The Effects of the Habitat Fragmentation on the Common Vole (Mammals: Rodentia) Meta-Populations

Humans have affected 83 percent of the land surface till now (Sanderson et al., 2002). Habitat fragmentation is the process of subdividing a contiguous habitat into smaller pieces (Kolbert, 2014). There is a major concern that land use change and habitat fragmentation have direct and indirect effects on biodiversity, which can lead to the extinction of many species (McInerny et al., 2007). To all intents, the major cause of species extinction is habitat loss (Keenleyside et al., 2012). Although roads are a major cause of habitat fragmentation (the process during which a large expanse of habitat is transformed into a number of smaller isolated patches) and usually negatively affect many mammal populations, different mammal species can be highly variable in their tolerance to the fragmentation and other human developments (Schuster et al., 2013). Landscape fragmentation seriously affects the survival of meta-populations. Patch size can affect the resilience of ecosystems and population structure. In larger patches, the populations are more stable and population viability could increase under the conditions. Rodents are mammals belong to the order Rodentia. About 40% of all mammal species are in this order and they play a considerable role in ecosystems (Amori & Gippoliti, 2000), but they are rarely taking into account by the legislation and only very few small mammal species are currently protected according to national and international laws (Bertolino et al., 2015).

This research is a filed study which focuses on the habitat fragmentation caused by civilization development. In order to study the impact of habitat fragmentation on the population dynamics of common voles (Microtus arvalies), three small habitat patches (0/3 – 2 ha) that are surrounded by roads and highways were selected. These patches with the grassland cover type are located in Louvain-la-Neuve city in Belgium. This city is an almost newly born town (created in 1969) that is situated in the French-speaking part of Belgium, in the Wallon Brabant province. In this study, the common voles’ colonies of each patch were considered as a single meta-population.
The study used Capture-Mark-Recapture which is one of the most widely used techniques for demographic studies. This technique mostly can be used to assess population status (such as abundance fluctuations) or to investigate population dynamics. To capture the common voles, 65 ugglan small mammal live capture traps that have high efficiency were used. This study was conducted in a period of 1/5 year (during four seasons). Trapping was done in 13 sessions. During each session, traps were opened over 2 nights and were closed during the day. In order to differentiate between the captured animals, each animal was tagged by two 11.2 mm “Michele clips” (ear tags). Captured animals were released back to their habitats after some information such as tag number, sex, age class, body mass and reproductive status were noted. Population dynamics and population structure were analyzed using CMR specialized package and Microsoft office 2007, respectively.

A total of 283 specimens were captured and tagged; 176 specimens were new and they were being caught for the first time. In general, all the studied patches showed the highest population size in June and July. Persistence curves of successive cohorts (have been caught during the same session) in studied plots revealed abundance fluctuations in each plot and the differences in population survival between the studied plots. Plot B was considerably different from the two others. The common voles in this plot showed an instability or low persistence and strong downward trends of population size.
In plot C, with larger size in comparison to other patches, more stability in the population structure and abundance were observed. This study showed how habitat fragmentation has negatively affected meta-populations of common voles and showed that the risk of local extinction is high in the studied meta-populations.
The results clearly indicated that patch size and habitats isolations have an important role in animal population survival and its structural stability. Moreover, this study demonstrated that the remained small isolated meta-populations of common voles after huge landscape fragmentation and civilization of Louvain-la-Neuve city, generally failed to find adaptive mechanisms to their new man-made conditions.

The study proposes considerable differences among studied meta-populations in the survival and sex ration resilience. The results demonstrated that the meta-population of patch B was not able to recover itself. Consequently, common voles in this patch are facing a local extinction. The preventive efforts for maintaining the integrity of the ecosystems can have an effective protection against environmental disturbances. Development and construction projects must be done with full attention to landscape structure and regional biodiversity. Nevertheless, re-establishment of populations would be very costly, time-consuming and mostly impossible for the government and biodiversity conservationists.