Landscape of fear in Europe: wolves affect spatial patterns of ungulate browsing in Białowieża Primeval Forest, Poland

Abstract

Large carnivores can either directly influence ungulate populations or indirectly affect their behaviour. Knowledge from European systems, in contrast to North American systems, on how this might lead to cascading effects on lower trophic levels is virtually absent. We studied whether wolves Canis lupus via density-mediated and behaviorally-mediated effects on their ungulate prey species influence patterns of browsing and tree regeneration inside the Białowieża National Park, Poland. Browsing intensity of tree saplings (height class  150 cm), irrespective of tree species or forest type, was lower inside a wolf core area (50.5%) where predator presence is highest, than in the remainder of the wolf pack's home range (58.3%). Additionally, browsing intensity was reduced when the amount of coarse woody debris (CWD), which can act as a 'ungulate escape impediment', increased (within 5-m radius) inside the wolf core area. No relationship existed outside the core area. As a result, the proportion of trees growing out of herbivore control increased more strongly with increasing amount of CWD inside compared to outside the wolf core area. This suggests that next to direct effects of wolves on ungulate density caused by a higher predation pressure inside the core area, risk effects are important and are enhanced by habitat characteristics. These results indicate that behaviorally-mediated effects of predators on prey can become more important than density-mediated effects in affecting lower trophic levels. This is the first study we are aware of, that shows CWD can create fine-scale risk effects on ungulates with the potential for cascading effects of large predators on patterns of tree regeneration for a European forest system. This knowledge broadens the discussion on how the impact of large predators on ecosystem functioning depends on the physical landscape, by illustrating these effects for a system which largely contrasts in this respect to the North American systems.

Paws without claws? Ecological effects of large carnivores in anthropogenic landscapes

“…Whereas a growing number of studies show how carnivores can affect the numbers and behaviour of herbivores and mesopredators in these landscapes, there are virtually no studies of what this means for lower trophic levels. The few studies that do exist [82,85] come from areas with relatively low human density. Future studies should address the potential for trophic cascading effects, using the recently proposed gold standard approach [88], in more intensively used anthropogenic landscapes, explicitly including humans as part of the food web and as agents altering the functional role of large carnivores.…”

Incorporating anthropogenic effects into trophic ecology: predator–prey interactions in a human-dominated landscape

“…First, apex predators limit herbivores through predation and behaviourally mediated changes in habitat use, thereby promoting vegetation growth (i.e. tri-trophic cascades [16][17][18]). Second, apex predators limit mesopredators through interference competition, including in its most extreme form, intraguild predation [19][20][21].…”

Combining paleo-data and modern exclosure experiments to assess the impact of megafauna extinctions on woody vegetation

“…In landscapes characterized by intense herbivory, woody plants can persist by defending themselves, by associating with defended species, or by growing in areas that are physically inaccessible or that are risky for herbivores because of high activity of predators (34,45). The resulting variation in the local intensity of herbivory can create spatial mosaics of herbaceous plants, shrubs, and trees.…”

“…As a response to perceived predation risk, often heterogeneously distributed across the landscape (52), herbivores may select less risky areas, creating spatial variability in herbivore pressure and thus varying impacts on vegetation (34,53). Therefore, the presence of predators can allow local increases in the abundance of woody species, such as observed after the introduction of wolves in temperate woodlands followed by reduced browsing pressure from deer and locally enhanced recruitment of palatable shrubs and trees (45,(54)(55)(56), resembling that observed in exclosures (Fig. 1E).…”