Characterizing the trophic niche of non-native psedorasbora parva and the consequences for native fish communities.

Abstract

Introductions of non–native fish can be a key driver of environmental change that has major implications for biodiversity and ecosystem functioning, including the adverse consequences of increased inter-specific competition for native fishes. Here, the consequences of an introduction of a model non-native fish on the trophic position and trophic niche size of native fishes were investigated, along with assessment of the mechanisms of resource partitioning or sharing between the co-existing species. The model non-native fish was topmouth gudgeon Pseudorasbora parva, a highly invasive fish in Europe that originates from Southeast Asia. The study was completed over three spatial scales: experimental mesocosms over 100 days, small and established aquaculture ponds where P. parva had co-existed with native species for approximately 8 years, and wild ponds colonized by P. parva. Given difficulties in using stomach contents analysis for small cyprinid fishes, stable isotope analysis (13C and 15N) was used to determine the effects of P. parva on the trophic ecology of co-existing fishes. The experimental mesocosms used P. parva and three native fishes in allopatric and sympatric contexts. At the end of the 100 day period, in all cases it was revealed that there was strong trophic niche divergence between P. parva and the sympatric native fishes, with no evidence of food resource sharing, and with P. parva always feeding at a significantly lower trophic level. For all species, trophic niche sizes were reduced in sympatry when compared with allopatric contexts. This pattern was also observed in the small aquaculture ponds, with strong divergence between P. parva and all co-existing species, with no sharing of food resources between species, and with P. parva again always feeding at lower trophic levels than the native fishes. In four wild fish communities, the situation was more complex, as P. parva was present in multispecies communities that also contained other non-native fishes. In these communities, there was some evidence of trophic niche overlap between P. parva and the other fishes, although the extent of this was always low. Moreover, P. parva tended to have a limited trophic niche breadth compared with the other fishes, with little evidence suggesting P. parva was strongly influencing food web structure and the feeding relationships of the other species. In entirety, these outputs suggest that introductions of P. parva rarely compete directly with native fishes for food resources, with trophic niche divergence more evident. This suggests that following P. parva introduction, their consequent resource partitioning with native fishes avoids the adverse consequences of interspecific competition, promoting their co-existence in the community. Given that current risk assessments for P. parva tend to indicate high risks to native fishes due to impacts including the adverse consequences of inter-specific competition, then these outputs might have important implications for their risk management.