Trophic cascades in agricultural landscapes: indirect effects of landscape composition on crop yield

Past studies from our research group show that the composition of the surrounding landscape can influence the abundance and diversity of predatory insects within a field, where complex landscapes (i.e., landscapes with a greater proportion of natural areas) generally support a greater abundance and diversity of predatory insects compared to simplified landscapes (i.e., landscapes surrounded by monocultures of annual crops). However, we know little about how the composition of the landscape might influence plants. Predatory insects can have beneficial effects on plants by eating insect pests (a phenomenon known as “trophic cascades”); therefore we predict that the composition of the landscape might influence plants through their effects on insects.

Recently our group published a study in Ecological Applications examining the effects of landscape composition on the strength of trophic cascades in soybean fields (“Trophic cascades in agricultural landscapes: indirect effects of landscape composition on crop yield” by Heidi Liere, Tania Kim, Ben Werling, Tim Meehan, Doug Landis, and Claudio Gratton). In 2011 and 2012, we monitored predatory insect densities, soybean aphid densities, and soybean yield in fields that spanned a gradient of landscape complexity. We found that both habitat diversity (the number of different habitat types) and proportion of soybean fields in the landscape increased predatory insect densities, which had positive effects on pest suppression and soybean yield. While these results seem intuitive, this is the first study to document the effects of landscape composition on plants through their effects on predatory and pest insects and might explain why the prevalence and strength of trophic cascades is highly variable in nature. These results have implications for applied fields such as IPM where landscape composition might be an important factor to consider.