No single explanation for the biodiversity on Madagascar, experts say

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Ask any biologist or student of the natural sciences and they’ll agree: Madagascar is a peculiar menagerie of unique creatures, many of which live there and nowhere else on the planet. And according to a group of scientists, there’s no one reason or “one-size-fits-all” model to explain the biodiversity on Madagascar.

Madagascar, located 300 miles east of the African coast and separated from the mainland for 80 million years, has provided its residents, both flora and fauna, with a totally isolated and near-undisturbed environment in which they could evolve and develop. And the island has captivated the imaginations of scientists and naturalists worldwide since its official colonization in the late 18th century due to the unparalleled diversity found there. For instance, there are over 700 species of reptiles and amphibians–snakes, geckos, chameleons, iguanas, skinks, frogs, turtles and tortoises–and about 90% of species cannot be found anywhere else. In fact, Madagascar is home to a staggering 5% of all species found on earth.
As a result of the wealth of biological diversity found there, a Duke University study investigated a possible source for how biodiversity hotspots like Madagascar could be, and they’ve found that there’s no single cause that can explain it.

Biodiversity Hotspots

There’s a whole area of biological scholarship devoted to the study of natural anomalies called ‘biodiversity hotspots’. By definition, a biodiversity hotspot is “a biogeographic region with significant diversity that is at risk from humans.”

For a region to qualify as a biodiversity hospot, it must meet two criteria: It must have 0.5%, or 1,500, vascular plant species endemic to the area, and it has to have lost 70% or more of its primary vegitation. Currently, there are 25 sites considered biodiversity hotspots with nine more under consideration. Collectively, these areas are host to 60% of all the plant and animal species in the world with very high levels of endemics, or species that live nowhere else.
Other biosiversity hotspots include the Caribbean islands, the entire Mediterranean Basin, the island nation of Sri Lanka, New Caledonia, and New Zealand.

Madagascar’s Diversity

Scientists have sought to understand how Madagascar, which comprises a mere 0.5% of the Earth’s total landmass, could be home to so many distinct and unusual species, many of which exist nowhere else, given its near complete geographic isolation for millions and millions of years. In fact, the present study is part of a larger body of work that seeks to identify factors of climate, geography and other environmental features that not only allow for the development of new plant and animal species, but also sustain them and allow them to flourish.

According to an article on ScienceDaily.com, a visitor to the bizarre hamlet of Madagascar “may come across neon green geckos that can grow up to a foot in length, and tiny tree frogs that secrete toxic chemicals from their skin and come in combinations of black and iridescent blue, orange, yellow and green. They’ll also find about half of the world’s chameleons–lizards famous for their bulging eyes, sticky high-speed tongues and ability to change color.”
In particular, the study looked at the geographic distribution of species on Madagascar in an attempt to identify contributing factors to the biodiversity seen there. They looked at features of the landscape such as steep slopes that could isolate different species and act as natural barriers between different areas. Smaller species, such as some lizards, would have trouble navigating greater distances over difficult terrain. Such features would create a number of distinct habitats in a relatively small area.

No Single Cause for Biodiversity
Duke University biologist Anne Yoder and her colleagues looked at the geographic distributions of 325 species of amphibians and 420 species of reptiles that live on Madagascar today. They compared that data with historical and present-day estimates of local attributes like amount of rainfall and local topography among other variables across the island. They noted the steep tropical regions and the flat, desert-like areas and analyzed three key measures in biodiversity: number of species, proportion of unique species, and similarity of species composition from one site to another.

“Not surprisingly, we found that different groups of species have diversified for different reasons,” Yoder said. “For example, changes in elevation–due to the mountains, rivers and other features that shape the land–best predicted which parts of the island had high proportions of unique tree frog species. But the biggest influence on why some areas had higher proportions of unique leaf chameleons was climate stability through time.”

“The results suggest that climate change and land use in Madagascar will have varying effects on different species,” said Jason Brown of the City College of New York. “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. A one-size-fits-all model doesn’t exist.”

Practical Applications
One of the greatest benefits to the findings of this study is that we better understand how the species in areas of great biological diversity respond to environmental fluctuations, which will help in identifying the groups most vulnerable to global warming and deforestation. Other studies have shown that some of Madagascar’s reptiles and amphibians are relocating to higher elevations because of climate change, and due to the effects of logging and farming on forest habitats roughly 40% of reptile species are threatened with extinction.

“One of the lessons learned is that when trying to assess the impacts of future climate change on species distribution and survival, we have to deal in specifics rather than generalities, since each group of animals experiences its environment in a way that is unique to its life history and other biological characteristics,” Yoder said.
For more information, read the article on Science Daily here, the full report here, or on the Duke University website here.
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My name is Dane. I'm a writer at Android Authority as well as a tech journalist in general. As well, I'm a marketing guru, designer, and a budding web developer. My passions include portmanteaus, artisanal coffees, jackets, and the smell of fresh technology in the morning.