Group size elicits specific physiological response in herbivores

Abstract

).With increasing group size, individuals commonly spend less time standing head-up (scanning) and more time feeding. In small groups, a higher predation risk is likely to increase stress, which will be reflected by behavioural and endocrine responses. However, without any predator cues, we ask how the predation risk is actually processed by animals as group size decreases. We hypothesize that group size on its own acts as a stressor. We studied undisturbed groups of sheep under controlled pasture conditions, and measured in situ the cortisol and vigilance responses of identified individuals in groups ranging from 2 to 100 sheep. Both vigilance and average cortisol concentration decreased as group size increased. However, the cortisol response varied markedly among individuals in small groups, resulting in a lack of correlation between cortisol and vigilance responses. Further experiments are required to explore the mechanisms that underlie both the decay and the convergence of individual stress in larger groups, and whether these mechanisms promote adaptive anti-predator responses.

Mitigates The Negative Behavioral Effects Of Rut Season In Camels: - Group Size

“…While, this data was disagreed with previous finding of Faerevik et al (2007) and Sabek et al, (2017) who find not significantly effect of group size on growth parameters. Table (3) showed that, there are a significant decrease in cortisol level with the group size increasing this data was in agreement with previous work of Michelena et al (2012) who reported that, cortisol concentration in sheep decreased as a group size increased. While, it disagreed with finding of Veissier et al (1998); Abdelfattah et al, (2013); Ahmed et al, 2017and Sabek et al (2017) who reported that, group size did not alter circulating cortisol.…”

“…This result disagrees with Telezhenko et al (2012) as well as Hesham and Mohamed (2013) found that, group size had no effect on movement; Michelena et al (2012) who reported that, with increasing group size, individuals commonly spend less time standing and moving respectively.…”

Costs and benefits of group living in primates: an energetic perspective

“…B 372: 20160239 of these studies found that individuals in larger groups have higher glucocorticoid concentrations relative to individuals in smaller groups (meadow voles [131]; African elephants [132]; cliff swallows [133]; American red squirrels [134]; rhesus monkeys [135]; king penguins [136]; see also review [137]). By contrast, other studies have found that individuals in smaller groups had higher glucocorticoid concentrations (sheep [138]; prairie voles [139]). Two other studies found that intermediate group size was optimal (yellow baboons [78]; ring-tailed lemurs [140]).…”

One size fits all? Relationships among group size, health, and ecology indicate a lack of an optimal group size in a wild lemur population

“…Studies on group size effects on glucocorticoid output yielded a heterogeneous pattern across taxa, including primates, rodents, ungulates, and birds. While the majority of studies found a positive correlation between GC secretion and group size (Foley et al 2001;Raouf et al 2006;Dantzer et al 2013;Dettmer et al 2014), there were also studies reporting opposite findings (Michelena et al 2012;Blondel et al 2016), or no link (Snaith et al 2008;Ebensperger et al 2011). In principle, both, larger and smaller groups inflict energetic costs on individuals based on resource competition and predation risks (Chapman and Chapman 2000), which in turn may cause elevated GC concentrations.…”