Roads as barriers to animal movement in fragmented landscapes

Abstract

Roads can act as barriers to animal movement through mortality during crossing attempts or behavioral avoidance. This barrier effect has negative demographic and genetic consequences that can ultimately result in local or regional extinction. Here we use radio-telemetry data on three terrestrial vertebrates (eastern massasauga Sistrurus catenatus, eastern box turtle Terrapene carolina and ornate box turtle Terrapene ornata) to test whether roads acted as barriers to movement. Specifically, we test whether individuals avoided crossing roads by comparing the number of observed crossings with the number of road crossings predicted by randomizations of individual movement paths. All species crossed roads significantly less often than predicted by chance, indicating strong road avoidance. Results of this study showing behavioral avoidance and previous studies on road mortality indicate that roads are strong barriers to these species. High mortality during crossing attempts would select for road avoidance, reducing the number of individuals killed on roads over time but leading to genetically partitioned subpopulations due to a lack of gene flow. In species that are long-lived and latematuring, negative genetic effects might not be observable over short time-scales, thus placing populations at high risk of extinction because of a failure to detect an incrementally worsening problem. Formulating successful management strategies for many species in decline will require integrating data on road mortality, animal behavior and population genetics in order to understand more clearly the barrier effect of roads.

Effects of roads and roadside fencing on movements, space use, and carapace temperatures of a threatened tortoise

“…Several other studies have documented similar avoidance of road crossings in several turtle and tortoise species (Forman and Alexander, 1998;Bowne et al, 2006;Shepard et al, 2008). However, environmental and life history variation can create notable exceptions.…”

“…Populations can become fragmented when roads act as barriers to animal movement, either through mortality when animals are killed crossing roads, or because animals avoid crossing roads altogether (Anderson, 2002;Forman et al, 2003;Andrews et al, 2005;Shepard et al, 2008). Roads also contribute to habitat loss and degradation (Forman and Alexander, 1998); not only are paved areas uninhabitable for many species, but many species have reduced abundances that extend for hundreds of meters on either side of roads, resulting in road-effect zones (Forman and Deblinger, 2000;Eigenbrod et al, 2009;Shanley and Pyare, 2011;Peaden et al, 2015).…”

Diversity, activity patterns, and habitat use of the snake fauna of Chapada dos Veadeiros National Park in Central Brazil

“…13,no. 1 to reduce the negative impacts of roads on wildlife in the region (Forman et al 2003, Shepard et al 2008. The species abundance curve shows a sigmoid pattern resembling a lognormal distribution (Whittaker 1970).…”

The Potential Effects of Forest Roads on the Environment and Mitigating their Impacts

“…Shepard et al [18] provided a literature review of the impact of roads on a variety of species from large mammals (such as wolves and grizzly bears) to small invertebrates (such as beetles) to document the impact of roads on wildlife movement through their preferred habitat. In a capture-mark and recapture study, for example, Keller and Largiadèr [19] were able to show that only one of the 742 large, flightless beetles that were recaptured had crossed a six-meter wide road.…”