Talk Simulating population effects of infrastructure permeability and the performance of mitigation strategies

Barrier and mortality effects to wildlife populations induced by transport infrastructure and traffic have provoked comprehensive prevention and mitigation programs in many countries. Such programs are, however, often driven by practical or political considerations rather than by scientific knowledge. In particular, it is often unclear how much mitigation effort may be needed and what type of mitigation will be most efficient to remedy the identified conflicts. To aid this decision making process, we developed a metapopulation & road permeability model (PERM) that allows for calculations of changes in population viability and allele frequency (genetic effects) resulting from changes in connectivity between local populations across infrastructure networks. Hence the model quantifies what effect mitigation measures will have on populations and can be used to optimize road mitigation plans. The model employs two routines: a) an individual-based local population routine (life history, fecundity, survival, dispersal, and allele frequency) and b) a connectivity routine to estimate the degree of permeability of infrastructural barriers between adjacent populations. We defined “local populations" as inhabiting meshes within the infrastructure network, whereby roads with a certain traffic volume were considered as theoretical population boundaries. High road permeability practically implies a merging of local populations, whereas strong boundaries cause isolation and/or high traffic mortality. Changes in permeability can result from the installation of wildlife crossings or fences, from speed reduction and traffic rerouting, etc. Because species respond differently to traffic and thus to mitigation options, we simulated four generic response types (avoiders, speeders, pausers, non-responders, as proposed by Jacobson et al. 2015), representing species groups such as large herbivores, large carnivores, small carnivores and amphibians. The model identifies under which traffic conditions and for which types of species it may be more efficient to reduce mortality through fencing, increase permeability through the construction of wildlife crossing structures or to both reduce mortality and increase permeability through changes in traffic parameters such as speed reduction.

At present, our simulations are ongoing. We will update this abstract within 4-6 weeks from now with first results of the model.

de-fragmentation, barrier effects, traffic mortality, deer-vehicle accidents, wildlife-vehicle collisions, hunting, transport infrastructure, ecological impact, mitigation, metapopulation dynamics, modeling