Being “hangry”: food depletion and its cascading effects on social behaviour

Abstract

Evolutionary theory suggests two alternative ways in which competitive interactions could vary in response to different levels of food abundance. Competition theory suggests that aggression should be greater when resource availability is lower, as an evolutionary stable strategy to access food. Alternatively, energy allocated to aggressive interactions should increase when the available spectrum of food resources is wider, in turn allowing a greater selec-tion. We tested these hypotheses on a group-living herbivore, the Apennine chamois, Rupicapra pyrenaica ornata. We compared social, aggressive and vigilance behaviour and relevant endocrine correlates across three areas: two 'poorer' areas, i.e. with a lower availability of nutritious pasture, and a 'richer' one. In the richer area, we observed: (1) the largest group size/greatest proportion of young individuals in groups; (2) the lowest rate/intensity of aggression between individuals, at feeding; (3) the lowest duration of vigilance and proportion of 'costly' vigilance, i.e. postures performed without chewing food; and (4) the lowest levels of testosterone and cortisol metabolites, suggesting a lower endogenous aggressiveness/stress response. Our findings agree with the competition theory, suggesting a role of food depletion in increasing aggression between foraging individuals, as an evolutionary stable strategy, with cascading effects on group phenology, vigilance and stress.

To scan or not to scan? Occurrence of the group‐size effect in a seasonally nongregarious forager

“…Overall, our findings seem to militate against an effect of interference on vigilance. This is in apparent contrast to what has been reported for many gregarious species in which social monitoring of competitors triggers alert behaviour (birds: Ely, ; McKinstry & Knight, ; Goss‐Custard et al, ; mammals: Favreau et al, ; Fattorini, Brunetti et al, ; Pecorella et al, ). The difference could be related to the small number of individuals in roe deer groups (maximum six individuals; Supporting Information Figure S1): few competitors may be tolerated, if the increase in collective vigilance within a group provides individual feeding benefits (cf.…”

“…Accordingly, we found a decrease in both time in vigilance and vigilance rate—along with an increase in time spent foraging—with increasing group size of roe deer. Either an absence or a reversal of the group‐size effect is expected in individuals belonging to sex/age classes involved in agonistic interactions, for example because of feeding/mating interference (birds: McKinstry & Knight, ; Goss‐Custard et al, ; mammals: Fattorini, Brunetti et al, ; Pecorella, Fattorini, Macchi, & Ferretti, ). Unlike females (but see Roviani, ), roe deer males are territorial from late winter to mid‐summer and show aggressive behaviours to conspecifics (reviewed in Liberg et al, ); dominance hierarchies have been reported in winter, through aggressive interactions within roe deer groups (Espmark, ).…”

Development and Implementation of Baseline Welfare Assessment Protocol for Captive Breeding of Wild Ungulate—Punjab Urial (Ovis vignei punjabiensis, Lydekker 1913)

“…In our study, we found that animals in CU3 showed the highest aggression (66.59%), followed by CU1 (43.64%) and CU2 (37.75%). We assumed that the higher aggression in CU3 was due to the presence of other species [52]. Punjab urial males were frequently observed chasing chinkara, showing comparatively less aggression toward mouflon sheep.…”

Male aggressiveness in a polygynous ungulate varies with social and ecological context

“…Alternatively, the energy allocated to aggressive interactions could increase with the value of a disputed resource (Enquist et al, 1985;Geist, 1978;Parker, 1974). Accordingly, individuals could invest more in body growth (e.g.…”

“…First, because of the mating system and reproductive seasonality in migratory guanaco populations (Franklin, 1982(Franklin, , 1983Young & Franklin, 2004a), we expected that the probability and frequency of aggressive interactions between male guanacos would peak during the mating period (Prediction I) and would be higher in males from family groups because of the behaviour's reproductive significance (Prediction II). Second, because resource-defence ungulates fight for territories which contain attractive food resources for females (Emlen & Oring, 1977;Franklin, 1983;Young & Franklin, 2004a, 2004b, we expected that the presence and the frequency of aggressive interactions in territorial males (family groups and solitary males) would be higher in areas of greater forage quality and productivity (Prediction III), given that territorial males can invest more energy in aggressive interactions where resources are higher (Enquist et al, 1985;Geist, 1978;Parker, 1974) and that they also have priority access to females and mating. Finally, because non-territorial males (bachelors and mixed groups) do not engage in reproduction, we expect that aggression in these social units will be linked to food resources (Fattorini, et al, 2018;Sirot, 2000) and will be higher in areas of lower forage quality and productivity due to increased competition (Prediction IV).…”