Native top-predator cannot eradicate an invasive fish from small pond ecosystems

Pumpkinseed (Lepomis gibbosus) originates from North America and has been widely introduced in Europe where invasive populations have established. We tested the effectiveness of a biomanipulation approach based on the stocking of a native top-predatory species, the northern pike (Esox lucius), in 23 small and oligotrophic ponds at the Pinail Nature Reserve (Vienne, France) among which 10 ponds were stocked twice. In addition, 16 ponds with similar environmental characteristics were used as control with no pike stocking. Our study revealed that, even with limited space and limited alternative prey species, northern pike did not eradicate pumpkinseed populations. Instead, we found that pumpkinseed were younger and larger when reaching sexual maturity in the stocked ponds, suggesting an increased growth rate in ponds with the predator. These results suggest that invasion populations might adapt and respond to management practices. These changes were likely driven by an adaptation to predation pressure and/or changes in food availability with reduced intraspecific competition. Importantly, such changes might actually modify the level of invasiveness potential of non-native populations and lead to counterproductive results for managers.