Summary1. Because of their popular appeal, top vertebrate predators have frequently been used as flagship or umbrella species to acquire financial support, raise environmental awareness and plan systems of protected areas. However, some have claimed that the utilization of charismatic predators may divert a disproportionate amount of funding to a few glamorous species without delivering broader biodiversity benefits, an accusation aggravated by the fact that the conservation of top predators is often complex, difficult and expensive. Therefore, tests are needed of whether apex predators may be employed to achieve ecosystem-level targets. 2. To test such a hypothesis, we compared the biodiversity values recorded at the breeding sites of six raptor species, differing widely in diet and habitat associations, with those observed at three types of control locations, (i) sites randomly chosen in comparable habitat, (ii) breeding sites of a randomly selected bird species of lower trophic level and (iii) breeding sites of a lower trophic level species with specialized ecological requirements. Biodiversity was measured as the richness and evenness of bird, butterfly and tree species. 3. Biodiversity levels were consistently higher at sites occupied by top predators than at any of the three types of control sites. Furthermore, sites occupied by top predators also held greater densities of individual birds and butterflies (all species combined) than control sites. 4. In a reserve-selection simulation exercise, networks of protected sites constructed on the basis of top predators were more efficient than networks based on lower trophic level species, enabling higher biodiversity coverage to be achieved with a smaller number of reserves. 5. Synthesis and applications . Our results provide evidence of a link between the strategic utilization of top predatory species and ecosystem-level conservation. We suggest that, at least in some biological systems, conservation plans based on apex predators could be implemented to deliver broader biodiversity benefits.

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Summary 1.Intraguild predation (IGP) has been studied extensively in predatory fish, amphibians and mammals, but less so in top avian predators. We studied the impact of IGP by large eagle owls Bubo bubo Linnaeus (body mass ∼ 1·5-4 kg) on diurnal black kites Milvus migrans Boddaert ( ∼ 0·5-1 kg) in eight populations located in the Italian Alps. Eagle owls preyed on both adult and nestling kites, especially when kites nested within 2 km of an owl nest. Food overlap was low as kites preyed mainly on fish and owls on mammals. Eagle owls were absent from two study areas, bred very close to another area and were present at medium-high densities in the other five. Within-population effects varied and were most severe in areas with high owl densities. Overall, kites responded to predation risk through predator spatial avoidance, being concentrated in interstitial predationrefugia bordering the core home range of owl pairs. 2. Kite productivity declined steeply with increasing predation risk; no nestling fledged within 1 km of an owl nest. Brood predation was higher in an area with medium owl density than in an area lacking eagle owls. 3. The abandonment of kite territories increased near owl nests, but close coexistence was maintained by new kite territories being established occasionally in areas of high predation risk and high food abundance, which probably functioned as ecological traps. Compared to a random nest dispersion, colonial nesting was avoided within 1 km of an owl pair and peaked in conditions of medium predation risk. 4. At the population level, kite density and productivity were related to a complex interaction of IGP risk and food abundance, and were probably shaped by a mixture of top-down and bottom-up effects. These results may apply to many other vertebrate mesopredators, whose individual decisions and population responses are probably the result of a trade-off between predator avoidance and food acquisition. 5. At the community level, the density of different diurnal avian predators responded differently to IGP risk, some of them even increasing with this risk. The diversity of the assemblage peaked at medium-high eagle owl density. Future studies of top vertebrate predators need to take more account of IGP effects. Their conservation management needs to be highly case-specific and framed within a broader ecosystem perspective.

We studied a population of 23–25 Eagle Owl Bubo bubo pairs between 1994 and 2000 in a 1330‐km2 study plot in the central‐eastern Italian Alps. Compared to random sites, territories were located at lower elevation and closer to intensively cultivated‐urbanized valley floors. Early laying was associated with low elevation and negatively affected productivity. Diet was dominated by rats, hedgehogs and dormice (n = 978 prey items), all of them typical of low‐elevation habitats. Higher productivity was associated with a higher proportion of rats in the diet of individual pairs. Low availability of rats resulted in a more diverse diet, in turn associated with low productivity. Territories were occupied every year in a non‐random fashion, and those most occupied were characterized by higher productivity and higher occurrence of the favoured prey types in the diet, suggesting they were of superior quality. Eagle Owls also paid a cost associated with nesting near human‐altered habitats: the main cause of mortality reported to local authorities was electrocution. This is an increasing cause of death for many European populations and may be a cause for conservation concern. Human persecution is also an important cause of mortality in some parts of the European range. Apart from such costs, the study population appeared to have adapted well to the proximity of humans: estimates of density and productivity were comparable to those recorded elsewhere in Europe. The pattern found in our population also held at higher spatial scales: data from 17 European populations showed density to be highest in low‐elevation, human‐altered landscapes.

Intraguild predation is increasingly reported as a population-limiting factor for vertebrate predators. However, long-term coexistence of the intraguild prey with its predator is a common occurrence usually maintained by some form of predator avoidance, which may be achieved through distance-sensitive avoidance (selection of sites as far as possible from the intraguild predator), and/or habitat-mediated avoidance (avoidance of habitats associated with high predation risk). The former is expected when the distribution of the predator is heterogeneous, leaving gaps which can be exploited by the prey, while the latter is expected at high predator densities, when few predation refugia are available. To date, few studies have focused on such switch in predator avoidance under changing scenarios of intraguild predator density. To test this hypothesis, we censused tawny owls (Strix aluco, body mass w0.4e0.7 kg) and their intraguild predator, the eagle owl (Bubo bubo, w1.5e4 kg), in 12 areas of the Alps. As predicted, tawny owls were indifferent to predator distance in an area of low predation risk, they switched to distance-sensitive avoidance in an area of medium predator density and to habitat-mediated avoidance in an area of high predator density with few available refugia. Actual predation rates were low, but increased with proximity to the intraguild predator nest. Similarly, tawny owl breeding output declined with closeness to an eagle owl nest. Habitat loss associated with predator avoidance translated into population effects, leading to a negative relationship between the densities of the two owl species. The spatial gaps in tawny owl distribution caused by eagle owls indirectly favoured other owl species, resulting in higher diversity of the overall owl community and suggesting that eagle owls acted as keystone predators. Our results suggest that intraguild predation may alter habitat choices and affect density, productivity and guild structure of vertebrate mesopredators. Such effects are probably more common than previously thought.