RESUMO
The investigation of ecological processes that maintain species coexistence is revealing in naturally disturbed environments such as the white-sand tropical forest, which is subject to periodic flooding that might pose strong habitat filtering to tree species. Congeneric species are a good model to investigate the relative importance of ecological processes that maintain high species diversity because they tend to exploit the same limiting resources and/or have similar tolerance limits to the same environmental conditions due to their close phylogenetic relationship. We aim to find evidence for the action and relative importance of different processes hypothesized to maintain species coexistence in a white-sand flooded forest in Brazil, taking advantage of data on the detailed spatial structure of populations of congeneric species. Individuals of three Myrcia species were tagged, mapped, and measured for diameter at soil height in a 1-ha plot. We also sampled seven environmental variables in the plot. We employed several spatial point process models to investigate the possible action of habitat filtering, interspecific competition, and dispersal limitation. Habitat filtering was the most important process driving the local distribution of the three Myrcia species, as they showed associations, albeit of different strength, to environmental variables related to flooding. We did not detect spatial patterns, such as spatial segregation and smaller size of nearby neighbors, that would be consistent with interspecific competition among the three congeneric species and other co-occurring species. Even though congeners were spatially independent, they responded to differences in the environment. Last, dispersal limitation only led to spatial associations of different size classes for one of the species. Given that white-sand flooded forests are highly threatened in Brazil, the preservation of their different habitats is of utmost importance to the maintenance of high species richness, as flooding drives the distribution of species in the community.
RESUMO
Resource partitioning allows for interspecific coexistence and is frequently reported for similar species. Here, we predicted the existence of resource partitioning among species of Astyanax that co-occur in the Low Iguaçu River and tributaries in Brazil. A total of 848 stomachs of five species of Astyanax were analyzed. Algae, terrestrial plant and fruit/seed were the most consumed resources. Astyanax bifasciatus and A. dissimilis had predominantly herbivorous diets, A. gymnodontus and A. lacustris were omnivorous, and A. minor was mainly algivorous. Permutational analysis of variance showed the species had different diets, and similarity percentage analysis indicated that fruit/seed and terrestrial plant contributed the most to this differentiation. A paired comparison indicated that the trophic breadth of A. gymnodontus differed from that of other species. The food overlap was low for 55% of Astyanax pairs. These results showed alignment with the niche theory, in which differentiation in the use of food resources facilitates the coexistence of species and minimizes competition. These adjustments to coexistence become relevant in the context of endemic species in a highly isolated basin under intense threat (dams, species introduction, deforestation, and pollution) as is the case for the Iguaçu River basin.(AU)
O particionamento de recursos permite a coexistência interespecífica e é frequentemente relatado para espécies semelhantes. Predizemos a existência de partição de recursos entre espécies de Astyanax que co-ocorrem no baixo rio Iguaçu. O total de 848 estômagos de cinco espécies de Astyanax foi analisado. Algas, plantas terrestres e frutos/sementes foram os recursos mais consumidos. Astyanax bifasciatus e A. dissimilis apresentaram dietas predominantemente herbívoras, A. gymnodontus e A. lacustris foram onívoras e A. minor foi principalmente algívora. As espécies apresentaram diferentes dietas (PERMANOVA) e a análise SIMPER indicou que frutos/sementes e plantas terrestres tiveram maior contribuição para esta diferenciação. A comparação pareada mostrou que a amplitude trófica de A. gymnodontus diferiu das outras espécies. A sobreposição alimentar foi baixa para 55% dos pares de Astyanax. Nossos resultados mostraram-se alinhados com a teoria de nicho, em que a diferenciação no uso de recursos alimentares facilita a coexistência de espécies e minimiza a competição. Estes ajustes para coexistência tornam-se relevantes no contexto de espécies endêmicas em uma bacia altamente isolada e sob intensa ameaça (barramentos, introdução de espécies, desmatamento e poluição), como é o caso da bacia do rio Iguaçu.(AU)
Assuntos
Animais , Dieta/veterinária , Caraciformes/fisiologiaRESUMO
Resource partitioning allows for interspecific coexistence and is frequently reported for similar species. Here, we predicted the existence of resource partitioning among species of Astyanax that co-occur in the Low Iguaçu River and tributaries in Brazil. A total of 848 stomachs of five species of Astyanax were analyzed. Algae, terrestrial plant and fruit/seed were the most consumed resources. Astyanax bifasciatus and A. dissimilis had predominantly herbivorous diets, A. gymnodontus and A. lacustris were omnivorous, and A. minor was mainly algivorous. Permutational analysis of variance showed the species had different diets, and similarity percentage analysis indicated that fruit/seed and terrestrial plant contributed the most to this differentiation. A paired comparison indicated that the trophic breadth of A. gymnodontus differed from that of other species. The food overlap was low for 55% of Astyanax pairs. These results showed alignment with the niche theory, in which differentiation in the use of food resources facilitates the coexistence of species and minimizes competition. These adjustments to coexistence become relevant in the context of endemic species in a highly isolated basin under intense threat (dams, species introduction, deforestation, and pollution) as is the case for the Iguaçu River basin.(AU)
O particionamento de recursos permite a coexistência interespecífica e é frequentemente relatado para espécies semelhantes. Predizemos a existência de partição de recursos entre espécies de Astyanax que co-ocorrem no baixo rio Iguaçu. O total de 848 estômagos de cinco espécies de Astyanax foi analisado. Algas, plantas terrestres e frutos/sementes foram os recursos mais consumidos. Astyanax bifasciatus e A. dissimilis apresentaram dietas predominantemente herbívoras, A. gymnodontus e A. lacustris foram onívoras e A. minor foi principalmente algívora. As espécies apresentaram diferentes dietas (PERMANOVA) e a análise SIMPER indicou que frutos/sementes e plantas terrestres tiveram maior contribuição para esta diferenciação. A comparação pareada mostrou que a amplitude trófica de A. gymnodontus diferiu das outras espécies. A sobreposição alimentar foi baixa para 55% dos pares de Astyanax. Nossos resultados mostraram-se alinhados com a teoria de nicho, em que a diferenciação no uso de recursos alimentares facilita a coexistência de espécies e minimiza a competição. Estes ajustes para coexistência tornam-se relevantes no contexto de espécies endêmicas em uma bacia altamente isolada e sob intensa ameaça (barramentos, introdução de espécies, desmatamento e poluição), como é o caso da bacia do rio Iguaçu.(AU)