Temperature-dependent feeding interactions between two invasive fishes competing through interference and exploitation

Context-dependent ecological interactions between invasive species are important in determining the outcomes of their introductions. The consequences of competitive interactions between the Nile tilapia Oreochromis niloticus (interference competitor) and common carp Cyprinus carpio (exploitative competitor) were investigated here across a temperature gradient (20–28°C). These highly invasive fish are now present in many regions where populations increasingly coexist, inducing trophic interactions and niche overlaps. Experimental feeding and growth trials revealed the feeding rate (items s−1) and specific growth rate (% day−1) of these fishes were not significantly different at 24°C, but were significantly higher for C. carpio at 20°C and significantly higher for O. niloticus at 28°C. An additional experiment completed at 24°C revealed that O. niloticus rapidly form hierarchies, where dominant fish monopolise food resources through interference, resulting in their faster growth. Introductions of 1 and 3 C. carpio (an exploitative competitor) into the hierarchy had no effect on this food monopolisation as carp were excluded through aggression. The addition of 6 C. carpio did, however, significantly reduce the food intake of the dominant tilapia. This was due to increased exploitative competition rather than breaking of the hierarchy. The effect of adding 3 O. niloticus was similar to 6 C. carpio, suggesting inter- and intra-specific competitive strength was similar. These findings suggest when populations co-exist, temperature-dependent feeding interactions may result in the competitive exclusion of C. carpio through the aggressive interference by O. niloticus, potentially influencing invasion outcomes.