Naturally occurring predator and parasitoid communities are well known to respond to multiple scales of environmental heterogeneity within and around agroecoystems, yet our understanding of which scales are most influential on different functional guilds of enemies is limited. Using vote-counting methodology, we synthesized the results from 40 empirical studies that observed how natural enemy richness, diversity, or parasitism rate is affected by environmental heterogeneity at a local scale (e.g. a focal field), an intermediate scale (e.g. habitat in immediate proximity of a focal field), and landscape scale (e.g. habitat within >200 m radius around focal field). Heterogeneity at all scales was more commonly beneficial than antagonistic to natural enemies as a whole, where positive responses were always significantly larger than negative responses. However, when using a conservative approach of comparing the positive and ‘non-positive’ (combined neutral and negative responses), landscape heterogeneity was the only scale where positive responses significantly outweighed non-positive responses. The same trend held for natural enemy guilds; though all guilds had more positive than negative responses to all scales of heterogeneity, intermediate and landscape scales were the only scales where any guild had significantly more positive than non-positive responses. These results suggest the importance of incorporating geographically large-scale strategies when seeking to conserve natural enemies and enhance or sustain conservation biological control services.
Iverson, Aaron; Burnham, Robyn; and Vandermeer, John
"Agricultural natural enemies benefit predominantly from broader scales of environmental heterogeneity: A quantitative review,"
The Great Lakes Entomologist, vol 54
Available at: https://scholar.valpo.edu/tgle/vol54/iss1/7