Fish fauna disassembly after the introduction of a voracious predator: main drivers and the role of the invader’s demography

Abstract

The introduction of Cichla kelberi to the Rosana Reservoir (Parana River basin, Brazil) was followed by a substantial loss of fish diversity in macrophyte patches, and this study investigated the hypothesis that C. kelberi was the driver of faunal disassembly via certain demographic dynamics (i.e. a pulse of juvenile fish). We analysed the variation in the structure of fish assemblages, the abundance of C. kelberi and habitat quality between 2003 and 2007, including time points that preceded and followed the introduction of the predator. A stepwise regression analysis showed that macrophyte biomass was positively correlated with assemblage attributes (richness and abundance), whereas C. kelberi density showed a strong negative correlation. Variables related to habitat quality were not included in the model, and exhibited little variation over the study years. As predicted, the density of small-bodied fish was negatively associated with the pulse of juvenile C. kelberi, and a tethering experiment revealed that predation pressure increased in the macrophyte patches when young C. kelberi were abundant. This study therefore obtained strong evidence supporting the hypotheses that C. kelberi caused the fish fauna disassembly and that the predator’s demography was the driver underlying the diversity loss.