Experimental analysis testing resource use competition between native and invasive species of omnivorous fish

Abstract

Biological invasions are a major threat to biodiversity. Their implications in freshwater ecosystems are linked to reductions in biodiversity, economic problems, ecosystem degradation, predation and competition with native species. Invasive species of poeciliid fishes are known as good invader due to a variety of characteristics which allow their establishment in new environments. Guppies (Poecilia reticulata), generalist and omnivorous fishes from Central America, became widespread around the world due to their use for mosquito control and the aquarium trade. They can sometimes reach very high densities in the invaded habitat, but their impact on phylogenetically close species (e.g. native poeciliids) is unknown. Our aim in this study is to understand, using laboratory and mesocosm experiments if guppies and a native species of poeciliid in Brazil (Phallocerosharpagos) compete for resources. To compare the efficiency in resource use, we tested the consumption and attack rates of both species in aquarium experiments. Mesocosms experiments - long and short duration - with species alone and together were performed to analyze the resource competition between them by gut content analysis. Our results showed that the native species had similar attack rates and higher consumption rates when compared to the invasive species. In the long-term experiment, the native species consumed fewer larvae when were together with the invasive. When we lived fishes for a shorter time in the experiment, there were no significant differences between species and treatments. The individual variation analysis shows us a small variability between species, while species in both treatments show high variability within them. With these results we cannot observe robust evidence that guppies are superior competitors for diet resources when they co-occur with native species, nor their high efficiency in the consumption of invertebrates as an invasive species