Tigers and pandas live in Asia, kangaroos and koalas in Australia and polar bears and snowy owls in the Arctic. The world can be divided into regions based upon the unique types of animals that live there. Or so the thinking went when Alfred Russel Wallace published the scientific world's first global biodiversity map in 1876.
More than a century has come and gone since Wallace released this groundbreaking work, yet his map largely still serves as a cornerstone for understanding modern distributions of biodiversity. An updated version was due, a group of researchers decided.
"Wallace's map still makes a lot of sense," said Jean-Philippe Lessard, an ecologist at McGill University in Montreal who was formerly at the University of Copenhagen. "We're not inventing anything here, we're just implementing Wallace's vision at an age where we have tons of DNA and more information on where species are on the planet."
As Craig Leisher noted here last month, Wallace is something of a folk hero among biologists. He simultaneously thought up the theory of evolution by natural selection alongside Charles Darwin yet also made time for clambering around collecting specimens in the most exotic spots in the world. His wanderings and studies eventually led to that first map of animal distributions across the continents.
Wallace recognized that the world is divided into so-called biogeographic regions, which today we know reflect the breakup of the continental plates roughly 200 million years ago. As the former mega-continent of Pangaea split apart, the evolutionary branches of those species cleaved off from one another. Millenniums of isolation following this divergence led to Australia's wildly unique marsupials, for example, and Madagascar's beloved lemurs.
Wallace recognized these differences and produced a map identifying six major global biodiversity regions. Other maps have been produced since, but for this new effort, the researchers decided to take into account not only the current distribution of vertebrates, but also how they relate genetically.
"Genetic sequencing allowed us to do things that weren't possible before," Dr. Lessard said. "Looking at these evolutionary links allows us to know which parts of the world are more closely related to other parts of the world."
With a team of 14 international colleagues, Dr. Lessard helped compile and analyze the phylogenetic relationships of 21,037 species of amphibians, birds and mammals. Whereas Wallace highlighted six major animal realms, the team identified 11, and within those realms made 20 regional distinctions. The results were published online today by the journal Science.
A few surprises turned up in their analyses. For example, new realms in Central America, East Asia and Oceana emerged. The northernmost stretches of the Canadian tundra make more sense grouped with the Palearctic realm, which encompasses Siberia, Europe and North Asia, than with North America's Nearctic realm. "Apparently, plant people kind of informally recognized that grouping in the past," Dr. Lessard said. "But for animals, I've never seen a map of biogeographic regions showing that connection."
The dividing lines will soon be uploaded and freely accessible on Google Earth, and the researchers hope to add information detailing which big animal families are found in each realm and region for curious citizens or researchers to explore.
The new map is by no means definitive, however. As more animal groups are added — reptiles, for example, or freshwater fishes — the lines between regions and realms may shift. Although the required distribution and genetic data needed to incorporate those additions are still lacking, Dr. Lessard and his colleagues used scalable methodology to build their map, so adding more animal classes should be fairly straightforward.
The maps may also shift as the planet warms as a result of climate change. Having this baseline may help scientists understand how species distributions change in the coming decades. "The earth will surely change, but we don't know how it will change," Dr. Lessard said. "We know what biodiversity on the planet looks like now, but 50 years from now we could come back and redo the whole thing so we can quantify those changes in the future."
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