One size fits all? Relationships among group size, health, and ecology indicate a lack of an optimal group size in a wild lemur population
Rudolph, Katja ; Fichtel, Claudia ; Schneider, Dominik ; Heistermann, Michael ; Koch, Flávia ; Daniel, Rolf ; Kappeler, Peter M.
Citable Link (URL):http://resolver.sub.uni-goettingen.de/purl?gs-1/16408
Journal Article (Published version)
Group size is a key component of sociality and can affect individual health and fitness. However, proximate links explaining this relationship remain poorly understood, partly because previous studies neglected potential confounding effects of ecological factors. Here, we correlated group size with various measures of health while controlling for measures of seasonality and habitat quality, to explore trade-offs related to group living in a mainly folivorous primate—Verreaux’s sifakas (Propithecus verreauxi). Over a course of 2 years, we studied 42 individuals of 7 differently sized groups (range 2–10) and combined measures of faecal glucocorticoid metabolites (n > 2300 samples), parasitism (n > 500 samples), ranging and activity patterns, together with estimates of habitat quality (measures of ~ 7000 feeding trees). None of our measures was correlated with group size, while seasonality, but not habitat quality, impacted almost all examined variables. We conclude that group size alone might be insufficient to explain patterns in the sociality-health nexus or that the small range of group sizes in this species does not induce effects suggested for species living in larger groups. An optimal group size balancing the advantages and disadvantages of living in differently sized groups may not exist for Verreaux’s sifakas. Our results do not support predictions of the ecological constraints hypothesis or the optimal group size hypothesis as they may only account for species limited in group size by ecological factors—a condition that may not apply to the majority of folivorous mammals, which seem to be limited by social factors.