Imagine that you are lactose intolerant, and then you discover that all of the grocery stores in your vicinity sell only dairy products. That’s how a Duke University, North Carolina, ecologist describes the predicament of sifakas, a genus of lemur.
Exclusively found in Madagascar and the Comoro Islands in the Indian Ocean, lemurs are already identified by the International Union for Conservation of Nature as one of the world’s most endangered mammals. Now, however, in addition to the threats of climate change and deforestation, their survival appears to hinge on a new peril: gut microbes that dictate diets that are extremely local, specialized for the particular forests in which the animals live.
For them, moving to a new place when their old habitat gets destroyed just isn’t an option. When their forests go, they will, too.
Madagascar has the third-highest rate of biodiversity on Earth, after Brazil and Indonesia. Eight of every 10 of its plants and animals are endemic. It has 300 species of reptiles and 300 species of amphibians, 99 percent of them found nowhere else.
But since the arrival of humans 2,000 years ago, Madagascar has lost more than 90 percent of its original forests. Although the clearing of old-growth trees for agriculture, logging and mining has been banned since 2015, half of 1 percent of Madagascar’s vestigial protected forests are disappearing every year.
Much of the forest destruction comes about by the hand of small farmers and herdsmen, but the full story of environmental degradation is complicated and deeply rooted in economic, historical, political and social factors. Madagascar is one of the world’s poorest nations, with an individual’s average yearly income at $440 per year. About 80 percent of residents are subsistence farmers, many of whom continue to practice traditional slash-and-burn agriculture for cultural reasons and because they know of no other means to survive.
Rural people also depend on the forest in other ways. They may use several hundred species of animals and plants for clothing, construction, firewood, food, household implements, medicines, resin and shelter.
The human population of Madagascar is expected to double in the next few decades, from 27 million in 2020 to 54 million in 2050, which will only increase the pressure on existing natural habitats and resources.
The loss of valuable habitat is bad news for all species, including lemurs, but some lemurs are even more vulnerable to deforestation than others. Of 113 known lemur species, almost a third (31 percent) in Madagascar are critically endangered—just one step away from extinction—with 98 percent of them threatened.
In a June 12, 2019, paper published in The Royal Society science journal Biology Letters, researchers reported on a study that compared the gut microbiomes of 12 species representing two branches of the lemur family tree: brown lemurs and sifaka lemurs. Both groups of lemurs eat plant-based diets culled from hundreds of species of trees. But while brown lemurs consume mostly fruits, sifakas are known for eating leaves, full of fiber and tannins.
In an effort to understand how such varied diets impact the primates’ adaptability, the research team collected fecal samples at seven sites across Madagascar from 128 lemurs, both fruit-eaters and leaf-eaters. They found that fruit-eating brown lemurs hosted a similar mix of microbes no matter which part of the island they lived on. For sifaka species, however, the assemblage of gut microbes varied with their habitats: microbes that were common in lemurs living in dry forests were rare or absent in rain-forest dwellers, and vice versa.
The study’s results suggest that if you take away a fruit-eating lemur’s forest, theoretically the animal could move next door. But a leaf-eating lemur may not be able to do so.
Leaving only a long shot
How habitat loss affects species is a growing field of research. Scientists are increasingly interested in the link between microbial environments and broader ecologies.
In 2015, a study published in the journal Ecology and Evolution predicted that some lemurs would experience significant range reductions—59.6 percent in some cases—in the next 70 years due entirely to climate change. The ranges were also projected to shift considerably in that time; for many by hundreds of miles.
Unfortunately, animals that are constrained to particular dietary items, to specific geographic regions or to select habitats are then even more likely to go extinct, compared to animals with more flexible strategies and wide geographic distributions.
For lemurs to live, Madagascar’s niche forest habitats will need to endure. In the present climate, that’s a long shot, but the only one the lemurs really have left.
Here’s to finding your true places and natural habitats,