Does diversity matter? Farm- and landscape-level vegetation diversity and structure effects on biocontrol

Background/Question/Methods

Agricultural lands currently cover ~40% of the earth’s terrestrial surface, and increased agricultural intensification has resulted in the degradation of biodiversity and various ecosystem services associated with agriculture. However, individual agroecosystems have varying impacts on ecosystem services, and attention is turning to methods of agricultural management that are capable of providing not only food, but also multiple services. In determining how to optimize food production and ecosystem service provision, it is crucial to first understand what ecological factors—both at a local- and landscape-level scale—are most influential in providing these services. I addressed the question of how pest predation by vertebrates and biodiversity conservation are influenced by local- and landscape-level heterogeneity in Puerto Rican coffee farms. Central to this question is whether plant diversity or simply vegetation structure has a stronger influence on service provision. At the farm level, we recorded various plant diversity and vegetation structure metrics, while at the landscape-level we measured the surrounding area in different landuses. To assess biocontrol of insect pests on coffee bushes, we excluded birds and bats in one treatment and birds, bats, and anoles in another treatment. To determine biodiversity conservation, we surveyed parasitoid wasps, ground-foraging ants, birds, and anoles.

Results/Conclusions

Based on the vertebrate predator exclusions, we observed an additive effect of bird, bat, and anole predation on Petrusa epilepsis (Hemiptera: Flatidae), the largest coffee pest we studied. Both exclusion treatments (all three vertebrates as well as only birds/bats) showed an increased abundance of the coffee leafminer (Leucoptera coffeella; Lepidoptera: Lyonetiidae), whereas no effect was seen for the coffee berry borer, Hypothenemus hampei (Coleoptera: Curculionidae). We found that the predation of Petrusa epilepsis was highest on farms with a medium amount of shade and that the predation of the coffee leafminer was highest on medium- and low-shade farms. Other pests did not show a significant difference across shade levels. Bird and anole abundance and diversity was highest in medium and high shade farms. We show that vertebrates can be important predators of coffee pests but their effect varies and depends on both the type of pest, especially in regards to its level of conspicuousness, and the management intensity of the farm. Although values of biocontrol and biodiversity vary largely depending on the organism, we found that overall farms with medium levels of shade provide the highest provision of both biocontrol and biodiversity conservation.