Behavioural mechanisms of conflict and conflict reduction in a wild breeding polygynous pinniped

Abstract

Aggressive interactions arise as a means of resolving access to resources such as food, habitat or mates, but these interactions are often costly in time, energy, or physical damage. Therefore, natural selection favours social systems, spatial organisations and behavioural mechanisms which can balance the trade-offs between conflict and increasing fitness. The diversity of behaviours associated with animal conflict has been investigated in a variety of species; however, rarely are these investigations done in wild systems or with consideration of geographic and intra-seasonal variation in environmental factors, resource availability or social dynamics.

Therefore, the aim of this thesis was to examine the behavioural mechanisms underpinning population and individual conflict and conflict reduction at a variety of temporal and spatial scales. I focused my investigation on a particular form of animal contest, male-male breeding aggression, and used the colonial, wild grey seal (Halichoerus grypus) as my model. Specifically, I studied males at Donna Nook, an atypical breeding colony, in order to: (1) update our current knowledge of grey seal breeding systems by comparing the behavioural patterns at recently expanding mainland colony to previously examined, offshore colonies, (2) investigate the information present in a geographically isolated behaviour used in male grey seal conflict, (3) identify the variation in assessment strategies used by individuals in grey seal conflict and conflict reduction, (4) examine how environmental, anthropogenic, and social environments shape individual variation in aggression, and (5) assess the individual variation in decision-making processes such as mating strategies within- and across seasons.

Draws were identified as a common conflict outcome for male grey seals, and the acceptance of draws represented a behavioural mechanism which can promote conflict reduction. Assessment strategies relied on individual energetics when costs of conflict were high, but mutual assessment was used in low-cost contexts. Activity budgets were relatively conserved across colonies, and social stability played a key role in mediating conflict. These findings all demonstrate the trade-offs between conserving energy for reproductive activities and expending energy to ensure exploitation of resources. Methodological approaches which accounted for variation in individual partitioning of aggression and reproductive effort within- and between-seasons revealed that the relative importance of dominance as a driver of conflict, the use of specific aggressive behaviours, and broad assessment and mating strategies were all context-dependent at a variety of temporal and spatial scales.

Overall, these findings have provided new insights into the evolution of conflict and conflict reduction within polygynous mating systems. This work highlights the importance of incorporating the natural environmental variation and social dynamics into models of individual behaviours. Such approaches not only reveal the plasticity or consistency in how individuals deal with tradeoffs, but they also allow for observing the importance of behavioural mechanisms such as draws, which might have been ‘artificially selected out’ in controlled, laboratory settings. Finally, by using the grey seal breeding system as a model, this work has contributed to our knowledge of this species’ behavioural repertoire, and the role of topography in the evolution of polygyny and aggression in pinnipeds.