IS SPECIES GEOGRAPHIC OVERLAP CONSTANT ACROSS LATITUDE? A HOMAGE TO E. H. RAPOPORT

Abstract

E. H. Rapoport's seminal book, Areography, was significant for the foundation of macroecology and development of geographical ecology. Indeed, one of the most studied macroecological patterns is the so-called Rapoport's rule -- the tendency of species geographic ranges to be smaller towards lower latitudes. However, several of Rapoport's pioneering ideas have been rarely studied or completely overlooked. Related to the ecogeographical rule that carries his name, he proposed the existence of a latitudinal geographical trend in the overlap of species ranges of the same genus: the constant overlap hypothesis. Such constancy, he argued, appears despite the existence of both latitudinal gradients in species richness and range size. This overlap pattern has not, to our knowledge, being revisited and tested. Here, we intend to honor his legacy by revisiting this particular hypothesis. Using current data for the original rodent genera that Rapoport studied and for phyllostomid bat genera, we applied this framework along with modern macroecological tests to evaluate the overlap among species of the same genus across latitude. We conducted correlation and linear regression analyses to describe this pattern and compared our results to a null model of simulated range construction and placement. Based on the observed vs. simulated pattern comparison, we found that Rapoport's original idea of a constant overlap across latitudinal bands is actually the expected pattern under the conditions of our null model. This may suggest that range cohesion and size, the only range properties kept in the null model, are sufficient to explain the overlap patterns among species of the same genus across latitude. We discuss our findings in light of potential biological and methodological explanations. In doing so, we highlight the enduring legacy that E. H. Rapoport had and will continue to have on our investigations of geographical ecology and macroecology.