Population persistence in landscapes fragmented by roads: Disentangling isolation, mortality, and the effect of dispersal

Ana Ceia-Hasse,Laetitia M Navarro,Luís Borda-De-Água,Henrique M Pereira

doi:10.1016/j.ecolmodel.2018.01.021

Abstract

Linear infrastructures, one of several forms of land-use, are a major driver of biodiversity loss. Roads impact populations at many levels, with direct road mortality and barrier effect contributing to decreased population abundance, higher isolation and subdivision, and therefore to increased extinction risk. In this paper, we compared the effect of road mortality and of the barrier effect on population isolation, persistence and size, and assessed the interaction of these effects with dispersal. We used a spatially explicit, process-based model of population dynamics in landscapes fragmented by varying levels of road density. We modelled a barrier effect independently from road mortality by varying the probability with which individuals avoid crossing roads. Both road mortality and the barrier effect caused population isolation. While road mortality alone had stronger negative effects than the barrier effect without extra mortality, the latter also resulted in decreased population size. Yet, road avoidance could, in some cases, rescue populations from extinction. Populations with a large dispersal distance were more negatively affected as road mortality increased. However, when there was no road mortality they maintained larger sizes than populations with a short dispersal distance. Our results highlight the much higher relative importance of road mortality than the barrier effect for population size and persistence, and the importance of assessing relevant species traits for effective long-term transportation planning and conservation management. Our model can be used in species-specific situations and with real landscape configurations in applications such as conservation planning.

Highlights

The current biodiversity crisis is mainly driven by land-use change (Pereira et al, 2012; Maxwell et al, 2016)
When there was no road mortality and no road avoidance, the probability of extinction was higher and the population size was smaller at higher road densities, suggesting an effect due to habitat loss (Fig. 4)
With no road mortality and no road avoidance, the probability of extinction was zero or close to zero, even with high road density (Fig. 4a); and the population size was considerably larger than with either complete road avoidance, or complete road mortality (Fig. 4b). These results suggest that in such cases there was an effect of road avoidance or of road mortality, respectively

Summary

Introduction

The current biodiversity crisis is mainly driven by land-use change (Pereira et al, 2012; Maxwell et al, 2016). One of many forms of land-use, cause major impacts on populations. As the road network is predicted to strongly increase in the coming years (van der Ree et al, 2015), it is crucial to assess its impact on populations, in order to apply suitable mitigation measures, and improve conservation and road planning. Roads cause direct mortality through wildlife collisions with vehicles, and act as a barrier to movement (van der Ree et al, 2015). These direct and indirect impacts of roads can contribute to population isolation and subdivision, to decreases in population abundance, and can increase population extinction risk

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Discussion

Conclusion