The domino effect of roads on biodiversity: How the impacts of wildlife-vehicle collisions propagate through food webs
Written by Vinicius Augusto Galvão Bastazini, Frederico Mestre & Fernando Ascensão
July 10th 2025
Figure 1. Representation of the simplification of food webs in response to increasing road density.
Wildlife-vehicle collisions: More than meets the eye
The direct impact of wildlife-vehicle collisions on fauna mortality is well documented. However, the effects can extend far beyond the loss of individuals or populations, with consequences that might propagate across entire ecosystems. When a species’ population is reduced or lost due to road mortality, the entire network of ecological interactions in which the species is embedded may be affected. However, we still know very little about how these effects can propagate across multiple levels of ecological organisation within the food web, potentially triggering a cascading effect on other species and ecological processes (Figure 1).
Investigating the indirect effects of roadkill on food webs
In our study, we investigated how roads indirectly affect wildlife populations and communities by examining the impact of roadkill on food webs. We began by using the maximum road density a given species can withstand without negative population effects, which is an output of the trait-based model, developed by Grilo et al. (2020). This model links species’ ecological traits with their vulnerability to road mortality by using empirical roadkill data and biological traits (like body size, reproductive rate, and mobility) to predict mortality risk across species.
With these estimates, we identified high-risk areas where roadkill occurs more frequently and where species loss is more likely. We then mapped predator-prey interactions across Europe, constructing regional food webs including 551 species (349 birds and 202 mammals). Finally, through computational simulations, we assessed how the disappearance of prey species due to high road density could disrupt these trophic interactions. This approach allowed us to predict not just species-level impacts but also cascading effects on entire ecological networks of predators and prey.
A prey (wild rabbit), a top predator (lynx) and a top predator with a prey (Eurasian eagle-owl). Photo credits: Joaquim Pedro Ferreira
The cascading consequences of road density on food webs
Among the species we analysed, 15% had more than 10% of their range in areas with road density above their vulnerability threshold, putting them at significant risk of local extinction due to roadkill. Some species at the base of the food chain – e.g., the broom hare – could lose nearly all of their viable habitat due to high road density.
Beyond direct roadkill, our study showed that roads affect the entire ecological network, not just each individual species. On average, 4.5% of species interactions are threatened by roads, but this can exceed 90% in highly urbanised areas of Europe, such as Belgium, France, Germany, and the northern Iberian Peninsula (Figure 2). The loss of interactions in local food webs is strongly related to road density, with up to 30% loss when road density approaches 1 km of road per km².
Figure 2. The cascading effects of road mortality in Europe. The top panel depicts a schematic representation where vulnerable populations are shown by red dots, and these vulnerable populations are lost in areas with higher road density. The middle panel shows a food web example before and after the extinctions induced by high road density. The map below shows the number of potentially lost trophic interactions due to roadkill, typically corresponding to areas with higher road density.
This happens because when a species disappears due to road mortality, all of its ecological interactions may also be affected. For example, apex predators such as the golden eagle and wolf, as well as mesopredators (mid-ranking predators, occupying typically a position below apex predators), like the little owl and wildcat, may lose much of their prey in some regions, making their local persistence even more unlikely in the long term.
Areas of lower risk for predator-prey interactions
As expected, we found that regions with lower road density, typically mountainous regions like the Alps, Carpathians, and Pyrenees, have a lower risk of losing predator-prey interactions, supporting greater species diversity and unique ecological interactions, including the presence of apex predators.
Implications for conservation and road network planning
Although our study focused on just one type of ecological interaction, it showed that road impacts go far beyond direct roadkill. It also identified critical areas where road-induced cascade effects may be most pronounced and highlights the trophic groups most vulnerable to these impacts. The consequent loss of ecological interactions could compromise the functioning of ecosystems on a large scale, affecting ecosystem services upon which we all depend. Our findings highlight the need for tailored conservation measures to reduce roadkill risk in order to preserve the integrity of ecological networks in areas with existing roads and on new road projects. It is also critical that the impacts of roadkill on different levels in the food chain, from apex predators at the top to lower-order prey at the bottom, are considered.
Author information
Vinicius Augusto Galvão Bastazini
Independent Researcher, Belgium
Vinicius Bastazini is a researcher interested in ecological and evolutionary dynamics and exploring species interactions and diversity.
Frederico Mestre
CCMAR—Algarve Centre of Marine Sciences, University of Algarve, Faro, Portugal.
Frederico Mestre’s research explores the dynamics of ecological networks, with a particular focus on the impacts of climate change and human-induced disturbances on species distributions and interactions.
Fernando Ascensão
CE3C - Center for Ecology, Evolution and Environmental Changes & CHANGE - Global Change and Sustainability Institute, Universidade de Lisboa, Lisboa, Portugal
Fernando Ascensão is an Assistant Professor at Univ. de Lisboa, in Conservation Biology, focusing on how transport and energy infrastructures affect ecological processes and population dynamics.
Source citation
Mestre, F., Bastazini, V. A. G., & Ascensão, F. (2025). Effects of road density on regional food webs. Conservation Biology, e70007. DOI: https://doi.org/10.1111/cobi.70007
Editor:
Rodney van der Ree
Cite this summary:
Bastazini, V.A.G., Mestre, F. & Ascensão, F. (2025). The domino effect of roads on biodiversity: How the impacts of wildlife-vehicle collisions propagate through food webs. Edited by van der Ree, R. TransportEcology.info, Accessed at: https://transportecology.info/research/roadkill-cascading-effects-food-webs