It’s well demonstrated that increased habitat complexity tends to increase arthropod biodiversity and, importantly, the abundance of natural enemies. Therefore, it is thought that increasing complexity in agricultural landscapes should increase the level of pest control too.
But is this true? Does increased landscape complexity actually result in fewer pests?
There have been a few great studies that have looked at this question (e.g. Gardiner et al. 2009 Ecol Appl), but the overall trend has been less clear. Enter Rusch et al. (2016); they completed a quantitative synthesis of aphid exclusion experiments conducted in different cropping systems. They defined complexity as “the amount of non-crop habitats in a landscape sector surrounding the crop field…” up to a 1 km radius. The synthesis looked at 15 studies for a total of 175 field sites.
As their Figure 1 (above) shows, there is a significant effect of landscape complexity on aphid population control. This is nice to see, and I particularly like their Table 1 which summarizes all of the included studies. But I’ve got to say, it looks like an awfully low R², and the slope isn’t very steep considering they went from 2 to 100% landscape simplification. What else is going on here that might explain all the added variation? How do we manipulate habitat to get greater than a 10% biological control impact on pest density?