Pollination by bats enhances both quality and yield of a major cash crop in Mexico

Abstract

Bats pollinate many plants of high socio-economic value, including the majority of columnar cacti (Cactaceae) in Mexico, which have been used by humans for food and materials for thousands of years. However, the importance of bats as pollinators has been overlooked, with a consequent lack of knowledge of the reliance of crops on bats for harvest yield and quality. We used exclusion experiments to determine the effect of different pollinator taxa on the yield and quality of pitayas (fruit of Stenocereus queretaroensis (F.A.C. Weber) Buxbaum), a major crop in central Mexico. We studied the three most economically important cultivars and wild individuals in the principal region for pitaya production. For each pollinator taxon we recorded fruit set and measured three key parameters of fruit quality: weight, sucrose concentration and seed set. We placed camera traps to determine pollinator identity and the effect of visitation rate on fruit quality. We found the primary pollinators of pitayas to be nectarivorous bats in the genus Leptonycteris. When bats were excluded from flowers and flowers were pollinated by other taxa (i.e. diurnal birds and insects), pitaya yield decreased by 35%, though pollination dependence varied between cultivars. Fruit quality decreased significantly in the absence of bat pollination across all cultivars, with fruits 46% lighter and 13% less sweet when pollinated by other taxa; reducing economic value, as size determines market price. Additionally, seed set (an indicator of effective pollination) was significantly lower in the absence of bat pollinators. Visitation rate had no effect on fruit quality. Synthesis and applications. Our study shows that bats provide a vital ecosystem service by pollinating a crop of major socio-economic importance, and that consideration of both crop quality and yield are essential to fully understanding the benefits of bat pollination. A reduction of this service would result in a decrease in both the size and quality of the harvest, causing substantial loss of income for rural communities. Bats world-wide face many threats, and management efforts targeted to the enhancement of wild bat pollinator populations would preserve the sustainability of both bat-pollinated crops and wild plants.

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