Cooperation, leadership and numerical assessment of opponents in conflicts between groups of feral dogs (Canis lupus familiaris)

Abstract

This thesis attempted to assess the adaptive value of the behaviour of feral dogs (Canis lupus familiaris) by using such species as a model for testing predictions based on evolutionary theories. In particular, the following topics concerning dogs’ behaviour were examined: intergroup agonistic behaviour in relation to numerical assessment of opponents, cooperative behaviour during intergroup conflicts and decision making processes during collective activity changes. The research focused mainly on three dogs packs living in a suburban environment whose members were not socialized to human beings although subsisted mostly on food provided by “volunteer dog caretakers”. Game theoretical arguments predict that in conflicts between social groups competitors should adjust their agonistic behaviour according to the relative size of the interacting groups. In the feral dogs studied, the overall probability of at least one pack member approaching aggressively opponents increased significantly with decreasing the ratio of the number of opponents to that of the present pack members. Moreover, a retreat response by more than half pack members was more likely to be elicited the higher the ratio of the number of opponents to that of the present pack members. However, such a ratio had no significant effect on the aggressive/retreat response of dogs when both the interacting packs comprised more than 4 individuals. A higher asymmetry in size between the interacting packs was actually required to make optimal decisions about the aggressive/retreat response when numbers larger than 4 were involved, but not with smaller numbers. This results suggest that feral dogs are able to assess relative group size and to adjust their agonistic behaviour accordingly. Moreover, two different cognitive mechanisms, one of these based on noisy mental magnitudes, may be involved in such numerical assessment. Social animals need to reach consensus decisions about the nature and timing of group activities in order to maintain group cohesion. Group members which contribute more to the decision outcome are termed leaders. Patterns of distribution of leadership within social groups are expected to be influenced by group size, age, gender and social relationships. In all feral dog packs studied, but the smallest, a limited number of habitual leaders made group decisions about activity changes. In one large pack the number of habitual leaders decreased after such pack underwent a drastic reduction in size. Individuals which behaved more frequently as leaders were those which received active submissions during greeting cerimonies from a higher number of partners. The results are consistent with the view that animal collective movements may result from the need by low-ranking individuals to maintain close proximity with specific valuable social partners. Unravelling factors which promote individual participation in costly cooperative activities may help to explain how cooperation may evolve in animal societies despite the consistent defection of specific individuals. In the feral dogs studied, the individual level of cooperation during intergroup conflicts seemed to decrease with decreasing the difficulty of winning: the proportion of cooperating animals decreased when there were more companions present; the individual probability of cooperating decreased significantly, in one pack, when such pack outnumbered opponents; dogs belonging to the smallest pack tended to be more cooperative than those belonging to larger groups. Such pattern may be consistent with the view that individuals cooperate to maximize individual mutualistic benefits. Contrary to the predictions of the handicap hypothesis, social prestige (measured as the amount of active submissions received) did not correlate with cooperation. The individual level of cooperation was, instead, positivey affected by the number of affiliative partners. In conclusion, the overall results of this thesis suggest that, despite a very long history as domesticated animals, feral dogs may still match some of the predictions based on evolutionary theories.