Human disturbance of tropical rainforests in Madagascar — including wildfires, burning and timber exploitation — have led to reduced rainfall and a longer dry season, further pushing greater bamboo lemurs to the brink of extinction, according to a new study in the journal Current Biology.
The study, "Feeding Ecology and Morphology Make a Bamboo Specialist Vulnerable to Climate Change," is co-authored by University of Arizona primatologist Stacey Tecot, Stony Brook University primatologist Patricia Chappell Wright, Auburn assistant professor of disease ecology Sarah Zohdy, and researchers Jussi Eronen and Jukka Jernvall of the University of Helsinki in Finland, among others.
The researchers' evidence suggests that as the climate changes, Madagascar's greater bamboo lemurs will gradually be forced to eat culm, the woody trunk of the bamboo, for longer periods of time throughout the year. Based on an analysis of anatomical, behavioral, paleontological and climate data, the researchers suggest that this dietary constraint ultimately will impact greater bamboo lemurs' ability to thrive and reproduce, and shorten their lifespan.
"This is why, for extreme feeding specialists like the greater bamboo lemur, climate change can be a stealthy killer," Wright said. "Making the lemurs rely on a suboptimal part of their food for just a bit longer may be enough to tip the balance from existence to extinction."
Greater bamboo lemurs are equipped with highly complex and specialized teeth, just like giant pandas — the only other mammal capable of feeding on culm. Those teeth make it possible for them to consume and survive on woody culm for part of the year.
To find out more about greater bamboo lemurs' feeding habits, the researchers spent hours watching them in their natural habitat in Madagascar's Ranomafana National Park over a period of 18 months, collecting more than 2,000 feeding observations. Those data showed the lemurs spend 95 percent of their feeding time eating a single species of woody bamboo. But they only eat the culm from August to November, when dry conditions make tender shoots unavailable.
According to the researchers' findings, rainfalls in Madagascar are changing annually, and the dry season on the island is expected to lengthen. Over the past two years, there has been a three-month delay in the rainy season, and new tender shoots that greater bamboo lemurs use for sustenance are appearing in January and February — 14 days after the first rainfall. Since new offspring are born in November, the delayed rainy season is dangerously affecting the survival of baby lemurs because of the lack of nutrition available for both mothers and their offspring.
"With an increasingly prolonged dry season, greater bamboo lemurs have to rely upon this challenging food source for longer," said Tecot, an associate professor in the UA School of Anthropology. "Prolonged dry seasons can also interfere with the reproduction of species like the greater bamboo lemur that rely on annual changes in day length to reproduce, once per year. Day length is a great cue if it aligns with seasonal changes in the food supply, so mothers have sufficient nutrients for conceiving, gestating and nursing their growing offspring. But, if the dry season is prolonged, reproduction won't be well aligned with these important nutrients."
Thirty years ago, new bamboo shoots would appear in December, but now they don't start until February, Wright said.
"These challenges can translate to decreased life span, increased tooth wear and decreased birth rate. All of this adds to the lemurs' already serious predicament: Their population is in the hundreds and they've already suffered decades of poaching and habitat destruction due to human encroachment," she said.
Most bamboo-feeding mammals are considered threatened by extinction. In Asia, both giant and red pandas have much diminished geographical ranges, and, similarly, in Madagascar, the two larger bamboo lemurs — the greater bamboo lemur and the golden bamboo lemur — have highly restricted distributions on the island. In fact, the greater bamboo lemur, once the most broadly distributed lemur in existence, is now one of the most critically endangered of all lemurs, with only an estimated 600 in the wild.
"By studying specialists like the greater bamboo lemur, we can identify the different ways that climate change can cause extinction," Jernvall said. "And if we do not study these endangered species now, they may go extinct before we know all the reasons why, and we'll be less able to protect what remains."