Severe conservation risks of roads on apex predators

Light at the end of the tunnel: Innovative opportunities for saving tropical biodiversity

The expansion of roads into wilderness areas and biodiversity hotspots in the Global South seems inevitable and is predicted to bring about significant biodiversity loss. Even so, existing widespread strategies aiming to mitigate the direct and indirect impacts of roads on the environment have been of limited effectiveness. These tactics, including construction of fencing, wildlife crossings on paved roads, and establishment of protected areas along the roads, are unlikely to be sufficient for protecting diverse species assemblages from roadkill, habitat fragmentation, and anthropogenic activity in tropics. This indicates the need for integration of more ambitious approaches into the conservation toolkit, such as the constructing tunnels, covered ways, and elevated roads. Although these tools could significantly support conservation efforts to save tropical biodiversity, to date, they are rarely considered. Here, we discuss factors which determine the need for application of these approaches in the Global South. We highlight the often-overlooked long-term benefits associated with the application of the proposed tools. We also discuss the potential challenges and risks, and the ways to minimise them. Hopefully this article will encourage practitioners to integrate these strategies into conservation toolkits and allow policy-makers and investors to make informed decisions on sustainable road infrastructure development in the Global South.

Impacts of existing and planned roads on terrestrial mammal habitat in New Guinea

New Guinea is one of the last regions in the world with vast pristine areas and is home to many endemic species. However, extensive road development plans threaten the island's biodiversity. We quantified habitat fragmentation due to existing and planned roads for 139 terrestrial mammal species in New Guinea. For each species, we calculated the equivalent connected area (ECA) of habitat, a metric that takes into account the area and connectivity of habitat patches in 3 situations: no roads (baseline situation), existing roads (current), and existing and planned roads combined (future). We assessed the effect of roads as the proportion of the ECA remaining in the current and future situations relative to the baseline. To examine whether there were patterns in these relative ECA values, we fitted beta-regression models relating these values to 4 species characteristics: taxonomic order, body mass, diet, and International Union for the Conservation of Nature Red List status. On average across species, current ECA was 89% (SD 12) of baseline ECA. Shawmayer's coccymys (Coccymys shawmayeri) had the lowest amount of current ECA relative to the baseline (53%). In the future situation, the average remaining ECA was 71% (SD 20) of baseline ECA. Future remaining ECA was below 50% of the baseline for 28 species. The montane soft-furred paramelomys (Paramelomys mollis) had the lowest future ECA relative to the baseline (36%). In general, currently nonthreatened carnivorous species with a large body mass had the greatest reductions of ECA in the future situation. In conclusion, future road development plans imply extensive additional habitat fragmentation for a large number of terrestrial mammal species in New Guinea. It is therefore important to limit the impact of planned roads, for example, by reconsidering the location of planned roads that intersect habitat of the most threatened species, or by the implementation of mitigation measures such as underpasses.

Rapid behavioral responses of endangered tigers to major roads during COVID-19 lockdown

Roads pose a major, and growing, challenge for the conservation of endangered species. However, very little is known about how endangered species behaviorally respond to roads and what that means for road mitigation strategies. We used the nation-wide lockdown in Nepal during the COVID-19 pandemic as a natural experiment to investigate how dramatic reductions in traffic volume along the national highway affected movements of two GPS-collared tigers (Panthera tigris)-a globally endangered species. This work is the first systematic research on tigers in Nepal using radiotelemetry or GPS tracking data since the 1980s. We found that the highway more strongly constrained the space use and habitat selection of the male in Parsa National Park than the female in Bardia National Park. Over the entire study period, the female on average crossed 10 times more often per week than the male, and when he was near the highway, he was over 11 times more probable to not cross it than to cross during the day. However, we also found that the cessation of traffic during the pandemic lockdown relaxed tiger avoidance of roads and made the highway more permeable for both animals. They were 2-3 times more probable to cross the highway during the lockdown than before the lockdown. In the month following the lockdown, the space use area of the male tiger tripled in size (160-550 km²), whereas the female's shrunk to half its previous size (33-15 km²). These divergent patterns likely reflect differences between the two parks in their highway traffic volumes and regulations as well as ecological conditions. Our results provide clear evidence that vehicle traffic on major roads impede tiger movements, but also that tigers can respond quickly to reductions in human pressures. We conclude by identifying various actions to mitigate road impacts on tigers and other endangered species.

Forecasting effects of transport infrastructure on endangered tigers: a tool for conservation planning

The rapid development of transport infrastructure is a major threat to endangered species worldwide. Roads and railways can increase animal mortality, fragment habitats, and exacerbate other threats to biodiversity. Predictive models that forecast the future impacts to endangered species can guide land-use planning in ways that proactively reduce the negative effects of transport infrastructure. Agent-based models are well suited for predictive scenario testing, yet their application to endangered species conservation is rare. Here, we developed a spatially explicit, agent-based model to forecast the effects of transport infrastructure on an isolated tiger (Panthera tigris) population in Nepal's Chitwan National Park-a global biodiversity hotspot. Specifically, our model evaluated the independent and interactive effects of two mechanisms by which transport infrastructure may affect tigers: (a) increasing tiger mortality, e.g., via collisions with vehicles, and (b) depleting prey near infrastructure. We projected potential impacts on tiger population dynamics based on the: (i) existing transportation network in and near the park, and (ii) the inclusion of a proposed railway intersecting through the park's buffer zone. Our model predicted that existing roads would kill 46 tigers over 20 years via increased mortality, and reduced the adult tiger population by 39% (133 to 81). Adding the proposed railway directly killed 10 more tigers over those 20 years; deaths that reduced the overall tiger population by 30 more individuals (81 to 51). Road-induced mortality also decreased the proportion of time a tiger occupied a given site by 5 years in the 20-year simulation. Interestingly, we found that transportation-induced depletion of prey decreased tiger occupancy by nearly 20% in sites close to roads and the railway, thereby reducing tiger exposure to transportation-induced mortality. The results of our model constitute a strong argument for taking into account prey distributions into the planning of roads and railways. Our model can promote tiger-friendly transportation development, for example, by improving Environmental Impact Assessments, identifying "no go" zones where transport infrastructure should be prohibited, and recommending alternative placement of roads and railways.