Spatial scales and the invasion paradox: a test using fish assemblages in a Neotropical floodplain

Abstract

The invasion paradox refers to the existence of biotic resistance and biotic acceptance hypotheses. According to the biotic resistance hypothesis, the higher the richness present in a community, the more resistant it is against invaders. In contrast, the biotic acceptance hypothesis states that if the environment is suitable for a high richness of native species, it will be similarly suitable for establishment of non-native species. Previous studies on terrestrial plant communities considered the scale-dependent nature of native and non-native relationships: the relationship tends to be negative at small scales (biotic resistance) and positive at broader scales (biotic acceptance). We tested the hypothesized role of spatial scale on the relationship between non-native and native species richness using a spatially nested design and a long-term dataset (146 communities sampled during 13 years) of fish species richness from the upper Parana River floodplain, Brazil. Contrary to expectations, non-native fish species richness was positively correlated with native species richness at all spatial scales. Mobility of vertebrates, mode of invasion, and environmental disturbance may affect the role of spatial scale in potentially mediating relative importance of biotic acceptance versus resistance. In this context, the present study provides a unique contribution towards resolving the invasion paradox.