Influence of Natural and Anthropogenic Factors on the Distribution of the Field Mouse in the Sikhote-Alin Mountains

==Abstract==

This paper describes the distribution of the field mouse along the gradient heights in the primary vegetation formations affected by anthropogenic transformation of forest ecosystems in the Sikhote-Alin Mountains. Based on the obtained data, schemes of the altitude-biotopical accordance of this mouse in undisturbed and transformed habitats were built. The results demonstrated that the field mouse is able to penetrate into the upper belts of the mountains to heights of 1200 to 1400 m above sea level.

==Keywords==

Field mouse ; Anthropogenic transformation ; Forest ecosystems ; Vertical zonation ; Sikhote-Alin

==Introduction==

For many decades, the natural ecosystems of the Primorsky Krai have been intensively exploited. As a result, vast forest territories have been subjected to logging, which significantly disrupted autochthonous plant communities and caused the formation of a wide range of plant derivative groups in their place (e.g., [[#bb0035|Manko, 1968]]  ;  [[#bb0015|Kurentsova, 1973]] ). Logging also contributes to numerous forest fires that occur annually in the Primorsky Krai territory (e.g., [[#bb0065|Shemetova, 1970]]  ;  [[#bb0010|Kiselev and Kudryavtseva, 1982]] ).      

Problems caused by changes in the number of individual species of rodents caused by human factors have received considerable attention ([[#bb0045|Munteanu and Savin, 1986]]  ;  [[#bb0005|Bolshakov ''et al'' ., 1997                            ]] , and others) in many areas including the Far East (e.g., [[#bb0040|Matyushina and Slabinsky, 1982]] ; [[#bb0025|Kostenko and Nesterenko, 1989]]  ;  [[#bb0020|Kostenko, 2000]] ). However, there is a lack of studies devoted to the transformation of the animal population caused by natural and anthropogenic successional vegetation formation on specific altitude levels that are lacking in the Sikhote-Alin Mountains ([[#bb0060|Simonov and Simonov, 1999]] ; [[#bb0055|Simonov, 2003]]  ;  [[#bb0050|Simonov, 2004]] ).      

Five rodent species are widespread in the Primorye: the reed vole (''Microtus fortis'' ), red vole (''Myodes rutilus'' ), red–grey vole (''Myodes rufocanus'' ), field mouse (''Apodemus agrarius'' ) and East Asian mouse (''Apodemus peninsulae'' ). The field mouse is the most abundant rodent in the woodless areas. Additionally, ''A. agrarius''  widely penetrates into the forest vegetation.      

In this paper, we examined the characteristics of the population dynamics of the field mouse caused by natural and anthropogenic successional vegetation formation at specific altitude levels.

==Materials and Methods==

The present work is based both on the personal observations of the author captured while performing research in the south of the Sikhote-Alin in 1999–2003 and on data collected at the biogeography and ecology laboratory of the Pacific Institute of Geography from 1973 to 1986 in the Middle and Southern Sikhote-Alin. To minimise the effect of fluctuations in the number of rodents in different population cycle phases and to analyse the distribution of animals in a wide range of habitats, the animals were studied during periods of population maxima (peaks).

It should be noted that for the remote and rarely visited sites located 1200 m or more above sea level, there is a lack of information on the habitat distribution of small mammals.

To estimate the distribution of rodents and their exposure to natural and anthropogenic factors, a scheme of altitudinal zones of the Sikhote-Alin vegetation proposed by [[#bb0030|Liverovskii and Kolesnikov (1949)]]  was applied; in our opinion, this was the most optimal scheme for the purposes of our study. The scheme was modified based on the specific characteristics of the vegetation distribution in the areas being studied. At a later stage, the scheme served as a basis for determining the quantitative distribution of field mice in autochthonous habitats and their derivatives. The scheme allowed us to estimate the effect of vegetation changes on the differentiation of high-altitude landscapes inhabited by the studied species.      

==Results and Discussion==

The field mouse is a typical representative of meadow field faunal assemblage. On the Sikhote-Alin, it exists in a wide range of autochthonous habitats (see [[#f0005|Fig. 1]] ). Field mice have been captured in the spruce–pine forests at altitudes of 400–800 m above sea level, larch forests from 400 to 700 m above sea level and fir–spruce forests at up to 1000 m above sea level. At those altitudes, the number of field mice did not exceed 1.0 animal unit per 100 t-n (see [[#t0005|Table 1]] ). Only in the thinned reed spruce forests on the upper boundary at a height of 1200–1400 m above sea level did the field mouse population reach up to 2.0 animal units per 100 t-n. Deciduous and oak forests growing to 300 m above sea level remain the most optimal habitat for this species; according to our results, the average number of animals in those forests is 9.0 individuals per 100 t-n. When these forests are violated, cut, scarified and converted to farmland, the rodent abundance increases to 11.0 animal units, and the upper boundary of the field mouse expansion in deciduous forests extends to the upper border of the deciduous and oak forests (400–500 m above sea level).

<span id='f0005'></span>

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[[Image:draft_Content_184388534-1-s2.0-S2078152014000029-gr1.jpg|center|389px|Influence of anthropogenic transformation of vegetation communities on field ...]]


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Fig. 1.

Influence of anthropogenic transformation of vegetation communities on field mouse populations.

A — number of primary vegetation formations; B — number of secondary vegetation formations.

Vegetable formations:

1 — mountain tundra,

2 — cedar elfin woodland,

3 — fir/fir-tree forests with a birch stone,

4 — fir/fir-tree forests,

5 — fir-tree and cedar woods,

6 — cedar and broad-leaved woods,

7 — broad-leaved woods,

8 — oak woods,

9 — larch woods.

</span>
|}

<span id='t0005'></span>

{| class="wikitable" style="min-width: 60%;margin-left: auto; margin-right: auto;"
|+

Table 1.

The number of field mice in the main vegetation formations.

|-

! rowspan="2" | Altitude (m)                                                    
! colspan="9" | Vegetation formations
|-

! Oak forests
! Broadleaf forests
! Cedar–broadleaf forests
! Spruce–pine forests
! Spruce–fir forests
! Spruce–fir forests with stone birch
! Elfin cedar
! Mountain tundra
! Larch forests
|-

| 0–100
| 3.3/5.1
| 9.0/8.4
| N
| N
| N
| N
| N
| N
| N
|-

| 100–200
| 0.7/2.7
| 4.2/11.0
| 0.5/0.0
| N
| N
| N
| N
| N
| N
|-

| 200–300
| 1.3/0.0
| 0.5/6.9
| 0.0/0.1
| N
| N
| N
| N
| N
| N
|-

| 300–400
| 0.0/N
| 0.0/1.3
| 0.0/0.0
| 0.0/N
| 0.0/N
| N
| N
| N
| N
|-

| 400–500
| 0.2/N
| 0.0/0.4
| 0.0/0.05
| 0.01/0.0
| N
| N
| N
| N
| 0.2/1.8
|-

| 500–600
| N
| N
| 0.0/0.1
| 0.01/0.1
| 0.0/0.0
| N
| N
| N
| 0.5/N
|-

| 600–700
| N
| N
| 0.0/1.07
| 0.5/0.0
| 0.1/0.0
| N
| N
| N
| 0.1/N
|-

| 700–800
| N
| N
| 0.0/0.13
| 0.7/0.0
| 0.0/0.0
| N
| N
| N
| 0.0/N
|-

| 800–900
| N
| N
| N
| 0.0/0.0
| 0.0/0.0
| N
| N
| N
| N
|-

| 900–1000
| N
| N
| N
| 0.0/N
| 0.0/0.0
| N
| N
| N
| N
|-

| 1000–1200
| N
| N
| N
| N
| 0.5/N
| 0.0/0.4
| 0.0/N
| N
| N
|-

| 1200–1400
| N
| N
| N
| N
| 2.0/N
| 0.0/N
| N
| N
| N
|-

| > 1400
| N
| N
| N
| N
| 0.0/N
| 0.0/N
| 0.0/N
| 0.0/N
| N
|}

Note: number of field mice on 100 trap–nights: the numerator is the number of field mice in undisturbed vegetation formations, and the denominator is that in transformed vegetation formations. “N” indicates a lack of studies or the absence of plant formations at these altitudes.

The field mouse was not observed in autochthonous cedar–broadleaf forests growing 200 m or more above sea level. The anthropogenic transformation of these forests conditioned primarily by logging has contributed substantially to the omnipresent expansion of the species ([[#f0005|Fig. 1]] ).      

It should be noted that in the upper boundary forests near Oblachnaya Mountain, the field mouse was found in thinned spruce–fir forests with developed grass cover, often pine purple grass. Similar reed grass communities were observed on the Livadia crest, where field mice were also captured. Nevertheless, the conditions of those regions are highly unfavourable for the habitation of the field mouse. It appears that animals exist in those regions on a casual basis during resettlement in years of high population numbers. This is supported by the fact that after capturing field mice in the upper edge of the forest in 1999, they were not observed again during regular observations over the next four years. In general, autochthonous forest communities are unfavourable habitats for the field mouse. The destruction of vegetation contributes to the all-out expansion of the field mouse in cedar–broad-leaved forests, although this is not typical for the transformed spruce–pine and spruce–fir forests.

After analysing the changes in the altitude and landscape distribution of ''A. agrarius''  in the Sikhote-Alin Mountains caused by the human transformation of the environment, the following conclusions were made.      

The field mouse is common in lowland meadow-field landscapes, and in mountain habitats, it is most abundant in foothill oak and deciduous forests (up to 300 m above sea level). The reduction and ploughing of the territories occupied by these forests led to an increase in the abundance of the field mouse. Ubiquitous felling of the coniferous–deciduous forests contributes to the widespread penetration of the field mouse into the forest communities located at a height of up to 800 m above sea level. Certain field mice, due to the high ecological flexibility of the species, are able to penetrate to the mountain ecosystems located 1200 to 1400 m above sea level through burnt, cut over areas, meadows and cultivated lands.

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