Climate warming in a tri-trophic system: effects of experimental warming on soybeans, aphids, and ladybugs

Background/Question/Methods

Climate warming may affect community dynamics through its impact on trophic levels or trophic interactions, but the precise mechanisms remain unclear.  To understand the mechanisms through which climate warming might shape a tri-trophic community, this study examined how experimental warming would affect plants (the soybean Glycine max), herbivores (the aphid Aphis glycines), predators (the ladybug Coccinella septempunctata), and their interactions in three environmental chambers (18.5, 21.5, 24.5^oC).  The chamber at 18.5 ^oC served as control, reflecting the average monthly temperature when local farmers grew soybeans in our study region.  Each chamber included three treatments, representing systems with different trophic structure: 1) soybeans; 2) soybeans and aphids; 3) soybeans, aphids, and ladybugs.

Results/Conclusions

The results showed that warming impact was trophic-structure dependent: 1) In the system with soybeans only, warming increased plant productivity and developmental rate.  2) In the system with soybeans and aphids, warming increased the top-down control of plants by herbivores.  3) In the system with soybeans, aphids, and ladybugs, warming increased the top-down control of aphids by ladybugs, yielding a stronger trophic cascade (from predators to plants) and higher soybean production.  These results suggest that climate warming will likely affect crop production, pest outbreaks, and biocontrol effectiveness, via warming effects on specific trophic levels and/or trophic interactions.