Group Sizes of Wolves Hunting Bison | MacNulty, Tallian, Stahler , Smith (2014)

Human organizations may learn from wolves, with groups of 2 to 6 taking down elk, and cooperative expert groups of 9 to 13+ taking down larger bison. #DanielMacNulty, #AimeeTallian #DanielRStahler #DouglasWSmith (2014).

Abstract: [….] Whereas improvement in elk capture success levelled off at 2–6 wolves, bison capture success levelled off at 9–13 wolves with evidence that it continued to increase beyond 13 wolves. These results are consistent with the hypothesis that hunters in large groups are more cooperative when hunting more formidable prey. Improved ability to capture formidable prey could therefore promote the formation and maintenance of large predator groups, particularly among predators that specialize on such prey.

Group-size specific success of wolves hunting bison

The influence of group size on the success of wolves attacking and capturing bison was not linear (Fig. 2). The top models of attacking and capturing included a linear spline for group size (Table S1), indicating a threshold at which the effect of group size on hunting success suddenly changed. [….]

Figure 2. Effects of hunting group size on the probability that wolves attack (a) and capture (b), bison.

The threshold group size was smaller for attacking than for capturing. The confidence set of spline models for each predatory task (Table S1) indicates the threshold group size was 3–6 wolves for attacking and 9–13 wolves for capturing. The most parsimonious models in the set included thresholds at 4 and 11 wolves for attacking and capturing, respectively (Fig. 2a–b). […]

Comparative effects of group size on the success of wolves hunting bison and elk

… attack and capture success were effectively constant beyond each threshold. Below these thresholds, each additional wolf had a slightly larger effect on the odds of attacking bison (OR  = 1.67) versus elk (OR  = 1.45; Fig. 3a) but a similar effect on the odds of capturing each species (bison: OR  = 1.40; elk: OR  = 1.44; Fig. 3b).

Figure 3. Comparative effects of group size on the success of wolves attacking (a) and capturing (b) bison and elk.

Whereas the threshold group size of wolves attacking bison and elk was the same (4 wolves; Fig. 3a), the threshold group size of wolves capturing bison (11 wolves) was nearly 3 times larger than that of wolves capturing elk (4 wolves; Fig. 3b).

Source: MacNulty DR, Tallian A, Stahler DR, Smith DW (2014) Influence of Group Size on the Success of Wolves Hunting Bison. PLoS ONE 9(11): e112884. https://doi.org/10.1371/journal.pone.0112884

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