According to a 5-year study discussed in Audubon's August 2006 issue (and excerpted in Utne's Nov-Dec 2006 issue, which is where I read about it), organic farms in England have 105% more plant species than their non-organic counterparts. This provides more habitat, leading to 48% more winter birds and 75% more bats.
Not having read the original article in Audubon (let alone the actual study!), I don't know if they tallied the increased number of insect species found, but I'd be willing to bet a fair amount that insects showed similar gains. More importantly, I'd be willing to bet that insect predator species rebounded significantly, working to control insect plant eaters and balance the farms' ecosystems naturally.
If farmers, who have to make their livelihood from their land, can increase habitat and species diversity like this, just think what us homeowners could do if we all decided to go organic!
I need to try to find the Audubon article. Better yet, I'd like to read the original study. But why wasn't this study widely reported in the national news? It seems to me that its conclusions are one more clue pointing us in the direction of a healthier and more balanced lifestyle.