Data from: Decoupling of latitudinal gradients in species and genus geographic range size: a signature of clade range expansion
Tomašových, Adam; Jablonski, David (2017), Data from: Decoupling of latitudinal gradients in species and genus geographic range size: a signature of clade range expansion, Dryad, Dataset, https://doi.org/10.5061/dryad.23cn7
Aim. Clade range size is a function of species range sizes but also depends on the geographic deployment of species; clade range expansion should therefore depend partly on a clade’s tendency to produce new species. Under high speciation pressure, species-rich clades can migrate outside its present distribution, and thus overcome niche conservatism. A simple probabilistic mechanism for an out-of-tropics dynamic (OTT) for clade range expansion can thus operate in the absence of species-level differences in probability of range expansion, with speciation into novel climates more likely to occur in species-rich clades. In this scenario, (a) species and clade range sizes are decoupled and (b) clade range expansion is a function of per-clade species diversification. To test these predictions that can discriminate between a weaker and a stronger climatic niche conservatism, we contrast the latitudinal and thermal range sizes of marine bivalves at the species and clade (genus) level.
Location. Western Pacific, Eastern Pacific, and Western Atlantic.
Methods. We decompose the latitudinal and thermal distribution of genera into within-species and among-species dispersions and quantify their contributions to genus range size and species richness. We model the latitudinal gradient in per-genus species richness with a scenario where species range expansion does not vary with latitude.
Result. Genus latitudinal range size cannot be predicted from the latitudinal range sizes of congeneric species, but strongly depends on latitudinal distances among species centroids, which correlate strongly with per-genus species richness. Genus thermal ranges correlate with the thermal ranges of congeneric species and thus support thermal conservatism of genera, but they correlate even more strongly with thermal differentiation among congeneric species. Genus latitudinal and thermal range sizes increase towards higher latitudes because genera that are species-rich anywhere within their range increase in proportion towards higher latitudes.
Main Conclusions. The probabilistic model represents a first-order neutral expectation of clade-level range expansion at multiple phylogenetic levels arising from clade differences in net species diversification. Unless opposed by a strong niche conservatism, clade species richness can promote genus range expansion to new latitudes and climates. Species diversification thus plays a significant role in range expansion of marine genera even when thermal range sizes and limits of clades are conserved.