COMPARISON OF FUNCTIONAL RESPONSES BETWEEN EXOTIC SPECIES LEPISOSTEUS OCULATUS AND NATIVE SPECIES CHANNA MACULATA

Exotic fish garpikes have caused some social panic due to their occurrence in the freshwater lake. As ferocious predators, they have high threats to native fish species and the aquatic ecosystem. However, we know very little about how strong garpikes feed on native fish species, and whether they are different from other native predators in feeding efficiency. Using a manipulative experiment, we studied the functional response of a common garpike, Lepisosteus oculatus on three prey, Cirrhinus molitorella, Megalobrama terminalis, and Ctenopharyngodon idellus. The functional response of L. oculatus was further compared with that of native similar predatory species, Channa maculata. Specifically, we studied the types of functional response, constructed the functional response curves, estimated the parameters representing feeding efficiency. By combining the functional responses and food conversion efficiency, we constructed a mechanistic model to simulate their population developments with time when considering the potential different mortality rates due to intraspecies density dependence. We found that both L. oculatus and C. maculata had Type-Ⅱ functional responses. It was not significantly different in the rate of unit resource consumption between the two species, that is, there was no significant difference neither in the attack rate (P=0.383) nor in the handling time (P=0.663). While the relative growth rate of L. oculatus was higher than that of C. maculata (P<0.05), there was no significant difference in food conversion efficiency between these two species (P=0.132). We also found that L. oculatus had faster population growth and higher stable population density than C. maculata. Collectively, our results indicate that L. oculatus have neither a higher resource consumption rate nor food conversion efficiency than native similar predators. However, we suggest that it is still very necessary to monitor and control this exotic fish in the natural aquatic ecosystem, given that it has no natural enemies, consumes many native fishes, and competes with native predatory fish. Our quantification of functional responses provides a basis for future systematic assessment on the ecological impacts of L. oculatus, and can serve as a reference for assessing resource consumption rate and potential ecological impacts of other exotic fishes.