CONICET | Buscador de Institutos y Recursos Humanos

Understanding the factors underlying species coexistence is a major focus incommunity ecology. When dealing with competition between native and exoticspecies, the competitive exclusion of the weaker species can have consequencesfor biodiversity conservation. We examined interspeciﬁc interactions duringforaging between black vultures Coragyps atratus and Andean condors Vulturgryphus in Southern Argentina. Previous studies suggest facilitatory interactionsbetween them. However, in most parts of their distribution ranges, these speciesdid not coexist until recently, when black vultures expanded their geographic rangefollowing human development. Thus, facilitatory processes or segregation patternscould not be ﬁne-tuned enough to allow their coexistence. Our hypothesis is thatblack vultures and Andean condors compete for food resources, and that thiscompetitive scenario can change depending on local species abundances andhabitat humanization. We experimentally placed sheep carcasses in two habitatsdiffering in degrees of humanization to study the foraging patterns in these species.Both species exploited carcasses with similar temporal patterns. However, the ﬁrstto arrive and the dominant species were different in both habitats, according totheir abundances. Although black vultures do not completely prevent the arrival ofAndean condors to carcasses, they represent serious obstacles for feeding. Thus,while dominance hierarchy at carcasses could be related to body size, carcassconsumption was determined by species abundance. Our results support thehypothesis that the expansion of a winning species may trigger interspeciﬁccompetition with other loser species, with negative responses towards humanactivities when they became abundant. Although the results are not conclusive,invasion and extinction processes could be occurring and they can have seriousconsequences for the diversity (i.e. richness and evenness) of the New Worldscavenger guilds.

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