Toads on Roads : Effect of Linear Barrier on the Movement Ecology of Common Asian Toad (Duttaphrynus melanostictus)

Abstract

Amphibians in India are threatened by population decline and extinction. Conservation efforts are hindered by scanty knowledge on their movement pattern, habitat use and dispersal. Thus, I conducted first ever radio telemetry study on an Indian Amphibian species in Krishnan kovil, a village in Virudunagar district in Tamil Nadu state of India. The study was conducted over a stretch of 1.5 km on both sides of Kollam-Thirumangalam highway (NH 208). The objective was to know if there is any effect of road on the movement and population abundance of Duttaphrynus melanostictus, commonly known as common Asian toad. Reason for selecting a widespread perianthropic species is that such species can better indicate how gene flow is structured in an urban landscape. Total 9 adult individuals (5 ~ and 4 c)I) were tracked ranging between 12 to 41 days from February 1 - April 9, 2015. Findings of the study revealed that NH 208 has a significant effect (estimate 0.007589; standard error 0.003108) on linear displacement of toads that increases away from the road. However in case of village roads the linear displacements were higher near to the roads (estimate -0.01569; standard error 0.002977). This indicates that NH may be affecting the movement of amphibians as a potential physical barrier. However, village roads still seem to be permeable by the toads as they are using it for movement. Orientation data shows no significant orientation (Chi square value 1.19, P value 0.55) of movement of the toads. However, field observations show that movement of toads with NH was always along or away but never across it. Home range estimates show that animal # 6 (NHR6M) used largest home range of 4262.92 sq. meters and showed maximum linear displacement in one night up to 333m. Another aspect of the study was to determine effect of NH on population abundance of common Asian toad. I conducted mark recapture studies in one hectare plot at three sites. The abundance estimates are 228.97 (S.E. 14.09) individuals per hector for site 1, 125.59 (S.E. 9.68) individuals per hector for site 2, 365.94 (S.E. 46.85) individuals per hector for site 3. Abundance estimates at the 3 sites show an increasing trend with the increasing perpendicular distance from the NH. This indicates that the road may have an effect on the population of Duttaphrunus melanostictus. The study is limited to only one non breeding season (3 months), thus, is biased towards movement in less activity period. The study provides hitherto unknown information on toad movement with respect to linear barrier. Such studies are useful in developing realistic, predictive models useful for mitigation and restoration of dispersal corridors in a rapidly changing urban landscape. Results of this first ever amphibian radio telemetry study from India add to a new dimension in Indian amphibian research- beyond taxonomy.