Lemurs in Madagascar
On the world's fourth largest island, and virtually nowhere else, lives an entire "infraorder" of primates: the three dozen or so lemur species. But Madagascar has radically transformed since another primate—humans—arrived two thousand years ago. Rampant deforestation, habitat fragmentation, and other anthropogenic factors are impacting lemurs much faster than evolution can mitigate the effects. Follow American and Malagasy scientists through the country's remaining forests to learn how these compelling creatures are coping with change.
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The lemurs of Madagascar, the most diverse group of primates in the world, had even more members in their ranks before humans first arrived to the island two millennia ago. There was Palaeopropithecus ingens, a lemur that hung from branches like a sloth. There was Daubentonia robusta, or an oversize version of the current-day aye-aye—a lemur with long, skeletal fingers, large eyes, and rodentlike teeth. The lumbering Archaeoindris fontoynontii weighed in at 160 kg, the size of a male gorilla. The 45–85 kg Megaladapis edwardsi had a prehensile upper lip to pluck leaves while slowly ascending trees like a koala.
These four species, all larger than current-day lemurs, are now extinct. In fact, about 16 of the perhaps 70 species of wildly diverse lemurs that existed upon human arrival aren’t around anymore. Of the species still living, four top Conservation International’s “World’s 25 Most Endangered Primates” list. Despite the disappearances of plants and animals on Madagascar, the country remains incredibly rich biologically. Its environments vary from desert to rain forest to shrubby highlands. The country still boasts a huge variety of species, 90 percent of which are found nowhere else. How did Madagascar develop such a range of wildlife? The reasons can be traced back to when Madagascar began to be decidedly its own place, some 160 million years ago.
A Fateful Split
At that time, Madagascar (then attached to India, Australia, and Antarctica) began to split from the supercontinent Gondwanaland. Just before the start of the Late Cretaceous period, 124 million years ago, Madagascar arrived at its present position, separated from Africa by the 770 km wide Gulf of Mozambique. Now the fourth-largest island in the world, it straddles many latitudes. This helps foster its myriad climates and habitats. This geographic seclusion from other land is one reason why Madagascar is considered a “laboratory of evolution” by researchers like University of Massachusetts paleontologist Laurie Godfrey. The country’s flora and fauna have evolved independently, with little influence from species migrating from adjacent areas. As evidenced by Charles Darwin's discovery of a unique finch for each unique island of the Galapagos chain, physical barriers to interbreeding are key to the development of new species in an area. Such evolutionary isolation of the island of Madagascar would have telling consequences for its lemur populations.
“There is some evidence that there was a single colonizing ancestor of lemurs on Madagascar, long after the island was already separated from Africa and other bodies of land,” says Godfrey. She digs and studies lemurs’ “subfossil” bones—i.e. bones buried too recently to fossilize—to learn which species lived here when. DNA analysis of present-day lemurs suggests that lemurs’ original ancestor lived nearly 70 million years ago, a few million years before the dinosaurs disappeared. No one is certain if this “proto-lemur” negotiated the surrounding waters to arrive on the island or if primates (including lemurs) evolved on the once-connected landmasses from earlier inhabitants. Several theories exist about lemur origins, but molecular studies have repeatedly shown that this ancestor diversified into eight families of lemurs: three extinct and five still alive. Scientists call this evolutionary process “adaptive radiation.” “The idea suggests that high diversity results because animals adapted to different niches, different habitats, and different foods within the same habitat,” says Godfrey.
Coping with Change
Such an ancient adaptive radiation means that the lemurs of Madagascar—both extinct and living—are quite different from one another. Every extinct lemur was larger than the largest living today, the domino-colored, bushy-eared, tailless indri, which is the size of a 7-month-old child. The tiniest lemur, the mouse lemur, is closer in size to its namesake. Some lemurs eat leaves, others fungus, and still others the soil near termite mounds. Many lemurs have odd adaptations that give them a competitive edge, such as the aye-aye’s lengthy fingers, which it uses to pluck wood boring insect larvae. Another instance is the bamboo lemur’s resistance to the cyanide naturally present in its food, bamboo shoots. This allows it to exploit a resource others avoid.Some scientists argue that lemurs may have evolved in the many ways they did to cope with limited resources on a constantly changing island environment. "Madagascar is a great place to study both natural and human-induced changes in the environment," says Godfrey. "It's a natural experiment, so to speak. We desperately need to understand its dynamics if we are going to conserve the remaining primates not only on Madagascar but also in the rest of the world."
The ring-tailed lemurs that romp around the research camp at the Beza Mahafaly Special Reserve in southwest Madagascar spend plenty of time behaving badly. They slide down tents, peer at their reflections in pickup truck windshields, and rummage through trash cans. It's their playful and versatile nature, in part: as "generalist" species, ring-tails can adapt to a range of habitats. But this population also resides in a conservation area with abundant resources and few threats. "The lemur group at the camp has a lot of luxury in terms of time," says Michelle Sauther, an anthropologist from the University of Colorado at Boulder who spends three months of the year at Beza Mahafaly. "If they don't have to run around looking for food all the time, even ring-tailed lemurs can sit back and relax."
Local villagers offered to set aside 600 hectares of the Beza Mahafaly forest to form the reserve in the late 1970's. Remote and nearly the smallest protected area of the 46 on the island, it is hardly as popular with eco-tourists as the rain forests of Ranomafana and Perinet. But the range of Malagasy habitats it contains is remarkable. These include a lush "gallery" forest that lines the seasonal Sakamena River and a dusty "spiny desert" forest with towering cactus-like trees. Beza's habitats support five of the dozens of lemur species on Madagascar, most notably the housecat-sized, raccoon-faced ring-tails and the paler, silkier Verreaux's sifaka.Sauther has monitored lemurs at Beza Mahafaly for about twenty years. With conservation as its goal, her work aims to understand how changes to Madagascar's environment—mostly brought about by human beings—affect the behavior, health, and evolution of lemurs. In the land outside the reserves, these changes have not afforded lemurs much time to goof off.
Madagascar was one of the last landmasses settled by humans. It is likely that maritime traders sailing the Indian Ocean first stepped on its southwest coast some 2,300 years ago. The earliest indirect evidence of the "human footprint" is the slashed bones of extinct lemurs found at Taolambiby, a dusty creek bed seven kilometers or so from Beza Mahafaly. Hundreds of hacked bones of Verreaux's sifaka were also dug up at Taolambiby. The cut marks, probably exacted by iron butchering tools, are an eerie testament to some of humans' first impacts on lemurs.
The locals near Beza Mahafaly no longer eat sifakas (it's taboo), but lemurs are still hunted elsewhere in rural Madagascar. More deleterious than hunting pressure, however, has been the swift, dramatic effects of agriculture. Much of Madagascar's original forest has been converted to cropland, pastureland, or eroded wasteland via axe, machete, and fire. (Besides reducing habitat for arboreal species like lemurs, slash-and-burn deforestation exacerbates soil erosion, which occurs at a higher rate in parts of Madagascar than anywhere else in the world.) These days, deforestation occurs at a rate of just under 1 percent a year. Although there are only 32 humans per square kilometer on Madagascar, the island's population is poised to double by the year 2025. At least 16 species of lemurs have disappeared since humans arrived, and all lemurs living today are threatened with extinction to some degree.
Generalists vs. Specialists
Lemur research in the protected areas helps inform conservation. At Beza Mahafaly, ring-tailed lemurs and sifakas are observed, counted, captured, DNA-sampled, checked for parasites, collared with radio-tracking tags, then released; they even have casts made of their teeth. Both populations at the reserve appear stable. "Ring-tailed lemurs are widespread in the south of the island, but that's not to say they're not threatened," says Sauther. "But they seem to be able to deal biologically with habitat change." The generalist ring-tails can cope with, and even take advantage of, some anthropogenic change. For one, they'll eat anything: flowers, insects, fruit, but also less-nutritious tourist handouts, crops, and food refuse. "They're able to exploit a wider resource base than the sifakas, who have a more narrow folivorous, or leaf-eating, diet," explains Sauther.Ring-tails are also more terrestrial than the arboreal, "specialist" sifakas. "Ring-tailed lemurs are able to utilize all parts of the forest," says Sauther, "from the very tops of the trees to the ground itself." Biologically, sifakas can't afford the energy costs of frequent travel across a denuded habitat, so they leap on trees instead. But when the trees disappear, sifakas are stuck. "Many of the fossil lemurs, the extinct species, were hyperspecialized," says Sauther. "They simply could not adjust to the loss of habitat."Many regions around Beza Mahafaly are largely treeless, instead dotted with cassava, maize, and sweet potatoes and with grazing zebu cattle and goats. Scientific comparisons of lemurs inside and outside the park show that the reserve animals generally travel less far to forage and are healthier. The rich resources of the reserve do appear to be a magnet for ring-tailed lemurs: the population density within the reserve is much greater than in the surrounding habitats. But higher animal densities in these isolated reserves bring new population pressures.
Many Populations, Same Island
"One of the things that I've noticed over the almost 20 years that I've worked here is that reserves really do work," says Sauther. "But they only work when you have the local people involved." Beza Mahafaly was among the first Madagascar conservation projects to involve local residents, a few thousand of whom live in straw-roofed huts outside the reserve. The villagers agreed to protect the lemur habitat, and governmental and nongovernmental organizations agreed to improve the residents' water access, roads, schools, and other infrastructure. "The villagers are participating in the long-term research that we've been undertaking at Beza Mahafaly," says Joelisoa Ratsirarson. He's Madagascar's general secretary of the minister of the environment, water and forestry and also a biologist who studies the park's sifakas. "We train the villagers to monitor the survivorship and movement of the lemurs. The local population is very helpful in protecting the reserve and really respects the lemurs."Ratsirarson says that although the Malagasy government "lacks the means for conservation activities," habitat protection is a political priority. It is mostly accomplished in cooperation with international groups like the World Wildlife Fund and Conservation International. Marc Ravalomanana, Madagascar's president, has vowed to extend its protected area to 10 percent of the country by 2008. Right now, it's about 3 percent. "So it's really a challenge," says Ratsirarson. Sauther admits, "I used to feel depressed when I came here, because you see the habitat changing and a lot of fragmentation occurring." She says that the government may expand Beza Mahafaly to include surrounding fragmented areas and the people that live in them. "The locals would still use the resources here, but in ways that support both the humans and the lemurs themselves," she says. "So I'm feeling a lot more hopeful than I used to."
The dozens of diverse lemur species on Madagascar are a motley crew. Still, none look and act quite like the aye-aye. In fact, this lemur is considered one of the world's strangest animals altogether. Just ask Eleanor Sterling: she's a conservation biologist, the director of the Museum's Center for Biodiversity and Conservation, and one of the world's few experts on the aye-aye.
What makes the aye-aye so strange?
First off, it’s got continuously growing front teeth like a rodent. It has a really thin middle finger that is mostly tendon and bone. A protective film also covers its eye when it is gnawing wood and bits are flying everywhere. These features are not found in any other lemur nor any other primate, even. Most animals have behavioral characteristics that allow them to adapt well to their environment, but very few animals have such extreme morphological changes in body form and shape.
How do those adaptations help it survive?
Its features make it exquisitely well suited to acquire food, including insect larvae. Larvae live inside chambers in tree trunks and branches. The aye-aye taps along a branch with its funny finger and listens carefully with its large ears. It echolocates where larvae might be, opens up the chamber with its teeth, then sticks a finger in and pulls one out.I’ve seen aye-ayes eat really big, chunky larvae just like a child eating an ice cream cone. First it bites the little head off and spits out the mouth parts—those are hard to digest. The insect’s insides then drip down the aye-aye’s fingers, so the animal runs it tongue around its hand to lick the juicy parts up fast.
Well, larvae are high in both fat and protein, so they’re good for both quick and long-term energy. And if you can gain access to hard-to-acquire, “structurally defended” food sources like larvae with your specialized adaptations, you don’t have a lot of competition from other animals.
So does that mean the aye-aye is smarter than other lemurs?
Not necessarily. The finger is certainly very advanced in its manipulative abilities. It has incredible flexibility—aye-ayes can move it 360 degrees around the joint with the hand. Interestingly, the aye-aye has an enormous brain for its body size compared to that of other lemur species. The mechanics of its manipulative operations and the sophisticated echolocating ears might explain the size of the brain.
Why else does the aye-aye look like it does?
It has dark fur and big bright eyes because it lives in a dark rain forest. It is well specialized for nocturnal living. The eyes are designed to pick up any available light, even on a night with very little moonlight, and reflect it to discern the smallest changes in the environment. Aye-ayes also have very acute senses of smell and hearing.
How did you become so well acquainted with these animals?
I lived on a little island off the coast of Madagascar called Nosy Mangabe for about two years studying aye-ayes for my doctoral thesis. I conducted the first long-term study of the animal, following single aye-ayes through the night to figure out exactly what they do, whom they meet, and how they interact with each other. Only a few researchers have studied aye-ayes in the wild since, as field conditions are very difficult. You have to put a radio telemetry collar on the animal to track it—a very expensive, difficult, and time-consuming project—then follow the aye-aye for the life of that collar, which can be months. It’s only after following individuals through the seasons that you get a sense for how they live their lives.
What was it like following aye-ayes so intensely for two years?
It was one of the most amazing experiences of my life. There were no roads—just barely paths—and I lived in a tent surrounded by the sea. I would wake up in the afternoon and start work at 5 p.m. to find where a radio-collared aye-aye was sleeping in a nest. I’d wait for it to wake up, then two other people would keep the aye-aye in the crossbeam of their flashlights while I would watch it with binoculars. We’d follow it all night over rugged mountainous terrain, and I was trailing headphone wires and antennae that constantly got caught in the thick vegetation we were wading through. Aye-ayes can move easily in the canopy, but I would have to go down and up and down on the ground, leaping over dark canyons and doing other Herculean things to keep up. If I lost the animal, I had to go back to the tent and start again the next night. It was interesting to get to know an animal as well as we did, to get a sense for not just how it lives but how we can do a better job of conserving it.
What is the conservation status of aye-ayes on Madagascar?
We know there was another kind of aye-aye once. It was bigger than the existing species and lived when humans first arrived on the island about 2,000 years ago. The paleontological evidence for it includes teeth with holes bored in them, so humans may have used the teeth in some kind of jewelry. That aye-aye is now extinct. We don’t know why or how just yet.As for the smaller aye-aye that now remains, people were unclear about the animal’s status for a long time. Some of the French explorers in the early 1900’s noted that it was quite rarely encountered on Madagascar. In fact, in 1935 they declared it extinct, because they hadn’t seen it in a while. Then a group of scientists from Paris visited Madagascar in the 1950’s and found a couple of aye-aye populations. They captured nine aye-ayes and put them onto the island of Nosy Mangabe as a protected reserve.
Are aye-ayes really that rare?
We know that the chances of people running into an aye-aye are much lower than for diurnal lemurs, which come out during the day. Aye-ayes tend to wander about alone and don’t congregate often. So you have to be at the right time and place to run into one.Today, we can tell definitively that an aye-aye has been in an area by the particular marks they make on nuts they crack open. The good news is that aye-ayes are fairly widely distributed around Madagascar. But we still don’t know the population size in any one of those places. There’s a lot more work on the aye-aye that needs to be done.