Effects of roads on spatial behaviour and abundance of small mammals: gaps in knowledge

The main goal of this study was to update the current understanding of the spatial behaviour and abundance of small mammals in the vicinity of roads through a complete literature review to identify knowledge gaps. We also examined spatial patterns of small mammals taking into account the biological and road-related factors to provide recommendations for future research. We found 38 papers documenting effects of roads on small mammals during 1974-2013, located mainly in North America and Europe. Results were obtained for 56 species in three mammalian orders considered. We found a high diversity of individual behaviours towards roads within the same species in different studies. Nevertheless, we can summarize some general patterns found in the review: 1) roads may not represent a barrier to movements because individuals are able to cross the roads; 2) although road verges with herbaceous cover favour the small mammal's abundance, there is no clear relationship between road verges and their abundance; 3) as expected, home range size and body mass are positively related with road crossing rates; 4) pavement is the road related feature that seems to limit road crossing rates. Based on our review, we found four key knowledge gaps: 1) absence of detailed information related with habitat and climate conditions in the studies; 2) lack of representativeness of small mammals with different ecological traits; 3) missing data on the effects of roads on species dispersal; and 4) scarce data on the role of crossing structures to maintain population connectivity and which features favour their use.