Road construction enables establishment of a novel predator category to resident anuran community: a case study from a primary lowland Bornean rain forest

For a total of 17 mo, we investigated the impact of a road constructed through pristine tropical lowland rain forest, on the composition and structure of the resident anuran community in the Ulu Temburong National Park (Brunei Darussalam). One year after road construction, eight new anuran species had immigrated into the impacted area. Encounter surveys were conducted and radio-transmitters attached to a total of 16 frogs to identify habitat use and distribution of the largest (> 130 mm SVL) immigrant species (Limnonectes ingeri) in comparison with a similar sized resident congener. A strong preference for roadside habitat was found for the immigrant. However, several incursions of more than 500 m beyond the road into the pristine forest were also recorded. Over 200 stomach content samples as well as stable nitrogen isotope ratios of 76 individuals were used to assess the trophic ecology of the two species. Invertebrate diet composition did not differ. However, the immigrant species ate over 400% more frogs than its resident congener and had a significantly higher delta N-15 ratio, indicating a higher position in the food web. This suggests that L. ingeri acts as a new top frog predator in the system and indicates that it may have a significant negative impact on the local anuran community. Overall, road construction in the absence of logging has led to the immigration of new frog species with impacts far beyond the linear disturbance of the road itself.