Network Assemblages of Elevational Niche-Associated Diversity in Fijian Native Bees

Abstract

Species assemblages constrained by ecological and evolutionary processes (and the interactions between them) are vulnerable to changes in their environment. Network analyses do not explicitly build in phylogenetic histories when exploring how they are assembled, yet they can be a critical source of information for understanding how and when species may be incorporated into ecological webs. Recent studies have revealed unexpected species diversity in a monophyletic clade of native Fijian bees in the subgenus Lasioglossum (Homalictus). These bees have undergone a remarkable and recent radiation with evidence for phylogenetic conservatism in elevational niches and physiological traits. Here we use bipartite network analyses, as an adjunct to phylogenetic analyses, to further inform likely ancestral elevations for these bees and to explore patterns in how they have occupied other elevational niches. Our approach is novel in that we categorize elevation into bands that are then treated as the lower hierarchical level onto which we map individual bee species. These analyses support earlier inferences that highland elevations (or the climates that correspond to them) are ancestral niches and that barriers to occupation of lower elevations are significant. In addition, we provide important insights into co-occupancy of elevational niches and whether competition occurs for these niches. Our results suggest convergences in niche expansion and a lack of competitive exclusion for those specific niches, but a strong extinction risk for loss of current elevation-related niches.