MODELING OF THE RODENTS ABUNDANCE IN FOREST HABITATS OF THE WESTERN PODILLIA (MYODES GLAREOLUS)

Abstract

Monitoring and predicting the dynamics of abundance of species living in natural habitats is an important component stability analysis of ecosystem as well as dynamics and direction of change of biotic communities under global climate change and pressure of the alien species. The aim of the work was to build a matrix model and study the state of stabilisation of the dynamics of the bank vole population within the Leslie model. The object of the study was the population dynamics of Myodes glareolus Schreber, 1780 = Clethrionomys glareolus auct. The study is based on materials obtained during 2017–2019. This period covered one phase of the long-term population dynamics of the bank vole, named “population growth”. The research was carried out according to generally accepted methods. A total of 6400 trap-days were processed, and 358 forest fistulas were collected and studied. The intensity of harmful activity of rodents is due to the variability of the number of animals in the population. The quantitative population changes are the result of three factors: births, deaths, and migrations. The main condition for the existence of the species is the stability of the population, which is determined by the action of thecompensatory mechanisms. The growth phase of the bank vole lasted all three years of the research, the quantitative indicators were respectively: 2017 – 1.8 individuals per 100 trap-days; 2018 – 2.0 individuals per 100 trap-days; 2019 – 2.7 individuals per 100 trap-days. Low levels of the abundance in the spring of each year of the study, namely at the beginning of the breeding season (3.7 – 2.6 – 8.9 individuals per 100 trap-days). Favourable for the abundance growth was the sex ratio of the population (approximately 1:1), with some rise in the share of females, which decreases on the period of spring 2018 to autumn 2019). Some decrease in the share of immature individuals (4.5 – 3.9 – 3.1 %) is an indirect confirmation of the stability of puberty of animals with subsequent replenishment of the "stock", which led to accelerated reproduction and, consequently, provided prerequisites for further population growth. The causal mechanisms of population control established by us, without a doubt, can serve as a basis for further prognosis, of the number of pests in natural habitats. To predict population changes, the Leslie model, which is widely used in mathematical analyses of the abundance of both plant and animal groups, was chosen. The algorithm for building a matrix model, detailed in the article, has five following steps. The exponential nature of the actual and projected growth of the bank vole population during the five-year cycle (2017–2019 with a prognosis until 2023) revealed in the analysis can be explained not so much by the power of the species' reproductive potential as by the lack of the significant changes in habitat, caused by constant weather conditions, low individual mortality from predators and non-communicable diseases or other accidents. The application of the matrix model allowed to confirm the key role of the main compensatory mechanisms of population dynamics, as they contribute to the stabilisation of the population and, as a consequence, are an important condition for the existence of the species.