent, Tunisian modules showed the highest species richness and were identified as hubs, characterized by species with regional distributions that behave as source in a biogeographic context. The paleogeographic history of the host seagrass and the ecology of associated amphipods, both suggest the joint effect of species persistence and post-Last Glacial Maximum expansion in explaining the pattern of amphipod distribution in the Mediterranean Sea.

Determinants of different facets of beta diversity in Mediterranean marine amphipods

“…The study area covered a large portion of the Mediterranean Sea, characterized by different geographic, hydrological and geological features, as well as differences in the potential connectivity due to general circulation models (Bianchi 2011, Berline et al 2014. In a previous work (Bellisario et al 2019), network analysis was applied to identify the bioregional (aka modular) partition of local assemblages composed of 147 amphipod species from P. oceanica meadows in 28 sites (Fig. 1).…”

“…PCA explained almost 90% of total variation and the first two axes (PCA1 = 70.92%, PCA2 = 18.94%) were used to calculate the Euclidean distance between each pair of sites. Finally, we used the biogeographic (aka modular) partition already derived from our previous study (Bellisario et al 2019) to account for the biogeographic-level effects in determining the patterns of dissimilarity. We therefore assigned a numeric code to each site corresponding to the bioregion it belonged (Fig.…”

“…We extended our previous dataset (Bellisario et al 2019) by including information on the body size and living habit (i.e. free living vs. tube builders), which are considered as key functional traits in the community assembly processes of seagrass amphipods and that are characterized by a strong phylogenetic signal when compared to other niche related traits as temperature tolerance and feeding habits (Best et al 2013, Best and Stachowicz 2014, Lürig et al 2016).…”

“…Conversely, the richness difference component can be related to the extremely low affinities of the eastern sectors (i.e. Adriatic and Ionian Sea) with the central-western part of the basin, as evidenced by the reduced occurrence of Mediterranean endemics and number of shared species with other biogeographic sectors (Bianchi et al 2011, Bellisario et al 2019. Thus, the balanced contribution of the turnover and the net loss/gain of taxa and lineages would stem from the repeated isolation and contraction of biotas and associated speciation events, which might have contributed to the overall diversity of taxa and the divergence of lineages.…”

“…We characterized the sampling sites by using distribution data on the occurrence of P. oceanica seagrass habitat and information on specific environmental features known to have a direct influence on the distribution of biota in the Mediterranean Sea (Coll et al 2010). Moreover, as rates of trait evolution and speciation may differ among biogeographic regions (Arnan et al 2017), we used a previously identified biogeographic partition of the same dataset (Bellisario et al 2019), to reveal the role of different environmental and historical conditions in determining the pattern of assemblages' differentiation.…”