title: Network topology of stable isotope interactions in a sub-arctic raptor guild.
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 analyzes based on network topology to species-specific data on the stable isotopes (13)C and (15)N 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.
authors.affiliation: Research Unit of Biodiversity (UO-CSIC-PA), University of Oviedo, Mieres Campus, 33600, Mieres, Spain. dalerumjohan@uniovi.es.|Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Private Bag X20, Pretoria, 0028, South Africa. dalerumjohan@uniovi.es.|Department of Zoology, Stockholm University, 106 91, Stockholm, Sweden. dalerumjohan@uniovi.es.
authors.forename: F
authors.initials: F
authors.lastname: Dalerum
authors.affiliation: Department of Zoology, Stockholm University, 106 91, Stockholm, Sweden.|Department of Environmental Research and Monitoring, Swedish Museum of Natural History, Frescativägen 40, 114 18, Stockholm, Sweden.
authors.forename: P
authors.initials: P
authors.lastname: Hellström
authors.affiliation: Centre for African Ecology, School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Private Bag 3 Wits 2050, Johannesburg, South Africa.|Department of Economics, University of Oviedo, 33203, Oviedo, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Miranda
authors.affiliation: Department of Zoology, Stockholm University, 106 91, Stockholm, Sweden.
authors.forename: J
authors.initials: J
authors.lastname: Nyström
authors.affiliation: Department of Zoology, Stockholm University, 106 91, Stockholm, Sweden.
authors.forename: J
authors.initials: J
authors.lastname: Ekenstedt
authors.affiliation: Department of Zoology, Stockholm University, 106 91, Stockholm, Sweden.
authors.forename: A
authors.initials: A
authors.lastname: Angerbjörn
mesh_terms: D000818:Animals; D046093:Falconiformes; D005241:Feathers / Q000737:chemistry*; D007554:Isotopes; D011235:Predatory Behavior; D020304:Raptors
chemical_list: D007554:Isotopes
keywords: Competition; Graph theory; Inter-specific interactions; Predation; Resource partitioning