Journal of Biogeography (J. Biogeogr.) (2014) 41, 8–22 SPECIAL Why are there so many species PAPER in the tropics? James H. Brown Department of Biology, University of New ABSTRACT Mexico, Albuquerque, NM 87131, USA Known for centuries, the geographical pattern of increasing biodiversity from the poles to the equator is one of the most pervasive features of life on Earth. A long- standing goal of biogeographers has been to understand the primary factors that generate and maintain high diversity in the tropics. Many ‘historical’ and ‘ecolog- ical’ hypotheses have been proposed and debated, but there is still little consen- sus. Recent discussions have centred around two main phenomena: phylogenetic Correspondence: James H. Brown, Department niche conservatism and ecological productivity. These two factors play important of Biology, University of New Mexico, roles, but accumulating theoretical and empirical studies suggest that the single Albuquerque, NM 87131, USA. most important factor is kinetics: the temperature dependence of ecological and E-mail:
[email protected] evolutionary rates. The relatively high temperatures in the tropics generate and This is an open access article under the terms of the Creative Commons Attribution- maintain high diversity because ‘the Red Queen runs faster when she is hot’. NonCommercial License, which permits use, Keywords distribution and reproduction in any medium, – provided the original work is properly cited Ecological interactions, evolutionary rates, Janzen Connell dynamics, latitudi- and is not used for commercial purposes. nal diversity gradient, metabolic theory, Red Queen, species diversity, tropics. There is, however, one natural feature of this country, the inter- INTRODUCTION est and grandeur of which may be fully appreciated in a single walk: it is the ‘virgin forest’.