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I examine the niche partitioning between native ring-tailed lemurs, Lemur catta, and an introduced hybrid brown lemur population of Eulemur rufus x E. collaris in Malaza gallery forest of Berenty reserve, in comparison with the natural sympatric population of ring-tailed lemurs and red collared brown lemurs, Eulemur collaris, in Ambatotsirongorongo forest and with allopatric ring-tailed lemurs at Bealoka forest, in order to determine the impact of the introduced brown lemur population at Berenty reserve on the behaviour and distribution of native ring-tailed lemurs. Behavioural observations were conducted from September 2008 to December 2009; lemur population survey was conducted from 2005 to 2009. Behavioural sampling methods include scan group sampling, focal animal sampling and ad libitum of social behaviour and feeding behaviour. Two groups of each lemur species were followed in Malaza Berenty forest, one group of ring-tailed lemurs in Bealoka forest and one group of each lemur species was followed in Ambatotsirongorongo forest. Vegetation study was conducted in Bealoka and Berenty forests, whereas preliminary data on vegetation structure was already available for Ambatotsirongorongo. At Berenty reserve, the dynamic of the native ring-tailed lemur population was conditioned by food availability and habitat quality. The brown lemur growth and distribution appear to be affected by the water availability. Individual energy demands for various activity rhythms play a big role in brown lemurs' ecology. Food availability, hierarchy and territory are the main niche dimensions that shape ring-tailed lemurs' ecology. Niche partitioning between native population of ring-tailed and collared brown lemurs at Ambatotsirongorongo forest relies mainly on habitat use. Feeding ecology of ringtailed lemurs in Bealoka forest is dominated by fruits. Habitat utilization differs markedly from both Berenty and Ambatotsirongorongo forest. Changes in ring-tailed lemurs' behaviour and distribution at Berenty reserve are partly due to the competition with the introduced brown lemurs. This situation has resulted in a niche partitioning between both species by creating a bimodal niche for ring-tailed lemurs: the marginal habitat and the closed canopy forest. The comparisons with ecological mechanisms and evolution of Bealoka and Ambatotsirongorongo forests show that Berenty has shifted from a situation more like Bealoka's to a situation more like natural sympatry. |
