Limited dispersal ability and restricted niche characterize “depauperons” in Melastomataceae

The asymmetric pattern in species richness is a notable feature across different lineages and geographic regions. While some lineages have high richness, diversity and wide distribution, others have the opposite. Despite low rates of diversification, the latter might also be phylogenetically isolated. Lineages that accumulate these characteristics are known as “depauperons'' and explaining their existence and persistence through time is still a challenge. The plant family Melastomataceae contains both megadiverse lineages (such as the tribe Miconieae, with around 1900 species) and groups with few species (such as the tribes Eriocnemeae, Lithobieae, and Rupestreeae with 7, 1 and 2 species, respectively). These three clades are restricted to eastern Brazil, where they have been seldom studied. The lack of information about their basic biology as well as which processes determine their distribution have not been previously studied. Here we integrated metrics of dispersal ability, species distribution models (SDMs) and natural history data compilation in order to uncover common patterns shared by these depauperons in Melastomataceae and raise conservation concerns. For all nine species we estimated the dispersal ability and generated SDMs in different time-periods (past, present and future). Dispersal ability was associated with predicted distribution models under future scenarios to evaluate shifts and/or retractions in suitable areas. In addition, we compared the climatic tolerances of the depauperons with their megadiverse sister tribes via climatic envelopes. Overall, our results indicate limited dispersal ability, dependency on water for dispersal, and restricted niche as common characteristics for all species in the deupauperon tribes Eriocnemeae, Lithobieae and Rupestreeae. Our analyses also show that the climatic niche spaces of the depauperons are limited and totally included within the niche space of its sister tribes. Based on our findings, the level of threat in these groups can be potentiated by rapid climate change, mainly due to their inability to spread over long distances, restricted niches and increased habitat fragmentation. We suggest that future conservational actions prioritize these unique taxa in Melastomataceae, especially if a phylogenetic diversity perspective is taken into account.