The first chapter of my dissertation to be published is now out in the Journal of Animal Ecology, detailing a close connection between the diversity of primates and the abundance of their food tree resources. Lemurs are primates endemic to Madagascar – they are indigenous and found nowhere else on earth. They are also highly threatened with extinction; 95% of lemurs are considered at risk of extinction. The primary threats to lemur persistence are habitat loss due to deforestation for agriculture, cattle grazing, logging, and mining, as well as hunting for bush meat. The new study illustrates the tight links between lemur diversity and ecosystem health.
In case this is your first time on my page, my name is James Herrera, and I am a researcher at the American Museum of Natural History. I conducted the study as a Ph.D. student at Stony Brook University. I spent two years trekking across rainforests in southeast Madagascar to count lemur species and determine their abundance in relation to habitat characteristics such as human disturbance, altitude, and tree community composition. I surveyed five different habitats with teams of Malagasy field assistants and graduate students. The study was conducted in Ranomafana National Park and an adjacent forest corridor that connects Ranomafana to the Fandriana Park to the north. Some habitats were low altitude pristine rainforests like green cathedrals of massive, broad canopy trees. Other habitats were high mountain peaks of granite, festooned with forest clinging to rocks. I also surveyed heavily disturbed sites, some of which had been logged or cultivated in the past and subsequently grew back, while others were actively being logged and mined for gold around his camp site. This variety of habitat types allowed me to compare the primate communities in relation to variation in habitat features.
The study revealed the overwhelming effect of food tree abundance on lemur diversity. While some small nocturnal lemurs eat insects, many lemurs are vegetarians, and most specialize on the fruits or leaves of just a few key tree species to obtain most of their diet. Collaborating with Malagasy botanists, I enumerated the food trees in each habitat compared to non-food trees, and found the relative abundance of preferred food trees was most closely tied to lemur diversity. Where food trees were most abundant, the lemur communities were dominated by a few large-bodied species that form large groups, while small species with small group size were rare or absent. When food trees became scarce, those previously dominant large-bodied species became rare or absent and other species increased in abundance. This result illustrates how resource limitation affects the abundance and diversity of lemurs. This finding is especially pertinent for healthy ecosystem functioning. The fruit-eating lemurs are important seed dispersers; when lemurs eat the fruits, they pass the seeds whole which germinate much better than seeds not passed by lemurs. Different lemurs specialize on different trees and disperse the seeds far from the parent trees, like gardeners sowing the future forests. Without these lemurs, the trees may not be able to reproduce as efficiently, and so lemur extinctions could have cascading effects on ecosystems.
Surprisingly, human disturbance did not have a strong effect on lemur diversity, possibly because of the indirect effects on food tree abundance. For example, while some heavily degraded sites had low food tree abundance, so did high altitude pristine forests. The study illustrates that some lemur species may be resilient to habitat disturbance, especially those small-bodied species that have small group sizes and can be sustained with lower resource abundance. The result is important for understanding how entire lemur communities will respond to future habitat loss, which is especially important because of the ongoing degradation of natural habitats. While I surveyed corridor forests that connect two national parks, migrants from far-away cities were cutting forest, damming rivers and panning for gold. The recent surge is especially troubling because it attracts bandits who rob gold miners and threaten the safety of rural villages. Further, many of the miners are immigrants from cities, not the local land owners with rights to the forest resources. Protective action is needed to suppress the burgeoning deforestation, and this corridor is especially important to maintain safe passageways for lemurs to move among parks and maintain healthy stable populations.
This study was funded by the National Science Foundation, Margot Marsh Biodiversity Foundation, Conservation International, Explorer’s Club, Leakey Foundation, Primate Conservation, Inc., Rufford Small Grants Foundation, International Primatological Society, American Society of Primatologists, La Conservatoire pour la Protecion des Primates, and the Turner Fellowship while at Stony Brook University, as well as a Gerstner Scholarship and Postdoctoral Research Fellowship from the Richard Gilder Graduate School, American Museum of Natural History. I also acknowledge the help of over 30 Malagasy research assistants, especially Tongasoa Lydia, a Malagasy Ph.D. student who worked with me during this study.