Effects of simazine herbicide on a plant-arthropod-lizard tritrophic community in territorial indoor microcosms: Beyond the toxicity

Agricultural source pollution has been hypothesized as one of the main reasons for reptile declines over recent decades. In addition to their direct toxicity to reptiles, agrochemicals can also enter complex interactions with environmental factors, which alter the interspecific relationships within communities. The potentially resulting cascading effects affect our understanding of the links between contaminants and the extent of declines of reptile species. In the present study, plant-arthropod-lizard tritrophic microcosms were assessed to identify the ecological effect of the widely used herbicide simazine in simulated steppe ecosystems. Three dosages of simazine (0, 0.060, and 0.006 g a.i./m2) were applied to microcosms, and the responses of organisms at three trophic levels were examined after 30-day exposure. The results showed that simazine could inhibit the growth and ecological functions of primary producers, and caused a reduction in the content of primary and secondary metabolites. The number of arthropod populations decreased in the lower simazine application but increased in the higher simazine application, compared with the control. Simazine led to slow growth and poor physical conditions in lizards. The impact of simazine on the community could be attributed to the following three aspects: (1) a direct effect of simazine, (2) the driving force of food resources, and (3) behavioral dynamics. The physical conditions of lizards and of the arthropod population in the microcosms showed different responses to standard toxicological tests, and the forces of cascading causalities were identified as the main factors beyond the direct simazine toxicity. Therefore, the propagation and cascade across multitrophic levels should be considered in future assessments to avoid distorting conclusions.