Abstract
ABSTRACT 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.
Highlights
Unlike terrestrial species or those with aerial or winddispersed life stages, species confined to freshwater environments generally cannot disperse from one catchment to another, unless corridors of aquatic habitats exist to connect them (Abell et al, 2008)
The first four species are endemic to the Iguaçu River basin, while A. lacustris is distributed throughout the basin of the Upper Paraná River
Astyanax is known for its opportunistic feeding habits (Lobón-Cerviá, Bennemann, 2000) and the use of different feeding strategies (Abelha et al, 2001, 2006; Mazzoni et al, 2010) that enable the species to forage at almost all trophic levels (Abelha et al, 2006)
Summary
Unlike terrestrial species or those with aerial or winddispersed life stages, species confined to freshwater environments generally cannot disperse from one catchment to another, unless corridors of aquatic habitats exist to connect them (Abell et al, 2008). The connections and disconnections between adjacent river basins have long been recognized as essential for the diversification of freshwater fish in the Americas (Buckup, 2011). The geographic isolation promoted by this natural barrier has led to the occurrence of many endemic species, which represent more than 50% of the fish species in the Iguaçu River basin (Baumgartner et al, 2012). Threats to the integrity of this fish fauna diversity (dams, species introduction, deforestation, and pollution) (Baumgartner et al, 2012), coupled with the high endemism, were recognized by Abell et al (2008), who included this basin as one of the 426 global freshwater ecoregions requiring urgent conservation planning efforts
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