Abstract
Roadways pose serious threats to animal populations. The installation of roadway mitigation measures is becoming increasingly common, yet studies that rigorously evaluate the effectiveness of these conservation tools remain rare. A highway expansion project in Ontario, Canada included exclusion fencing and ecopassages as mitigation measures designed to offset detrimental effects to one of the most imperial groups of vertebrates, reptiles. Taking a multispecies approach, we used a Before-After-Control-Impact study design to compare reptile abundance on the highway before and after mitigation at an Impact site and a Control site from 1 May to 31 August in 2012 and 2013. During this time, radio telemetry, wildlife cameras, and an automated PIT-tag reading system were used to monitor reptile movements and use of ecopassages. Additionally, a willingness to utilize experiment was conducted to quantify turtle behavioral responses to ecopassages. We found no difference in abundance of turtles on the road between the un-mitigated and mitigated highways, and an increase in the percentage of both snakes and turtles detected dead on the road post-mitigation, suggesting that the fencing was not effective. Although ecopassages were used by reptiles, the number of crossings through ecopassages was lower than road-surface crossings. Furthermore, turtle willingness to use ecopassages was lower than that reported in previous arena studies, suggesting that effectiveness of ecopassages may be compromised when alternative crossing options are available (e.g., through holes in exclusion structures). Our rigorous evaluation of reptile roadway mitigation demonstrated that when exclusion structures fail, the effectiveness of population connectivity structures is compromised. Our project emphasizes the need to design mitigation measures with the biology and behavior of the target species in mind, to implement mitigation designs in a rigorous fashion, and quantitatively evaluate road mitigation to ensure allow for adaptive management and optimization of these increasingly important conservation tools.
Highlights
Increasing rates of urbanization, with associated habitat destruction and fragmentation, have led to the imperilment of much the world’s biodiversity [1, 2]
The percentage of dead reptiles detected at the Impact site increased by 20% for turtles and 25% for snakes between the Before and After periods, while the Control site had an increase of only 2% for turtles and 11% for snakes
We found that the success of the connectivity structures was reliant upon the success of the exclusion structures, and that the entire mitigation system was compromised at our site because of failures in the materials, implementation, and design of the exclusion structures
Summary
Increasing rates of urbanization, with associated habitat destruction and fragmentation, have led to the imperilment of much the world’s biodiversity [1, 2]. The threats posed by roads extend from individual mortality to population-wide effects, as barriers within populations can lead to loss of genetic diversity and isolation [4]. Tied to this research effort is the development of mitigation strategies aimed at protecting wildlife from the negative effects of roads [8], with particular focus on large-bodied species [9, 10]. Far fewer studies have examined effectiveness of road mitigation for small-bodied species [11, 12]. Reptiles, considered one of the most imperilled groups of animals globally [13], have been substantially affected by the proliferation of roads [14, 15, 16], and conservation strategies to minimize threats posed by roads are being implemented [17, 18]. Few studies have evaluated the effectiveness of these conservation efforts [7]
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