Fission-fusion sociality in southern muriquis (Brachyteles arachnoides) in continuous Brazilian Atlantic forest

The factors that shape the evolution and maintenance of fission-fusion dynamics are determined in this thesis, by investigating the egalitarian muriqui, inhabiting a dense-ombrophilous, sub-montane forest with mild seasonality in fruit availability. A habituated study group at Parque Estadual Carlos Botelho, São Paulo State, Brazil was observed for 13 months, in dry and wet seasons. Instantaneous scans (6393 scans, 1599 observation hours), focal samples and ad libitum observations were conducted on parties to record individual and party-level behaviours. Food availability was determined at two spatio-temporal scales: i) habitat-wide (absolute) using data from vegetation transects and monthly monitoring of phenophase productivity, and ii) patch-level (effective) using data from actual food resources exploited by the muriquis. Southern muriquis had a relatively small mean party size (3.34 adults) and showed lower group cohesion compared with other fission-fusion species. However, variation in party duration or spatial arrangement and sub-group size highlights a continuum in fragmentation patterns. The lack of a relationship between party size and fruit availability suggests that muriquis experience substantial travel costs associated with being in larger than optimal party sizes (despite non-territoriality and multiple central-place foraging). In conclusion, fission-fusion dynamics and facultative behaviours may not solely function to decrease feeding competition. Social preferences constrain the formation of the parties, and same-sex associations within parties reflect sexual segregation between parties throughout the year. The prevalence and complexity of fission-fusion dynamics in the study population is suggested to be due to social factors (e.g. social foraging, individual based decision making) in an environment where fruit is aseasonal and fruit species asynchronous in availability.EThOS - Electronic Theses Online ServiceGBUnited Kingdo