FEEDING RELATIONSHIPS AND COMPETITIVE INTERACTIONS BETWEEN PHYLOGENETICALLY UNRELATED PREDATORS (OWLS AND SNAKES)

Feeding relationships between sympatric owls (Athene noctua, Strix alu co, Asio otus and Tyto alba) and snakes (Vipera aspis, Coluber viridif lavus, Elaphe longissima, and Elaphe quatuorlineata) were studied in a n agro-forest landscape of central Italy, province of Rome. The availa bility of small mammals in four different environmental types was also investigated by means of live-trapping and mark-and-recapture procedu res. All snakes fed primarily on small mammals and lizards, whereas ow ls preyed essentially upon small mammals. A. noctua was also largely i nsectivorous. In general, diet composition of phylogenetically unrelat ed predators was similar (as shown by relatively high overlap estimate s), and several prey taxa were eaten by all predators (including both owls and snakes). However, (i) interphyletic comparisons and (ii) mult ivariate statistical procedures revealed some interesting differences in predator diet composition. Owls were found to prey mainly upon smal l mammal taxa from semicultivated open grassy habitats, whereas snakes did so upon forest-associated small mammals. Correlation analyses con firmed this evidence. The potential for competition for food seems to be higher between phylogenetically related than between phylogenetical ly unrelated taxa, due to separation among groups in frequented macroh abitat and, possibly, also to daily activity rhythms. Food niche parti tioning was more evident among owls than among snakes, in agreement wi th the fact that snakes, contrary to owls, are low-energy organisms th at can survive on limited food resources.