Bioregionalization: From Wallace and Humboldt to deep-time paleoregion dynamics

Bioregionalization methods allow us to classify and map biogeographic units using data on species composition and traits. Here, we reviewed the evolution of the field during the last 70 years, seeking to summarize its history, and identify gaps and future avenues for research. Our results show that the aim of the studies using bioregionalization methods changed in time. First, bioregionalization were used to unveil the drivers of the observed spatial patterns of biodiversity on Earth, and to understand the role of dispersal limitations on the evolutionary history of clades, but recently, these methods are mostly used for conservation management. Further, data used to map biodiversity regions, the ones that we are now defining conservation strategies, are taxonomically and geographically biased, with a large percentage of the papers using vertebrate data from developed continents/countries. Finally, we show how key papers in the field, the ones with most citations, heavily depend on expert criteria and non-reproducible workflows, preventing direct comparison of maps of bioregions from different papers. Following our findings, we identified 3 gaps for the advance in the field, 1) We need to move beyond maps of vertebrate composition. Ideally, we need to increase the taxonomic diversity of the studies, but also to add other type of information, like data on species traits, genetic diversity, or phylogenetic distances. 2) we need reproducible and standardized methods 3) we need to further explore the temporal dimension of bioregions, to understand how they evolved through time.