Severe conservation risks of roads on apex predators

Abstract

The global expansion of road networks threatens apex predator conservation and ecosystem functioning. This occurs through wildlife-vehicle collisions, habitat loss and fragmentation, reduced genetic connectivity and increased poaching. We reviewed road impacts on 36 apex predator species and assessed their risk from current roads based on road exposure and species vulnerability. Our findings reveal all apex predators are exposed to road impacts. Eight of the ten species with the highest risk occur in Asia, although other high-risk species are present in the Americas, Africa and Europe. The sloth bear suffers the highest risk of all apex predators, followed by the tiger and dhole. Based on species risk from roads, we propose a widely applicable method to assess the potential impact of future roads on apex predators. We applied this method to proposed road developments in three areas: the Brazilian Amazon, Africa, and Nepal, to locate high-impact road segments. Roughly 500 protected areas will be intersected by these roads, threatening core apex predator habitats. We advocate the need for rigorous road development planning to apply effective mitigation measures as an urgent priority and to avoid construction in wilderness areas and predator strongholds.

Figure 1

(A) Global apex predator richness (n = 36) calculated from IUCN species distribution maps. (B) Global road density at 5-arcmin resolution, equivalent to approximately 8 km in the tropics, representing four road types (highways, primary, secondary, and tertiary roads), data from the Global Roads Inventory Project. (C) Total number of Wildlife-Vehicle Collisions (WVC) of apex predators recorded in a single year (between 1963 and 2021) for each country with available WVC data. (D) WVC sampling effort per country, referred to the sum of years of study (ranging from 1963 to 2021). Maps were generated in R software v4.0.3 (https://www.R-project.org/).

Figure 2

Apex predators risk to roads calculated as the product of exposure to roads (road density within the species range) and vulnerability of species. Gauges indicate the risk value of each species. Bars indicate the standardized road density, the proportion of species distribution area unprotected, standardized number of IUCN listed threats, and standardized value of the categorized average body mass (i.e., very large (> 100 kg), large (25–100 kg), medium (15–25 kg), small (8–15 kg)). The IUCN conservation of each species is shown. P. uncia, L. pictus and L. canadensis silhouettes were drawn by Gabriela Palomo-Muñoz, all predator silhouettes were acquired from PhyloPic (http://phylopic.org/).

Figure 3

Cumulative road risk of apex predators globally used for predicting the potential impact of future roads. The cumulative risk is based on the aggregation of the road risk for each species and the presence of protected areas (see Methods), calculated at 5-arcmin resolution. Blue boxes indicate the three case studies used for assessing the potential impact of future road developments in (A) the Brazilian Amazon, (B) Africa, and (C) Nepal. Maps were generated in R software v4.0.3 (https://www.R-project.org/).

Figure 4

Potential impact of future road developments in (A) the Brazilian Amazon, (B) Africa, and (C) Nepal. Bubble sizes indicate the percentage of road length under each level of impact. Green areas denote protected areas, and in darker green are the areas that will be intersected directly or within a 10-km buffer around proposed roads. Bar graphs indicate the potential impact of future road developments on predator species present in (D) the Brazilian Amazon, (E) Africa, and (F) Nepal. Bars on the left show the length (km) of future roads that will cross the species distribution range; numbers beside the bars indicate the percentage in relation to the complete length of the future development. Bars on the right indicate the proportion of future road length crossing the species range in relation to the size of the species total distribution. FRL = Future Road Length. Colours in bars represent the road risk for each species calculated in our assessment. Maps were generated in R software v4.0.3 (https://www.R-project.org/). L. pictus silhouette was drawn by Gabriela Palomo-Muñoz, all predator silhouettes were acquired from PhyloPic (http://phylopic.org/).