How do forest management and wolf space-use affect diet composition of the wolf’s main prey, the red deer versus a non-prey species, the European bison?

Abstract

We analyzed the effect of forest management and wolf (Canis lupus) space-use on diet composition of red deer (Cervus elaphus) and European bison (Bison bonasus) in Białowieża Primeval Forest (BPF), Poland. The red deer is the main prey species for the wolf, whereas the European bison is rarely preyed upon. As both species behave as intermediate feeders in BPF, we expected a large overlap in their diet composition. The red deer perceives the risk of wolf predation; thus, we hypothesized that its diet would change in relation to the intensity of wolf space-use, whereas bison’s would not. We compared diet composition between two contrasting management regimes: a national park managed as a protected area (no hunting, no forestry activities, restricted tourism), and an adjacent production forest managed for timber growth and extraction, where hunting on ungulates (but not wolves) does occur. We collected dung pellets of bison and red deer along transects in low and high wolf-use areas (with distance to settlements as proxy for wolf space-use) in both management types and analyzed diet composition using DNA-metabarcoding. In the national park both the bison and red deer had higher proportions of broadleaved tree species in their diet (bison 39%, red deer 42%) than in the managed forest (bison 26%, red deer 28%). The bison diet contained a higher proportion of shrubs, and specifically Rubus in the managed forest (shrubs 29%, Rubus 31%), compared to the national park (shrubs 21%, Rubus 8%). Only in the national park, red deer ate relatively more broadleaved tree species (51%) and fewer forbs (23%) in the high wolf-use area than in the low wolf-use area (33% broadleaved trees versus 37% forbs). Bison showed a qualitatively similar shift in diet composition as red deer, but the shift was not significant and also much smaller in extent. Our results indicate that forest management shapes the diet composition of both ungulate species. In addition, red deer showed larger shifts in diet composition than bison in high versus low wolf-use areas. This suggests that in addition to habitat differences, predation risk also plays a role in shaping the red deer diet. While earlier studies in BPF illustrated that wolves affect fine-scale deer foraging behavior, this study suggests this could potentially lead to changes in diet composition. We present alternative explanations for these diet shifts and urge others to look further into predation risk as a possible driver of dietary shifts in red deer.