Influence of population density on group sizes in goitered gazelle (Gazella subgutturosa Guld., 1780)
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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, intermediate between social-dwelling ungulate species, living
south-eastern Kazakhstan during 1981–1989 to investigate in large groups and demonstrating continuous (linear)
how group sizes and group class frequencies change with increases of group size with population density and those that
increasing population densities in goitered gazelles. In are solitary or territorial ungulate species with no relationship
addition, we compared our study to data on group size between population size and group size, though the goitered
and group class frequency of various goitered gazelle gazelle population’s weak response was distinctively closer to
populations in Kazakhstan with very variable population the one of solitary ungulate species.
densities. We found that mean group size was a more
variable index than group class frequency. Population Keywords Goitered gazelle . Group size class . Mean group
density had some effect on mean group sizes, but the size . Population density
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 Introduction
class frequency was not correlated with population den-
sity at all. The impact of the yearly breeding cycle on Density dependence is a key concept in population dynamics
group size was bigger than population density. The because it determines resource availability and the partitioning
density-dependent response of goitered gazelle population of food among individuals. Most studies on density
was curvilinear in fashion, and it may be classified as dependence deal with physical conditions, growth, births
and mortality rates (Caughley 1970; Kie et al. 1980; Skogland
Communicated by P. Acevedo 1983, 1985). Less often, researchers considered the influence
D. Blank (*) : W. Yang
of population density on ungulate social behaviour (Berger
Key Laboratory of Biogeography and Bioresource in Arid Land, 1978; Fowler 1987). Obviously, the available forage biomass
Xinjiang Institute of Ecology and Geography, declines with increasing ungulate density, and per capita food
The Chinese Academy of Sciences, intake declines with decreasing availability (Wickstrom et al.
Urumqi 830011, China
e-mail: blankdavidalex@yahoo.com
1984). Increasing density should force ungulates to change
their behaviour and, in the first place, group size and
D. Blank sometimes the whole social structure, due to scramble
Institute of Zoology, Kazakh Academy of Sciences, competition over limited food supplies. Various ungulate
Alma-Ata, Kazakhstan
species live in different habitats, have different body sizes,
K. Ruckstuhl variable diets and feeding styles and, as a consequence, have
Department of Biological Sciences, University Calgary, different group sizes or social structures (Brashares et al.
Calgary, Canada 2000; Jarman 1974). Environmental factors have been
considered as a key factor in explaining ungulate social
K. Ruckstuhl
Zoology Department, University of Cambridge, organisation, although other factors, such as predation
Cambridge, UK risk, reproductive strategies and social affinities, haveEur J Wildl Res been identified as being equally important in shaping 1992). Gorals (Nemorhaedus goral), duiker (Sylvicapra group types and sizes (Bon et al. 2001; Hamilton 1971; grimmia) and steenbok (Raphicerus camelus) are not Roberts 1996; Underwood 1982). particularly social and predominantly solitary species, According to the optimal group size hypothesis, every and their group size is very stable and does not change individual prefers to be in a group whose size is a close as over the seasons (Bergstrom and Skarpe 1999; Pendharkar possible to the value that maximises its vital physiological and Goyal 1995). From this, it becomes clear that population and social requirements (Pepin and Gerard 2008). Groups of density is more likely affecting group size in social species, some animals (cetaceans, proboscideans and many primates) which form mostly large groups and even huge aggregation are quite stable, and their mean group size is independent of under some conditions, whereas such impacts would be weak population density (Dittus 1987; Henzi et al. 1997; Lehmann for ungulates that prefer a solitary lifestyle or are staying in and Boesch 2004; Karczmarski et al. 2005; Wittemyer et al. small groups. 2005), while others (some ruminants and kangaroos) form Goitered gazelles (Gazella subgutturosa Guld., 1780) are fission–fusion groups, whose size is very sensitive to able to gather in groups of several tens of individuals, population density (Gerard et al. 2002) and their group sizes though singletons and small groups (
Eur J Wildl Res
protected Kapchagaj population and the other desert we used the following method. We did a south–north parallel
populations. Because of the severe effect of poaching transects every 5 km, which covered the whole study area (24
on gazelle densities, we did not consider the impact of transects, between 8 and 20 km in length each). We moved not
rainfalls and consequently plant densities, composition more than 20 km/h (vehicle) from west to east along transects,
and biomass on goitered gazelle group size and its stopped every 3 km and counted gazelles along transects from
frequencies. We thus were primarily interested in testing each side forward using binoculars (magnification ×8) and
if mean group size and frequency of gazelle groups telescopes (magnification ×30, ×60), but did not count any on
would correlate with their local population densities. 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
Materials and methods deserts, we used the same method of counting along parallel
transects every 15–20 km (along existing roads in the sandy
We conducted the study on goitered gazelles living in the deserts) covering different areas within every desert and
Kapchagaj Nature Reserve (Ili depression, south-eastern stopping every 3 km for sampling gazelles from elevated
Kazakhstan) from 1981 to 1989. This area is now within watch points and registered all visible ungulates within
the Altyn-Emel National Park, with a size of 4,600 km2. distances of 0.5 km. According to our estimations, we
Periodically, additional population censuses were carried out sampled more than 80 % of the entire gazelle population in the
in various deserts of Kazakhstan (Aktau, 300 km2; Panfilov Kapchagaj Nature Reserve, Aktau, Panfilov Karakum and
Karakum, 250 km2; Boguty, 1,200 km2; Taukum, 8,000 km2; Boguty, while not more than 25 % of the population
Saryishikotrau, 24,000 km 2; Muunkum, 37,500 km2; was sampled in Taukum, Saryishikotrau, Muunkum and
Betpakdala, 75,000 km 2—Skotselias 1995). We used Betpakdala because of the huge sizes of these deserts. It
two kinds of indices: mean group size (number observed is possible that the gazelle populations of the Aktau
individuals per encountered group) and group size class have some kind of limited connections with the Kapchagaj
frequency (10 classes from 1 to 10 individuals and the Nature Reserve population, while gazelle population from
11th class for groups that are larger in size than 10 other deserts do not have any connections with each other at
individuals). For checking our hypothesis, we compared all.
the number of two types of groups with each other: During scans, we recorded the number, size and location
singletons and groups from 2 to 4 individuals. We of groups. Gazelles were noted as member of a group if they
proceeded from two assumptions. (1) If the group size wereEur 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 December
1981–1.53 – – – – – N0230
3.23±0.20
1982–1.65 N0256 N0211 – N0186 N053 N091
2.53±0.15 2.26±0.14 2.89±0.17 2.30±0.16 2.55±0.17
1983–1.74 – N0211 N085 – – –
2.23±0.11 1.73±0.14
1984–1.69 N0286 N0433 N0162 – – N0127
2.14±0.12 2.29±0.10 2.09±0.10 2.80±0.21
1985–1.83 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
1986–2.15 – N0328 N0439 – N0429 N0306
2.26±0.09 2.35±0.08 2.85±0.13 3.89±0.25
1987–2.29 N0285 N0853 – N0217 – –
1.76±0.08 2.39±0.14 4.29±0.39
1989–3.67 N01037 – – N01517 – –
1.83±0.07 3.29±0.12
Significance of difference t test ANOVA ANOVA ANOVA ANOVA ANOVA ANOVA
F013.537 F06.872 F00.998 F06.633 F05.252 F05.422 F08.269
df0771 df05 df04 df03 df02 df03 df02
PEur J Wildl Res
Fig. 1 Portion of different 45
group-size classes in goitered
40 Groups Individuals
gazelle among all observed
groups (groups) and number of 35
Portion in percentage, %
individuals observed inside of
every class (individuals) 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 but not others (Table 4); there were no differences for
increase in the portion of groups of more than 10 individuals desert comparisons (GLM, F02.232, df016, P00.353).
(from 0.1 to 2.4 %—Fig. 1). In regards to the proportion of The high-density population of Kapchagaj Reserve had
individuals staying in the different group size classes, most the same mean group sizes as the considerably lower-
gazelles were found to form groups of 3 individuals (17.7 % of density populations of Aktau and Boguty and other
all gazelles), 2 (16.6 %), groups of more than 10 individuals comparisons yielded similar results despite having different
(15 %) or remain as singletons (14.3 %). These portions were population densities (Taukum, Saryishikotrau, Muunkum
not significantly different from each other (chi-square-goodness- and Betpak-Dala). Only Panfilov Karakum, Taukum and
of fit test, χ2 00.625, df03, P00.891). The rest of the gazelles sometimes the Boguty populations had significantly
stayed in groups of 4–10 individuals (10.8 % of gazelles stay in smaller group sizes compared to the Kapchagaj population,
groups of 4 and 2.3 % in groups of 10 individuals). which had the highest density among all of them (Table 4).
Group size only changed when population densities were
Changing characteristics of the Kapchagaj Reserve population more than seven times higher, whereas there were no
over years The mean group size of the Kapchagaj Reserve significant changes in mean group sizes if population
population varied significantly over the years for all checked densities did not get above this value. In regards to the
months, except for June (Table 1). In April and December, frequency of occurrence of different group size classes
mean group sizes increased over the years, whereas in May, occurring at different population density, the only effect was
they generally had a decreasing trend. During July, September found for populations which had difference in density of more
and November, mean groups size increased and decreased than seven times larger that typically observed (Table 5). The
without any clear trend (Table 1, r0−0.19, N08, P00.964). only one case of comparison of Aktau and Panfilov Karakum
Neither population density (GLM, F00.465, df07, P00.843) was an exception to this. GLM analyses demonstrated
nor month significantly affected mean group size (GLM, insignificant impact of density on singletons (GLM, F03.047,
F00.339, df06, P00.155). df017, P00.375) and a low effect of density on groups of two
Unlike mean group size, which significantly changed to four individuals (GLM, F0403.645, df017, P00.032).
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 Discussion
correlation between population density and proportion of
singletons and groups was significant only for May and Our results demonstrated that group sizes in goitered
partially for December (Table 3). There was no effect gazelles are highly variable across seasons and years. This
of density and month on group size frequency (GLM, variability is mostly driven by their breeding cycle, when
F00.707, df07, P00.668 and F00.339, df06, P00.903, females prefer to stay alone during the birthing period in
respectively). May–June and males protect their individual territories during
the rutting period in November–December. As a result of
Comparing characteristics of the gazelle populations of these two events, mean group sizes decrease considerably
different deserts The mean group size of the goitered gazelle during these seasons, especially distinctively during the
populations of various deserts with different population birthing period (Blank 1986; 1998). The group size
densities only significantly differed between some cases frequency in the Kapchagaj population was the following:Eur J Wildl Res
Table 3 Pearson Correlation index for proportion (singletons/groups arid environment goitered gazelles live in and the sparse
of 2–4 gazelles) changing in the Kapchagaj population over years
distribution of their forage. This is likely why Jarman (1974)
Months Group size Pearson index, N and P classified all gazelles as animals with small to mid-size
groups. Other authors also reported that goitered gazelles
May Singletons 0.855, N06, P00.030 prefer to stay in small groups in Saudi Arabian hot deserts
Groups −0.852, N06, P00.031 (Cunningham and Wronski 2011b) and in Central Asian’s
June Singletons 0.083, N05, P00.894 cold arid areas (Qiao et al. 2011).
Groups −0.265, N05, P00.666 Our results showed that mean group sizes changed
July Singletons −0.084, N04, P00.916 significantly over the years for all checked months;
Groups 0.117, N04, P00.883 however, these changes were not correlated with increasing
September Singletons 0.680, N03, P00.524 population density in the Kapchagaj population. The group
Groups −0.995, N03, P00.061 size class frequency also did not change with the population
November Singletons 0.514, N04, P00.486 density except for in May. Moreover, in contrast to our
Groups 0.471, N04, P00.529 expectation, the portion of singletons increased and the
December Singletons −0.448, N03, P00.704 number of groups of two to four individuals each decreased
Groups −1.000, N03, P00.013 with increasing of the population density during May
(Table 3). This pattern was completely contrary to our
hypothesis of group size increasing with population
The portion of singletons as a kind of group was more than density. However, as mentioned above goitered gazelles
others and groups of two to four individuals followed after preferred to stay in small groups because of sparse
singletons. Most gazelles stayed in groups of one to three distribution of their forage which limits group size.
individuals. The bigger groups were noted much less often Our results thus confirm Krause and Ruxton’s (2002)
decreasing their frequency with enlarging group sizes. We prediction that median group sizes initially increase with
thus conclude that goitered gazelles seem to prefer smaller population density, until the preferred group size is
groups, and those singletons are the most typical kind of group reached, and that a further increase in the population
found for this species. Such group sizes are likely due to the density will subsequently lead to higher numbers of
Table 4 The mean group size of
goitered gazelle among popula- Populations Density ind/km2 Mean group size ind N t test P value
tions in various deserts with dif- per group
ferent density
Kapchagaj Reserve 2.15 3.55±0.266 221 F00.943 0.333
Aktau (12.1986) 0.30 4.00±0.712 34 df0243
Kapchagaj Reserve 2.29 2.39±0.144 853 F00.185 0.667
Aktau (06.1987) 0.54 2.56±0.287 54 df0905
Kapchagaj Reserve 2.29 2.39±0.144 853 F04.259 0.039
PanfilovKarakum 0.35 1.33±0.106 39 df0890
Aktau 0.54 2.56±0.287 54 F019.323 0.000
PanfilovKarakum 0.35 1.33±0.106 39 df091
Kapchagaj Reserve 2.29 2.39±+0.144 853 F011.839 0.001
Boguty1 (05.1987) 0.23 1.73±+0.080 234 df01085
Kapchagaj Reserve 2.29 2.39±0.144 853 F05.261 0.022
Boguty1 (06.1987) 0.23 1.41±0.113 56 df0907
Kapchagaj Reserve 3.67 3.17±0.119 1506 F01.872 0.171
Boguty2 (08.1989) 0.27 2.81±0.322 48 df01552
Kapchagaj Reserve 1.65 4.05±0.266 266 F06.763 0.010
Taukum (12.1982) 0.22 2.62±0.299 31 df0295
Taukum (09.1988) 0.31 1.88±0.147 69 F00.372 0.543
Chu Muunkum 0.17 1.90±0.204 24 df087
Taukum (07.1983) 0.22 1.50±0.107 46 ANOVA 0.155
Saryishikotrau 0.07 1.70±0.300 19 F02.770
Chu Muunkum 0.10 1.90±0.246 20 df02
Taukum 0.18 1.73±0.159 30 ANOVA 0.591
Saryishikotrau 0.08 1.95±0.223 22 F00.532
BetpakDala (09.1986) 0.05 2.00±0.246 12 df02Eur J Wildl Res
Table 5 Group size classes of the goitered gazelle in various popula- sizes was found in other animals, where group size
tions with different density
varied with the square root of population density (for
Populations Density ind/ Singles/ Chi-square (χ2) fishes, Bonabeau and Dagorn 1995; Gueron and Levin
km2 groups 1995) or in a logarithmic fashion [for red kangaroo
Kapchagaj Reserve 2.15 32/44 18.021, df01, P00.000
(Macropus rufus), Johnson 1983, and for Alpine ibex
Aktau (12.1986) 0.30 44/29 (Capra ibex), Toigo et al. 1996), and a threshold
Kapchagaj Reserve 2.29 58/33 38.574, df01, P00.000 (abrupt) or curvilinear response was found for population
Aktau (06.1987) 0.54 41/46 growth rates in some African antelopes (Tragelaphus,
Kapchagaj Reserve 2.29 58/33 584.616, df01, P00.000
PanfilovKarakum 0.35 74/26
Connochaetes, Owen-Smith 2006). The group size class
Aktau - 0.54 41/46 18.062, df01, P00.000
frequencies showed the same pattern as for mean group
PanfilovKarakum 0.35 74/26 size with the same sevenfold difference threshold for
Kapchagaj Reserve 2.29 58/33 263.108, df01, P00.000 population density, with the exception of the Aktau-
Boguty1 (05.1987) 0.23 62/35 Panfilov Karakum population. We did not find any
Kapchagaj Reserve 2.29 58/33 518.423, df01, P00.000
Boguty1 (06.1987) 0.23 71/27
correlation pattern for group class frequencies entirely.
Kapchagaj Reserve 2.75 41/43 7.040, df01, P00.008
Our research indicates that mean group sizes were more
Boguty2 (08.1989) 0.27 38/46 variable than group size class frequencies, likely because
Kapchagaj Reserve 1.65 29/40 11.481, df01, P00.001 goitered gazelles preferred to be alone or stay in small
Taukum (12.1982) 0.22 39/42
groups within very wide ranges of population densities.
Taukum - (09.1988) 0.31 48/49 2.391, df01, P00.122
Muunkum 0.17 40/60
The group size frequencies had no correlation with population
Taukum 0.22 63/37 3.130, df01, P00.077 density or if they had it was completely the opposite of what
Saryishikotrau (07.1983) 0.07 50/50 we had hypothesised, when the singleton portion increased
Taukum 0.22 63/37 2.000, df01, P00.157 and group (from 2–4 individuals) frequency decreased with
Muunkum (07.1983) 0.10 45/50
rising population density during birthing period in May. This
Saryishikotrau 0.07 50/50 0.053, df01, P00.819
Muunkum 0.10 45/50
means that the impact of the breeding cycle and especially the
Taukum 0.18 50/50 0.519, df01, P00.471 birthing period is more distinctive in goitered gazelle than the
Saryishikotrau (09.1986) 0.08 42/58 impact of population density, as most females continued to
Taukum 0.18 50/50 3.320, df01, P00.068 stay alone during birthing and most males led a solitary
BetpakDala (09.1986) 0.05 33/67
lifestyle during the rut in the condition independent of the
Saryishikotrau 0.08 42/58 0.712, df01, P00.399
BetpakDala (09.1986) 0.05 33/67
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
groups, but not to further increases in group size. Mean gazelle (Gazella subgutturosa marica), which mainly formed
group size and group size class differed significantly small groups in Saudi Arabia (Cunningham and Wronski
between May and other months, with a considerable 2011a), and Gazella gazella farasani (Cunningham and
decrease with population density. During birthing in Wronski 2011b) with their mainly solitary lifestyle and for
May, most females leave their herds and stay alone for several forest antelope species from the genus Tragelaphus, which
weeks. In addition, the high level of synchronisation of also have an “almost solitary” lifestyle (Wronski et al. 2009).
birthing, with most females giving birth within a few Various factors, other than population density, will also
days of each other is very typical for this species (Blank 1986). affect group sizes: Human hunting pressure, for example,
Since goitered gazelles have female-skewed populations can lead to an increase in group sizes (probably because
where the portion of females in the population may exceed animals feel safer in larger numbers) regardless of density
60 % of the entire population (Zhevnerov et al. 1983), and in (Jedrzejewski et al. 2006). Predominantly solitary gorals
May, when most females leave their groups, mean group size formed groups of more than 10 individuals under habitat
and group size frequency of the whole population decreases disturbance (Pendharkar and Goyal 1995). However, in
considerably. mountain gazelles (Gazella gazella), human disturbance
Comparisons of various populations with different had opposite effects and lead to a decrease in mean group
densities revealed that mean group sizes did not change sizes of this species (Manor and Saltz 2003). The openness
within a wide range of densities, and started to change of the habitat (Estes 1974; Korte 2008; Walther 1972), food
only when such differences were considerable. It was abundance (Borkowski 2000; Elgar 1989; Raman 1996;
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