Earthwatch-supported scientists in Madagascar find infant survival depends on high rainfall
Earthwatch Institute, Maynard, MA, November 16, 2005-As evidence for global warming grows, biologists are scrambling to predict how local climate change will affect plant and animal populations. A paper published in this week's Proceedings of the National Academy of Sciences demonstrates how even subtle changes in climate directly result in lower reproductive success among Milne-Edward's sifakas (Propithecus edwardsi) in Ramomafana National Park, Madagascar. The key is dental senescence, or excessive tooth-wear.
"The conservation implications are immense," said co-author Dr. Pat Wright, an anthropologist at Stony Brook University and principal investigator of the Earthwatch-supported Madagascar's Lemurs project. "This paper shows how a slight change in climate, even in the rainforest where we assume there is plenty of water, can impact infant survival. What we see in Madagascar is a window into the future of many other tropical ecosystems."
Like other primates, humans included, Milne-Edward's sifakas have low-crowned teeth that wear down before old age. Wright and her colleagues used GIS (Geographical Information Systems) analysis to study the changing "landscape" of tooth crowns in three dimensions, the first time such techniques were applied to a wild lemur population.
The researchers found that sifaka teeth remain functional until the animals are nearly 20 years old, but these lemurs can live and reproduce until they are nearly 30. In fact, female fertility remains high.
"For their last ten years, when teeth are worn flat, adult females use their dominance to eat more," said Wright. "This may be because they can't get as much nutrition or water from their food, since cell walls can't be sheared or crunched by the flat basins of their teeth."
Although these older females readily reproduce, 20 years of field data showed that their infants only survived if it was a good rainy season during their lactation period. Sifaka milk relies on large quantities of water and nutrients drawn from their leaf food. With a potential five more births during the latter decade of each female lemur's life, after dental senescence, the impact of local climate on the population is enormous.
"With deforestation and habitat fragmentation increasing daily in the region, as well as global climate change, the immediate effects are the drying out of habitats like the rainforest of Ramomafana National Park," said Wright. "I was shocked to see the effect of rainfall decreases of such small magnitude on the survival of infant sifakas. The implications are immense in a world full of endangered species."
The study used population data from a 20-year field study at Ramomafana, supported by Earthwatch volunteers, to determine the reproductive success of individual sifakas. Volunteers working with Wright and co-author Summer Arrigo-Nelson (Stony Brook University) collected data on the sifakas in the field, participated in capturing individuals, and assisted in the process of molding teeth impressions for analysis.
"Earthwatch volunteers took some of the behavioral and demographic data that made these findings possible," said Wright, who continues her research at Ranomafana with Earthwatch support. "They habituated group IV, making our sample size of studied sifakas much larger than was possible before."
Earthwatch Institute is an international nonprofit organization that supports scientific field research by offering members of the public opportunities to work alongside leading field scientists and researchers. Earthwatch's mission is to engage people worldwide in scientific field research and education and promote the understanding and action necessary for a sustainable environment.
For more information, see "Dental senescence in a long-lived primate links infant survival to rainfall." Stephen J. King, Summer J. Arrigo-Nelson, Sharon T. Pochron, Gina M. Sembrebon, Laurie R. Godfrey, Patricia C. Wright, and Jukka Jernvall. November 15, 2005. PNAS, 102 (46): 16579-16583, or the abstract on the web at www.pnas.org/cgi/doi/10.1073/pnas.0508377102