There is increasing recognition of the importance to investigate multiple climate driver impacts on terrestrial ecosystems at the community level, especially when considering the role of plant-insect community associations in ecosystem functioning. To address how multiple climate factors affect these associations, we examined how [CO₂], temperature, and soil moisture manipulation within a constructed old-field plant community altered the insect community. The Old-Field Community Climate and Atmospheric Manipulation (OCCAM) experiment was established in 2002 at the Oak Ridge National Environmental Research Park. In 2005, we sampled insects that naturally colonized the plant community established within open-top chambers. Our objective was to determine if three potentially interacting climate drivers would alter insect abundance and community structure. Insects were sampled using a combination of sticky traps and vacuum sampling over the growing season. Individuals were identified to morphospecies, assigned to feeding guilds and abundance, richness, and evenness calculated and compared between treatments.  

Results/Conclusions

Although there were occasional effects of [CO₂] and water, the effects of elevated temperature on the insect community were considerable and consistent. Warming significantly increased Thysanoptera (thrips) abundance on sticky traps, but significantly decreased overall morphospecies richness and evenness. Rarefaction determined that observed temperature effects on richness were due to numbers of individuals. Non-metric multidimensional scaling found that only temperature affected insect community composition and a Sørensen similarity index showed insect communities between temperature treatments had less similarity compared to those for [CO₂] or soil water treatments. Within the herbivore guild, elevated temperature significantly reduced richness and evenness, while [CO₂] and water had no effect. Regression found that expected herbivore richness significantly predicted the richness of a higher trophic level (parasitoids), suggesting possible trophic level effects due to warming. Individual effects of temperature in the most abundant insects demonstrated that treatment effects were limited to a relatively small number of morphospecies. A 12% reduction in whole-community plant [N] at elevated [CO₂] did not result in any observed effects on herbivores, indicating that this guild was able to compensate for reduced foliar quality in this community. In conclusion, because we found consistent effects of warming on morphospecies diversity and evenness, and few significant interactions between the three climate drivers we examined, our data show that within this old-field ecosystem warming had the greatest impact on the insect community under future climatic conditions.