Crowder et al. (2010) studied organic and conventional potato fields in Washington State. They analyzed in several ways the impact of species diversity and the evenness of populations on pest control and feeding damage.
By “evenness,” they refer to the degree to which any one organism dominates an ecosystem. In conventional potato fields, they found that “just one species accounted for up to 80% of individuals...” while in the organic fields, the dominant species never accounted for more than 38%.
In their field work in Washington State, the higher degree of evenness in the organic potato fields “translates into pest densities 18% lower and plants 35% larger.” In a meta-analysis of 38 published studies on predator-prey levels and impacts on yields, the team concluded that “natural enemy evenness increases yield.”
Their conclusions are striking and of great significance. After explaining that conventional, pesticide-based control systems disrupt species diversity and tend to create ecological niches filled by a few highly dominate species, the authors conclude that –
“...organic farming methods mitigate this ecological damage by promoting evenness among natural enemies....very even communities of predator and pathogen biological control agents, typical of organic farms, exerted the strongest pest control and yielded the largest plants.”
And just to drive home the point, Nature covered this important paper in an “Applied Ecology” news item that states matter-of-factly –
“There is little doubt that organic farms generally support more biodiversity, with a higher abundance and greater species richness of many plant and animal groups.” (Turnbull and Hector, 2010)
