Can net diversification rates account for spatial patterns of species richness?

Abstract

The diversification rate hypothesis (DRH) proposes that spatial patterns of species richness result from spatial variation in net diversification rates. We developed an approach using a time-calibrated phylogeny and distributional data to estimate the maximum explanatory power of the DRH, over a given time period, to current species richness in an area. We used this approach to study species richness patterns of a large family of suboscine birds across South America. The maximum explanatory power of the DRH increased with the duration of the time period considered and grain size; it ranged from 13 - 37 fold local increases in species richness for T = 33 Ma to less than 2-fold increases for T [&le;] 10 Ma. For large grain sizes ([&le;] 8{degrees} x 8{degrees}) diversification rate over the last 10 Ma could account for all the spatial variance in species richness, but for smaller grain sizes commonly used in biogeographical studies (1{degrees} x 1{degrees}), it could only explain < 16% of this variance. Thus, diversification since the Late Miocene, often thought to be a major determinant of Neotropical diversity, had a limited imprint on spatial richness patterns at small grain sizes. Further application of our approach will help determine the role of the DRH in explaining current spatial patterns of species richness.\n\nNote to readersThis manuscript has been seen by a few researchers, some of whom suggested that before publishing our work in a peer-reviewed journal we should conduct simulations to demonstrate that our methods properly estimate the contribution of variance in diversification rates to spatial variation in species richness. Although we believe that our approach derives logically from theory and statistics and is therefore valid, we understand that it is rather unique and see why some readers would think that an independent validation is necessary. Unable to complete such validation in the near future, however, we decided to make this manuscript available as a preprint to share our ideas and hopefully stimulate discussion on what we believe is a most interesting topic. We also hope to receive feedback that may enable us to improve our work for publication in a journal at a later date.