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Impact of an introduced population of Eulemur fulvus on a native population of Lemur catta at Berenty Reserve, Madagascar Pinkus, Susan Elizabeth

Abstract

One of the largest protected populations of the Ringtail lemur (Lemur catta) lives in Berenty Reserve, a 400ha riverine forest in semi-arid southeastern Madagascar. Nine Brown lemurs (Eulemur fulvus) were introduced into Berenty in 1974. When these two species exist in natural sympatry, they overlap little in diet or habitat use. Brown lemurs specialize on closed-canopy forest but Ringtails are semi-terrestrial and use both forest and adjacent scrub habitat. In contrast, preliminary data at Berenty indicated broad interspecific overlap. I tested the hypothesis that the increasing Brown lemur population is having a negative demographic impact on Ringtails at Berenty. I also sought to understand what factors affect Ringtail and Brown lemur population density there. I studied the resource use, population dynamics, and response to drought, of Ringtails and Brown lemurs at Berenty. I compared the diet and habitat use of seven troop-pairs each with one Ringtail and one Brown lemur troop living in overlapping home ranges, and thus sharing access to the same resources. I found that paired Ringtail and Brown lemur troops living in the same habitat type overlapped more in diet than did adjacent troops of the same species. Census data showed that between 1974 and 2000, the numbers of both species increased, and the combined density of the two populations quadrupled. Ringtail numbers have been stable since 1995, while Brown lemur numbers continue to grow. However, juvenile recruitment in Ringtails declined with increasing Brown lemur density in scrub habitat. Juvenile recruitment in Ringtails, but not in Brown lemurs, also declined following droughts. This is likely the result of reduced productivity in the keystone food tree species Tamarindus indica after droughts. Despite the high overlap in diet of Brown lemurs and Ringtails at Berenty, I found no evidence that the socially dominant Brown lemur is lowering the demographic performance of the Ringtail. I suggest that water provisioning at Berenty explains this apparent paradox.

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