In the situation of intensifying anthropogenic activities worldwide [
48], natural habitats are transformed. Currently, urban development covers ca. 5% of the world, with residential yards covering much of the area [
9]. Anthropogenic changes of habitats create new challenges and pressure on wildlife. Organisms are exposed to modified environments, which results in a loss of biodiversity, changes in communities, and at the individual level [
49]. Though many mammal species successfully thrive in this novel environment, it is still not clear which traits enable their survival and persistence [
38]. Small mammals referred as pests, such as rats or house mice, exhibit plasticity to sudden changes, depending on human activity and fluctuation of resources [
1]. Moreover, migrations between agricultural environments and surrounding habitats are characteristic to small mammals [
1,
18], buffering anthropogenic pressure.
While the urban environment is being evaluated in terms of anthropogenic disturbance, including that to small mammals [
4,
8,
10,
11,
16,
20,
21,
22,
27,
50], these groups are not being extensively studied in farmsteads, homesteads, and kitchen gardens [
5,
9,
14,
15,
26]. It must be recognized that the homestead environment is subjected to unpredictable and unseasonal changes, resulting in fluctuating resources [
1].
Most species suffer from urbanization and intensification of agriculture, followed by fragmentation of habitats, declines in gardening, and reduced availability of natural habitats [
51,
52], though a few may have no negative effects [
53,
54]. Our results show that the diversity of small mammals in homesteads was reduced, breeding disturbances were common, and body condition of most species was worse than in commercial orchards.
4.1. Species Composition and Diversity of Small Mammal Communities in the Other Homesteads and Commercial Orchards
A comparison of the obtained results with previously published data from the indoor environment of homestead buildings (site B, [
14] and site C, [
15]), as well as commercial fruit orchards (D, data from several sites pooled), berry plantations (E) and neighboring natural meadows (F) in Lithuania [
18], showed several differences (
Figure 4). In these earlier investigated homesteads, small mammals were trapped in the buildings where food was available—living houses, larders, porches, cellars, box-rooms, and barns. Fruit orchards, berry plantations, and surrounding meadows were used as the habitats most similar to the gardens in our investigation.
Species accumulation curves (
Figure 4a) showed the poorest diversity in homesteads at sites A and C and berry plantations (E), while the highest values of the diversity index were found in the homestead at site B with the longest period of investigations, as well as fruit orchards (D) and meadows (F). The differences of diversity index B > A, D > A, F > A, and C < A were significant (
p < 0.01 and lower). Similarly, small mammal communities in sites B, D, and F were most polydominant, with the differences of dominance index between sites B < A, D < A, F < A, C > A, and E > A significant (
p < 0.05 and lower).
The number of trapped species (10) was the highest in the homestead buildings of site B with the longest trapping time (four seasons), significantly exceeding all other sites (
p < 0.05) where the number of small mammal species was similar, 7–9 (
Figure 4b). Site B was the only place where two species of rats,
R. norvegicus and
R. rattus, were found in numbers.
In the commensal habitats (site A, current investigation), the dominant species was
A. flavicollis, accounting for 43.4% of all trapped individuals, while
M. musculus was dominant in the buildings of sites B and C (36.7% and 73.8%, respectively),
M. arvalis in berry plantations (E)—(50.6%), and
A. agrarius in fruit orchards (D) and meadows (F) (24.1% and 36.8%, respectively).
M. glareolus (
Figure 4b) was also among best represented species.
For comparison, in UK, four small mammal species, namely wood mouse (
Apodemus sylvaticus), field vole (
Microtus agrestis)
M. musculus and
M. glareolus, were recorded in sheep and pig farms [
55], while a study of residential UK gardens only showed two species,
A. sylvaticus and
M. glareolus [
4]. An earlier study of Dickman [
56] in UK urban environment showed a low diversity of small mammals in urban allotments and the gardens of semi-detached houses (3–4 species), with higher diversities in urban orchards and larger gardens (8–9 species). A limited trapping effort in farms and houses in Hungary yielded three species—
M. musculus,
R. norvegicus, and under-represented
M. minutus [
27]. Of seven species recorded indoors in Chernogolovka research station in Russia, the dominant was
M. musculus, while out of six species trapped in outside gardens, the dominant was sibling vole (
Microtus rossiaemeridionalis) [
7]. In general, the most widely distributed synantropic rodent species in Russia are
R. norvegicus,
M. musculus,
A. agrarius,
M rossiaemeridionalis, and
M. arvalis [
13].
Trapping in various urban habitats, including buildings, yielded 13 rodent and shrew species in Nitra, Slovakia, dominated by
M. arvalis, which accounted for 42% of individuals [
22]. In Riga, Latvia, nine rodent species were found, being dominated by
A. agrarius, accounted for 37.7% in unbuilt zones. No shrews were reported [
16], but in downtown Chelm in Poland, four shrews and five voles (with
M. arvalis being most represented) were reported and three species of
Apodemus mice—
A. agrarius,
A. flavicollis, and
A. sylvaticus, representing no less than 93% of all individuals [
21].
Differences in the small mammal community composition may vary between localities, “reflecting regional human behaviours, cultures, and technologies” [
1]. Buildings in the homesteads represent novel habitats, related to the degree of human influence, and favoring different small mammal species [
57]. Not only the intense competition for the fluctuating resource, but also movements of so called “occasional commensals” between houses and outdoor habitats constantly changes their communities [
1,
55]. In some cases, even arboreal small mammals may invade indoor habitats. When households are close to the natural habitats of the edible dormouse (
Glis glis) and the garden dormouse (
Eliomys quercinus), these species easily penetrate into the houses, causing problems [
58].
4.2. Body Condition of Small Mammals in Commensal Habitats, Seasonal Changes and Importance
For comparison, published data [
15] or recalculated data from [
18] on the body condition of several small mammal species from homesteads and commercial orchards were used (
Table 5). The similarity of the body condition of the same species between the compared homesteads is obvious (see
Table 3). In more natural habitats (commercial orchards, berry plantations, and neighbouring control meadows), the body conditions of the rodents were higher, however not significantly.
In general, body condition is considered as a proxy of animal health and fitness [
59,
60], depending on the food supply [
61] and raising the chances of reproductive success [
62]. While a decrease in body mass might depend on the
Bartonella presence [
63], it is still not clear whether poor body condition is a cause or consequence of pathogen infection [
64]. In our study, pathogen analysis of the collected material will follow later.
In the natural habitats, a seasonal decrease of body condition in autumn and winter was characteristic to
A. flavicollis [
42],
M. glareolus (recalculated from [
43]), and
M. arvalis (recalculated from [
44]). Significant decreases of body condition towards winter also were observed in rodents that were trapped in berry plantations and meadows. However, body condition increased in
A. flavicollis and
M. arvalis from the commercial fruit orchards (not significantly).
While a decrease of body mass and, consequently, body condition, is a mechanism ensuring better survival of voles in winter [
65,
66], this is not the rule. For example, in the short-lived
Octodon degus, adult survival was directly related to body condition in males and females [
67].
The decline in small mammal abundance in autumn in the commensal habitats was possibly influenced by several factors—outweighing natural population growth, the recorded declines were likely caused by the trapping, and, as available foods decreased sharply immediately after harvest, possibly by emigration. We have no data on the levels of movement between the gardens and surrounding territories, but based on the configuration of sites, we presume that some emigration and immigration of small mammals might have occurred at Site 1, while it was probably limited at Site 2.
4.3. Breeding Failures in Rodents under Anthropogenic Impact
Reproduction in small mammals depends on several factors: the availability of food [
68], population density [
59,
69], stress [
69], and body size [
70]. Interspecies and intraspecies variations are also known and significant [
71]. In a period of shortage of acorns, fat dormouse (
Glis glis) respond by increasing resorption rates [
68]. However, a larger litter size in
M. glareolus was related to life in risky environments and increasing population densities [
69], and with bigger body length in
M. arvalis [
70]. Such a multi-sided dependency limits the possibility of multidimensional statistical analysis (large sample sizes required) and comparisons across habitats, as important factors may be omitted. According to [
39], we expected a higher reproductive output in the habitats with a higher degree of anthropogenic activities and, consequently, a higher level of disturbance.
In Lithuania, we found that litter sizes in the commercial orchards (
Table 6) were lower than those in homesteads (see
Table 4). However, there were no significant differences between potential and observed litter size in homesteads and in commercial orchards, or between these habitats. Breeding failures (percentage of the pregnancies with non-implantations or resorptions) were recorded in all species. The proportions of disturbed pregnancies in mice were higher in the homestead, while those in voles were higher in commercial orchards. Thus, based on the litter size and breeding failures, we might expect both food availability and disturbance levels to be higher in the homesteads.
According to [
1], local environments are frequently repopulated after population crashes in fluctuating environments (both homesteads and commercial gardens in our case). Thus, higher fecundity gives a definite advantage to anthropo-related taxa, as they must frequently re-start from low numbers.
4.4. Significance of Small Mammal Studies in Commensal Habitats
The importance of studies of small mammal species composition in homesteads and kitchen gardens is connected with urban development [
19], which in some countries includes the expansion of residential gardens [
53], as well as with rodent damage and development of control measures [
55,
72], and problems with pathogen transmission by synantropic, agrophilic and peridomestic rodents [
25,
27,
28,
32,
73]. For example,
M. glareolus, being the second by numbers in the homestead, was found carrying the human pathogenic Puumala virus in East Lithuania [
74]. According to [
39], our results will contribute to an understanding of the ability of small mammals to persist under anthropogenic pressure (differences between species in the use of resources, adaptation patterns, and selection of traits) and ensuring cohabitation.
In the future, we plan to evaluate the isotopic niches of rodents from commensal habitats (as a proxy to their diet) and the accumulation of various chemical elements in their bodies, thereafter to compare to both the values found in rodents from different habitats. Future studies should seek to quantify in more detail the availability of food resources, levels of disturbance, and other factors that may influence small mammals to better understand patterns in their abundance and diversity in commensal habitats.