Modest Experimental Warming Reduces Species Diversity and Biomass of Arthropods in a Tibetan Alpine Meadow

Climate warming is expected to contribute to the decline of arthropod species diversity and biomass around the world. However, direct experimental evidence is lacking. Here, we report on a field experiment documenting arthropod species diversity and biomass responses to passive simulated warming for six consecutive years in an alpine meadow on the Tibetan Plateau. The field warming experiment consisted of six large open-top chambers (15 × 15 × 2.5 m), with three chambers warmed and three non-warmed, resulting in mean temperature differences of 0.18°C and 0.57°C in the growing season and the non-growing season, respectively. Warming decreased arthropod species diversity by 39% and arthropod biomass by 18% during the experiment. Specifically, the richness of large-bodied species decreased, while small-bodied species were not significantly affected. Moreover, the abundance of small-bodied species increased, but that of large-bodied ones decreased, resulting in decreases in community size spectrum and community-weighted mean body size under warming. Results of structural equation model suggest that the decreases in arthropod species diversity (represented by species richness and community size spectrum) and biomass were primarily caused by a warming-induced shift from forb- to graminoid-dominated plant communities, which could be attributed to a warming-induced decrease in soil moisture. Moreover, the warming effect on arthropod species diversity and biomass was more pronounced in later years of the experiment, which could be partly related to the increase in mean annual temperature over the course of the experiment and progressing shift in plant community species composition over time. Our study provides unique experimental evidence that even very modest warming may result in declines in both species diversity and biomass of arthropods through cascades of indirect effects, and identifies important mechanisms underlying biodiversity loss.