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J Environ Manage
2023 Sep 15;342:118346. doi: 10.1016/j.jenvman.2023.118346.
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Potential hotspots of amphibian roadkill risk in Spain.
Morelli F
,
Benedetti Y
,
Szkudlarek M
,
Abou Zeid F
,
Delgado JD
,
Kaczmarski M
.
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We test a forecasting strategy to identify potential hotspots of amphibian roadkill, combining the spatial distribution of amphibians, their relative risk of collision with vehicles and data on road density in Spain. We extracted a large dataset from studies reporting road casualties of 39 European amphibian species and then estimated the 'relative roadkill risk' of species as the frequency of occurrence of casualties for each amphibian and standardized by the range of distribution of the species in Europe. Using a map with the spatial distribution of Spanish amphibians at a spatial resolution of 10 × 10 Km squares, we estimated the 'cumulative relative risk of roadkill' for each amphibian assemblage as the sum of risk estimates previously calculated for each species. We also calculated the total length of roads in each square (road density). Finally, combining all layers of information, we elaborated a forecasting map highlighting the potential amphibian roadkill risk across Spain. Our findings are relevant to suggest areas that should be focused on at more detailed spatial scales. Additionally, we found that the frequency of roadkill was unrelated to the evolutionary distinctiveness score and conservation status of amphibian species, while was positively correlated with their distribution range.
Fig. 1. Map with the spatial distribution of the number of amphibian species, road network, and the mean and cumulative (relative) risk of roadkill in amphibian assemblages in Spain. The variables are shown using a gradient of colours from lower (light yellow), moderate (orange), to higher (dark brown). All variables were mapped in a grid of 10 × 10 km squares, covering Spain. To optimize data visualization were used different quantiles as a classification criterion.
Fig. 2. Predictive map of overall roadkill risk of amphibians in Spain. The outputs are created by combining data on road density and cumulative relative risk of roadkill in amphibian species assemblages (communities) in each spatial unit (10 × 10 km). The bivariate map shows the pairwise relationships between both variables. Values are organized on each axis, showing four quartiles (from lower to higher values from left to right along the x-axis and bottom to top on the y-axis). The colours indicate the intensity, with lower values characterized by light-grey areas (where both categories align being lower). The degree of blue and purple colours, instead, illustrates squares where one variable is maximized while the other one is low. Finally, squares represented with the indigo colour, indicate the potential hotspots of overall roadkill risk of amphibians (with both categories maximized, simultaneously highest road density and highest cumulative relative risk of roadkill in the amphibian assemblage).
Fig. 3. A potential hotspot of amphibian roadkill risk in Spain on the northwest side of Madrid. The hotspot was identified regarding the cumulative relative risk of roadkill of the amphibian assemblages and road density. The cumulative relative risk is based on the addition of the relative roadkill risk estimated for each amphibian in the species assemblage.
Fig. 4. Association between roadkill frequency and the ED score of amphibians. The colour of the plots is proportional to their distribution range (light blue indicates the largest distribution area) and the IUCN conservation status of species (LC = Least Concern, NT= Near Threatened, and VU= Vulnerable) is indicated by the shape of the dots.