Abstract
The ornamental fish trade is one of the major pathways for freshwater fish invasions, with their co-occurrence increasingly common due to rising numbers of non-native species. This co-occurrence can yield ecological surprises through non-additive trophic effects, which can influence levels of predatory impacts. In freshwaters, biotic interactions are heavily mediated by waterborne chemical cues, which could potentially alter the intensity of impacts from multiple invaders. We adopted the comparative functional response approach to quantify and predict the potential ecological impacts under the exposure of undisturbed conspecific and interspecific odours of two commonly traded exotic ornamental fish species: the convict cichlid Amatitlania nigrofasciata, a species with substantial invasion history worldwide, and the T-bar cichlid Amatitlania sajica , a tropically analogous congener with no invasion history thus far. Both species exhibited a potentially prey population destabilising Type II FR under all cue treatments. However, differential ecological impacts from the two species were mediated by olfactory cues. Specifically, there was no difference in FR between the two species in the conspecific water treatment, while the invasive convict cichlid demonstrated a significantly greater prey consumption rate and shorter handling time in the interspecific condition. These results suggest that the invasive convict cichlid may have an advantage in interspecific exploitative competition over the non-invasive T-bar cichlid, which could lead to greater impact potential on food web dynamics and native species. Nonetheless, the potential ecological impacts of T-bar cichlids should not be underestimated, and their release into non-native habitats alongside other exotic fishes should be strictly prevented. The influence of chemical cues on invader ecological impacts should be increasingly considered in predictive efforts.