Study area — selection of experimental plots

Daghestan is the southernmost region of Russia, located in the northeastern Caucasus. The study was performed in the foothill zone of Daghestan during five years (2002–2004, 2009–2010). Two typical areas were selected: lower foothill (250–400 m a.s.l., 45° 54′ 34′′ N, 47° 27′ 37′′ E) - oak forest and upper foothill (750–800 m a.s.l., 41° 39′ 21′′ N, 47° 59′ 59′′ E) - hornbeam-beech forest (Fig. 1).

The foothill zone of Daghestan forms a multitude of ridges separated by valleys, basins, and canyons (Akaev et al. 1996). The climate here is moderately warm. Winters are characterized by comparatively mild temperatures with the average of three winter months around +1.5 °C, and a summer average of +17 °C (Akaev et al. 1996). The vegetation is composed mainly of oak, beech, and beech-hornbeam types of forest (Lvov 1964).

Fig. 1.

Study area.

Handling of animals

To estimate the relative abundance of D. nitedula, standard trap-lines of Gero traps were used (Kucheruk 2006). Each night from 50 to 100 traps were set at 3–5 m intervals. All abundance data were standardized “as catch per 100 trap-nights”. During the entire period of the studies there were 4870 trap-nights employed and 173 animals were caught. In addition, numbers of D. nitedula nests per route line (10 km) were recorded. In order not to count accidentally the nests of birds, each nest was checked to determine its inhabitants. All the animals captured were weighed, had their body length measured and sex determined. To describe rates of reproduction, the following parameters were used: size (volume) of testes (using sliding calipers accurate to 0.01 cm), sex ratio and percentage of breeding females. Volume of testes were calculated using formula of ellipse V = 4/3 π*a*b*c, where a, b, c are axes of testes. The percentage of females participating in reproduction was determined from the relationship between the number of reproducing, lactating females and the total number of females caught. Animals were divided into two age groups: juvenile (≤ 19.5 g) and adult (> 19.5 g), following Kryštufek (1985).

Vegetation

For botanical description, 11 parameters were selected: density, height and diameter of trees (at the chest level), closeness of their crowns, production of seeds. For shrubs, the density, height and diameter (at the chest level), closeness of their crowns and protective cover were recorded, as well as the production of grasses (Voronov 1973). Six sites were selected and in each one geobotanical description was performed in four plots. Trees and shrubs were described at plots with an area of 50 × 50 m, and grass vegetation, 1 × 1 m. Production of seeds and root crops was determined by using plots of 1.0 m2, and samples were dried to constant mass and weighed. STATISTICA 5.0 was used for r analysis of the empirical data obtained (Borovikov 2001).

Fig. 2.

Vertical distribution of D. nitedula nests in an oak forest (а, n = 90 per 10 km transect) and in a hornbeam-beech forest (b, n = 36 per 10 km transect).

Table 1.

Vegetation characteristic of habitats of D. nitedula.

Table 2.

Dynamics of numbers of D. nitedula (ind./100 trap-nights).

Table 3.

Microhabitat distribution of D. nitedula individuals (ind./100 trap-nights).

Characteristics of forest biotopes

Table 1 provides data characterizing the state of the vegetation in habitats of D. nitedula. Oak forest as a whole consisted of Quercus sessiliflora and Quercus pubescens (up to 80 %) with an admixture of Pinus sosnovsky and Acer campestre. In the understory well developed shrubby vegetation was recorded: Crataegus pseudogeterophilla, Mespilus germanica, Cornus mas, Prunus spinosa, Paliurus spina-christi, Rosa canina, etc. The hornbeam-beech forest consisted of Carpinus betulus, Fagus orientalis, Quercus sessiliflora, Quercus pubescens, and Tilia caucasica. The shrubby vegetation was sparse, consisting of Crataegus pseudogeterophilla, Rosa canina, Rubus sanctum, and Corylus avellana (Table 1).

The sites differed significantly from each other. The densities of trees and shrubs were higher in oak forest than in hornbeam-beech forest, whereas linear sizes of trees and shrubs were higher in the latter (Table 1). Production of trees and grass vegetation was higher in oak forest.

Populations and habitat

Table 2 shows the dynamics of D. nitedula numbers in both forest biotopes. For a given study period, average numbers of these dormice in oak forest was 1.7 times higher than in hornbeam-beech forest (t = 5.7, p < 0.0002).

To assess microhabitat distribution of D. nitedula individuals the forest canopy was divided into five microhabitats: open sites, forest edge, high-standing forest, undergrowth, and shrubby vegetation. Table 3 shows that maximum numbers of D. nitedula were found in shrub associations and in parts of a forest dominated by young trees in both forest area types. Minimal numbers of the species were found in high forest microhabitats (Table 3).

Additionally we estimated vertical distribution of D. nitedula nests and found optimal height of nests in both forest biotopes was 2–3 m above the ground surface (Fig. 2).

Table 4.

D. nitedula reproduction characteristics. %♀ - reproductively active females.

Table 5.

Spearman rank correlations between D. nitedula state and forest habitats structure attributes in both habitats. Significant values are in bold (p < 0.05).

Reproduction rates and sex ratio

Sexual activity of D. nitedula males was measured by the size of testes. The first signs of sexual activity among males were recorded soon after the animals came out of hibernation in both forest biotopes. The maximum size of testes was seen in April in both forest biotopes: 0.834 ± 0.99 cm³ (n = 49) in oak forest and 0.872 ± 0.11 cm³ (n = 18) in hornbeambeech forest. Subsequently sexual activity of males began to decline and, by August, the size of testes was 0.195 ± 0.06 cm³ in oak forest and 0.185 ± 0.09 cm3 in hornbeam-beech forest. Thus, sexual behavior of D. nitedula males was not significantly different in the two biotopes (t = 0.02, p = 0.98). Sex ratios showed domination of males in both forest biotopes: 1.18:1 (n = 118) in oak forest and 1.11:1 (n = 55) in hornbeambeech forest (Table 4).

Age groups of D. nitedula did not differ significantly between biotopes (p > 0.05). The spring population of D. nitedula consisted only of adult individuals in both biotopes. By the end of summer (August juveniles formed 48 % and 43 % of the population in oak and hornbeam-beech forests respectively.

Diet

We found a wide spectrum of items in the diet of forest dormice including animal material, along with fruit and seeds of almost all species of trees and shrubs occurring at the study sites. The main types of food of D. nitedulа were animals and seeds; 29.6, 24.05 %, respectively, in oak forest and 30.88, 27.06 %, respectively, in hornbeam-beech forest.

Species composition of the diet was revealed by analyzing food remains. The diet of individuals of the species from oak forest consisted of 18 species of foods, and in individuals from hornbeam-beech forest of 19 species. The degree of similarity between diets of dormice from both forest biotopes was 86 %. In both biotopes the animals attained similar body weight during the active phase of the year: 35.63 ± 0.79 g (n = 73) in oak forest and 34.33 ± 1.14 g (n = 46) (p > 0.05) in hornbeam-beech forest. Thus, food cannot be a key factor limiting numbers and distribution of the species in the study areas.

We used numbers and body weight of adult individuals to indicate relative “success” in the two habitats. Table 5 shows values of Spearman Rank correlations comparing the state of the dormouse population and vegetation parameters. Body weight significantly correlates with production of seeds and protective cover provided by grassy vegetation in both biotopes. The second indicator of the species success (numbers) demonstrated significant dependence on six parameters of the vegetation in both biotopes. Numbers of D. nitedula positively correlate with an increase in the density of trees, shrubs, and closeness of crowns and negatively correlates with the height of trees, shrubs, and the diameter of trees in both biotopes. Thus, D. nitedula does well in areas with abundant vegetable foods, although the numbers of dormice are higher in oak forest.