Abstract
BackgroundIntraguild predation (IGP) is widespread but it is often neglected that guilds commonly include many layers of dominance within. This could obscure the effects of IGP making unclear whether the intermediate or the bottom mesopredator will bear higher costs from the emergence of a new top predator.Methodology/Principal FindingsIn one of the most extensive datasets of avian IGP, we analyse the impact of recolonization of a superpredator, the eagle owl Bubo bubo on breeding success, territorial dynamics and population densities of two mesopredators, the northern goshawk Accipiter gentilis and its IG prey, the common buzzard Buteo buteo. The data covers more than two decades and encompass three adjacent plots. Eagle owls only recolonized the central plot during the second decade, thereby providing a natural experiment. Both species showed a decrease in standardized reproductive success and an increase in brood failure within 1.5 km of the superpredator. During the second decade, territory dynamics of goshawks was significantly higher in the central plot compared to both other plots. No such pattern existed in buzzards. Goshawk density in the second decade decreased in the central plot, while it increased in both other plots. Buzzard density in the second decade rapidly increased in the north, remained unchanged in the south and increased moderately in the center in a probable case of mesopredator release.Conclusions/SignificanceOur study finds support for top-down control on the intermediate mesopredator and both top-down and bottom-up control of the bottom mesopredator. In the face of considerable costs of IGP, both species probably compete to breed in predator-free refugia, which get mostly occupied by the dominant raptor. Therefore for mesopredators the outcome of IGP might depend directly on the number of dominance levels which supersede them.
Highlights
Intraguild predation (IGP) is the complex interaction between member species of a guild, that both compete for resources and kill each other [1]
For that period in the central plot, the only predictor of goshawk reproductive success was the presence of an eagle owl breeding pair within 1.5 km (Figure 1A, eagle owl within 1.5 km x2 = 9.91, p = 0.002, model weight = 0.87)
In the central plot, brood failure was predicted by the presence of an eagle owl breeding pair within 1.5 km and marginally by goshawk nearest neighbour distance (NND) (Figure 1B, eagle owl within 1.5 km x2 = 7.22, p = 0.007, NND x2 = 3.31, p = 0.069, model weight = 0.51)
Summary
Intraguild predation (IGP) is the complex interaction between member species of a guild, that both compete for resources and kill each other [1]. IG predators can actively persecute competitors so that IG prey experiences an even greater risk of attack than extraguild prey [2]. They are potentially less adapted to negate predation through strategic and tactical responses. Coexistence of apex predators and mesopredators can depend on ecosystem productivity and prey abundance [3], and on habitat complexity [4] The latter is important for prey refugia but probably for competitors limited to a greater degree by habitat-sharing than by food competition. Intraguild predation (IGP) is widespread but it is often neglected that guilds commonly include many layers of dominance within. This could obscure the effects of IGP making unclear whether the intermediate or the bottom mesopredator will bear higher costs from the emergence of a new top predator
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