Links between agricultural landscape structure, insect diversity, and ecosystem service provision

Background/Question/Methods

Human activities are significantly altering the structure of landscapes, and in turn, the biodiversity and ecosystem functions they encompass. Evidence is rapidly accumulating that biodiversity is positively correlated with the provision of multiple ecosystem services. However, our understanding of the links between landscape structure, biodiversity, and ecosystem services remains incomplete. In agricultural landscapes, this lack of knowledge can lead to unintended losses of biodiversity and ecosystem services as we attempt to maximize crop yield. We investigated how landscape structure influenced insect biodiversity, and how this in turn influenced ecosystem service provision in soybean fields east of Montreal, Quebec. Over two years, we measured insect and aphid predator species richness, pest regulation services (i.e., aphid abundance and soybean herbivory), and soybean yield adjacent to and 500m from forest fragments. We then used generalized linear mixed models and model averaging to determine if landscape structure (i.e., distance from forest, field width, field orientation, land use in the surrounding landscape), biodiversity (i.e., insect and forest plant species richness), and management (i.e., tillage practices) were related to the provision of pest regulation and food.

Results/Conclusions

Insect diversity varied most with distance from forest and field width. Insect species richness was two times greater adjacent to forest versus 500m away. Conversely, aphid predator species richness was 1.2 times greater at 500m. Species richness for both groups decreased as field width increased (p<0.05). Pest regulation was best explained by distance from forest and insect diversity. Aphid numbers in both years doubled at 500m from forest, while grazing was 1.8 to 1.1 times greater. Both insect and aphid predator species richness were negatively related to pest regulation early in each year, but positively related later in each year (p<0.003). Despite these relationships with pest regulation, insect diversity was not strongly related to food provision. Instead, soybean yield differed most with distance from forest and was on average 1.8 times greater at 500m. Our results suggest that insect species disperse from forest patches and field margins into fields, and that the importance of insect diversity for pest regulation varies during the growing season. There are also tradeoffs between insect diversity and soybean yield with distance from forest. Understanding these patterns is key to determine how landscape structure change may ultimately affect biodiversity and the provision of multiple ecosystem services.