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
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