Effects of experimental warming on a grassland insect and spider community

Background/Question/Methods

One of the major threats to Earth’s biodiversity is climate change. To date, most ecological studies of the impacts of climate warming on earth’s biota are focused on select species or single trophic levels. Multi-species warming studies tend to be observational, exploring phenology changes or range shifts. There is a need for rigorous experimental investigation of the impact of climate warming on the structure and function of entire multi-trophic communities.

I am investigating the impacts of warming on the community structure of insects and spiders in a tallgrass prairie heating experiment. At Cedar Creek Ecosystem Science Reserve, an LTER site in Minnesota, plots of vegetation are warmed using overhead heating elements, but otherwise left open to sun, wind, and rain. Thirty-eight plots with varying plant species richness are continuously heated to approximately 2.5 ºC above ambient, which corresponds with predictions of temperature increase in the upper Midwest region of 2-3 ºC by 2050. Paired control plots are unheated. In 2010, I collected insects and spiders in each of the 38 heated and 38 control plots using a modified Blow&Vac suction apparatus. The insects were sorted and identified to family level, were measured, and were assigned to trophic position and guild.

Results/Conclusions

A total of 5,177 insects and spiders were collected. Initial analyses show that across all insects, there are approximately 24% more individuals and 51% greater insect biovolume in warmer plots. The increase in biomass is driven both by the increase in number of individuals and the size of individuals. While no one insect group is responsible for the differences between warmed and control plots, some groups appear to respond more to warming. Araneae (spiders), Lepidoptera (moths and butterflies), and Thysanoptera (thrips) had significantly higher biovolume in warmed plots.