Editor’s Choice 57:03 – The economic implications of pollination by bats

For our March Editor’s Choice, Michael Pocock (Associate Editor) highlights the importance of recent research by Tremlett et al into pollination by bats and the value this brings to communities in Mexico.

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The slideshow above of images by César Guzmánr shows the journey of the pitaya fruit, for which bats are of key importance, from growth to market.

One of the reoccurring themes in applied research over recent years has been a focus on pollinators, as shown by the many studies published in Journal of Applied Ecology and related journals. Pollinators are a key group of ecosystem service providers, partly because their benefits are so obvious at an individual level (the pollinator visits the flower, leading to fruit set) and because their activity is so hard to replace. The loss of native pollinators, and increased production of crops requiring cross-pollination, has contributed to the need for costly solutions, such as the mass transportation of honey bee hives across North America following the seasonal flowering of blueberry crops, or the hand-pollination of orchard trees in China.

In many situations, pollinators means insects (and many people think only of honeybees), but in this month’s Editors Choice, Tremlett et al. show the importance of bats as pollinators for a locally important fruit: the pitaya. Pitaya fruits are produced by columnar cacti in the genus Stenocereus and are similar to the better-known ‘dragon fruit’ (or pitahaya) that is produced by different species of cacti. Pitaya have been harvested from wild cacti in Mexico for a long time, but increasingly Stenocereus cacti are being cultivated in small plantations and the fruit is becoming an important cash crop in central Mexico.

The authors undertook pollinator exclusion experiments by individually bagging the cacti flowers – presumably no mean feat compared to exclusion experiments that others have carried out on bean plants or strawberries! There were several combinations in this experiment, with flowers being left open during the day, the night, both or neither, and excluding vertebrates (bats and birds) or both vertebrates and insects. Overall they found that bats were, indeed, important to the pollination of this plant. Bat pollination led to a 35% increase in the numbers of pitaya fruits that were produced. Even more importantly, bat pollination affected the quality of the fruits: with bat pollination the average fruit size doubled, and sugar concentration increased by 15%. This means that bat pollination directly affects the market value and the yield of this crop.

In this part of Mexico, half of people have an income insufficient for their wellbeing, so the increase in pitaya cultivation and the developing export market for the fruits, could benefit people’s livelihoods. However, across Latin America, bats are under threat, particularly because roost sites are destroyed to kill vampire bats. This, in turn, causes economic damage to livestock farmers. Tremlett et al.’s detailed study of pollination reveals the crucial inter-dependence of nature and people’s livelihoods and demonstrates the vital importance of conserving bats in this region.

Read the full article, Pollination by bats enhances both quality and yield of a major cash crop in Mexico, in Journal of Applied Ecology.

See a video of bat pollination in action here.

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