DOI: 10.5061/dryad.79cnp5hvb
title: Lethal interactions among forest‐grouse predators are numerous, motivated by hunger and carcasses, and their impacts determined by the demographic value of the victims

description: New vertebrate communities are emerging in Europe following the recovery
 of multiple native predators to highly anthropized landscapes where
 predator control is still prevalent. While the lack of reference points
 for these communities creates novel challenges for conservationists and
 wildlife managers, they also provide opportunities to further our
 understanding of species interactions. Despite a growing body of evidence,
 many aspects of interactions among predators remain poorly understood,
 impairing our ability to anticipate the effects of such changes in
 predator communities. Through a systematic literature review, we gathered
 all the available evidence concerning the existence, strength, and
 demographic impacts of lethal predator interactions among forest grouse
 predators in Europe. We found a highly interconnected predator community,
 with 44 pairwise lethal interactions among 12 taxa. Three of these
 resulted in some degree of population suppression of the victim, while
 another three did not. However, most interactions (38) have not been
 evaluated for population suppression. Additionally, we highlight how
 predators interact simultaneously with a large range of other predators
 and identified at least two further species likely suppressed through the
 combined impacts of multiple predators. We propose that interactions
 causing demographic suppression are characterized by impacts on
 individuals with high survival elasticity, and that they are motivated by
 food limitation and additionally, in mammals, by competition for
 carcasses. Predator interactions, and our still poor understanding of
 them, introduce large uncertainties to conservation actions based on the
 management of predator abundances, which should be carefully evaluated.
description: We retrieved articles, book chapters and reports published up to
 July 2019 and available online that addressed interactions amongst forest
 grouse predators in Europe. We used electronic database search engines
 (Web of Science, Google Scholar, ResearchGate) for two searches. The first
 sought to review predator’s diet and detect instances of intraguild
 predation, while the second sought to document the strength and impact of
 such interactions. The first was structured as “predator and diet” using
 the following search terms for predator: “lynx”, “red fox”, “golden
 eagle”, “eagle owl”, “goshawk”, “buzzard” and “pine marten”. The diet of
 the smallest predator taxa (diurnal raptors, owls, corvids, stoats and
 weasels) was not reviewed but instances of intraguild predation by these
 predators were included if available. The second search was structured as
 “predatorA AND predatorB AND type of interaction”, where the type of
 interaction was a combination of: “intraguild”, “predation”, “killing”,
 “suppression”, “impact”. Additionally, the terms: “stoat”, “weasel”,
 “mustelid”, “corvid”, “owl”, “raptor” were added to the list of predators.
 Articles were first appraised from the title and abstract to include data
 on diet, killing or population impacts of our predators of interest and
 within the geographical boundaries of this study. Reference lists of
 retrieved articles were screened for additional studies. Where a study was
 cited by another but itself not available, the data was extracted if the
 study area, sample size and method were reported. This yielded a total of
 240 studies. Eighty were later discarded multiple reasons. Seventy-nine
 were dietary studies that did not contain accounts of intraguild
 predation, focused on specific components of the diet (e.g. plants), were
 aggregated at a high taxonomic level (e.g. carnivora, passerines) or were
 already included in another study. The majority were of pine marten (36)
 and red fox (19) as well as three of both species. Eight were of common
 buzzard, the same number as golden eagle’s, three of lynx and two of eagle
 owl. One other study by Björklund et al. (2016), which addressed the
 relationship of northern goshawks and common buzzards in Finland, was
 excluded because it considered a migratory population of buzzards (unlike
 in the rest of Europe). Hence, the study did not report demographic
 effects. CNW and LR performed the literature search.
 Results from diet studies of birds of prey are usually presented
 as the proportion of prey items belonging to a particular species relative
 to the total number of prey items across samples, while for mammalian
 predators these are generally presented as the proportion of samples
 (scats, kills, stomachs) with a given prey category in them. Occasionally
 avian diet was quantified in the latter manner. We refer to these as
 Frequency of Occurrence (% FO, hereafter) irrespective of the method used.
 Dietary studies often report data aggregated at different arbitrary levels
 (e.g. nests, territories, regions, seasons, multi-annual periods). Where
 available, the total frequency of occurrence per study was extracted from
 the papers or calculated from the data provided. To summarize the data, we
 averaged the frequency of occurrence of a given intraguild prey in the
 diet of an intraguild predator by method, weighting by the sample size of
 each study. For this, we only included papers with non-zero occurrence for
 a given species-pair. Note that dietary data does not allow discerning
 predation from scavenging. The data is presented per species pair and,
 where relevant, by method. Multiple species pairs were grouped in single
 sections were deemed reasonable (e.g. similarities in the species
 involved). For each species pair, dietary data is presented first,
 followed by killings, annual killing rates and any evidence of impacts on
 demographic parameters (i.e. breeding success, mortality). Evidence of
 population-level effects, direct or indirect, is presented last and
 qualitatively evaluated as the depression or, in their absence, release of
 a predator’s abundance by another through lethal predator interactions.
 Interactions were deemed anecdotal when a single account was found across
 all the literature reviewed and empirical when there were two or more
 independent accounts.