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1. Barrier effect is a road-related impact affecting several animal populations. It can be caused by behavioural responses towards roads (surface and/or gap avoidance), associated emissions (traffic-emissions avoidance) and/or circulating vehicles (vehicle avoidance). Most studies so far have described road-effect zones along major roads, without determining the actual factor inducing the behavioural response. 2. The purpose of the present study was to assess the factors potentially causing road-effect zones in a heterogeneous road network (with variations in road width, road surface and traffic volume) and eventually to estimate the reduction of habitat quality imposed by roads within a protected area (Doñana Biosphere Reserve, Spain). As model species, we used two ungulates, red deer Cervus elaphus and wild boar Sus scrofa. 3. We surveyed the presence of both species along 200-m transects. All transects started and were perpendicular to reference roads (those with a traffic volume above 10 cars per day), often intersecting unpaved minor roads with virtually no traffic. 4. The presence probability of both species was mainly affected by the distance to the nearest road (in most cases unpaved roads without traffic), but also by the proximity to reference roads. Red deer presence was also affected by the traffic volume of the nearest reference road. At a regional scale, the overall road network within the protected area imposes a reduction in presence probability of 40% for red deer and 55% for wild boar. A road network optimization, decommissioning unused and unpaved roads, would re-establish almost entirely the potential habitat quality (91% for both species). 5. Synthesis and applications. We found that both study species avoided roads regardless of their surface or traffic volume, suggesting a response due to gap avoidance which may be based on the association between linear infrastructures and the possibility of vehicles occurring along them. The overall behavioural response can substantially decrease habitat quality over large scales, including the conservation value of protected areas. For this reason, we recommend road network optimization by road decommissioning to mitigate the impact of roads at a regional scale, with potential positive effects at ecosystem level.

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Habitat specialists inhabiting scarce and scattered habitat patches pose interesting questions related to dispersal such as how specialized terrestrial mammals do to colonize distant patches crossing hostile matrices. We assess dispersal patterns of the southern water vole (Arvicola sapidus), a habitat specialist whose habitat patches are distributed through less than 2% of the study area (overall 600 km2) and whose populations form a dynamic metapopulational network. We predict that individuals will require a high ability to move through the inhospitable matrix in order to avoid genetic and demographic isolations. Genotypes (N = 142) for 10 microsatellites and sequences of the whole mitochondrial Control Region (N = 47) from seven localities revealed a weak but significant genetic structure partially explained by geographic distance. None of the landscape models had a significant effect on genetic structure over that of the Euclidean distance alone and no evidence for efficient barriers to dispersal was found. Contemporary gene flow was not severely limited for A. sapidus as shown by high migration rates estimates (>10%) between non-neighbouring areas. Sex-biased dispersal tests did not support differences in dispersal rates, as shown by similar average axial parent-offspring distances, in close agreement with capture-mark-recapture estimates. As predicted, our results do not support any preferences of the species for specific landscape attributes on their dispersal pathways. Here, we combine field and molecular data to illustrate how a habitat specialist mammal might disperse like a habitat generalist, acquiring specific long-distance dispersal strategies as an adaptation to patchy, naturally fragmented, heterogeneous and unstable habitats.

Despite their potential importance, biological processes like competitive exclusion have been mostly neglected in phylogeographic studies. Here we analyze the role of glacial events and competitive exclusion in the evolutionary history of the lesser white-toothed shrew, Crocidura suaveolens, in Iberia based on cytochrome b sequences. All the Iberian samples grouped together with the rest of western European populations within the previously described clade IV. We identified three distinct evolutionary lineages within this major clade, two of them occurring exclusively in Iberia. Iberian lineage B extends throughout the northwest with a continuous distribution and diversity values from moderate to high, whereas Iberian lineage C has a highly-patched distribution and is structured in four sublineages, all having low diversity values. No signs of demographic growth were detected for any of the lineages. The evolutionary history of C. suaveolens in Iberia supports the refugia-within-refugia scenario, but ecological studies in areas of sympatry, molecular and fossil datings, and contrasting patterns in the Italian Peninsula, suggest that competitive exclusion exerted by C. russula since its arrival to Iberia has been the main factor shaping the distribution, phylogeograhy and population genetics of lineage C.