Evolution and the latitudinal diversity gradient: speciation, extinction and biogeography

Abstract

A latitudinal gradient in biodiversity has existed since before the time of the dinosaurs, yet how and why this gradient arose remains unresolved. Here we review two major hypotheses for the origin of the latitudinal diversity gradient. The time and area hypothesis holds that tropical climates are older and historically larger, allowing more opportunity for diversification. This hypothesis is supported by observations that temperate taxa are often younger than, and nested within, tropical taxa, and that diversity is positively correlated with the age and area of geographical regions. The diversification rate hypothesis holds that tropical regions diversify faster due to higher rates of speciation (caused by increased opportunities for the evolution of reproductive isolation, or faster molecular evolution, or the increased importance of biotic interactions), or due to lower extinction rates. There is phylogenetic evidence for higher rates of diversification in tropical clades, and palaeontological data demonstrate higher rates of origination for tropical taxa, but mixed evidence for latitudinal differences in extinction rates. Studies of latitudinal variation in incipient speciation also suggest faster speciation in the tropics. Distinguishing the roles of history, speciation and extinction in the origin of the latitudinal gradient represents a major challenge to future research.

Faunal breaks and species composition of Indo-Pacific corals: the role of plate tectonics, environment and habitat distribution

“…The need to understand the genesis and maintenance of such patterns is becoming ever more urgent as we seek to manage the effects of global environmental change on biodiversity [3]. However, despite the plethora of hypothesized explanations, the underlying mechanisms driving these patterns are elusive [4,5]. The species (and genus) richness of reef-building corals in the Indo-Pacific exhibits a peak in biodiversity in the Indo-Australian Archipelago (IAA), with a gradual decline in richness with increasing distance from the IAA hotspot, particularly in the highly depauperate eastern Pacific and at higher sub-tropical latitudes [6][7][8][9][10][11].…”

“…However, these weighted randomizations also suffer from important limitations, primarily due to the use of empirical range size frequency distributions. Such issues have led to calls for new approaches to distinguish among the mechanisms that underpin patterns of biodiversity [1,4,16].…”

Out of Asia: Natricine snakes support the Cenozoic Beringian Dispersal Hypothesis

“…Using phylogenetic inference, divergence dating, and ancestral area estimation, the various biogeographic factors including vicariance, dispersal, speciation, and extinction can be investigated in an evolutionary context. Moreover, understanding the historical biogeography of a group provides the structure for testing when and how adaptive radiations occur, how communities assemble with respect to regional taxonomic pools, and how species richness is controlled by areas of origin, rates of diversification, and niche conservatism (Blackburn and Gaston, 2004;Webb et al, 2006;Burbrink and Lawson, 2007;Mittelbach et al, 2007;Pyron and Burbrink, 2009a;Wiens et al, 2009;Kozak and Wiens, 2010). For many organisms, though, a basic understanding of their historical biogeography is unclear, and the commonality of various patterns and processes that have shaped their modern distribution is largely unknown.…”

Influences of geographic differentiation in the forewing warning signal of the wood tiger moth in Alaska

“…Over the course of the late Holocene glacial cycles influenced the biota of northern and tropical regions. Expanding and contracting ice sheets have left genetic imprints on species whose distributions were influenced by those patterns (Schmitt & Hewitt 2004, Hewitt 2004, Provan & Bennett 2008 and diversity in general (Dynesius & Jansson 2000, Mittelbach et al 2007). It has even been suggested that these climate oscillations influenced the evolution of dispersal ability and range sizes, selecting for greater dispersal ability in some species (Dynesius & Jansson 2000).…”