Competitors and predators alter settlement patterns and reproductive success of an intraguild prey

Abstract

The spatial distribution of predators is affected by intra‐ and interspecific interactions within the predator guild. Studying these interactions under fluctuating food availability, while taking habitat characteristics into account, offers a quasi‐experimental setup to determine the relative impact of con‐ and heterospecifics on reproductive success of predators. We analyzed the settlement decisions and reproductive success of Eurasian Pygmy Owls (Glaucidium passerinum) in the presence of both breeding conspecifics and their competitor and intraguild predator, Tengmalm's Owls (Aegolius funereus), under fluctuating abundance of their primary prey (voles). We used detailed data, collected across 11 years in a large study area (1300 km²), on the spatial and temporal variation of habitat characteristics in all available nesting sites, local densities of both species, and vole abundance. We found that Pygmy Owls strongly avoided breeding close to conspecifics but did not avoid Tengmalm's Owl nests. Nest box occupation of Pygmy Owls was positively correlated to the proportion of old spruce, mature and old pine forests, and farmlands, and occupation probability was higher at high vole abundance and in areas occupied in previous years. Pygmy Owl avoidance of conspecifics decreased when voles were abundant. At high conspecific density, Pygmy Owls showed lower hatching success and delayed hatching date, in agreement with the observed spatial avoidance. Finally, even though breeding Pygmy Owls did not spatially avoid Tengmalm's Owls, the density of heterospecifics correlated with low hatching and fledging success in Pygmy Owls. This suggests short term fitness costs when living close to competitors, even when lethal effects of intraguild interactions are subtle. Our results suggest that joint costs of exploitative and interference competition by Tengmalm's Owls, as well as intraguild predation, were lower than those induced by intraspecific competition only. This result might be due to the similar body size between the species considered, Tengmalm's Owls being only twice as large as Pygmy Owls. Interactions among con‐ and heterospecifics can therefore modify the spatial settlement and reproductive success of individuals on a landscape scale, also within the predator guild.

Food supplementation and predation risk in harsh climate: interactive effects on abundance and body condition of tit species

“…It is possible that few pygmy owls were storing additional prey in natural cavities. In our study area however this seems unlikely since the number of suitable natural cavities seem to be low due to small coverage of old growth forests (see methods in Terraube et al , Morosinotto et al ).…”

Why do top predators engage in superpredation? From an empirical scenario to a theoretical framework

“…the likelihood that a superpredator will detect a mesopredator species during a given time t) may be influenced by three major components: 1) landscape structure; 2) mesopredator density; and 3) mesopredator behaviour. Landscape structure is related to differences in the detectability of mesopredators according to habitat and the availability of refugia (Sergio et al 2007, Sergio and Hiraldo 2008, Morosinotto et al 2017). The relevance of the mesopredator density in the hunting range of the superpredator for the observed superpredation frequency is quite straightforward (Lourenço et al 2011a, Dröge et al 2017.…”

“…A practical approach to unravelling the causes of lethal interactions among top predators involves analysing the relationships between the percentage of superpredation in individuals' diet and the abundance of both main prey and mesopredators in nature (Lourenço et al 2011a, Hoy et al 2017). In addition, to determine the competitive degree of the interaction, it is important to compare the frequency of superpredation on mesopredators that compete with the top predator and the frequency of superpredation on mesopredators that do not compete or pose a serious threat (Sunde et al 1999, Serrano 2000, Lourenço et al 2014, Morosinotto et al 2017.…”

Top‐down limitation of mesopredators by avian top predators: a call for research on cascading effects at the community and ecosystem scale

“…the Buzzard, showed increased aggressiveness towards the top predator). Further evidence of multi-level intraguild predation and superpredation exists in bird of prey assemblages (Hoy et al 2015, 2017, Bj€ orklund et al 2016, Morosinotto et al 2017; however, research on the top-down limitation of other mesopredator species (e.g. Corvidae) by avian top predators is scarce and the potential cascading effects at the ecosystem level have rarely been investigated (Box 1; Fig.…”