Ecologists have improved scientific understanding of how giant pandas moved from humid, low-altitude environments to drier, cooler and more elevated habitats by using a novel approach that the researchers say will be able to better predict the iconic animal's future distribution as climate changes.
By drawing on not just historic distributions of giant pandas but the varieties of three genera of bamboo, the researchers confirmed prior research that giant pandas diversified around 2.7 million years ago as they moved up into the mountains, and traded meat for bamboo. Using a food source to study historical giant panda distribution, rather than using the locations of the animal alone, can open up new avenues of study for not only giant pandas but other species, as well.
The researchers' findings were published April 30 in the Journal of Mammalogy.
"We proceeded with the panda because it is a very important species for conservation. It is an umbrella species, and also a flag species for conservation, even used by a lot of organizations as a symbol," said lead author Carlos Luna Aranguré, a recent Ph.D. graduate of Universidad Nacional Autónoma de México.
The giant panda is what conservationists call an "umbrella species" because its preservation can incidentally help other species, making it an ideal target for protection. The World Wildlife Fund, for example, uses the giant panda in its logo to symbolize "all endangered species that would be able to thrive if permitted the range and natural environment of their origin."
Endangered since 1990, the giant panda moved to the International Union for Conservation of Nature's "vulnerable" list after years of slow but steady population growth in the wild. There are now about 1,864 giant pandas in the wild, living across a small range in the mountains of southwest China.
"We thought that we could try to understand a little better the relationships between the species and the environment, particularly considering the possible changes in the future due to climate change," Aranguré said.
Aranguré and his co-author Ella Vázquez-Domínguez, a professor of ecology and genetics at Universidad Nacional Autónoma de México, began their study to better understand the ecological nature of giant pandas and how it could be changing since the Last Glacial Maximum, the time period between 19,000 and 26,500 years ago when global ice coverage peaked, encompassing most of North America, Northern Europe and Asia.
The researchers devised a unique method of analysis by drawing on fossil data, ecological niche modeling and phylogeography, the latter being processes that account for present and historical distributions of genetic diversity in a species. These have typically been used to examine the giant panda in the past, but the phylogeographic patterns the researchers drew for the new study centered around habitat climate and bamboo locations. According to Aranguré, this data helps outline the giant panda's evolutionary trajectory, including what past environmental conditions it could withstand.
"We found that a lot of those combinations are not represented by where the panda is actually today, so this tells us how in the past, the distribution and environmental conditions the panda was found in are separate," Aranguré said.
To find out how the giant panda's range changed since the Last Glacial Maximum, Aranguré and Vázquez-Domínguez compared the location of the bamboo genera as well as climate data from that period with the range of giant pandas today. The duo found that the giant panda's niche has dropped from temperatures around 17 to 20 degrees Celsius (63 to 68 degrees Fahrenheit) to 2 to 16 degrees Celsius (36 to 61 degrees Fahrenheit).
Agriculture has wrought much of this change, according to Vázquez-Domínguez, as farmers cleared lowlands and pushed giant pandas farther into the hills.
"What is worrisome is that, in these isolated highlands that the panda is now distributed, the conditions are now more in the limit of what the panda is historically incapable of withstanding — low temperature, the low precipitation — and it has nowhere else to go," Vázquez-Domínguez said.
To prove the accuracy of their new model, Aranguré and Vazquez-Domínguez drew on fossil data from the Last Glacial Maximum, and found that 85% of the fossil data, based on location, correlated with the occurrences of bamboo.
Though it is "wishful thinking" for now, Aranguré says that conservationists can potentially draw on this type of research to help understand how the loss of genetic diversity in geographically shifting giant panda populations may have resulted in the species' loss of tolerance to warmer conditions. For Aranguré, this line of study would be an interesting next step, but would also require additional genomic study at a level that is outside this new study.
In future research, Aranguré would like to better understand how climate and more general environmental patterns have been shaping the evolution and distribution of species. These patterns aren't limited to terrestrial organisms. In underwater habitats, for example, warming waters are forcing tens of thousands of fish, shrimp and mollusk species away from the tropics.
Instead of looking at one type of bear, Aranguré intends to continue his research more generally, using broader groups of organisms, such as carnivores, to investigate the relationship between climate, environment and evolution. According to Aranguré, these factors are integral to species distribution, and understanding how they shape distribution is one of his greatest inspirations.
"It's one of the most defining questions in biogeography,"Aranguré said. "I would really like to try to understand this, because it is the basis of the distribution of the species, and that's quite important."
The study, "Of pandas, fossils, and bamboo forests: ecological niche modeling of the giant panda (Ailuropoda melanoleuca) during the Last Glacial Maximum," published April 30 in the Journal of Mammalogy, was authored by Carlos Luna Aranguré and Ella Vázquez-Domínguez, Universidad Nacional Autónoma de México.