Fission-fusion dynamics in black-and-white ruffed lemurs may facilitate both feeding strategies and communal care of infants in a spatially and temporally variable environment
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Species with greater expression of fission-fusion dynamics show greater variability in the size, composition, and cohesion of subgroups over time. This may allow their adjustment to local environmental, social, and demographic conditions. We tested which environmental and social factors influenced subgroup size in one such species, the black-and-white ruffed lemur (Varecia variegata) at two sites within a fragmented forest landscape. Using instantaneous focal sampling at 15-min intervals, we collected data on subgroup size and composition, fruit and flower availability, and location. We also collected biweekly data on site-wide fruit and flower availability. We used these data to test the influence of season, food availability, reproduction, and predation risk on adult subgroup size in this species. Ruffed lemur adults consistently formed significantly larger subgroups in times of lower site-wide fruit availability, during the wet season, and when one or more infants were present. There were differences between sites in the relationship between subgroup size and tree size, fruit patch size, and site-wide flower availability. Variables measuring indirect predation risk showed no significant relationship with subgroup size. These results emphasize the strong relationship between fission-fusion dynamics and spatial and temporal variation in food availability, as well as the importance of sociality in a species with communal care of infants. Fission-fusion dynamics may serve as an evolutionary strategy to adapt to the unpredictable and sometimes harsh environmental conditions of Madagascar and may facilitate the persistence of communities of this critically endangered lemur despite widespread anthropogenic habitat modification.
Fission-fusion dynamics (the joining and separating of subgroups within a larger group of animals) may allow species to adjust social benefits to changing environmental conditions. This study examines the underlying ecological and social factors that might influence fission-fusion dynamics in black-and-white ruffed lemurs. Subgroup size in this species was strongly related to food availability, though not always in the direction expected. This suggests that the relationship between food availability and sociality changes when food availability reaches very low levels. Additionally, infant presence was linked to larger adult subgroups, indicating a connection between fission-fusion behavior and the cooperative rearing of offspring seen in this species. Relationships between subgroup size and some environmental variables differed between sites, emphasizing the flexibility of grouping patterns in this species and indicating that local conditions may play a large role in the expression of fission-fusion dynamics.
KeywordsSubgroup size Sociality Communal rearing Ecological conditions Seasonality Madagascar
We are grateful to Cressant Razafindravelo, Ferdinah Mbana, Jean Pierre Marolahy, Emilys Edgarçon Rakotoson, Gregor Pachmann, Melanie Vomscheid, Jean Samuelson Randrianarisoa, Jerrad Hayden, Sara Pearce Meijerink, Erin Moody, Jordon Traill, Eric Perlett, and Olivia Hanson for research assistance in Madagascar. We thank the BEAS editors and two anonymous reviewers for their comments on an earlier draft of this paper. We also thank the following organizations for funding: International Primatological Society, Omaha’s Henry Doorly Zoo and Aquarium, the Ahmanson Family Foundation, University at Albany, and the Natural Sciences and Engineering Research Council of Canada.
Compliance with ethical standards
All applicable international, national, and/or institutional guidelines for the care and use of animals were followed.
Funding for this research was provided by the International Primatological Society, Omaha’s Henry Doorly Zoo and Aquarium, the Ahmanson Family Foundation, University at Albany, and the Natural Sciences and Engineering Research Council of Canada.
This study did not involve human participants.
Conflict of interest
The authors declare that they have no conflict of interest.
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