Mechanisms of coexistence in a diverse Neotropical mammalian carnivore community

Abstract

Mammalian carnivore diversity within the Reserva Natural del Bosque Mbaracayú in eastern Paraguay is represented by five families (Canidae, Mephitidae, Mustelidae, Procyonidae, and Felidae) and includes large-bodied, apex predators, several omnivores, and numerous mesocarnivores. The competitive exclusion principle argues that sustained spatial and temporal coexistence of two or more species with identical ecological requirements is unsustainable. The Reserve is a mosaic of habitats that has become isolated due to extensive deforestation of the surrounding Upper Paraná Atlantic Forest. Nevertheless, it is remarkable in that 16 mammalian carnivore species are documented as coexisting within the Reserve. We sought to determine the extent to which this diverse community is mitigating competition through the partitioning of available niche space by assessing dietary ecology of mammalian carnivores present, including diet breadths and dietary overlap, and by examining spatial patterns within the reserve. Feces were collected from all 16 mammalian carnivore species from seven areas within the reserve and specific identifications were confirmed by molecular analyses. Diet breadth, B^, standardized diet breadth, B^A, and Pianka's Index for dietary overlap, O^, were calculated. A Chi-square goodness-of-fit test was performed to test for randomness of samples associated with survey areas. Diet analyses indicated a spectrum from dietary generalists to specialists. Species segregated into six dietary guilds, defined as groups of species with O^ > 0.5. Four guilds included only one species each (Neotropical otter, crab-eating fox, jaguar, and puma). The low dietary overlap between jaguar and puma contrasts with studies conducted elsewhere. One guild consisted of four highly omnivorous species (maned wolf, Molina's hog-nosed skunk, crab-eating raccoon, and South American coati). The sixth guild included eight species which mostly consumed small vertebrates, primarily mammals as well as birds and reptiles (bush dog, two mustelines, five small felids). The mustelines (tayra and lesser grison) had extremely high dietary overlap. Although they did not segregate spatially, they are known to occupy distinct niches in vertically stratified forests. The five small felids also showed extremely high dietary overlap. Three of them were found to segregate spatially within the Reserve and two did not, although one (jaguarundi) is known to segregate temporally, being more active diurnally. The exceptionally rich community of mammalian carnivore species at the Reserva Natural del Bosque Mbaracayú appeared to avoid unsustainable competition by a variety of mechanisms, some utilizing different food items, or, in the case of high dietary overlap, utilizing spatial or temporal resources differently.