Gerbils of the genus Meriones dominate among small mammals in arid zones of the northwestern Cas pian basin. Animals of this genus play a significant role.
ISSN 00124966, Doklady Biological Sciences, 2012, Vol. 443, pp. 120–122. © Pleiades Publishing, Ltd., 2012. Original Russian Text © V.V. Stakheev, 2012, published in Doklady Akademii Nauk, 2012, Vol. 443, No. 4, pp. 526–529.
GENERAL BIOLOGY
Population Dynamics and Population Trends of Meriones Gerbils in the Northwestern Caspian Basin and Their Connection with Atmospheric Circulation V. V. Stakheev Presented by Academician G.G. Matishov November 10, 2011 Received November 10, 2011
DOI: 10.1134/S0012496612020159
Gerbils of the genus Meriones dominate among small mammals in arid zones of the northwestern Cas pian basin. Animals of this genus play a significant role not only in the biotic community, but also in the main tenance of the natural focus of plague in the Caspian Sea region. The midday (Meriones meridianus Pallas, 1773) and tamarisk (Meriones tamariscinus Pallas, 1773) gerbils form adjacent and frequently mixed pop ulations in a vast area. At the same time, both species have distinctive ecological characteristics. The midday gerbil is a predominantly psammophilous species that prefers fixed and semifixed pitandmount sands. In contrast, the tamarisk gerbil is one of the most hydro phylous species widespread in relatively mesophytic areas [1, 2]. Indirectly, the variation in the dependence on water supply between these species is characterized by a gradual northward rise in the number of tamarisk gerbils. The population and distribution limits of the mid day and the tamarisk gerbils frequently fluctuated in the northwestern Caspian Sea region in the 20th cen tury [3–5]. Different factors caused these changes. One of them was anthropogenic transformation of areas as a consequence of irrigation and pasture load reduction [4–6]. We have analyzed the dynamics of relative popula tion density of two species of gerbils, the midday and tamarisk gerbils, in the center of their natural area. The trend of their population size change, as well as its correlation with the changes in atmospheric circula tion, were analyzed. The data were collected by the staff of the Northern Caucasian AntiPlague Station near the village of UlanKhol (Kaspiiskii raion, Republic of Kalmykia)
Institute of Arid Zones, Southern Research Center, Russian Academy of Sciences, ul. Chekhova 41, RostovonDon, 344006 Russia
in spring (May) and autumn (October) in 1972–2006. There were a total of 290 800 trap–days; 10 596 mid day gerbils and 3347 tamarisk gerbils were trapped during the period. Investigations were carried out at permanent plots according to the standard technique used in antiplague centers: crush traps were set pair wise in lines 5 m apart within a station. In the study area, Meriones inhabit all kinds of sta tions, frequently cooccurring. The midday gerbil dominated in all examined biotopes, while the tama risk gerbil was a subdominant species reaching the maximum number in the plots overgrown with tama risk. The abundance of the midday gerbil varied from 0.5 to 13.8 specimens per 100 trap–days in spring in dif ferent years (on average, 4.1%). The relative popula tion density of tamarisk gerbil over the period was in the range from 0.1 to 3.3 (on, 0.9%) (Fig. 1). The average autumn abundance of the midday gerbil was 4.0% (0.7–9.2); that of the tamarisk gerbil was 1.8% (0.6–4.0) (Fig. 1). The spring abundance of midday gerbils changed dramatically over the study period. The numbers of the midday gerbil reached a trapping rate of 6–8% or more in May in the 1970s; since the mid1980s, this value has always been less than 5%. At the same time, a sig nificant decrease in the numbers of the midday gerbil was not observed during the specified period. The abundance of the tamarisk gerbil showed an opposite trend. The relative density of this species was less than 0.5% in the initial phase of the study period, while the spring numbers of the tamarisk gerbil almost always reached or even far exceeded this level in the 1980s through 2000s. Note that the described trend of dynamics of the spring numbwers of both species fol lowed the same pattern in all stations studied. Significant changes in the autumn numbers of Meriones were not found. However, in general, their trends were similar to those for the spring numbers.
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POPULATION DYNAMICS AND POPULATION TRENDS
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Trapping rate, % 16 (a) 14 12 10 8 6 4
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Years Fig. 1. The population dynamics and trend of the (a) spring and (b) autumn numbers of gerbils in the study area: the solid line, midday gerbils; the dashed line, tamarisk gerbils.
Undoubtedly, the described transformations in the populations of gerbils were caused by changes in their habitat. Considering the biological characteristics of both species, it may be suggested that the reason was the steppe formation of plant associations of Kalmykia semideserts in the 1980s [7, 8]. That succession was caused by changes in pasture load [8] and the trend of a significant increase in annual atmospheric precipita tion [7, 9]. From our point of view, the last factor was related to the predominance of the western circulation pattern in European Russia [10]. The trend analysis of the dependence of the relative population density of gerbils and its dynamics on the DOKLADY BIOLOGICAL SCIENCES
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changes in the circulation pattern showed that the num bers of the tamarisk gerbil significantly varied depend ing on the western circulation pattern (Fig. 2), espe cially in spring. The correlation coefficient between the spring numbers and the number of days with the western circulation pattern per year was r = 0.73 (p < 0.001); for the autumn numbers, it was r = 0.53 (p < 0.01). Regres sion analysis also showed a significant correlation between the number of days with the western circulation pattern per year and multiannual dynamics of the spring (R = 0.63, p < 0.001) and the autumn (R = 0.46, p < 0.05) numbers of the tamarisk gerbil. The dynamics of the relative population density of the midday gerbil
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STAKHEEV Number per year 180 160 140 120 100 80 60 40
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Years Fig. 2. The dynamics and trend of the reproduction of the western atmospheric circulation pattern.
was unaffected by changes in the circulation pattern. Apparently, the change in the numbers of this species was mostly influenced by other factors, or the climatic effect was the strongest when the rodent numbers were small. Thus, during the past 35 years, a consistent increase in the numbers of the tamarisk gerbil, as well as a decrease in the relative population density of the mid day gerbil, have occurred in the northwestern Caspian Sea basin. The population dynamics of M. tamariscinus was correlated with the western circulation pattern, which should be used for predicting the changes in the numbers of this species, one of plague hosts in the region. The observed transformations of the population of small mammals indirectly confirm the change in the biocoenotic succession towards humidification in the northwestern Caspian Sea region. AKNOWLEDGMENTS I am grateful to G.A. Berberov for the possibility to use archive data of the NorthCaucasian AntiPlague Station, all zoologists assisting me in collecting the material, and V.S. Tuzhilkin for the data on atmo spheric circulation. This study was supported by the Program 14 of Basic Research of Earth Science Branch of the Rus sian Academy of Sciences “Environment State and Prediction of Its Dynamics Caused by Rapid Global and Local Natural and Socioeconomic Changes,” project “Recent Transformations of the Environment and Biota of the Arid and Semiarid Zones of Southern Russia under the Conditions of Climate Changes.”
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