2.1 ǀ Study site and animals
This
study was conducted around Duoma (103.01°E, 33.5°N), a village
approximately 8.5 km southwest of
the
town of Ruoergai County in the
Zoige
wetland, the biggest plateau peat bog in the world (Zhang et al., 2005).
The Zoige wetland is located in the
eastern Qinghai–Tibet Plateau, southwestern China. The study site is a
mosaic of grasslands, ground frost heaves, rivers and wet and dry
wetland patches (Guo et al., 2020),
and according to some local elders, the village has been here for at
least 80 years.
The three marmot populations have
been the subject of a ongoing behavioral ecology study since 2017,
they live in different locations
around the village and share the same habitat type
(dry, flat patches with short grass
and few frost heaves in the wetland) (Guo et al., 2020; Supporting
Information Figure S1), but suffer different degrees of anthropogenic
disturbances. The marmots living in front of the village, hereafter the
high disturbance habitat (HDH), are persistently disturbed by the daily
activities of local residents including passing motor vehicles and stray
dogs.
This
interference does not directly kill marmots and does not alter their
preferred habitat type (i.e. expel them from selected habitat to other
unsuitable habitats) (Guo et al.,
2020;
Figure S1). Marmots living behind
the village in the low disturbance habitat (LDH) endure relatively fewer
disturbances than those living in front of the village.
A
third population living to the west of the village lives in a
minimally-disturbed natural habitat (NH) and serves as a control group
(Figure 1). We had no direct
interactions like a routine
collection of blood or tissue samples or simulated behavioral
experiments with them during the burrow-related data collection in 2019.
To further exam the burrow diversification derived flee strategy under
different human disturbances, some individual-based
flight initiation distance (FID)
data were collected in June 2020 as an additional experiment to explore
how human activities act on their habitat utilization features.
2.2 ǀ Sampling method andstatistical analyses
During
the marmots’ active period (not in hibernation) in 2019, we classified
the intensity of human disturbance of each habitat based on the degree
of pressure from human activity on the different groups recorded during
behavioral observations in 2018. The three study groups were designated
as living in the high disturbance habitat (HDH), the low disturbance
habitat (LDH), and the natural habitat (NH). To quantify the amount of
human activity in the area, we recorded how many automobiles,
motorcycles and stray dogs passed by the marmot habitat every 15 days
from April 20 to October 5, 2019.
In
each of the three habitats, we recorded the coordinates of
reproductive burrows (the most
extensively used burrows) and
temporary burrows (used only
occasionally for shelter) of every breeding pair,
the pair-specific burrows were
determined according to behavioral observation. The natural feature
where all burrows occurred (i.e. hummock/mound or flat ground) and the
physical parameters (long diameter, short diameter and height) of the
mounds were also recorded to calculate their volume where burrows are
located (simplify mound into a cone).
The locations of all burrows were
mapped in Google Earth to find: (1)
the distance between each (adjacent) reproductive burrow, and
reproductive burrows with
geographical connectivity only were
included in the following analysis. For example, the distance between
NH8 and NH5, LDH3 and LDH14 were excluded in the subsequent analysis
because they are isolated by a ditch (Figures S4, S5). A criterion
finally result in 51, 47 and 31 inter reproductive burrow distances for
HDH, LDH and NH; (2) the distance between all burrows (distance between
temporary burrows, temporary burrows and reproductive burrows and 50
distances were randomly selected in each habitat to conduct the
subsequent analysis); and (3) the distance
from some reproductive burrows to the
nearest road (only burrows next to the road with no other reproductive
burrows between them and the road like HDH17, HDH18, LDH1 were included)
(for detail please see Figure S2 to S5 and sheet named “distance to
road” in Table S1).
We
calculated the density of breeding pairs by linking the outermost
burrows recorded to form a perimeter and measured number of pairs
inside, and link the outermost burrows of each breeding pair to
calculate pair-specific home range size. The same procedure was applied
to all three populations. Specially
for natural habitat, because there is no direct disturbance from motor
vehicles in the site, the same as the criterion in two disturbed
habitats, the distance from the outermost reproductive burrow (NH2)
(Figure S5) to the nearest road was used as the standard distance (311
m) to the road for all burrows in the natural habitat.
One adult individual in several
pairs from each habitat was randomly selected to measure the flight
initiation distance. A field assistant held binoculars from a long
distance to observe and record, while Zhou Shuailing approached the
focal marmot at a speed of 1m/s until the marmot started to run. FID
(the distance between Zhou and the start point of the flee) of the focal
individual was then measured (Blumstein et al., 2004). Finally, 28 FID
samples from HDH, 20 from LDH, and 20 from NH (three more individuals
from other undisturbed pairs were also included in the analysis) were
included in the following analysis.
A chi-square test was used to
determine: (1) whether there was seasonal variation in different human
activities, (2) diversification of breeding pair density between each
habitat, and (3) the variation of reproductive den site location in
three habitats. A t-test was used to determine: (1) whether the
intensity of different human activities was significantly different
among the three habitats, (2)
whether differences in parameters such as the number of burrows per
reproductive pair, the distance between reproductive burrows and between
all burrows, the distance between reproductive burrows and the
corresponding nearest road were significantly different by population,
and (3) the diversification of mound measurement (volume) selected as
reproductive burrow site among different habitats. Besides, a t-test was
also used to test if there were diversification on the FID of
individuals and pair-specific home range size in different populations.
All statistics were conducted in SPSS 20.0.