Efeitos de diferentes intensidades de ocupação aquícola sobre a estrutura taxonômica e funcional de assembleias de peixes em riachos Neotropicais.

Abstract

Biological invasion processes are complex phenomena and comprise one of the greatest challenges for the conservation of biodiversity in continental aquatic environments. The pressure of propagules, i.e., the number of non-native individuals released and the number of release events, is among the different mechanisms involved in these decisive processes for the successful establishment of non-native species. In this scenario, aquaculture is an important source of propagules of species with high invasive potential, such as Nile Tilapia (Oreochromis niloticus), as accidental escapes and intentional releases from production ponds are recurrent. Nine small streams, tributaries of the Piquiri River (Paraná, Brazil), were sampled to evaluate the effect of aquaculture on fish assemblages in neotropical streams. The watersheds of these streams differ in percentage of aquaculture occupation, and this difference was used as a proxy for propagule pressure of O. niloticus in natural environments. Therefore, the present research aimed to evaluate the effects of different intensities of aquaculture production of tilapia on the richness patterns, composition and structure of the ichthyofauna, testing the hypothesis that the increase in propagule pressure of this species alters the patterns of occurrence and abundance of assemblages, as well as discuss the effects of this species on the functional structure of ichthyofauna, observing the effect of aquaculture occupation on responses of functional diversity indexes and on dissimilarity patterns among the different streams. The results indicated that streams with no aquaculture occupation and with no presence of O. Niloticus had more similar compositions and differed in patterns of occurrence and distribution of ichthyofauna from streams under aquaculture activity. In addition, the presence of tilapia altered the functional diversity indexes in the streams, as the species presented more extreme traits that allow it to increase the functional space of receptor environments and promote greater niche differentiation. The results reinforce the potential of aquaculture as an important source of propagules of non-native species for natural environments and raise attention to the structuring power of tilapia on the taxonomic and functional composition of native ichthyofauna.