The ecological and economic importance of bat pollination services to pitaya production in central Mexico

Abstract

Bats provide a range of ecosystem services, such as seed dispersal, pest suppression and pollination. Despite this, bats worldwide are commonly disregarded as pests and persecuted, necessitating research emphasising the benefits provided by bats to people. For example, bats are key pollinators in both natural and agricultural ecosystems, and pollinate many plants of socio-economic importance. This thesis aims to highlight the importance of ecosystem service provision by bats, by assessing the ecological and economic importance of bat pollination services to a major cash crop in central Mexico.
The role of bats as pollinators is largely undervalued. Data on the contribution of bats to food security and crop production is scarce, and there have been no assessments on the impact of bat pollination on crop quality. Stenocereus queretaroensis is a species of columnar cactus endemic to central Mexico that is cultivated commercially for its fleshy fruits, pitayas. I carried out exclusion experiments to assess the impact of bat pollination on fruit yield and quality relative to other pollinating taxa (i.e. birds and insects). I showed that Leptonycteris bats are the principal pollinators of S. queretaroensis, enhancing both crop yield and quality. Fruit yield decreased by 35%, and fruits were 46% lighter, in the absence of bats (when pollination was carried out by birds and insects). I found that consideration of both crop yield and quality was essential therefore to fully understand the benefits of bat pollination, and that there would likely be severe socio-economic impacts on the pitaya production area if bat pollinator populations declined.
There have been no detailed assessments to date of the economic value of pollination services provided by bats to crops, and no disaggregated analysis of the distribution of f benefits between actors in the pitaya commodity chain and showed that pitaya production provides a key seasonal income at a time of low agricultural activity, supporting livelihoods and household activities of the rural poor. However, profits are concentrated with privileged actors that have access to capital, land and markets. The high economic value of bat pollination services may be a powerful argument for conservation in the pitaya production area, but efforts at the community, government or NGO level are necessary for a fairer distribution of benefits among actors.
Finally, there is a lack of knowledge of the year-round diet and resource use of nectar-feeding bats in the pitaya production area, and previous studies of have relied on visual identification of pollen grains in faeces, limiting the taxonomic resolution of results. I used metabarcoding techniques to identify plant taxa present in the diet of Leptonycteris yerbabuenae in the pitaya production area and showed that Stenocereus queretaroensis is likely to be an important part of the diet during the flowering and fruiting season, highlighting the mutualistic relationship between crop and pollinator. I also found that a iverse range of other plants found in tropical deciduous forest are consumed throughout the year, including when the availability of foraging resources within pitaya plantations was high. This indicates that the continued provision of bat pollination services to the pitaya crop necessitates landscape-scale conservation to maintain a high floristic diversity in the production area, for example by protecting remaining areas of tropical deciduous forest.
This thesis helps us to better understand the role that bats play in the pollination of a major crop, highlights the potential socio-economic consequences of declines in bat populations, and points to conservation actions to maintain pollination service provision.

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ORCID for Kelvin Peh: orcid.org/0000-0002-2921-1341

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