The Mystery of Madagascar's Biodiversity

Madagascar, while it only takes up less than 0.5 percent of Earth's land surface area, is home to numerous animal species, and researchers are trying to unlock the mystery behind the region's unique biodiversity.

According to a new study from Duke University, more than 700 species of reptiles and amphibians live on the African island of Madagascar. However, no single one-size-fits-all model can explain how such biodiversity hotspots are formed.

By analyzing the geographic distribution of Madagascar's lizards, snakes, frogs and tortoises, an international team of researchers has found that each group responded differently to environmental fluctuations on the island over time - suggesting that climate change will have different effects on different species.

"It means that there won't be a uniform decline of species - some species will do better, and others will do worse," Jason Brown of the City College of New York, a study co-author, said in a statement.

So how exactly did this treasure trove of unusual animals come to be? Madagascar is host to neon green geckos that can grow up to a foot in length, tiny tree frogs that range in color from blue and orange to yellow and green, as well as half of the world's chameleons. Previous studied have suggested that Madagascar's steep slopes can explain how the island has so many animals, about 90 percent of which are found no where else on Earth.

This new study is the first to incorporate various factors into a single model to find the answer. Brown, along with Duke University biologist Anne Yoder and colleagues, developed a model that combines the modern distributions of 325 species of amphibians and 420 species of reptiles that live in Madagascar today with historical and present-day estimates of topography, rainfall and other variables across the island. They took into account the number of species, the proportion of unique species, and the similarity of species.

"Not surprisingly, we found that different groups of species have diversified for different reasons," Yoder said.

For example, changes in elevation - from say, the mountains and rivers - best predicted which parts of the island had more unique tree frog species, whereas climate stability dictated which areas had more unique leaf chameleons.

"What governs the distribution of, say, a particular group of frogs isn't the same as what governs the distribution of a particular group of snakes," Brown explained. "A one-size-fits-all model doesn't exist."

Understanding how species distributions responded to environmental fluctuations in the past may help scientists predict which groups are most vulnerable to global warming and deforestation in the future, or which factors pose the biggest threat.

The findings were published in the journal Nature Communications.