Roads Reduce Amphibian Abundance in Ponds
Written By Andrew J. Hamer
Balaton Limnological Research Institute
16th December 2021
Road development is increasing in central Europe
The European continent is highly fragmented by transport infrastructure such as roads and railways. New highways have been recently constructed in central Europe and many more are being planned and constructed. In Hungary, road construction and other landscape changes have destroyed over 90% of the original wetlands. This situation is likely to negatively affect many animal species, including amphibians, which depend on connected terrestrial and aquatic habitats to allow dispersal. Roads can affect pond-breeding amphibians through road mortality and by fragmenting breeding and non-breeding habitats. It is, therefore, crucially important to evaluate impacts to amphibian communities in ponds from roads and other linear infrastructure.
Surveying and modelling amphibian communities in ponds
We conducted dip-net surveys in spring and summer for larval amphibians (tadpoles and newt larvae) at 30 ponds distributed at various distances from highways. The ponds were located about 50 km south-west of Budapest, Hungary, on predominantly agricultural land but also in urban and semi-natural areas. As such, the ponds were a mix of artificial and semi-natural pond types, including highway stormwater retention ponds, recreational fishing ponds, farm dams, ditches and canals, and floodplain ponds. During the amphibian surveys we identified, counted, and then released all captured larvae. We used a geographic information system (GIS) to measure landscape variables, including the distance from ponds to highways and a railway line, and the percentage cover of roads and aquatic and terrestrial habitat in the surrounding landscape. We used multi-species abundance models to estimate the mean abundance of amphibian larvae in each pond, and to examine relationships between abundance and the landscape variables.
Amphibian abundance is reduced in ponds near highways
Over the three aquatic surveys conducted at each pond, we found that the mean abundance of the larvae of seven amphibian species was predicted to be almost 40 times lower in ponds situated within 1 km of a highway, compared with mean abundances in ponds located farther from highways (Figure 1a). This result provides evidence of a road-effect zone, in which there are likely to be a range of detrimental impacts associated with the highway. Ponds surrounded by a high percentage of sealed roads within 1 km also had a lower mean abundance of larvae (Figure 1b). However, there was no apparent effect of the railway line on amphibian abundance.
Figure 1. Mean estimates of larval abundance (shaded areas are 95% credible intervals) across the amphibian community versus: (a) distance from highway; (b) % road surface within a 1000-m radius of the pond; and (c) % accessible habitat within a 1000-m radius of the pond.
Amphibian abundance in ponds relative to accessible habitat differs among species
We calculated the amount of accessible habitat within 1 km of ponds, which was the total amount of aquatic and terrestrial habitat that could be accessed by amphibians through movement without any highways or railways acting as barriers. The mean abundance of the larvae of four species increased with increases in the percentage cover of accessible habitat around a pond, including the common toad, European tree frog, common newt, and spadefoot toad (Figure 2). However, overall, the effect of accessible habitat on amphibian abundance was smaller than the effects of distance to a highway and the percentage cover of roads (Figure 1c). This result demonstrates the relatively strong effect of roads on amphibian communities in central Europe.
Figure 2. Larvae of: (a) common toad; (b) European tree frog; (c) common newt. Note the presence of both forelimbs and hindlimbs in (a) and (b) which indicates that the tadpoles are undergoing metamorphosis. Photo: B. Barta & A. Bohus
Implications for managing amphibian communities in fragmented landscapes
Our results suggest that new ponds constructed adjacent to highways may not always provide suitable habitat conditions to sustain abundant amphibian communities, because they lie within road-effect zones. These ponds are often created for stormwater management while some may be created as compensatory habitat if amphibian habitat is destroyed during highway construction. Within road-effect zones, amphibian communities may be impacted by roadkill reducing population sizes, traffic noise, modified hydrological patterns and contaminated runoff from the road surface. We recommend that road mitigation projects for amphibians create ponds for compensatory habitat in areas of low road density and with no nearby highways, preferably with connectivity to patches of forest and wetlands.
Monitoring amphibian populations is important to determine the longer-term effects of roads in fragmented landscapes, especially given the extent of transportation infrastructure expected to be built over the coming decades in Europe and elsewhere around the world. Repeated count surveys are a rigorous approach that could be used in monitoring programs, as we demonstrated in our study. Monitoring programs conducted at the community level will be important in detecting declines of both common and rare species. Accurate data on population abundance will be useful in alerting road managers to the need for mitigation measures if declines are occurring, whereas increases in species abundance may indicate that road mitigation measures have been successful in preventing roadkill and other road-related impacts.
Author information:
Andrew J. Hamer, Balaton Limnological Research Institute, Eötvös Loránd Research Network (ELKH), Klebelsberg K. u. 3, H-8237 Tihany, Hungary
Source:
Hamer, A.J., Barta, B., Bohus, A., Gál, B., Schmera, D., 2021. Roads reduce amphibian abundance in ponds across a fragmented landscape. Global Ecology and Conservation 28: e01663. https://doi.org/10.1016/j.gecco.2021.e01663
Editor:
Julia Kintsch & Rodney van der Ree
Cite this summary:
Hamer, A.J. (2021): Roads reduce amphibian abundance in ponds. Edited by Kintsch, J. & van der Ree, R. TransportEcology.info, Accessed at: https://transportecology.info/research/hungary-roads-amphibian-ponds [Date accessed].
