Download Influence of population density on group sizes in goitered gazelle

Eur J Wildl Res
DOI 10.1007/s10344-012-0641-3
ORIGINAL PAPER
Influence of population density on group sizes in goitered
gazelle (Gazella subgutturosa Guld., 1780)
David Blank & Kathreen Ruckstuhl & Weikang Yang
Received: 7 January 2012 / Revised: 20 March 2012 / Accepted: 22 May 2012
# Springer-Verlag 2012
Abstract We conducted our study in Ili depression,
south-eastern Kazakhstan during 1981–1989 to investigate
how group sizes and group class frequencies change with
increasing population densities in goitered gazelles. In
addition, we compared our study to data on group size
and group class frequency of various goitered gazelle
populations in Kazakhstan with very variable population
densities. We found that mean group size was a more
variable index than group class frequency. Population
density had some effect on mean group sizes, but the
strength of the influence was quite weak, and only in
cases where densities of two populations varied more
than sevenfold did group sizes start to change. Group
class frequency was not correlated with population density at all. The impact of the yearly breeding cycle on
group size was bigger than population density. The
density-dependent response of goitered gazelle population
was curvilinear in fashion, and it may be classified as
Communicated by P. Acevedo
D. Blank (*) : W. Yang
Key Laboratory of Biogeography and Bioresource in Arid Land,
Xinjiang Institute of Ecology and Geography,
The Chinese Academy of Sciences,
Urumqi 830011, China
e-mail: [email protected]
D. Blank
Institute of Zoology, Kazakh Academy of Sciences,
Alma-Ata, Kazakhstan
K. Ruckstuhl
Department of Biological Sciences, University Calgary,
Calgary, Canada
K. Ruckstuhl
Zoology Department, University of Cambridge,
Cambridge, UK
intermediate between social-dwelling ungulate species, living
in large groups and demonstrating continuous (linear)
increases of group size with population density and those that
are solitary or territorial ungulate species with no relationship
between population size and group size, though the goitered
gazelle population’s weak response was distinctively closer to
the one of solitary ungulate species.
Keywords Goitered gazelle . Group size class . Mean group
size . Population density
Introduction
Density dependence is a key concept in population dynamics
because it determines resource availability and the partitioning
of food among individuals. Most studies on density
dependence deal with physical conditions, growth, births
and mortality rates (Caughley 1970; Kie et al. 1980; Skogland
1983, 1985). Less often, researchers considered the influence
of population density on ungulate social behaviour (Berger
1978; Fowler 1987). Obviously, the available forage biomass
declines with increasing ungulate density, and per capita food
intake declines with decreasing availability (Wickstrom et al.
1984). Increasing density should force ungulates to change
their behaviour and, in the first place, group size and
sometimes the whole social structure, due to scramble
competition over limited food supplies. Various ungulate
species live in different habitats, have different body sizes,
variable diets and feeding styles and, as a consequence, have
different group sizes or social structures (Brashares et al.
2000; Jarman 1974). Environmental factors have been
considered as a key factor in explaining ungulate social
organisation, although other factors, such as predation
risk, reproductive strategies and social affinities, have
Eur J Wildl Res
been identified as being equally important in shaping
group types and sizes (Bon et al. 2001; Hamilton 1971;
Roberts 1996; Underwood 1982).
According to the optimal group size hypothesis, every
individual prefers to be in a group whose size is a close as
possible to the value that maximises its vital physiological
and social requirements (Pepin and Gerard 2008). Groups of
some animals (cetaceans, proboscideans and many primates)
are quite stable, and their mean group size is independent of
population density (Dittus 1987; Henzi et al. 1997; Lehmann
and Boesch 2004; Karczmarski et al. 2005; Wittemyer et al.
2005), while others (some ruminants and kangaroos) form
fission–fusion groups, whose size is very sensitive to
population density (Gerard et al. 2002) and their group sizes
increase with population density (Barrette 1991; Lawes and
Nanni 1993; Taylor 1983; Toigo et al. 1996; Wirtz and
Lorscher 1983).
Fowler (1987) considered the density dependence of
group sizes in 21 large herbivores species and reported that
17 of them had such dependence. He supported the idea of
Eberhardt (1977) that group sizes had different sensitivities
to changes in population density. The group size and its size
frequency in some social-dwelling deer species (Axis axis,
Capreolus capreolus, Cervus nippon, Cervus elaphus and
Dama dama), which prefer to stay in large groups (3–6 and
even larger size), were positively affected by population
density (Barrette 1991; Borkowski 2000; Hebblewhite
and Pletscher 2002; Stuwe and Hendrichs 1984; Thirgood
1996; Vincent et al. 1995). An increase in group size
with population density has also been reported for some
African antelopes (Kobus and Redunca—Spinage 1969;
Wirtz and Lorscher 1983). Alpine ibex (Capra ibex)
and chamois (Rupicapra pyrenaica), which usually live in
large groups of 3–10 individuals (Lovari and Consentino
1986; Toigo et al. 1996), also have a distinct tendency of
group sizes to increase with population density (Pepin and
Gerard 2008; Toigo et al. 1996). Peccaries (Tayassu pecari),
which are usually very social ungulates living in large groups
of 20–300 individuals, decreased their group size with decreasing population density (Reyana-Hurtado et al. 2009).
In contrast, moose (Alces alces) did not show such density
dependence on group sizes, and in Sweden, home range sizes
were not affected by differences in moose density (Sweanor
and Sandegren 1989). Comparison of various populations of
different subspecies of moose in Alaska, Minnesota and
Montana demonstrated that group size varied seasonally
according to the yearly breeding cycle, and though the
largest group sizes did occur with the densest populations,
density did not appear to influence trends in aggregation sizes
through the year (Peek et al. 1974). The oribi (Oerebia
ourebia) is a territorial antelope with small group sizes,
which may increase with population density (Arcese et al.
1995), but within very limited changes (Rowe-Rowe et al.
1992). Gorals (Nemorhaedus goral), duiker (Sylvicapra
grimmia) and steenbok (Raphicerus camelus) are not
particularly social and predominantly solitary species,
and their group size is very stable and does not change
over the seasons (Bergstrom and Skarpe 1999; Pendharkar
and Goyal 1995). From this, it becomes clear that population
density is more likely affecting group size in social species,
which form mostly large groups and even huge aggregation
under some conditions, whereas such impacts would be weak
for ungulates that prefer a solitary lifestyle or are staying in
small groups.
Goitered gazelles (Gazella subgutturosa Guld., 1780) are
able to gather in groups of several tens of individuals,
though singletons and small groups (<4 individuals) are
more typical than large herds (Zhevnerov et al 1983; Blank
1990, 1992). Males of goitered gazelles have individual
territories, but only during the rutting period (November–
December), whereas the rest of the year they roam freely all
over their home range and gather in groups of adult and
yearling males, which were expelled by territorial males
from the family groups during the rutting season (Blank
1998). Females leave their herds and stay alone for giving
birth (May), but they gather into groups several weeks after
the appearance of offspring and later they unite into larger
groups including several mothers and their young (Blank
1986). Mixed-sex groups are uncommon for goitered
gazelles during most of the year and only during migration
in March–April and October do they gather in large mixed-sex
groups of several hundred individuals (Blank 1990, 1992).
Goitered gazelles may thus change their group size according
to their biological life cycle, with most females staying
solitary during birthing in spring and males being solitary
during the rut in autumn–winter but gathering in especially
large herds for migrations twice a year (Blank 1992).
Therefore, goitered gazelles have a wide span of group
sizes from singletons to herds of several tens, occupying an
intermediate position between social-dwelling species, living
in large groups and exclusively solitary or territorial species,
for which large groups are atypical. That is why the
consideration of relationship between group size and
population density in goitered gazelles would be especially
interesting. We thus hypothesise that goitered gazelle groups
sizes will grow with increasing population density and that the
frequency of such large groups will increase as well.
The Kapchagaj population of goitered gazelle is protected
from poaching and therefore demonstrated the highest indices
of population density (Tables 1 and 2). Other populations in
Kazakhstan have virtually no protection from poaching and
have thus suffered substantial losses due to poaching (Blank
1990), and as a result, they occur at uncharacteristically low
densities (Tables 4 and 5). In fact, we reported before (Blank
1990) that poaching was the single-most factor explaining the
striking differences in population densities between the
Eur J Wildl Res
protected Kapchagaj population and the other desert
populations. Because of the severe effect of poaching
on gazelle densities, we did not consider the impact of
rainfalls and consequently plant densities, composition
and biomass on goitered gazelle group size and its
frequencies. We thus were primarily interested in testing
if mean group size and frequency of gazelle groups
would correlate with their local population densities.
Materials and methods
We conducted the study on goitered gazelles living in the
Kapchagaj Nature Reserve (Ili depression, south-eastern
Kazakhstan) from 1981 to 1989. This area is now within
the Altyn-Emel National Park, with a size of 4,600 km2.
Periodically, additional population censuses were carried out
in various deserts of Kazakhstan (Aktau, 300 km2; Panfilov
Karakum, 250 km2; Boguty, 1,200 km2; Taukum, 8,000 km2;
Saryishikotrau, 24,000 km 2; Muunkum, 37,500 km2;
Betpakdala, 75,000 km 2—Skotselias 1995). We used
two kinds of indices: mean group size (number observed
individuals per encountered group) and group size class
frequency (10 classes from 1 to 10 individuals and the
11th class for groups that are larger in size than 10
individuals). For checking our hypothesis, we compared
the number of two types of groups with each other:
singletons and groups from 2 to 4 individuals. We
proceeded from two assumptions. (1) If the group size
of goitered gazelle increases with density, then firstly, the
number of singletons are expected to decrease and the number
of small groups (2–4 individuals) to increase, as was observed
for sika deer, for example (Borkowski 2000); and (2)
singletons and small groups (2–4 individuals) are the
most numerous types of groups in gazelle population in
Kapchagaj reserve (X±SE086.9 %±1.2, n027) and in
other deserts (X±SE093.5 % ±2.5, n013).
We collected two data sets to verify our hypothesis that
population density affects average group sizes. Firstly, we
used the data from our long-term study of goitered gazelle
ecology and behaviour in the Kapchagaj Reserve, when this
population increased their density (from 1.63 to 2.75
gazelles per 1 km2) between 1981 and 1989 (Tables 1 and
2). Secondly, we used the census data from the various
desert populations, which turned out to have very different
population densities (from 0.05 to 2.75 gazelles per 1 km2—
Tables 4 and 5). Values of the goitered gazelle density in
various deserts were taken from published materials (Blank
1990; Blank and Kovshar 1988; Kovshar and Blank 1986).
In the Kapchagai Nature Reserve, we counted gazelles
along pedestrian transects (total of 2,000 km) and car routes
(10,000 km). Gazelle counts were done once every month.
To avoid re-sampling, the same individual during a census
we used the following method. We did a south–north parallel
transects every 5 km, which covered the whole study area (24
transects, between 8 and 20 km in length each). We moved not
more than 20 km/h (vehicle) from west to east along transects,
stopped every 3 km and counted gazelles along transects from
each side forward using binoculars (magnification ×8) and
telescopes (magnification ×30, ×60), but did not count any on
the way back when crossing an already sampled area. During
focal observations, we always moved the telescope clockwise
and registered antelopes within distances of 0.5 km. In other
deserts, we used the same method of counting along parallel
transects every 15–20 km (along existing roads in the sandy
deserts) covering different areas within every desert and
stopping every 3 km for sampling gazelles from elevated
watch points and registered all visible ungulates within
distances of 0.5 km. According to our estimations, we
sampled more than 80 % of the entire gazelle population in the
Kapchagaj Nature Reserve, Aktau, Panfilov Karakum and
Boguty, while not more than 25 % of the population
was sampled in Taukum, Saryishikotrau, Muunkum and
Betpakdala because of the huge sizes of these deserts. It
is possible that the gazelle populations of the Aktau
have some kind of limited connections with the Kapchagaj
Nature Reserve population, while gazelle population from
other deserts do not have any connections with each other at
all.
During scans, we recorded the number, size and location
of groups. Gazelles were noted as member of a group if they
were <50 m from each other, moved in the same direction
and stayed together longer than half an hour. These are
measures commonly used in defining groups of ungulates
(Ruckstuhl 1998).
The differences in mean group size over years were tested
with one-way ANOVA, as tests for normality of these data
were satisfied (Kolmogorov–Smirnov test). Fisher’s least
significant differences post hoc comparison was used to
compare means between separate pairs of values (subgroups).
In addition, we used a general linear model (GLM, type 4 sum
of squares) to test the impact of month and density on group
size of the gazelle population in Kapchagaj Nature Reserve
and other deserts. In addition, we performed independentsample t tests for comparing group size for pairs of different
goitered gazelle populations, living in different deserts. We
used chi-square-goodness-of-fit tests to analyse changes in the
frequency of various group sizes under different population
densities.
Results
Kapchagaj Reserve population We found significant
monthly variability for mean group size and group class
frequency between 1982 and 1985 (one-way ANOVA,
Eur J Wildl Res
Table 1 Mean group size of goitered gazelle population in the Kapchagaj Nature Reserve enlarging its population density (individuals per square
kilometer) over years
Years–density ind/km2
Months
April
May
June
July
September
November
1981–1.53
–
–
–
–
–
N0230
3.23±0.20
1982–1.65
N0256
2.53±0.15
N0211
2.26±0.14
–
N0186
2.89±0.17
N053
2.30±0.16
N091
2.55±0.17
1983–1.74
–
N0211
2.23±0.11
N0286
N085
1.73±0.14
N0433
–
–
–
N0162
–
–
2.14±0.12
2.29±0.10
2.09±0.10
N0516
N0412
N0752
N0760
N0254
N0313
3.96±0.23
2.45±0.12
2.28±0.08
2.71±0.09
3.71±0.25
2.88±0.16
–
N0328
N0439
2.26±0.09
N0853
2.39±0.14
2.35±0.08
–
–
–
ANOVA
F00.998
df04
P>0.05
1984–1.69
1985–1.83
1986–2.15
1987–2.29
t test
F013.537
N0285
1.76±0.08
N01037
1.83±0.07
ANOVA
F06.872
df0771
P<0.0001
df05
P<0.0001
1989–3.67
Significance of difference
F021.902, df05, P<0.000), though such differences were
much less significant for 1982 (one-way ANOVA, F02.289,
df05, P00.044). We thus decided to only compare yearly
indices of the same calendar month for our analyses.
The Kapchagaj population with the highest density of
goitered gazelle in Kazakhstan had the following distribution
December
N0127
2.80±0.21
–
N0429
N0306
2.85±0.13
–
3.89±0.25
–
–
–
ANOVA
F06.633
N01517
3.29±0.12
ANOVA
F05.252
ANOVA
F05.422
ANOVA
F08.269
df03
P<0.0001
df02
P00.005
df03
P00.001
df02
P<0.0001
N0217
4.29±0.39
of group class frequency (Fig. 1). Singletons were the most
often noted kind of group, followed by herds of two and three
individuals (chi-square test, χ2 04.587, df01, P00.032 and
χ2 010.286, df01, P00.001). The proportion of bigger size
groups was considerably smaller, decreasing continuously
from 7.5 % (groups from 4 individuals or class 4) to 0.1 %
Table 2 Proportion (%) of singletons to groups (2–4 individuals) of the goitered gazelle in the Kapchagaj Nature Reserve population enlarging its
population density (individuals per square kilometer) over years
Years–density
ind/km2
Months
April May
June
July
September
24/61
30/64
1981–1.53
November
December
33/46
1982–1.65
46/39 50/40
1983–1.74
43/48
59/38
1984–1.69
54/38
43/50
46/49
1985–1.83
28/48 42/45
49/42
32/57
30/46
40/44
40/52
36/57
38/48
36/39
1.254-0.001
0.592-0.045
1986–2.15
1987–2.29
60/36
1989–3.67
Chi-square
(χ2)
df01
P value
58/33
35/48
37/46
27/50
70/23
41/43
7.332 208.957–0.580
96.481-0.662
1
P00.000–0.416
P00.000–0.104
P00.000–0.650
P00.263–0.980
P00.442–0.832
Totally 6 of 10 cases
were P<0.05
Totally 4 of 6 cases
were P<0.05
Totally 2 of 3 cases
were P<0.05
Totally 6 cases
were P>0.05
Totally 3 cases
were P>0.05
P00.000-0.446
0.007 Totally 12 of 15 cases
were P<0.05
25.154-2.636
12.145-0.206
Eur J Wildl Res
45
Groups
40
Portion in percentage, %
Fig. 1 Portion of different
group-size classes in goitered
gazelle among all observed
groups (groups) and number of
individuals observed inside of
every class (individuals)
Individuals
35
30
25
20
15
10
5
0
1
2
3
4
5
6
7
8
9
10
>10
Group size
(from 10 individuals or class 10) and, after that, an abrupt
increase in the portion of groups of more than 10 individuals
(from 0.1 to 2.4 %—Fig. 1). In regards to the proportion of
individuals staying in the different group size classes, most
gazelles were found to form groups of 3 individuals (17.7 % of
all gazelles), 2 (16.6 %), groups of more than 10 individuals
(15 %) or remain as singletons (14.3 %). These portions were
not significantly different from each other (chi-square-goodnessof fit test, χ2 00.625, df03, P00.891). The rest of the gazelles
stayed in groups of 4–10 individuals (10.8 % of gazelles stay in
groups of 4 and 2.3 % in groups of 10 individuals).
Changing characteristics of the Kapchagaj Reserve population
over years The mean group size of the Kapchagaj Reserve
population varied significantly over the years for all checked
months, except for June (Table 1). In April and December,
mean group sizes increased over the years, whereas in May,
they generally had a decreasing trend. During July, September
and November, mean groups size increased and decreased
without any clear trend (Table 1, r0−0.19, N08, P00.964).
Neither population density (GLM, F00.465, df07, P00.843)
nor month significantly affected mean group size (GLM,
F00.339, df06, P00.155).
Unlike mean group size, which significantly changed
over the years for all months, the group size class frequency
in the Kapchagaj Reserve population varied significant only
in some cases (25 of 44 cases, Table 2). However, the
correlation between population density and proportion of
singletons and groups was significant only for May and
partially for December (Table 3). There was no effect
of density and month on group size frequency (GLM,
F00.707, df07, P00.668 and F00.339, df06, P00.903,
respectively).
Comparing characteristics of the gazelle populations of
different deserts The mean group size of the goitered gazelle
populations of various deserts with different population
densities only significantly differed between some cases
but not others (Table 4); there were no differences for
desert comparisons (GLM, F02.232, df016, P00.353).
The high-density population of Kapchagaj Reserve had
the same mean group sizes as the considerably lowerdensity populations of Aktau and Boguty and other
comparisons yielded similar results despite having different
population densities (Taukum, Saryishikotrau, Muunkum
and Betpak-Dala). Only Panfilov Karakum, Taukum and
sometimes the Boguty populations had significantly
smaller group sizes compared to the Kapchagaj population,
which had the highest density among all of them (Table 4).
Group size only changed when population densities were
more than seven times higher, whereas there were no
significant changes in mean group sizes if population
densities did not get above this value. In regards to the
frequency of occurrence of different group size classes
occurring at different population density, the only effect was
found for populations which had difference in density of more
than seven times larger that typically observed (Table 5). The
only one case of comparison of Aktau and Panfilov Karakum
was an exception to this. GLM analyses demonstrated
insignificant impact of density on singletons (GLM, F03.047,
df017, P00.375) and a low effect of density on groups of two
to four individuals (GLM, F0403.645, df017, P00.032).
Discussion
Our results demonstrated that group sizes in goitered
gazelles are highly variable across seasons and years. This
variability is mostly driven by their breeding cycle, when
females prefer to stay alone during the birthing period in
May–June and males protect their individual territories during
the rutting period in November–December. As a result of
these two events, mean group sizes decrease considerably
during these seasons, especially distinctively during the
birthing period (Blank 1986; 1998). The group size
frequency in the Kapchagaj population was the following:
Eur J Wildl Res
Table 3 Pearson Correlation index for proportion (singletons/groups
of 2–4 gazelles) changing in the Kapchagaj population over years
Months
Group size
Pearson index, N and P
May
Singletons
0.855, N06, P00.030
Groups
−0.852, N06, P00.031
June
Singletons
Groups
0.083, N05, P00.894
−0.265, N05, P00.666
July
Singletons
−0.084, N04, P00.916
September
Groups
Singletons
0.117, N04, P00.883
0.680, N03, P00.524
Groups
−0.995, N03, P00.061
November
Singletons
0.514, N04, P00.486
December
Groups
Singletons
0.471, N04, P00.529
−0.448, N03, P00.704
Groups
−1.000, N03, P00.013
The portion of singletons as a kind of group was more than
others and groups of two to four individuals followed after
singletons. Most gazelles stayed in groups of one to three
individuals. The bigger groups were noted much less often
decreasing their frequency with enlarging group sizes. We
thus conclude that goitered gazelles seem to prefer smaller
groups, and those singletons are the most typical kind of group
found for this species. Such group sizes are likely due to the
Table 4 The mean group size of
goitered gazelle among populations in various deserts with different density
arid environment goitered gazelles live in and the sparse
distribution of their forage. This is likely why Jarman (1974)
classified all gazelles as animals with small to mid-size
groups. Other authors also reported that goitered gazelles
prefer to stay in small groups in Saudi Arabian hot deserts
(Cunningham and Wronski 2011b) and in Central Asian’s
cold arid areas (Qiao et al. 2011).
Our results showed that mean group sizes changed
significantly over the years for all checked months;
however, these changes were not correlated with increasing
population density in the Kapchagaj population. The group
size class frequency also did not change with the population
density except for in May. Moreover, in contrast to our
expectation, the portion of singletons increased and the
number of groups of two to four individuals each decreased
with increasing of the population density during May
(Table 3). This pattern was completely contrary to our
hypothesis of group size increasing with population
density. However, as mentioned above goitered gazelles
preferred to stay in small groups because of sparse
distribution of their forage which limits group size.
Our results thus confirm Krause and Ruxton’s (2002)
prediction that median group sizes initially increase with
population density, until the preferred group size is
reached, and that a further increase in the population
density will subsequently lead to higher numbers of
Populations
Density ind/km2
Mean group size ind
per group
N
t test
P value
Kapchagaj Reserve
Aktau (12.1986)
Kapchagaj Reserve
Aktau (06.1987)
2.15
0.30
2.29
0.54
3.55±0.266
4.00±0.712
2.39±0.144
2.56±0.287
221
34
853
54
F00.943
df0243
F00.185
df0905
0.333
Kapchagaj Reserve
PanfilovKarakum
Aktau
PanfilovKarakum
Kapchagaj Reserve
Boguty1 (05.1987)
Kapchagaj Reserve
Boguty1 (06.1987)
Kapchagaj Reserve
Boguty2 (08.1989)
Kapchagaj Reserve
Taukum (12.1982)
Taukum (09.1988)
Chu Muunkum
Taukum (07.1983)
Saryishikotrau
Chu Muunkum
Taukum
Saryishikotrau
2.29
0.35
0.54
0.35
2.29
0.23
2.29
0.23
3.67
0.27
1.65
0.22
0.31
0.17
0.22
0.07
0.10
0.18
0.08
2.39±0.144
1.33±0.106
2.56±0.287
1.33±0.106
2.39±+0.144
1.73±+0.080
2.39±0.144
1.41±0.113
3.17±0.119
2.81±0.322
4.05±0.266
2.62±0.299
1.88±0.147
1.90±0.204
1.50±0.107
1.70±0.300
1.90±0.246
1.73±0.159
1.95±0.223
853
39
54
39
853
234
853
56
1506
48
266
31
69
24
46
19
20
30
22
F04.259
df0890
F019.323
df091
F011.839
df01085
F05.261
df0907
F01.872
df01552
F06.763
df0295
F00.372
df087
ANOVA
F02.770
df02
ANOVA
F00.532
0.039
BetpakDala (09.1986)
0.05
2.00±0.246
12
df02
0.667
0.000
0.001
0.022
0.171
0.010
0.543
0.155
0.591
Eur J Wildl Res
Table 5 Group size classes of the goitered gazelle in various populations with different density
Populations
Density ind/
km2
Singles/ Chi-square (χ2)
groups
Kapchagaj Reserve
Aktau (12.1986)
2.15
0.30
32/44
44/29
18.021, df01, P00.000
Kapchagaj Reserve
Aktau (06.1987)
2.29
0.54
58/33
41/46
38.574, df01, P00.000
Kapchagaj Reserve
PanfilovKarakum
2.29
0.35
58/33
74/26
584.616, df01, P00.000
Aktau PanfilovKarakum
0.54
0.35
41/46
74/26
18.062, df01, P00.000
Kapchagaj Reserve
Boguty1 (05.1987)
2.29
0.23
58/33
62/35
263.108, df01, P00.000
Kapchagaj Reserve
Boguty1 (06.1987)
2.29
0.23
58/33
71/27
518.423, df01, P00.000
Kapchagaj Reserve
Boguty2 (08.1989)
2.75
0.27
41/43
38/46
7.040, df01, P00.008
Kapchagaj Reserve
Taukum (12.1982)
1.65
0.22
29/40
39/42
11.481, df01, P00.001
Taukum - (09.1988)
Muunkum
0.31
0.17
48/49
40/60
2.391, df01, P00.122
Taukum
0.22
Saryishikotrau (07.1983) 0.07
63/37
50/50
3.130, df01, P00.077
Taukum
Muunkum (07.1983)
0.22
0.10
63/37
45/50
2.000, df01, P00.157
Saryishikotrau
Muunkum
0.07
0.10
50/50
45/50
0.053, df01, P00.819
Taukum
0.18
Saryishikotrau (09.1986) 0.08
50/50
42/58
0.519, df01, P00.471
Taukum
BetpakDala (09.1986)
0.18
0.05
50/50
33/67
3.320, df01, P00.068
Saryishikotrau
BetpakDala (09.1986)
0.08
0.05
42/58
33/67
0.712, df01, P00.399
groups, but not to further increases in group size. Mean
group size and group size class differed significantly
between May and other months, with a considerable
decrease with population density. During birthing in
May, most females leave their herds and stay alone for several
weeks. In addition, the high level of synchronisation of
birthing, with most females giving birth within a few
days of each other is very typical for this species (Blank 1986).
Since goitered gazelles have female-skewed populations
where the portion of females in the population may exceed
60 % of the entire population (Zhevnerov et al. 1983), and in
May, when most females leave their groups, mean group size
and group size frequency of the whole population decreases
considerably.
Comparisons of various populations with different
densities revealed that mean group sizes did not change
within a wide range of densities, and started to change
only when such differences were considerable. It was
clear from these results that group sizes changed with
population density in a non-linear or abrupt fashion.
Such a non-linear density-dependent response of group
sizes was found in other animals, where group size
varied with the square root of population density (for
fishes, Bonabeau and Dagorn 1995; Gueron and Levin
1995) or in a logarithmic fashion [for red kangaroo
(Macropus rufus), Johnson 1983, and for Alpine ibex
(Capra ibex), Toigo et al. 1996), and a threshold
(abrupt) or curvilinear response was found for population
growth rates in some African antelopes (Tragelaphus,
Connochaetes, Owen-Smith 2006). The group size class
frequencies showed the same pattern as for mean group
size with the same sevenfold difference threshold for
population density, with the exception of the AktauPanfilov Karakum population. We did not find any
correlation pattern for group class frequencies entirely.
Our research indicates that mean group sizes were more
variable than group size class frequencies, likely because
goitered gazelles preferred to be alone or stay in small
groups within very wide ranges of population densities.
The group size frequencies had no correlation with population
density or if they had it was completely the opposite of what
we had hypothesised, when the singleton portion increased
and group (from 2–4 individuals) frequency decreased with
rising population density during birthing period in May. This
means that the impact of the breeding cycle and especially the
birthing period is more distinctive in goitered gazelle than the
impact of population density, as most females continued to
stay alone during birthing and most males led a solitary
lifestyle during the rut in the condition independent of the
population density. Thus, population of the goitered gazelle
did not show a density-dependent response and behaved as an
ungulate species with a solitary lifestyle would be expected to
behave. A similar social structure was found for Arabian sand
gazelle (Gazella subgutturosa marica), which mainly formed
small groups in Saudi Arabia (Cunningham and Wronski
2011a), and Gazella gazella farasani (Cunningham and
Wronski 2011b) with their mainly solitary lifestyle and for
forest antelope species from the genus Tragelaphus, which
also have an “almost solitary” lifestyle (Wronski et al. 2009).
Various factors, other than population density, will also
affect group sizes: Human hunting pressure, for example,
can lead to an increase in group sizes (probably because
animals feel safer in larger numbers) regardless of density
(Jedrzejewski et al. 2006). Predominantly solitary gorals
formed groups of more than 10 individuals under habitat
disturbance (Pendharkar and Goyal 1995). However, in
mountain gazelles (Gazella gazella), human disturbance
had opposite effects and lead to a decrease in mean group
sizes of this species (Manor and Saltz 2003). The openness
of the habitat (Estes 1974; Korte 2008; Walther 1972), food
abundance (Borkowski 2000; Elgar 1989; Raman 1996;
Rowe-Rowe et al., 1992) or snow depth have also been
found to positively correlate with group size (Maruyama,
1981; Peek et al., 1974), and the reproductive cycle and
Eur J Wildl Res
even daily events can also significantly affect group sizes
(Jedrzejewski et al. 2006).
Conclusions
To conclude, we found that mean group size in goitered
gazelles increased with population density in a non-linear
and abrupt fashion, and significant responses of group sizes
was found only for populations with more than sevenfold
difference in population density. Group class frequency was
not correlated with population density at all. Such a densitydependent response of goitered gazelle population may be
classified as intermediate between social-dwelling ungulate
species, demonstrating continuous and even linear increases
of group size with population density and solitary and
territorial ungulate species that have no such response at
all. However, the goitered gazelle population response to
increasing density is more akin to that found in solitary
ungulate species than that found in social ungulates.
Acknowledgment We are grateful to the International Science &
Technology Cooperation Program of China (2010DFA92720), the
Chinese Academy of Sciences (Visiting Professorships for Senior
International Scientists—2009Z2-5), the Chinese Academy of Sciences Xi Bu Zhi Guang (LHXZ200701), and SINO-UAE Cooperation
Project (0866031) for granting our work and creating all conditions for
writing this paper. We thank also the Institute of Zoology, former
Academy of Sciences of Kazakhstan, which has given us possibility
for investigations of goitered gazelles in natural environment over a 10
year period. We thank Mrs. Patricia Johnston, who did a tremendous
initial job editing this manuscript.
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