Spatiotemporal changes in antlerless proportion of culled Sika deer in relation to deer density

Population management of herbivores is widely applied to decrease damage to forests in the northern hemisphere. Culling more antlerless deer, including females and fawns, is an effective means of reducing the population and helps to improve management efficiency. To increase the efficiency of antlerless-biased culling, we assessed the spatiotemporal distribution of the antlerless ratio in culled sika deer (Cervus nippon) in relation to population density. We hypothesized that the antlerless ratio is higher at the center of the distribution than at the margins of the deer’s range, because dispersal processes differ according to sex and age: Young male deer first disperse into an unoccupied area, and then males may become established in the new area for approximately 10–15 years before the number of females increases. A statistical model revealed spatiotemporal changes in the antlerless ratio of culled sika deer. The change in the ratio basically fit the density distribution of the deer, which was estimated independently on the basis of fecal pellet count surveys. The antlerless ratio estimated from the model increased asymptotically as deer density rose. The results support our hypothesis and suggest that antlerless sika deer will be more easily culled at the center rather than at the margins of the distribution range. These findings should help to increase the efficiency of managing the deer via antlerless-biased culling.

The relative and combined effects of herbivore assemblage and soil nitrogen on plant diversity

Plant diversity can be affected by both herbivore grazing and soil resources. However, it is unclear if the joint effects of herbivores and soil resources might vary with components of plant diversity. Here, we evaluated the relative and combined effects of herbivore assemblage and soil nitrogen(N) quantity and heterogeneity on the α and β components of plant diversity in a grassland that was subjected to four years of grazing under differing herbivore assemblages(no grazing, cattle grazing, sheep grazing, and mixed grazing). We found that herbivore assemblage combined with soil N quantity explained 41% of the variation in plant α-diversity, while herbivore assemblage combined with soil N heterogeneity explained 15% of the variation in plant β-diversity. The independent effects of herbivore assemblage explained more than those of soil N for both α-and β-diversity(α-diversity: 12% vs. 4%;β-diversity: 18% vs. 16%). We concluded that the effects of herbivores are stronger than those of soil N,and that grazing-induced changes in soil resources are important drivers of plant diversity change, especially α-diversity.Therefore, we suggest that managing herbivore species by accounting for the effects that their grazing can have on soil resources may be significant for plant diversity maintenance.