Landscape simplification and altitudinal variation affect biodiversity, herbivory, and Andean potato yield

Background/Question/Methods Agricultural systems have been subjected to a vast simplification at a landscape level which has been associated with the loss of functionally important biodiversity. In temperate region this reduced biodiversity has been considered to affect ecosystem services such as pest control and production, but evidence has been controversial. The objective of our study was to understand the importance of landscape scale diversity on pest regulation and production in tropical agro-ecosystems. 17 potato plots along gradients of altitude and landscape simplification were established to show their effects on herbivores, their natural enemies and potato production. Along the landscape simplification gradient complex landscapes were characterized by a higher percentage of native forest and shrubs while simpler landscapes were dominated by potato crops and pastures.

Results/Conclusions Our data show that altitude and landscape simplification reduced the richness and abundance of herbivores and their natural enemies, but did not affect potato production, giving the first field evidence that landscape effects on herbivores and natural enemies not necessarily affect yield. However, inter-seasonal changes show that this effect depends on the abundance of the main potato insect pest in the region, the potato tuber moth.  During a season with a high abundance of potato tuber moths, landscape simplification increased the presence of this pest, which increased potato damage and reduced final yield. We conclude that the landscape scale biodiversity can play a crucial role in controlling pest species which can have devastating consequences on final crop yield.