What drives flexibility in primate social organization?

Abstract

The importance of behavioral flexibility for understanding primate ecology and evolutionary diversity is becoming increasingly apparent, and yet despite the abundance of long-term studies across diverse sampling localities, we still do not understand the myriad factors responsible for amongsite variation in species' social organization. The goals of our study were to address this question via three main objectives: to quantify social organization flexibility (i.e., across-site intraspecific variation) of well-studied primate species, test the idea that closely related species exhibit similar levels of flexibility, and test hypotheses explaining variation in social organization flexibility among primate species. We obtained data for a total of 175 study sites from 32 primate species representing all major primate clades. We employed phylogenetic principal components analysis to quantify social organization flexibility for each species. We quantified the phylogenetic signal in social organization flexibility and then evaluated the best predictors of flexibility. We found that mean group size was positively related to social organization flexibility. Large social groups may be more flexible because the foraging costs and predation risk associated with adding or subtracting individuals are lower compared to small social groups. There was some support that absolute brain size and the presence of fission-fusion dynamics were also related to high levels of social organization flexibility, suggesting that cognitive ability and/or within-site behavioral flexibility may also lead to increased variation across sites. Our results serve as an early step in understanding the patterns and processes related to social organization flexibility in primates and other social mammals.

Variation in the social organization of gorillas: Life history and socioecological perspectives

“…Furthermore, male–male competition for access to females, both within and between groups, may limit or favor the formation of multimale groups . In addition to interspecies differences in social organization, socioecological theory has also been used to explain variation within species . In particular, there are species in all primate taxa that vary in the proportion of social groups that are one‐male and multimale (e.g., Verreaux's sifaka, Phayre's leaf monkeys, hamadryas baboons, ursine colobus monkeys, hanuman langurs, black howler monkeys, and mountain gorillas).…”

“…9 In addition to interspecies differences in social organization, socioecological theory has also been used to explain variation within species. [10][11][12][13] In particular, there are species in all primate taxa that vary in the proportion of social groups that are one-male and multimale (e.g., Verreaux's sifaka, 14 Phayre's leaf monkeys, 15 hamadryas baboons, 16 ursine colobus monkeys, 17 hanuman langurs, 18 black howler monkeys, 19 and mountain gorillas 20 ). In a critical review of primate socioecology, Clutton-Brock and Janson 21 recommend that to understand variability in within-species and between-species grouping patterns researchers should consider how feeding competition and predation interact with variation in reproductive strategies and life history parameters of both sexes.…”

Relative Brain Size Is Not Correlated with Display Complexity in Manakins: A Reanalysis of Lindsay et al. (2015)

“…Residuals from both nonphylogenetic linear [Sol and Price, 2008;Weisbecker and Goswami, 2010;Sol et al, 2012;Castillo-Morales et al, 2014] and reduced major axis regressions (RMA) [Shultz and Dunbar, 2006], and phylogenetically corrected RMA [Kamilar and Baden, 2014] or PGLS [Pérez-Barbería et al, 2007;Swanson et al, 2012;Smaers and Soligo, 2013;Symonds et al, 2014], have been used to obtain relative brain size, although phylogenetically corrected methods should always be used (see below; also see Hansen and Bartoszek [2012] for arguments against using RMA regressions in this context). However, several studies have shown that obtaining the residuals from a linear regression to remove the effect of one variable and perform subsequent analysis with these residuals is not appropriate [Darlington and Smulders, 2001;García-Berthou, 2001;Freckleton, 2002].…”

Assessing sources of error in comparative analyses of primate behavior: Intraspecific variation in group size and the social brain hypothesis

“…The effect of ignoring intraspecific variation in comparative analyses has been studied for only a few systems, predominantly relying on simulated rather than actual data (Harmon and Losos, 2005; Ives et al, 2007; Felsenstein, 2008; Hansen and Bartoszek, 2012). Researchers have only recently begun to assess intraspecific variation in a comparative context (e.g., Kamilar and Baden, 2014; Pap et al, 2015). …”

“…In chimpanzees, for example, communities range in size from approximately 20 to 200 individuals (e.g., Wilson et al, 2014), yet in one widely cited paper analyzing the relationship between neocortex size and group size, this variability is collapsed into a single value, 53.5 (Dunbar, 1992). While a species mean may accurately reflect the situation in solitary and socially monogamous primates where the only source of variation in “group” size is due to offspring being born and dispersing at maturity, a species mean is likely to conceal biologically meaningful variation for primates living in larger social groups (Kamilar and Baden, 2014; Patterson et al, 2014). …”