Phylogenetic patterns predicting variations in bark-stripping by sika deer

Phylogenetic signal of species traits is a potentially powerful tool in the conservation of biodiversity and wildlife management. To develop a predictor for evaluating deer foraging risk in forest ecosystems, we examined the phylogenetic patterns in susceptibility to bark-stripping by Cervus nippon across the Japanese archipelago. We tested the variance of phylogenetically independent contrasts among bark-stripped ratios of 180 tree species, and found a significant phylogenetic signal, i.e., phylogenetically closely related species had similar bark-stripped ratios. To assess evolutionary processes generating clade-specific patterns of bark-stripped ratios, we evaluated the strength of phylogenetic signal by using the K-statistics. The K-statistics were < 1, demonstrating that bark-stripped ratio was not tightly conserved in particular clades, i.e., woody plant traits related to palatability or anti-herbivore defense may be labile among families or genera. Based on phylogenetic relationships and bark-stripped ratios among species, we examined the vulnerability to deer foraging at the tree species assemblage level. We estimated the bark-stripped ratios for all Japanese woody plants (928 species) by phylogenetic imputation, and mapped the geographic pattern of the vulnerability at the 10 × 10-km grid cell level. Compared with taxonomic-based assessment focusing on 180 tree species with the records of bark-stripping, the phylogenetic-based vulnerability map showed spatially heterogeneous patterns. Our results demonstrate that the phylogenetic pattern in the interspecific variation of bark-stripped ratios serves as an indicator for better understanding the vulnerability of forests to deer foraging, and has 2 implications for the management of the deer population. First, phylogenetic constraint of selective foraging could be a driver that causes aggregated degradation of forest ecosystems containing palatable plant lineages for deer. Second, evolutionary lability of palatability or anti-herbivore defense across various tree families may be an important factor for the geographic spread of foraging damage in forests harboring taxonomically different species.