Land-use change is considered the strongest driver of biodiversity loss. An alarming fact considering that approximately 40% of the terrestrial land surface is now used for agriculture. Yet some agriculture practices maintain high levels of biodiversity, and therefore it is essential to understand which components are key for biodiversity conservation within these land-use types. We conducted a meta-analysis of the literature to determine the importance of local and landscape level factors in promoting within farm biodiversity. Based on a literature search in ISI Web of Science, we included data from studies that compared local management factors (organic vs. conventional, intensive vs. extensive, etc.), compared landscape level factors (% natural area, % forest, etc. in surrounding farms within >200m radius; hereafter % non-crop area), and measured richness or abundance within farm (55 studies). Within each study, the log response ratio (less intensive site/ more intensive site) was calculated as an effect size for mean richness and abundance. We also calculated the correlation coefficient (r) from the relationship between the landscape level (non-crop area %) and richness or abundance. We hypothesized that both local and landscape scale factors would have significant beneficial effects on richness within agricultural systems.
Results/Conclusions
Our results suggest that the mean log response ratio of species richness was significantly greater than zero, indicating that overall richness was higher in less intensively (organic or extensive) compared to more intensively managed farms (conventional) (mean response ratio = 0.34, lower 95% CI = 0.19, upper 95% CI = 0.49). Landscape factors also had a significant effect on richness within farms. The mean correlation coefficient for the relationship between percent non-crop area (landscape variable) and species richness was significantly greater than zero (mean response ratio = 0.21, lower 95% CI = 0.097, upper 95% CI = 0.323). Local and landscape factor effects on abundance paralleled effects on species richness; both local and landscape factors had significant effects on abundance. These results suggest that both local and landscape level factors are important for the conservation of biodiversity within agricultural systems. Thus conservation strategies within agricultural landscapes should take a local and regional approach.