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Response of alpine meadow communities to burrow density changes
of plateau pika (Ochotona curzoniae) in the Qinghai-Tibet Plateau
Zheng-gang GUO*, Xiao-feng LI, Xing-yuan LIU, Xue-rong ZHOU
State Key Laboratory of Grassland Farming Systems, College of Pastoral Agricultural Science and Technology,
Lanzhou University, Lanzhou, China
ABSTRACT: Plateau pika (Ochotona curzoniae) is a key component of alpine meadow ecosystem in the
Qinghai-Tibetan Plateau, and the increase of its number leads plant components of alpine meadow ecosystem to
adaptively response. A field survey was carried out to determine the response of alpine meadow community to
population densities of plateau pika by using available burrow density to replace the population density of plateau
pika. This study showed that the height of alpine meadow communities gradually increased, and the cover of
alpine meadow communities firstly decreased, and then increased as the available burrow density increased. With
the increase of available burrow density, the richness index of alpine meadow communities firstly decreased and
then increased, and the evenness index of alpine meadow communities firstly increased and then decreased,
however, the diversity index of alpine meadow communities firstly increased, and then decreased, finally increased.
In the increasing process of available burrow density, the total plant biomass and the unpalatable plant biomass
firstly decreased and then increased, and the palatable plant biomass firstly increased and then decreased,
indicating that the palatable plant biomass was the highest and the unpalatable plant biomass was the lowest at 14
available burrow per 625m2. In the economic groups of plant biomass, the weed biomass was the highest and the
legume biomass was the lowest at any available burrow densities, and the grass biomass and the sedge biomass
were related to available burrow densities, indicating that the sedge biomass were bigger than the grass biomass at
3 available burrow per 625m2, inverse at 54 available burrow per 625m2, similar between 3 and 34 available
burrow per 625m2. Accompanying by the increase of available burrow densities, the legume biomass and the sedge
biomass significantly decreased (P<0.05) and the legume became disappearance at 54 available burrow per 625m2;
the grass biomass firstly increased and then decreased, peaking at 14 available burrow per 625m2. The weed
biomass firstly decreased and then increased, and was the lowest at 14 available burrow per 625m2. This study
suggested that the responses of alpine meadow communities to population density of plateau pika at 14 available
Corresponding
author. Tel. +86-931-8913247
E-mail address: [email protected] (Z. G. Guo)
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burrows per 625m2 were more sensitive than that at other available burrow per 625m2 from plant species diversity,
biomass, height, cover and economic group.
Keywords：Plateau pika; Available burrow density; Alpine meadow; Qinghai-Tibetan plateau
1. Introduction
The continual increase in population density of the plateau pika (Ochotona curzoniae)
develops a rat trouble, which threatens the health of alpine meadow ecosystem and the
development of animal husbandry economy in the Qinghai-Tibetan Plateau, but the plateau pika is
a survival animal component of alpine meadow ecosystem in the process of ecosystem evolution.
Previous studies have proven that the plateau pika plays the negative and positive roles in meadow
alpine ecosystem, which depends on its population density [1]. The right density of plateau pika
not only provides foods for endemically carnivorous mammal and raptor which lives in the
Qinghai-Tibetan Plateau [2], but also acts as disperse carrier of plant seeds, which encourages
some plants to expanse their distribution [1,3]. The burrow produced by plateau pika not only
increases the conservation water ability of alpine meadow by enabling more rainfall to permeate
into deep soil, which increases water supplies for plant growth[4]，but also provides habitats,
reproductive place and shelter for insects, lizard and snow finch [1]. The plateau pika has
presently been considered as a keystone species in the alpine meadow ecosystem [2], and the great
change of its population density generally causes the structural and functional variation of alpine
meadow ecosystem. The lower density of plateau pika weakens its basically connecting link
between the preceding and the following creature in the food web of alpine meadow ecosystem,
however, its higher density often causes a rat trouble by competing food resources with livestock
and destructing the soil structures with burrowing behavior. From self-control view of ecosystem,
the increase or decrease of plateau pika density arouses the changes of vegetation components in
the alpine meadow ecosystem, inversely; the vegetation degradation or improvement often adjusts
the plateau pika density. Therefore, the aim of plateau pika control is to keep its density into a
rational density rather than never-ending decrease its density.
Plant community is the core component of alpine meadow ecosystem, and its structure and
components varies with the changes of plateau pika density because the activities of plateau pika
increase the environmental heterogeneity [2, 5] and distribution area of some spermatophyte [6],
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inhibits some specific plant growth due to selective intake of plateau pika [1]. The structural
changes of plant community affect the habitats of plateau pika, and further affect the migration
behavior of plateau pika. Previous studies have shown that the plateau pika considers the higher
height and cover vegetation as a predation risk, and lives in the habitat with low vegetation height
and cover, even in the habitat with bare patch [7]. Therefore, understanding the relationship
between plant community and density changes of plateau pika will provide useful profile for
quantifying the appropriate population density of plateau pika to control this small manual. The
objective of this study is to determine the effect of density changes of plateau pika on alpine
meadow communities in the Qinghai-Tibet Plateau by using available burrow density substituting
for plateau pika density.
2. Method and materials
2.1. Study area
The study was carried out in the Dawu town of Maqin County, Qinghai Province (32°31′–35°31,
96°54′–101°51′). The study area locates in the Yellow River source area of Qinghai-Tibetan
Plateau with the average elevation from 3874 m to 3780 m. the annual mean precipitation is 528.5
mm, mainly taking place during the period June to September, and the annual evaporation is 2470
mm. The mean temperature is -3.9 ℃ without free frost period. The climate in this area is plateau
continental climate, in which spring, summer, autumn and winter is not identified, and the climate
is divided into short warm season (from June to September) and long cool season (from October to
May). The accumulative temperature with ≥5 ℃ is 850 ℃ and the period of plant growth is only
156 d.
The soil is alpine meadow soil and alpine bush meadow soil with 30-50 cm thick [4], and
their parent materials are chiefly residual deposits with coarse texture, consisting mostly of sand.
Original vegetation is alpine meadow, which is dominated by Kobresia humilis with the main
associate plant species of K. pygmaea, K. capillifolia, Aconitum szechenyianum, Stekkera
chamaejasme, Ligularia virgaurea, Oxytropis coerulea, Elymus nutans, Poa annua, Stipa aliena,
Leontopodium leontonpodioides, Ajuga lupulina, Artemisia nanschanica and Potentilla sp.
2.2. Experimental design
A field survey was carried out on the cool season rangeland to avoid the effect of grazing on
alpine communities in the process of survey, in which the yak and Tibetan sheep was grazed from
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middle October to early April, and rangeland during warm season is close grazing. It is difficult to
determine plateau pika density by recording its number due to its family life pattern, therefore, the
available burrow density of plateau pika was used to substitute for its own density. The higher
available burrow density meant the higher plateau pika density [8]. 40 survey plots with the size of
25 m×25 m (625 m2) was randomly selected on the similar meadow flat and the available burrow
density in each plot was recorded by closing burrow exit for three days in May, 2009, and the
distance between plots was over 50 m. According to available burrow number in plot, the plots
was divided into four categories, in which 3(3±1), 14(14±2), 34(34±3), and 54(54±4) available
burrow density per 625 m2 were finally selected to investigate the response of alpine meadow
communities to available burrow densities of plateau pika, and each category was three plot as
replicates.
2.3. Field survey and sampling
The field survey was conducted from late July to early August in 2009. In each plot, five
subplots with the size of 1 m×1 m were designed with “W” pattern distribution to collect
quantitative data on the vegetation and distance between subplots was over 10 m. The total
number of subplots was 60. In each subplot, present species number, total biomass and every
species biomass (g), vegetation height and every species height (cm), total cover and every species
cover (%) were recorded. The total foliage cover was measured by using 100 points (1 mm wire).
Vegetation height was measured by lowering a perforated foam disc (diameter 0.1 m, weight 7 g)
onto the vegetation along a gauged stick. Aboveground materials of all plants rooted in each
subplot were collected by single species, and carried back, and then dried at 80 degrees centigrade
for 24 h and weighed in the laboratory. Subplot data within each plot were pooled.
2.4. Data analysis
Importance value of species was calculated with the equation, IV = (relative height +
relative cover + relative biomass)/3, and it was used to determine the dominant species and
associate species.
Three indices were chosen for estimation of α diversity [9], (1) the richness index (S) is
represented by number of species recorded in each subplot; (2) the diversity index was measured
n
by the Shannon-Wiener's index of diversity, H   Pi LnPi i ; and (3) the evenness index was
i 1
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measured by the Pielou's index of evenness, J sw  H / LnS , where Pi  Ni / N ; Ni is the
importance value of individual species i; N is the total individuals of all species present; S is
number of vascular species present.
Based on principle of grassland utilization, the plant in subplot was divided into four
economic groups, including grass group, sedge group, legume group, and weed group [10].
Differences in plant species diversity, cover, biomass, and soil parameters among alpine
meadows of four available burrow densities were analyzed by using one-way ANOVA.
3. Results
3.1. Effect of available burrow densities on component and vertical structure of plant communities
The number of plant species ranged from 43 to 32 in the subplot, and firstly increased and
then decreased as the available burrow density increased (Table 1). Although the dominant species
always was K. humilis, the associate species obviously changed with the increase of the available
burrow density, indicating that A. szechenyianum at 3 available burrow density per 625 m2 was
replaced by S. chamaejasma at 14 available burrow density per 625 m2, and replaced by L.
virgaurea and O. coerulea at 34 and 54 available burrow density per 625 m2, respectively. The
change of associate species in plant communities resulted in difference of family and genus. The
number of plant species and genus in the subplots firstly decreased and then increased, and was
the lowest at 34 available burrow density per 625 m2; however, the number of family in the
subplots firstly increased and then decreased, peaking at 14 available burrow density per 625 m2.
The available burrow density greatly affected the vertical structure of plant communities. The
plant communities at 3 available burrow density per 625 m2 were double layers, in which A.
szechenyianum occupied the upper layer and the plants from sedge family grew at low layer.
At 14 available burrow density per 625 m2 conditions, the upper layer was occupied by grass and
S. chamaejasma and the low layer was took up by plant from sedge genus and low weeds. The
vertical structure of plant communities varied with the growing season of main associate plants
when the available burrow density was over or equal to 34 burrow density per 625 m2, indicating
that the plant communities were single layer when L. virgaurea and O. coerulea was vegetative
growth stage and they were double layers when L. virgaurea and O. coerulea entered into
reproductive growth stage.
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Table 1 Effect of available burrow densities of plateau pika on community structure of alpine meadow
Species number
Familia Genus Species
Aconitum szechenyianum,
16
38
43
Kobresia capillifolia
Burrow densities
(number/ 625 m2)
Dominant species
3
Kobresia humilis
14
Kobresia humilis
Stellera chamaejasma,
Leontopodium alpinum
20
33
37
2
34
Kobresia humilis
Ligularia virgaurea,
Artemisia nanschanica
16
29
32
1or 2
54
Kobresia humilis
Oxytropis coerulea,
Ajuga lupulina
16
30
35
1or 2
Associate species
Vertical
structure
2
3.2. Effect of available burrow densities on height and cover of plant communities
The height of plant communites decreased as the available burrow density increased ( Figure
1A), indicating that the height of plant communites at 3 available burrow density per 625 m2 was
significantly bigger than that at 34 and 54 available burrow density per 625 m2 (P<0.05). The
cover of plant communities firstly decreased and then increased with the increase of available
burrow density (Figure 1B), and it was the lowest and was over or equal to 80% at 14 available
burrow density per 625 m2.
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a
Height(cm)
9
ab
b
b
6
3
0
3
14
34
54
A
2
Cover(%)
Available burrow densities(number/625m )
a
100
90
80
70
60
50
40
30
20
10
0
ab
a
34
54
b
B
3
14
2
Available burrow densities(number/625m )
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Fig. 1. Effect of available burrow densities of plateau pika on height (A) and cover (B) of alpine meadow
3.3. Effect of available burrow densities on species diversity of plant communities
With the increase of available burrow density, the richness index of plant communities firstly
decreased and then increased (Figure 2A), indicating that the richness index at 34 available
burrow density per 625 m2 was the lowest and signficantly lower than that at other burrow
densities per 625 m2 (P<0.05). The evenness index of plant communities firstly increased and then
decreased as the available burrow density increased (Figure 2B), and it peaked at 14 available
burrow density per 625 m2 and was significantly bigger than that at 3 and 54 available burrow
density per 625 m2. The diversity index of plant communities was not different between 14 burrow
number per 625 m2 and 54 available burrow number per 625 m2, and they were significantly
bigger than those at 34 and 3 available burrow number per 625 m2 (Figure 2C).
a
30
ab
ab
b
Richness index
25
20
15
10
5
0
3
A
14
34
54
Available burrow densities(number/625m2)
1.2
Evenness index
1
b
a
ab
b
34
54
0.8
0.6
0.4
0.2
B 0
3
14
Available burrow densities(number/625m 2)
7
3.5
Diversity index
a
b
3
a
b
2.5
2
1.5
1
0.5
0
3
14
34
54
Available burrow densities(number/625m 2 )
C
Fig. 2. Effect of available burrow densities of plateau pika on the richness index (A), evenness index (B), and
diversity index (C) of alpine meadow community.
3. 4. Effect of available burrow densities on biomass of plant communities
The total plant biomass firstly decreased and then increased as the available burrow density
increased (Figure 3A), and was the lowest at 14 available burrow densities per 625 m2. The
palatable plant biomass was not consistent with the unpalatable plant biomass (Figure 3B). The
palatable plant biomass increased from 3 available burrow density per 625 m2 to 14 available
burrow density per 625 m2 and decreased when the available burrow density per 625 m2 was over
14, and the unpalatable plant biomass firstly decreased and then increased with the increase of
available burrow density, and was the lowest at 14 available burrow density per 625 m2, and
these implied that the increase of available burrow density changed the total biomass and
palatable biomass, in which 14 available burrow density per 625 m2 was points of inflection
point.
a
Total biomass(g/m 2 )
180
b
150
b
ab
120
90
60
30
0
A
3
14
34
54
Available burrow densities(number/625m 2 ）
8
160
Palatable
Biomass(g/m2 )
140
a
a
a
Unpalatable
120
b
100
80
60
b
a
c
40
c
20
0
B
3
14
34
54
Available burrow densities(number/625m 2 )
Fig. 3. Effect of available burrow densities of plateau pika on the total biomass (A),
and palatable and
unpalatable biomass (B) of alpine meadow community (The same bar with the different a, b and c means
significant difference at 0.05 level)
3.5. Effect of available burrow densities on economic groups of plant communities
The biomass of weed group accounted for the largest percentage of the total plant biomass at
four available burrow densities (Table 2), mainly consisting of Delphinium grandiflorum, Ajania
purpurea, Pedicularis kansuensis, A. szechenyianum, L. virgaurea; however, the biomass of
legume group mainly deriving Astragalus membranaceus and Gueldenstaedtia verna was the
lowest. The percentage of grass and sedge group biomass in the total plant biomass varied with the
increase of available burrow density. The biomass of sedge group was bigger than the biomass of
grass group at 3 available burrow density per 625 m2, and was lower than the biomass of grass
group at 14 available burrow density per 625 m2, and the biomass of grass and sedge group was
similar when available burrow density was over or equal to 34 available burrow density per 625
m2. The biomass of legume group significantly decreased as the available burrow density
increased (P<0.05) and disappeared at 54 available burrow density per 625 m2. The biomass of
weed group firstly decreased and then increased with the increase of available burrow density, and
was the lowest at 14 available burrow density per 625 m2. This study showed that the most
sensitive response of weed, sedge, grass group to available burrow density was 14 available
burrow densities per 625 m2.
Table 2 Effect of available burrow densities of plateau pika on economic groups of alpine meadow (g/m2)
Burrow densities(number/ 625 m2) Grass
Sedge
legume
weed
3
11.75±1.23c
46.09±3.21a
1.88±0.23a
104.99±10.36b
14
30.26±2.34a
28.12±2.41b
1.52±0.12b
81.02±4.52c
34
12.39±1.98c
13.67±1.89c
0.99±0.08c
121.51±9.56a
54
16.75±2.01bc
11.94±2.12c
0
124.43±11.23a
Note: The data means the average value ± SE, and the data with the same letter in a column was not significantly
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different at 0.05 level.
4. Discussions
4.1. Relationship between the available burrow density and the structure and productivity of
alpine meadow
The activities of plateau pika redistribute the light energy and water resources to various
extent in the land surface and soil when the plateau pika enters into slightly degraded alpine
meadow, which affects the plant growth consisting of plant communities by directly or indirectly
ways [7], sometimes, developing a short-term stability habitat. This habitat often varies with the
increase of plateau pika density. This study suggests that the available burrow density affect the
primary productivity of alpine meadow by changing the vertical structure, plant species number,
height, cover and biomass. The disturbance of plateau pika activities on alpine meadow is very
weak at 3 available burrow density per 625 m2; consequently, the alpine meadow maintains its
own features and productivity. At 14 available burrow density per 625 m2, the vegetation cover
decreases because the more plant was grazed and buried by plateau feeding and burrowing
behavior. With the further increase of available burrow density, the bare patch increases [8], and
this provides invasion changes for opportunistic species, especially braod-leaves plant, resulting in
increasing the vegetation cover. The plateau pika affects the vertical structure of alpine meadow
community by causing the replacement of assocaite species, and the growth stages of these
assocaite species regulates the vertical structure. At 34 available burrow density per 625 m2, the
vertical structure of alpine meadow community changed from single layer into double layers when
L. virgaurea grows from vegetative stage with low height to reproductive stage with the high
height, and this implies that the influence of plateau pika on the vertical structure of alpine
meadow community is related to sample time because the height of broad-leaved plant was
different between vegetative stage and reproductive stage [11].
As the available burrow density increases, the total biomass and unpalatable biomass firstly
decreases and then increases, and the palatable biomass shows a inversely trend, at the same time,
the biomass of weed group accounts for the biggest percentage of the total biomass, and these
imply that the total biomass of alpine meadow is determined by weeds not palatable plant and the
activities of rational plateau pika improve the quality of alpine meadow [10] by increasing the
palatable biomass. Alpine meadow maintains its own competition pattern of plant populations
10
because the plateau pika has limited influence over alpine meadow when its density is low [12], in
which A. szechenyianum is mainly associate species with high height and rich leaves and
stems. The increase of available burrow density encourages S. chamaejasma and L.
alpinum with low height to replace the A. szechenyianum and to become the mainly
associate species, which provides the good light for palatable sedge plant growing at the
low layer, resulting in increasing the palatable biomass. With the further increase of
available burrow density, the bare patch increases and soil gradually become
mesophytization, which restrained the growth of sedge plants [13] because edge plants are
hygrophyte, however, in the mesophytization environment, the broad-leaved plants, such
as L. virgaurea and A. lupulina, grow well because of their good reproductive and strongly
adaptive ability [9], consequently, the palatable biomass decreases and the unpalatable
biomass increases.
3.2. Relationship between the available burrow density and the plant diversity of alpine meadow
The community structure of alpine meadow with different plant species affect where the
plateau pika lives, and further regulates the population density of plateau pika to some extent,
inversely, the population density of plateau pika affects on the plant species diversity of alpine
meadow [14] by consuming the specific plant. Although this study generally supports the
intermediate disturbance hypothesis [15], the effects of available burrow density on the richness
index, evenness index and diversity index are different in the increasing process of available
burrow density. The richness index and the evenness index reflect the absolute density of
population and the relative the density of population in a community, and the diversity index
reflects the both absolute and relative the density of population in a community [9]. The diversity
index at 54 available burrow density per 625 m2 is higher than that at 34 burrow density per 625
m2 because of two reasons, firstly, the bigger pare patch encourages the competition between
populations to become unsteadiness, and some plants from soil bank and some opportunistic
species have chance to germinate and grow well, resulting in increasing species number in plot
[16]; secondly, the increase of surface evaporation reduces the soil moisture, providing good
environments for xerophyte to invade into bare patch in the alpine regions [7], and this is in accord
to the result from plateau oker (Myospalax baileyi), in which grass plants invade into big molehill
and increase the species number [18].
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3.3. Relationship between the available burrow density and the economic group of alpine meadow
Although four economic groups are identified in the alpine meadow community, they shows
the different ability of transferring primary productivity into secondary productivity [10], in which
some economic groups perform higher transformation efficiency because livestock like to feed on
them. In this study, the biomass of each economic group is closely related to available burrow
density of plateau pika. In weed group, some plants, including Lagotis brachystachya, Aster
alpinus, Herba Taraxaci, Potentilla bifurca, P. Multifida, Polygonum sibiricum, Ajania trilobata,
Leontopodium alpinum, are fed by livestock to various extents; however, others are not fed by
livestock and they are L. virgaurea, Glaux maritime, Gentiana dahurica, Elsholtzia densa,
Veronica polita, Saussurea japonica. The biomass of weed group is the lowest at 14 available
burrow density per 625 m2 and is the highest at 54 available burrow density per 625 m2, and these
implies that the modest increase of plateau pika density, increasing from 2 to 14 burrow density
per 625 m2, is advantageous to improve the quality of alpine meadow by reducing the weed
percentage, in which plateau pika control weeds by feeding behavior. However, the plateau pika
can not effectively control the weeds when the available burrow density is over 34 available
burrow density per 625 m2, in which sedge plant with good quality is replace by weeds because
the stronger activities of plateau pika changes the habitats where the sedge plants grow, such as K.
humilis, K. pygmaea, and K. Capillifolia. The nutrient value and feeding value of legume group
varies with the plant species. Astragalus membranaceus is high in nutrient value and feeding
value, but O. coerulea is high in nutrient value and is low in feeding value, which reduces the
quality of alpine meadow [10]. The biomass of legume group decreases as the available burrow
density increases and disappears at 54 available burrow density per 625 m2 because plateau pika
possibly feed legume plant or legume plant is not suitable for new habitats, indicating that legume
group is more sensitive to environmental change than other groups. Grass group plant with high
crude protein is palatable at vegetative stage, and livestock likes to feed them. The biomass of
grass group increases when the available burrow density increases from 3 to 14 available burrow
density per 625 m2, contributing to palatable biomass, but they are still is associate species in
alpine meadow and contributing a little to the total biomass.
Acknowledgments
This study was supported by National Natural Science Foundation of China (31172258) and
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the National Science and Technology Plan of China (2009BAC53B04).
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