Interspecific variation in reproductive and foraging traits for raptors breeding in Norway
Arctic and boreal raptor communities are likely to be affected by borealization and other climate change related processes, providing a challenge for ecologists interested in predicting future community structure. However, by combining community assembly theory and species traits, we may be able to better predict future communities. In this study, we analyzed reproductive traits and interspecific variation within those traits and relate it to diet specialization for 29 raptor species breeding in Norway, together with two skua species and three corvid species used for comparative taxa. We also examined published functional response parameters and used specialization related foraging parameters in an illustrative predator-prey model. Specialist raptors produced larger mean clutch sizes and wider reported clutch size ranges than generalists. Specialists also had a higher proportion of fledged per clutch, but the difference was not statistically significant. These results suggest a relationship between diet specialization and reproductive traits which were also observed within phylogenetic orders. Specialist owls (Strigiformes) produced higher clutch sizes with a larger clutch range compared to generalist owls. The same pattern was observed for falcons (Falconiformes). No clear difference in reproduction was observed for specialist and generalist hawks, kites and eagles (Accipitriformes). Corvids expressed clutch sizes similar to that of specialist raptors while having the lowest proportion of fledged per clutch. Differences in foraging traits between specialists and generalists could be distinguished using functional response curves. In the modeled scenarios, a generalist with lower foraging efficiency could coexist with a resident specialist when it had access to prey unavailable to the specialist. The combined empirical and theoretical findings in this study suggest that diet specialization is associated with reproductive traits and may influence the conditions under which predator species invade and coexist.