INTRA- AND INTER-POPULATION VARIABILITY OF FOOD PREFERENCES OF TWO NATRIX SPECIES ON THE BALKAN PENINSULA

In aquatic and surrounding terrestrial ecosystems, snakes of the genus Natrix are among the top predators, feeding predominantly on fishes and amphibians, but also on other reptiles and small mammals. In the diets of Natrix natrix and N. tessellata, preferred food items vary geographically and during ontogeny. To understand these variations, we collected data on their diet composition in several habitats (river, wetlands, and two types of lakes), some of which are under severe anthropogenic pressures. Both Natrix species were able to quickly adapt to changes in available prey, and to feed even on non-indigenous, invasive, and potentially hazardous fish. Disturbed ecosystems are particularly susceptible to invasions. Therefore, if alien fishes become dominant, they may threaten populations of native snakes. On the other hand, semi-aquatic snakes can contribute to natural regulation of alien fish species abundance. The preliminary results presented herein emphasize the urgent need for integrative studies of natricine snakes and their prey ecology under various and/or dynamic circumstances. Better understanding of the functioning of different aquatic ecosystems may enable proper conservation and restoration for these snake species and their habitats.