Landscape conservation and orchard management influence carob tree yield through changes in pollinator communities

Worldwide pollinator declines are a major problem for agricultural production. However, understanding how landscape characteristics and local management influence crop production through its pollinators is still a challenge. The carob tree (Ceratonia siliqua) is a pollinator-dependent Mediterranean crop of high economic importance in food and pharmaceutical industries. To understand how crop production can be enhanced in a sustainable manner, we evaluated the effects of landscape (habitat loss) and orchard local management (farming system: conventional vs. ecological; male-to-female ratio) on pollinator communities and crop production using data on 20 carob tree orchards across Mallorca Island (Spain). We found that orchards surrounded by a greater proportion of natural landcover received more visits by wild bees and butterflies and fewer by honeybees. Overall pollinator abundance was slightly higher in ecological than conventional orchards, but the difference was not significant. High male-to-female ratio enhanced overall pollinator abundance and shaped pollinator composition, by increasing hoverfly abundance and decreasing wasp and fly abundance. Male-to-female ratio showed hump-shaped relationships with fruit and seed production per female tree (peak at 0.7 males/female), although this quadratic relationship was lost when the most male-biased orchards were removed from the analyses. Total orchard production maximized with 25-30% of males. Seed weight (farmer's highest economic value) increased in conserved landscapes where wild pollinators prevailed, and with overall pollinator abundance; however, it decreased with male-to-female ratio, likely due to seed number-size trade-offs. Management strategies to enhance carob production may optimize sex ratios and favor wild pollinators by preserving natural landscapes.