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Abstract
Social life involves costs and benefits mostly associated with how individuals interact
with each other. The formation of hierarchies inside social groups has evolved as
a common strategy to avoid high costs stemming from social interactions. Hierarchical
relationships seem to be associated with different features such as body size, body
condition and/or age, which determine dominance ability ('prior attributes' hypothesis).
In contrast, the 'social dynamic' hypothesis suggests that an initial social context
is a determinant in the formation of the hierarchy, more so than specific individual
attributes. Hierarchical rank places individuals in higher positions, which presumably
increases resource accessibility to their benefit, including opportunities for reproduction.
We evaluate the maintenance of hierarchy in a family group of guanacos (Lama guanicoe)
and evaluate the possible mechanisms involved in the stability of these interactions
and their consequences. We estimate the linearity of social hierarchy and their dynamics.
We find evidence of the formation of a highly linear hierarchy among females with
males positioned at the bottom of the hierarchy. This hierarchy is not affected by
physical characteristics or age, suggesting that it is established only through intra-group
interactions. Rank is not related with calves' weight gain either; however, subordinated
females, with lower rank, exhibit higher rates of allosuckling. We found no evidence
of hierarchical structure in calves suggesting that hierarchical relationship in guanacos
could be established during the formation of the family group. Hence, our results
suggest that hierarchical dynamics could be related more to social dynamics than to
prior attributes. We finally discuss the importance of hierarchies established by
dominance and their role in minimizing social costs of interactions.