FIGURE 9 Effects of foraging on saplings of Japanese yew
DISCUSSION4.1 Temporal strategies for foraging on the Japanese yew in two deer species In the present study, infrared camera detection revealed differences in the temporal strategies of two ungulates foraging on Japanese yew saplings. The daily activity rhythms of the wapiti presented two peaks throughout the year. However, there were significant differences between them, with a short duration but high density of foraging activity in the early morning, and a lower density but longer duration in the afternoon. This is similar to the results of Kamler’s study (Kamler et al., 2007), which may be due to temperature extremes in winter; their peak daily activity usually occurs during the warmer period before sunset. The Siberian roe deer foraged both day and night, but there was a large nocturnal difference between the two ungulates, which may be a competitive strategy. The activity patterns of species change with the season, demonstrating some plasticity in achieving coexistence by reducing temporal overlap with competitors during foraging activities (Monterroso et al., 2014; Romero-Muñoz et al., 2010; Rheingantz et al., 2016). The foraging frequency during the warm season was significantly lower than that during the cold season. The possible reasons are as follows: (1) The temperature is suitable and food resources are abundant in the summer. They can replenish nutrition with other types of green plants, thereby reducing their foraging in Japanese yew. (2) In summer, the level of concealment in the forest is higher, which is conducive to avoiding the enemy and does not require a higher intensity of foraging activity other than reproductive needs. (3) Japanese yew is one of the few green plants grown in winter that has higher energy, protein, and carbohydrate contents than other plants (Huang, 2015). 4.2 Foraging spatial strategies of the two ungulates The population size and distribution of ungulates are inextricably linked to plant resources (Wang et al., 2019b), and they often face trade-offs between high-quality food and food abundance in winter, which is related to the spatial scale (van Beest et al., 2010). The wapiti and Siberian roe deer have similar ecological niches. They had different foraging strategies in space in the current study, which may be due to two reasons. (1) The population size of Siberian roe deer is larger than that of the wapiti, and their reproductive capacity is better. ( 2) The foraging range of the Siberian roe deer was large. The predicted results demonstrated that the vegetation type, which is one of the main sources of competition, was the main factor influencing the suitability of foraging habitats. Their occurrence probability was negatively correlated with distance from the coniferous forest distribution. This is similar to the results of Tian Xinmin et al. in their 2022 study on the distribution number and habitat suitability of the wapiti populations in the Muling forest area (Tian et al., 2022). The response curves of the environmental variables demonstrated that suitable foraging areas are weakly avoided roads and farmland and are insensitive to human activities. This is because the Japanese yew is distributed far from roads and residential areas, and the frequency of human activity is low. Different habitat selection and utilization strategies are, therefore, key factors that promote the distribution of sympatric species (Liu et al., 2020; Xia et al., 2019). Populations with similar ecological niches tend to select different habitats to reduce competition and ensure survival and reproduction. It may be concluded that the relevant departments should target the management of the habitat of the Japanese yew population and strengthen the in situ conservation of scattered distribution saplings to create favorable conditions for the recovery of the population in the Muling Forest area. 4.3 Foraging characteristics of two ungulates and the effects on saplings In the long term, vegetation system dynamics may depend on seedling replenishment. A study of alpine plant communities found that trampling and foraging by large and small herbivores negatively affected plant communities (Feng et al., 2022). Zhou found that a few individuals in the regeneration layer were not conducive to the development and recovery of the population when he studied the resource characteristics of the Japanese yew population (Zhou et al., 2004). One reason for this is animal foraging (Diao et al., 2020; van Beest et al., 2010; Yang, 2018). In a study on the diet of the wapiti, it was found that Japanese yew accounted for a relatively large portion of its food composition and that Siberian roe deer and sika deer also consumed a certain amount of Japanese yew (Feng, 2022; Huang, 2015; Zhong, 2020; Zhu et al., 2019). The extent to which wapiti forage for Japanese yew belongs to heavy foraging. In addition, the wapiti looks for fallen trees, forage for several branches and leaves, and forage on as many mature tree branches as possible, which were found to be 3 m from the ground. Bergquist 2003 found that the foraging of roe deer (Capreolus capreolus ) has impacted the growth of saplings, which accumulate over time. Three consecutive years of foraging reduces growth height by one year (Bergquist et al., 2003; Olofsson et al., 2004). This current study received similar results. The average growth height of the main branches, number of new branches, and length of the lateral branches of the saplings decreased after foraging by both ungulates. The damage degree of the wapiti was much greater than that of the Siberian roe deer. Saplings that were heavily foraged on by wapiti branched out from the root. This may be due to the strong selectivity of wapiti in winter, making it difficult for saplings to grow beyond their foraging height. It may be considered that foraging by large herbivores affected the growth and survival rate of the saplings, causing damage. Considering their special biological characteristics, such as slow growth, poor stress resistance, and low survival rates (Yang, 2018), foraging by ungulates aggravates this phenomenon, which is not conducive to normal growth and may affect the natural regeneration of populations. In the short term, there are obvious differences between the two ungulates in foraging and the impact on saplings, which have a certain negative impact on their growth; however, the impact on succession and renewal needs further study.
CONCLUSIONThe wapiti and Siberian roe deer reduce or avoid direct competition for their resources through different foraging strategies in the Muling National Nature Reserve to ensure their nutritional requirements in the harsh winter environment. Temporally, they also preferred to forage for Japanese yew saplings during the cool season, with a moderate degree of overlap. Spatially, suitable foraging habitats of the Siberian roe deer were approximately twice those of the wapiti, and their overlap was less in location, direction, and distance from mature trees. Behaviorally, they have different foraging intensities, and the influence of wapiti on the growth of saplings is much greater than that of the Siberian roe deer. It is, therefore, recommended that the local conservation management department take necessary measures to restrict the wapiti from foraging on the saplings of the Japanese yew to protect the saplings in the scattered distribution. It is further recommended to provide favorable conditions for the succession and renewal of the forests of Japanese yew without affecting the habitat activities of the wapiti and the normal recovery of the trees to maintain the stability of the forest ecosystems and biodiversity of the region.REFERENCES
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