Effects of ramp slope and substrate type on the climbing success of Pelophylax nigromaculatus in agricultural landscapes

Habitat fragmentation has become a serious threat to amphibian populations worldwide. Concrete anti-seepage, widely applied in waterway construction, has posed a threat by causing amphibians to easily fall into concrete irrigation channels and struggle to escape. However, our understanding of the impact of irrigation channels on frog movement and survival remains limited. In this study, we evaluated the effects of concrete-lined irrigation channels on the escape ability of a common Chinese frog (Pelophylax nigromaculatus). We also analyzed the correlation between the morphology and locomotion ability of the frogs, tested the impact of irrigation channel slope gradient and substrate material on their escape ability, and proposed an optimized design for frog ramps to assist trapped frogs in escaping. The results showed that the frogs have easily fallen into these channels and encountered difficulties in escaping during field activities. As body size was positively related to the frogs’ ability to climb the slope of irrigation channels, the design parameters of the frog ramps should focus on the movement ability of the frogs. The maximum climbing gradients for most frogs on concrete, reverse slope (the protruding structure is placed in the opposite direction of the channel slope), grass and crushed stone are 40°, 50°, 60° and 65°, respectively. Based on experimental tests of the ability of the frogs to climb on various slopes and substrates, we suggest that the slope gradient of concrete irrigation channels should be less than 40°. The findings offer references for scholars and engineers to improve ecological engineering designs of irrigation channels throughout the world.