Abstract:
Predation is an ecologically important process, and intra-guild interactions may
substantially influence the ecological effects of predator species. Despite a rapid expansion
in the use of mathematical graph theory to describe trophic relations, network approaches
have rarely been used to study interactions within predator assemblages. Assemblages of
diurnal raptors are subject to substantial intra and interspecific competition. Here we used
the novel approach of applying analyses based on network topology to species-specific
data on the stable isotopes 13C and 15N in feathers to evaluate patterns of relative resource
utilization within a guild of diurnal raptors in northern Sweden. Our guild consisted of the
golden eagle (Aquila chrysaetos), the gyrfalcon (Falco rusticolus), the peregrine falcon
(Falco peregrinus) and the rough-legged buzzard (Buteo lagopus). We found a modular
trophic interaction structure within the guild, but the interactions were less nested than
expected by chance. These results suggest low redundancy and hence a strong ecological
importance of individual species. Our data also suggested that species were less connected
through intra-guild interactions than expected by chance. We interpret our results as a
convergence on specific isotope niches, and that body size and different hunting behaviour
may mediate competition within these niches. We finally highlight that generalist predators
could be ecologically important by linking specialist predator species with disparate
dietary niches.
