Predicting the competitive interactions and trophic niche consequences of a globally invasive fish with threatened native species

1. Novel trophic interactions between invasive and native species potentially increase levels of inter-specific competition in the receiving environment. However, theory on the trophic impacts of invasive fauna on native competitors is ambiguous, as while increased inter-specific competition can result in the species having constricted and diverged trophic niches, the species might instead increase their niche sizes, especially in omnivorous species.

2. The competitive interactions between an omnivorous invasive fish, common carp Cyprinus carpio, and a tropically analogous native and threatened fish, crucian carp Carassius carassius, were tested using comparative functional responses (CFRs). A natural pond experiment then presented the species in allopatry and sympatry, determining the changes in their trophic (isotopic) niche sizes and positions over four years. These predictive approaches were complemented by assessing their trophic relationships in wild populations.

3. CFRs rev...