Abstract
Birds often compete and engage in interspecific agonistic interactions for access to resources such as food and breeding territories. Based on the observed outcomes from such interactions (i.e., patterns of displacements) dominance hierarchies can be established. Knowing which species can outcompete others for essential resources allows researchers to make predictions about the broader ecological impacts of interspecific interactions. We constructed an interspecific dominance hierarchy of twelve avian species which visited an artificial water source in an arid region of coastal Patagonia, Argentina. Displacements were categorized into four types, based on the behaviors involved in the interaction, and we tested if they could predict the difference in dominance between the interacting species (the difference between calculated dominance coefficients for the two focal species). Indirect displacements, involving only the arrival of the dominant species to the water source without direct aggression toward the subordinate bird, occurred more frequently between species with a large difference in dominance. The most dominant bird observed was the kelp gull (Larus dominicanus), which, due to an increasing population and expanding range, in part due to food supplementation from fisheries waste, is likely to outcompete terrestrial and marine avian species for other scarce resources.
Highlights
Resource scarcity leads to both intra- and interspecific conflict as individuals compete with each other for access by using aggressive behaviors to gain and maintain control of these resources [1, 2]
We observed displacements involving 12 species; the kelp gull was the most dominant species and the mourning sierra-finch was the least dominant species recorded in the ranking (Table 1)
We explored the relationship between the position in the dominance hierarchy and body size and selected the Phylogenetic General Least Square (PGLS) regression considering an Ornstein-Uhlenbeck model of evolution (AIC value: 86.31vs 98.78 for Brownian Motion)
Summary
Resource scarcity leads to both intra- and interspecific conflict as individuals compete with each other for access by using aggressive behaviors to gain and maintain control of these resources [1, 2]. When there is a consistent pattern of aggressive behavior between individuals or different species, a dominance hierarchy that determines resource access is formed [3–6] These hierarchies reduce the frequency of aggressive interactions and the possibility of injury. Food is the limiting resource used most often to study interspecific agonistic interactions and the associated dominance hierarchies [5, 12] Among avian species, it is unclear how other essential resources such as water affect interspecies dominance. Our study takes a nuanced approach by piloting a new methodology that takes variations in the displacement behaviors into account in order to demonstrate that different types of displacements can act as indicators of the relative position of interacting species in the dominance hierarchy This work shows that interspecific dominance hierarchies can be created at a water source in an arid region
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