Influence of Population Density on Group Sizes in Goitered Gazelle (Gazella Subgutturosa Guld., 1780)

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 density 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 of population density on ungulate social behaviour (Berger D. Blank (*) : W. Yang Key Laboratory of Biogeography and Bioresource in Arid Land, 1978;Fowler1987). 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 1984). Increasing density should force ungulates to change e-mail: [email protected] 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;Jarman1974). 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, have Eur 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)arenot 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 (<4 individuals) are increase with population density (Barrette 1991; Lawes and more typical than large herds (Zhevnerov et al 1983; Blank Nanni 1993;Taylor1983; Toigo et al. 1996;Wirtzand 1990, 1992). Males of goitered gazelles have individual Lorscher 1983). territories, but only during the rutting period (November– Fowler (1987) considered the density dependence of December), whereas the rest of the year they roam freely all group sizes in 21 large herbivores species and reported that over their home range and gather in groups of adult and 17 of them had such dependence. He supported the idea of yearling males, which were expelled by territorial males Eberhardt (1977) that group sizes had different sensitivities from the family groups during the rutting season (Blank to changes in population density. The group size and its size 1998). Females leave their herds and stay alone for giving frequency in some social-dwelling deer species (Axis axis, birth (May), but they gather into groups several weeks after Capreolus capreolus, Cervus nippon, Cervus elaphus and the appearance of offspring and later they unite into larger Dama dama), which prefer to stay in large groups (3–6 and groups including several mothers and their young (Blank even larger size), were positively affected by population 1986). Mixed-sex groups are uncommon for goitered density (Barrette 1991; Borkowski 2000; Hebblewhite gazelles during most of the year and only during migration and Pletscher 2002; Stuwe and Hendrichs 1984;Thirgood in March–April and October do they gather in large mixed-sex 1996; Vincent et al. 1995). An increase in group size groups of several hundred individuals (Blank 1990, 1992). with population density has also been reported for some Goitered gazelles may thus change their group size according African antelopes (Kobus and Redunca—Spinage 1969; to their biological life cycle, with most females staying Wirtz and Lorscher 1983). Alpine ibex (Capra ibex) solitary during birthing in spring and males being solitary and chamois (Rupicapra pyrenaica), which usually live in during the rut in autumn–winter but gathering in especially large groups of 3–10 individuals (Lovari and Consentino large herds for migrations twice a year (Blank 1992). 1986; Toigo et al. 1996), also have a distinct tendency of Therefore, goitered gazelles have a wide span of group group sizes to increase with population density (Pepin and sizes from singletons to herds of several tens, occupying an Gerard 2008; Toigo et al. 1996). Peccaries (Tayassu pecari), intermediate position between social-dwelling species, living which are usually very social ungulates living in large groups in large groups and exclusively solitary or territorial species, of 20–300 individuals, decreased their group size with de- for which large groups are atypical. That is why the creasing population density (Reyana-Hurtado et al. 2009). consideration of relationship between group size and In contrast, moose (Alces alces) did not show such density population density in goitered gazelles would be especially dependence on group sizes, and in Sweden, home range sizes interesting. We thus hypothesise that goitered gazelle groups were not affected by differences in moose density (Sweanor sizes will grow with increasing population density and that the and Sandegren 1989). Comparison of various populations of frequency of such large groups will increase as well. different subspecies of moose in Alaska, Minnesota and The Kapchagaj population of goitered gazelle is protected Montana demonstrated that group size varied seasonally from poaching and therefore demonstrated the highest indices according to the yearly breeding cycle, and though the of population density (Tables 1 and 2). Other populations in largest group sizes did occur with the densest populations, Kazakhstan have virtually no protection from poaching and density did not appear to influence trends in aggregation sizes have thus suffered substantial losses due to poaching (Blank through the year (Peek et al. 1974). The oribi (Oerebia 1990), and as a result, they occur at uncharacteristically low ourebia) is a territorial antelope with small group sizes, densities (Tables 4 and 5). In fact, we reported before (Blank which may increase with population density (Arcese et al. 1990) that poaching was the single-most factor explaining the 1995), but within very limited changes (Rowe-Rowe et al. striking differences in population densities between the 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 km2; Muunkum, 37,500 km2; was sampled in Taukum, Saryishikotrau, Muunkum and Betpakdala, 75,000 km2—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. thenumberoftwotypesofgroupswitheachother: 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 were <50 m from each other, moved in the same direction of goitered gazelle increases with density, then firstly, the and stayed together longer than half an hour. These are number of singletons are expected to decrease and the number measures commonly used in defining groups of ungulates of small groups (2–4 individuals) to increase, as was observed (Ruckstuhl 1998). for sika deer, for example (Borkowski 2000); and (2) The differences in mean group size over years were tested singletons and small groups (2–4 individuals) are the with one-way ANOVA, as tests for normality of these data most numerous types of groups in gazelle population in were satisfied (Kolmogorov–Smirnov test). Fisher’s least Kapchagaj reserve (X±SE086.9 %±1.2, n027) and in significant differences post hoc comparison was used to other deserts (X±SE093.5 %±2.5, n013). compare means between separate pairs of values (subgroups). We collected two data sets to verify our hypothesis that In addition, we used a general linear model (GLM, type 4 sum population density affects average group sizes. Firstly, we of squares) to test the impact of month and density on group used the data from our long-term study of goitered gazelle size of the gazelle population in Kapchagaj Nature Reserve ecology and behaviour in the Kapchagaj Reserve, when this and other deserts. In addition, we performed independent- population increased their density (from 1.63 to 2.75 sample t tests for comparing group size for pairs of different gazelles per 1 km2) between 1981 and 1989 (Tables 1 and goitered gazelle populations, living in different deserts. We 2). Secondly, we used the census data from the various used chi-square-goodness-of-fit tests to analyse changes in the desert populations, which turned out to have very different frequency of various group sizes under different population population densities (from 0.05 to 2.75 gazelles per 1 km2— densities. 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). Results In the Kapchagai Nature Reserve, we counted gazelles along pedestrian transects (total of 2,000 km) and car routes Kapchagaj Reserve population We found significant (10,000 km). Gazelle counts were done once every month. monthly variability for mean group size and group class To avoid re-sampling, the same individual during a census 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 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 P<0.0001 P<0.0001 P>0.05 P<0.0001 P00.005 P00.001 P<0.0001

F021.902, df05, P<0.000), though such differences were of group class frequency (Fig. 1). Singletons were the most much less significant for 1982 (one-way ANOVA, F02.289, often noted kind of group, followed by herds of two and three df05, P00.044). We thus decided to only compare yearly individuals (chi-square test, χ204.587, df01, P00.032 and indices of the same calendar month for our analyses. χ2010.286, df01, P00.001). The proportion of bigger size The Kapchagaj population with the highest density of groups was considerably smaller, decreasing continuously goitered gazelle in Kazakhstan had the following distribution 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 Months ind/km2 April May June July September November December

1981–1.53 33/46 1982–1.65 46/39 50/40 24/61 30/64 35/48 1983–1.74 43/48 59/38 1984–1.69 54/38 43/50 46/49 37/46 1985–1.83 28/48 42/45 49/42 32/57 30/46 40/44 1986–2.15 40/52 36/57 38/48 36/39 1987–2.29 60/36 58/33 27/50 1989–3.67 70/23 41/43 Chi-square 7.332 208.957–0.580 96.481-0.662 25.154-2.636 12.145-0.206 1.254-0.001 0.592-0.045 (χ2) df011P00.000-0.446 P00.000–0.416 P00.000–0.104 P00.000–0.650 P00.263–0.980 P00.442–0.832 P value 0.007 Totally 12 of 15 cases Totally 6 of 10 cases Totally 4 of 6 cases Totally 2 of 3 cases Totally 6 cases Totally 3 cases were P<0.05 were P<0.05 were P<0.05 were P<0.05 were P>0.05 were P>0.05 Eur J Wildl Res

Fig. 1 Portion of different 45 group-size classes in goitered Groups Individuals gazelle among all observed 40 groups (groups) and number of 35 individuals observed inside of every class (individuals) 30

Portion in percentage, % in percentage, Portion 10

0 12345678910>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, χ200.625, 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 2 goitered gazelle among popula- Populations Density ind/km Mean group size ind Nttest 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 df02 Eur 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 2 km groups 1995) or in a logarithmic fashion [for red kangaroo (Macropus rufus), Johnson 1983, and for Alpine ibex Kapchagaj Reserve 2.15 32/44 18.021, df01, P00.000 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 Connochaetes, Owen-Smith 2006). The group size class PanfilovKarakum 0.35 74/26 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 0 0 Kapchagaj Reserve 2.29 58/33 518.423, df 1, P 0.000 correlation pattern for group class frequencies entirely. Boguty1 (06.1987) 0.23 71/27 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. 0 0 Taukum - (09.1988) 0.31 48/49 2.391, df 1, P 0.122 The group size frequencies had no correlation with population Muunkum 0.17 40/60 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;Elgar1989; Raman 1996; clear from these results that group sizes changed with Rowe-Rowe et al., 1992) or snow depth have also been population density in a non-linear or abrupt fashion. found to positively correlate with group size (Maruyama, Such a non-linear density-dependent response of group 1981; Peek et al., 1974), and the reproductive cycle and Eur J Wildl Res even daily events can also significantly affect group sizes Bon R, Rideau C, Villaret JC, Joachim J (2001) Segregation is not only (Jedrzejewski et al. 2006). a matter of sex in Alpine ibex, Capra ibex ibex. Anim Behav 62 (3):495–504 Bonabeau E, Dagorn L (1995) Possible universality in the size distribution of fish schools. Phys Rev E 51:5220–5223 Conclusions Borkowski J (2000) Influence of the density of a sika deer population on activity, habitat use, and group size. Can J Zool 78:1369– 1374 To conclude, we found that mean group size in goitered Brashares JS, Garland T, Arcese P (2000) Phylogenetic analysis of gazelles increased with population density in a non-linear coadaptation in behavior, diet, and body size in the African – and abrupt fashion, and significant responses of group sizes antelopes. Behav Ecol 11(4):452 463 Caughley G (1970) Eruption in ungulate populations, with emphasis of was found only for populations with more than sevenfold Himalayan thar in New Zealand. Ecology 51:53–72 difference in population density. Group class frequency was Cunningham PL, Wronski T (2011a) Population structure of Farasan not correlated with population density at all. Such a density- gazelle. 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