|Paroedura ground geckos illustrate species diversity on Madagascar. |
photo: Daniel Scantlebury
The evolutionary origins of Madagascar's biodiversity remain mysterious despite the fact that relative to land area, there is no other place with consistently high levels of species richness and endemism across a range of taxonomic levels. Most efforts to explain diversification on the island have focused on geographical models of speciation, but recent studies have begun to address the island's accumulation of species through time, although with conflicting results. Prevailing hypotheses for diversification on the island involve either constant diversification rates or scenarios where rates decline through time. Using relative-time-calibrated phylogenies for seven endemic vertebrate clades and a model-fitting framework, I find evidence that diversification rates have declined through time on Madagascar. I show that diversification rates have clearly declined throughout the history of each clade, and models invoking diversity-dependent reductions to diversification rates best explain the diversification histories for each clade. These results are consistent with the ecological theory of adaptive radiation, and, coupled with ancillary observations about ecomorphological and life-history evolution, strongly suggest that adaptive radiation was an important formative process for one of the most species-rich regions on the Earth. These results cast the Malagasy biota in a new light and provide macroevolutionary justification for conservation initiatives.
Keywords: adaptive radiation, diversity-dependent diversification, diversification rate, island biogeography, Madagascar
Daniel P. Scantlebury. 2013. Diversification rates have declined in the Malagasy herpetofauna. Proc R Soc B. 280: 20131109. http://dx.doi.org/10.1098/rspb.2013.1109
Research suggests Madagascar no longer an Evolutionary Hotspot
Madagascar has long been known as a hotspot of biodiversity. Although it represents only one percent of the earth's area, it is home to about three percent of all animal and plant species on the planet. But research suggests the island's heyday of species development may be all but over.
"A staggering number of species are found only on Madagascar," said Daniel Scantlebury, a Ph.D. student in biology, "but this research shows there are limits to the number of species the island can sustain, and Madagascar may currently be at those limits."
Scantlebury's paper is being published this week in the Proceedings of the Royal Society B.