Биологические науки/7.Зоология

Dr. Shilovа S.A., PhD Shekarova O.N., Savinetskaya L.E.
A.N. Severtsov Institute of Ecology and Evolution
Applied issues of small pest- mammals control as groundwork for basic research

Small pests -mammals control is carried out in almost all countries over the world, that can significantly reduce economic damage caused by these pest-species, can provide population health and welfare and reduce the risk of zoogenous infections morbility.

The modern pest control is based on extensive basic research on the structure, dynamics, population cycles and other biological parameters of pest species. Animals reaction to damaging factors (poison baits, poisons of acute and prolonged action) is detailed studied; the areas of the most inflicted damages and injury is identified, etc. (Prakash, 1988; Shilova et al, 1993). These data allow us to increase the deratization efficiency significantly and to provide the preservation of pest-animals biological diversity even being under constant target pest control pressure (Rylnikov, 2010; Shilova, 2011).

However, another important problem, concerning the study of possibility to detect previously unknown general biological patterns of pest species populations under target pest control pressure (another aspect of consequences of target pest -population reduction), has scarcely ever concerned in publications.

Some unknown in usual condition adaptive (deposited) biological features can appeared in animal populations, being under extreme conditions (disastrous habitat destruction, critical number decreasing, etc.).

For example, the study of survived after exterminative pest control measures small mammals allowed to reveal significant changes in different forms of their social behavior that doesn't appear under normal condition. Investigations were carried out in natural plague foci on the territories of Russian alpine steppes and semi-deserts (Tuva, Kalmykia), during pest control measures against rodents and pikas - carriers of this infection (Shilova, 1993 Shchipanov 2001, Shilova, Tchabovsky 2009, etc.)

After deratization 10-15% animals survive in the treated areas and they possess individual resistance to poisons or increased suspicion to baits. Survived animals cattered around the territory and be deprived of their usual social partners. Then strangers began to migrate from neighboring to treated territory. These animals are also separated, not familiar with the territory and are being under stress outside of well-known habitat. Stable population capable of reproduction groups restoring is possible only through these animals agregations.

Significant changes of social behavior after critical number decreasing caused by pest control treatments in the natural foci of plague have been happened in the settlements of Mongolian pikas (Ochotona pallasi Gray 1867). Considered as leading behavioral pattern high aggressivity of Mongolian pikas towards their conspecifics determines optimal forage use under food shortage in inclement extreme alpine conditions. This species have practically no any friendly forms of contacts. There no overlapping of individual home ranges, animals live ne by one and strongly protect their home territories from neighbors.

After the complete elimination of settled population from the study site the number of aggressive contacts between migrant Mongolian pikas has much reduced compared with the control (0.03 and 1.1, respectively, per 100 min. P> 0,999). Individual home ranges of strangers overlapped completely. Any territorial protection was absent. Investigating behavior increased: the time for territory investigation was 10.2% but in the control group –only 4.1% (Shilova, Orlenev, 2004; Shilova, Tchabovsky, 2009).

On another experimental site where only 29.31% of survived pikas has remained. Investigation activity of survived animals increased in 4.7 times and the frequency of territory marking - about 10 times (before and after the experiment it was 0.5 and 4.9 interactions per 100 min respectively.). Even on their own home ranges pikas stopped to protect their territory: number of aggressive interactions with neighbors declined from 1.4 to 0.6 interactions per 100 min. A trend to survived animals integration appeared: the number of integral contacts was before and after experiment 0.6 and 1, 5 per 100 min. respectively.

Comparative analysis of social behavior in closely related species after large-scale pest control treatment shows that the intensity of the stable population structures restoration is depended on the changes of survived animals behavior. Thus, the Mongolian gerbil (Meriones unguiculatus) is highly social species. After neighbors extermination survived animals need for social contacts very much, that allowed them to form reproductive capable intrapopulational group in a short time, that resulted in rapid population number recovery. Some forms of social behavior of survived Mongolian gerbils changes abruptly, that contributes to the animals integration, aggressive contacts replace on friendly ones etc. (Fig.1).

Unlike Mongolian gerbil social contacts between Midday gerbil (M. meridianus) are not the leading factor supporting population groups autonomy. After the extermination of the most part of the settled animals survived Midday gerbils don't show any modifications of their social behavioral patterns (Fig.1). Accordingly, the process of population number restoration in the cleared out of settled animals areas is very slow (Shilova, Orlenev, 2004; Shilova, Tchabovsky, 2009).

Fig.1 Proportion of different behavioral contacts in Mongolian (A) and Midday (B) gerbils in treated and untreated colonies (after Shilova and Tchabovsky 2009)

Study of the social behavior of small mammals after 80 - 90% population extermination as a result of deratization allowed N.A.Shchipanov (2001) to ground the conception of population structure recovery rate depending on the level of species sociality. According to this author there are two types of residual populations functioning after the critical number decreasing: "restoring" and "controlling». In the first case the animals number quickly increase after extermination to its original level. Population of "controlling type" slowly restores its original population structure. The reason of these functioning differences is in the specifics of their social organization forms.

A classic example of applied zoological studies application to solve fundamental ecological problems is the modern concept of density - dependent mechanisms of rodents number regulation. Back in 1948, having analyzed the disinfection station in Baltimore materials on the Brown rat control D. Davis (1951) showed that after sharp rats decrease as a result of control measures , the reproduction level of survived animals much increased that caused the number recovery in a short space of time.

Eco - physiological, behavioral and biochemical patterns of density - dependent regulation of different small mammals species number is now well studied and considered as one of the main traditional population ecology thesis (Christian 1971; Stenseth et al. 2001, etc.). For example, on the model of Mongolian gerbils it was shown that after 90% of the population extermination by zinc phosphide the age structure of breeding gerbils had much changed. Young females with an average weight of 31.0 g had already begun to take part in breeding (control - 58.0 g). After 4 weeks on the treated areas 91.4% of females were pregnant. At the same time on control areas breeding stopped. On the treated area spermatogenesis was registered in 92% of males (Shilova, Tchabovsky 2009).

Sometimes the data on the small pest-mammals state after pest control treatment successfully used to develop advanced statistical research methods. Thus, by the example of the bank vole (Myodes glareolus) after irrevocable animals removal in nature N.A. Shchipanov et al (2011) developed a model of estimation the ratio of settled and wandered parts of the population.

Thus, the analysis of population processes of animals, being under target pest control treatment as pests can reveal new adaptive patterns that conserve the biological systems stability.

We are grateful to N.A.Shchipanov, A.V.Tchabovsky, A.A.Kalinin , D.P.Orlenev, B.V.Krasnov . I.V.Khokhlova and many others members of the laboratory of population ecology IPEE RAS who much and constant helped us in the work on aforesaid problem. The study was supported by the Basic Research Program of The Presidium of RAS “Wildlife: Current Status and Problems of Development ", subprogram "Biodiversity:

Literature.

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Shilova S.A. 2011. Current problems in rodent pest population control and biodiversity cobservation. Russian Journal of ecology. V.42(2). P.165-169 (In Russian)

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Shchipanov N.A., Lyapina M.G. 2011.Evaluation of abundance of residence and immigration by irretrievable requisitioning of the Bank vole (Myodes glareolus Shreber 1780). Biology Bull. RAS. Biol. Ser. No 6. P. 747 -758. (In Russian)

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Shilova S.A., Tchabovsky A.V. 2009 Population response of rodents to control with rodenticides. Current Zoology 55(2). p. 81-91.