Food Niche Overlap of Avian Predators (Falconiformes, Strigiformes) in a Field and Forest Mosaic in Central Poland

Food niche overlap statistics are a common way to show competition for food resources in a group of animals. Niche breadths of various species are very variable and their diet composition changes reflecting prey availability. The aim of this study was to evidence the food niche overlap of the whole assemblage of avian predators (eight raptor and owl species, some of them reaching very high densities) in a field and forest mosaic of central Poland. The diet composition was assessed on the basis of pellet analyses and the identification of prey remains found under the nests in the breeding period. The extent of the niche overlap was calculated using a Pianka formula. The food niche overlap indices ranged from 0.02 to 0.93 (mostly below 0.5). The most separate food niche was that of the white-tailed eagle, who regularly preyed on fish. The highest niche overlap was recorded for the common buzzard and common kestrel, two species preying on field rodents, switching to soricomorphs when the former were scarce. Our results confirmed that the food niches of species coexisting in the same area were considerably separate, which is a result of preying on various prey species or searching for them in different habitats.

Pollinator specialization increases with a decrease in a mass-flowering plant in networks inferred from DNA metabarcoding

How native mass-flowering plants affect the specialization of insects at individual and species levels and the consequences for pollination networks have received much less attention than for mass-flowering crops or alien species and basically remain unexplored.Using existing DNA metabarcoding data on the pollen loads of 402 flower-visiting insects, we assessed the effects of a native mass-flowering plant of high reward quality, the shrub Rhododendron ferrugineum, on pollination networks by investigating: (a) the food niches of individual pollinators and pollinator species and (b) the structure of individual and species networks in subalpine heathland patches with extremely contrasted densities of R. ferrugineum.Relative to its high abundance in high-density patches, the shrub was greatly underrepresented and did not dominate individual's or species' generalized networks, rather individual and species specialization increased with a decrease in R. ferrugineum density. Furthermore, individuals of the more generalist dipteran Empididae species tended to extend exclusive interactions with rare plant species in low-density networks. The same trend was observed in the more specialist Apidea but toward rare species in high-density networks. Our results reveal a quite paradoxical view of pollination and a functional complementarity within networks. Niche and network indices mostly based on the occurrence of links showed that individual pollinators and pollinator species and networks were highly generalized, whereas indices of link strength revealed that species and above all individuals behave as quite strict specialists. Synthesis. Our study provides insights into the status of a native mass-flowering plant in individual's and insect species' food niches and pollination networks. It revealed that a generalist pollinator species can be highly specialized at the individual level and how rare plant species coexisting with mass-flowering plants may nevertheless be visited.