Network topology of stable isotope interactions in a sub-arctic raptor guild

Abstract

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 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.

Trophic niche similarities of sympatric Turdus thrushes determined by fecal contents, stable isotopes, and bipartite network approaches

“…Studies using stable isotopes for the construction of consumer-food bipartite networks involving birds are scarce (e.g., Dalerum et al, 2016;Miranda et al, 2014). In both cited studies, raw isotopic values were used for the construction of the interaction networks, grouping resources into categories according to the average of the the current study were one of the most important items in the networks, with strong links to all three thrushes.…”

“…Furthermore, the network structure helps to identify patterns of grouping between species and their resources and to evaluate the role of consumers according to their dietary specialization or generalization in the network (Bascompte, Jordano, Melian, & Olesen, 2003), which sometimes are uncovered by other data analytical tools. The use of isotopes coupled to network analysis is quite recent (Dalerum et al., 2016; Miranda, Dalerum, & Parrini, 2014) and thus is still being fully developed. The approach used here can provide a comparison between diet and isotopes in a way that has not been done yet, that is, using output of isotopic mixing models to depict bipartite networks, instead of previous studies based on raw stable isotope values (Dalerum et al., 2016; Miranda et al., 2014).…”

“…The use of isotopes coupled to network analysis is quite recent (Dalerum et al., 2016; Miranda, Dalerum, & Parrini, 2014) and thus is still being fully developed. The approach used here can provide a comparison between diet and isotopes in a way that has not been done yet, that is, using output of isotopic mixing models to depict bipartite networks, instead of previous studies based on raw stable isotope values (Dalerum et al., 2016; Miranda et al., 2014). We predict strong sharing of resources among the three consumers studied, but with marked differences in proportions of food items used (i.e., links strength), as a proxy of niche partitioning.…”

Isotopic niche partitioning and individual specialization in an Arctic raptor guild

“…To evaluate niche partitioning within the Arctic raptor guild, we focus on three sympatric species with different foraging strategies: the Golden Eagle (Aquila chrysaetos; a dietary generalist; Katzner et al 2020); the Gyrfalcon (Falco rusticolus; a facultative specialist; Booms et al 2020); and the Rough-legged Hawk (Buteo lagopus; a dietary specialist on arvicoline rodents; Bechard et al 2020). Although these species nest sympatrically and their diets overlap to some extent, it remains unclear how interspeci c competition and niche partitioning may in uence their trophic ecology (Poole & Bromley 1988, Dalerum et al 2016. By focusing on the trophic ecology of Arctic raptors under dynamic ecological conditions (i.e., uctuating arvicoline rodent abundance), we seek to evaluate niche partitioning under the mNVH paradigm, thereby characterizing their behavioral plasticity and providing broader context for the tundra food web.…”

Trophic structure of frog assemblages in coastal habitats in southern Brazil

“…Oliveira et al 2018). For instance, resource availability influences the number of trophic links in local food webs as well as resource and consumer contributions to energy flow within the network (Winemiller 1990;Dalerum et al 2016). Interspecific interactions may also be influenced by resource availability, with low resource availability resulting in either competitive exclusion or niche partitioning and species coexistence (Pianka 1974).…”