INTRODUCTION
Dens used by
cavernicolous
animals have a vital impact on their survival. Dens provide animals with
a place to rest, hide, and hibernate and help them avoid bad weather and
predators (Ross et al. 2010; Tsunoda et al. 2018). The ecological
characteristics of a den can accurately reflect the life, behavior, and
social networks of cavernicolous animals. For example, the
yellow-bellied marmot (Marmota flaviventris ) in North America
uses dens that resist harsh environments and predators during
hibernation and provide a protective shelter in summer (Svendsen 1976).
Pallas’s
cat (Otocolobus manul ), which inhabits the Mongolian plateau,
cannot dig burrows by itself, so it often uses Marmota sibiricadens to give birth, raise offspring, and avoid natural enemies; the
availability of M. sibirica dens thus has a very important impact
on the stability of the O. manul population (Ross et al. 2010).
The puma (Puma concolor ) living in the American continent uses
dens to defend against predators (e.g., adult Ursus arctos ) and
to maintain microclimate stability, therefore increasing the survival
rate of its cubs (Bleich et al. 1996; Benson et al. 2008). American
black bears (Ursus americanus ) use various types of dens
(excavated, trees, rock cavities) for hibernation, and their dens
provide safe places for female black bears to give birth and rear their
cubs; in addition, some individuals use tree dens that can resist
flooding (White et al. 2001). Therefore, dens offer an excellent means
of studying the ecological adaptation of cavernicolous animals.
Except for plateau rabbits (Lepus oiostolus ), Marmota
himalayana (hereafter referred to as the marmot) is the only large
rodent in the alpine meadows of the
Qinghai-Tibet Plateau (QTP). Marmots are herbivores and forage mainly on
the leaves and stems of Cyperaceae, Gramineae, and the flowers of legume
species. Marmots are of great significance to the stability of the
alpine meadow ecosystem. First, the marmot is an important part of the
food chain in the grassland ecosystem. It is important prey for
large
raptors, foxes, and wolves. In addition, marmots feed on grasslands that
cannot be reached by livestock, which is equivalent to grazing in these
areas and is good for the health of the grasslands (Oesterheld and
McNaughton 1991). The burrowing and digging behavior of marmots is
conducive to the circulation of organic matter in the grasslands.
However, marmots do also cause obvious harm, as they compete with
livestock for fine pasture, dig grass roots, and destroy turf all year
round. In the pasture, marmot holes are the main hidden danger that
causes livestock leg fractures (Chen 1982). Each of their excavated
mounds covers a large area of grassland (~2
m2), causing ground collapse, soil erosion, and
desertification. Marmots are also one of the main spreaders of the
plague in this region (Xu et al. 2020), which seriously threatens the
health of grassland herders and livestock.
Habitat selection is a reflection of the environmental, ecological, and
physiological requirements of a species (Kohji and Kenichi 1998). When
cavernicolous animals excavate dens, they typically show a strong
selectivity with respect to the surrounding environment. For example,
the Japanese red fox (Vulpes vulpes ) prefers to dig dens closer
to a water source (Kohji and Kenichi 1998). On the north coast of
Alaska, the arctic fox (Alopex lagopus ) prefers to choose dens on
the southern slope in an area with thin permafrost (Garrott et al.
1983), which helps to keep the den warm.
In this study, marmot dens that were present in different terrains
(sunny slopes, shady slopes, and flat areas) were located, and the
physical characteristics of these dens were measured under harsh
environmental conditions (low oxygen, low temperature, and high
precipitation) (Zhang et al. 2019). Here we determined (1) the general
physical characteristics and ecological functions of marmot dens and (2)
whether there are differences in den traits under different terrains.
Our findings highlight the adaptation mechanism of M. himalayanawith respect to its environment, which is of great significance for
further understanding the ecological characteristics of the marmot or
other cavernicolous animals all over the world.