Do all roads lead to resistance? State road density is the main impediment to gene flow in a flagship species inhabiting a severely fragmented anthropogenic landscape

Abstract

Aim Connectivity conservation is ideally based on empirical information on how landscape heterogeneity influences species‐specific movement and gene flow. Here, we present the first large‐scale evaluation of landscape impacts on genetic connectivity in the European wildcat ( Felis silvestris ), a flagship and umbrella species for connectivity conservation across Europe. Location The study was carried out in the core area of the distributional range of wildcats in Germany, covering about 186,000 km 2 of a densely populated and highly fragmented landscape. Methods We used data of 975 wildcats genotyped at 14 microsatellites and an individual‐based landscape genetic framework to assess the importance of twelve landscape variables for explaining observed genetic connectivity. For this, we optimized landscape resistance surfaces for all variables and compared their relative impacts using multiple regression on distance matrices and commonality analysis. Results Genetic connectivity was best explained by a synergistic combination of six landscape variables and isolation by distance. Of these variables, road density had by far the strongest individual impact followed by synergistic effects of agricultural lands and settlements. Subsequent analyses involving different road types revealed that the strong effect of road density was largely due to state roads, while highways and federal roads had a much smaller, and county roads only a negligible impact. Main conclusions Our results highlight that landscape‐wide genetic connectivity in wildcats across Germany is strongly shaped by the density of roads and in particular state roads, with higher densities providing larger resistance to successful dispersal. These findings have important implications for conservation planning, as measures to mitigate fragmentation effects of roads (e.g., over‐ or underpasses) often focus on large, federally managed transportation infrastructures. While these major roads exert local barrier effects, other road types can be more influential on overall connectivity, as they are more abundant and more widespread across the landscape.

Survival and cause-specific mortality of European wildcat (Felis silvestris) across Europe

“…Roadkills represented more than 50% of wildcat mortality across Europe. This finding corroborates the assumption that roadkill is the main source of mortality for the European wildcat (Westekemper et al, 2021). Our results are consistent with the high percentage of roadkills found by Falsone et al (2014) despite the different methodologies used, thereby confirming the reliability of both studies.…”

“…2, these road types occurred at lower densities in wildcat homeranges in comparison with secondary and tertiary roads, suggesting either an avoidance in second-order habitat selection or extinction of wildcat populations in areas with a high density of motorways and primary roads due to high mortality. Although denser in wildcats' homeranges and usually more widespread across the landscape (Blackburn et al, 2021;Westekemper et al, 2021), low-traffic roads did not significantly affect the survival in our study. This pattern can be explained by intrinsic properties of roads such as traffic intensity, roadway width and vehicular speed that make motorways and primary roads more hazardous to cross.…”

“…Even so, Klar et al (2009) found 30-40% of the wildcats living along the motorway were killed each year, confirming that wildcat does cross high-traffic roads leading to high mortality. On the other hand, even roads with lower traffic intensity but more widespread across the landscape have been found to severely hinder genetic connectivity between wildcats' populations in Germany (Westekemper et al, 2021). Further studies on wildcat movement behaviour are needed to clarify the barrier effect of different road types and the mortality associated with crossings attempts.…”

“…For instance, Klar et al (2009) showed that wildcat mortality on motorway sections was reduced by 83% after fencing. Finally, other aspects of wildcat ecology such as landscape-wide connectivity (Westekemper et al, 2021) should be considered to identify areas and types of roads requiring urgent management actions.…”

“…Felids are typically solitary species with large area requirements, which makes them struggle particularly with adapting to fragmented anthropogenic landscapes (Riley et al, 2003;Vickers et al, 2015). Their high mobility increases the likelihood of road crossings and encounters with anthropogenic structures that increase mortality (Haines et al, 2005;Vickers et al, 2015), especially in areas with high road density (Poessel et al, 2014;Westekemper et al, 2021). Roadkill indeed represents the main source of mortality for various felid species (e.g.…”