Niche conservatism in the Legume Amherstieae tribe: Insights from the tropical Berlinia and Brownea clades

The concept of niche conservatism describes the tendency of organisms to retain ecological traits through time and space. Reviewing this concept in different groups of angiosperms is critical to understanding what factors drove their expansion and geographic distribution, as well as assessing how, in taxonomic levels higher than species, ecological traits have remained relatively constant through time and space. Studying niche conservatism can also help us understand how the distribution of clades may be affected by climate change. Niche conservatism has been observed in many clades of legumes. Amherstieae, the largest tribe of the Detarioideae subfamily, has a geographic distribution, evolutionary history, and phylogeny that makes it a good candidate for evaluating patterns in niche conservatism. We analyzed the distribution of two Amherstieae suprageneric clades, the Berlinia and Brownea clades. The former is endemic to sub-Saharan Africa and the latter is restricted to the Neotropics. We used the geographic distributions of each clade to define their G-space (geographic space) and extracted 19 climatic variables to define the E-space (environmental space) of each clade. We used two tests to evaluate the similarity in the climatic niche of both clades, the niche overlap test (NOT) to estimate similarities between the occupied E-spaces (realized niche space) and the niche divergence test (NDT) to assess the similarity of the environmental niche relative to the accessible analogous E-space (potential niche space) of each biogeographic region. Our results suggest that the Brownea clade are descendants of a climatic subset of the Berlinia clade preferring less variable temperature and higher precipitation levels, and that the dry-adapted subset of Berlinia may represent a more recent evolutionary expansion.