Combined Impact of Pesticides and Other Environmental Stressors on Reptile Diversity in Irrigation Ponds Compared to Other Animal Taxa

Irrigation ponds (or farm ponds), as the secondary nature, harbour component species of floodplain ecosystems and hence make a significant contribution to biodiversity. However, biological communities in irrigation ponds are exposed to multiple environmental stressors. Survey data on Japanese irrigation ponds show that reptiles, consisting of turtles, are significantly different from other taxa comprising fishes, molluscs, crustaceans, insects and annelids, in the estimated combined impact (on taxonomic richness) of multiple stressors, including the insecticide 2-sec-butylphenyl methylcarbamate (BPMC, also known as fenobucarb), the fungicide probenazole, concrete bank protection, pond depth reduction, macrophyte decline and invasive alien fish. All these stressors are negatively correlated with the taxonomic richness of all sampled but are positively correlated with that of reptiles. The positive correlation of reptiles with concrete bank protection may stem from the suitability of concrete banks for turtles’ basking. The positive correlation of reptiles with insecticide concentration implies that some extent of insecticide pollution might favour turtles relative to other taxa, because of their potentially high tolerance against the pollution. The taxonomic richness of turtles may be useful as a bioindicator for the combined impact of environmental stressors on animal diversities in irrigation ponds.