Bats and Chocolate Production

By Merlin Tuttle
6/6/18

While conducting her Ph.D. thesis research, Bea Maas and her team (Maas et al. 2013) collected data that would surprise even her. When insect-eating bats and birds were excluded from cacao trees in Sulawesi, Indonesia, the crop yield fell by 31 percent. And when she compared losses due to night versus daytime exclusion, bats versus birds, she discovered that bats accounted for 22 percent of the prevented losses.

A control site in the same study (poles without netting).

To obtain such data, Bea selected 15 plantations where she enclosed 120 cacao trees in 60 exclosures (like huge, mesh cages) constructed of nylon mesh. There were four exclosure treatments per plantation, one daytime, one nighttime, one day and night, and one always left open as a control.

A bat/bird exclosure in Sarawak, Indonesia, built with bamboo poles and commercial nylon monofilament netting with a mesh size of 2 x 2 cm. These were opened and closed like curtains daily.

When closed, all bat and bird species were excluded, but arthropods were allowed entry, including large spiders, butterflies, and moths. The exclosures were opened and closed like curtains, daily at 5:30 am and at 6:30 pm for 15 continuous months. Using standardized systems, all arthropods were counted and digitally photographed daily and nightly, and cacao damage was documented every two weeks. More than 70,000 fruits were examined, including over 4,000 ripe, harvested fruits.

 

When Bea extrapolated the economic impact of bats saving growers an estimated 520 U.S. dollars per hectare across 1.5 to 1.6 million hectares of cacao, this value translated into savings of 780 to 832 million U.S. dollars annually! It is important to note that studied plantations were in or near natural vegetation. Without this biodiversity balance, such impressive savings likely would not have been possible.

 

She calculated the separate value of bats when quizzed about it after appearance of the original paper in Ecology Letters. Bats accounted for 22 percent, birds 9 percent, of savings (Maas et al. 2018, p 62). The economic extrapolations from these numbers are from her personal communication.

Intermediate roundleaf bats (Hipposideros larvatus) are exceptionally widespread, found in Sarawak and most of Southeast Asia. They roost in caves, rock crevices and buildings, and feed on a wide variety of insects, from moths and beetles to stink bugs and mosquitoes.
Trefoil Horseshoe Bats (Rhinolophus trifoliatus) range throughout most of Southeast Asia, living in understory forests. They roost alone in foliage, including beneath palm and rattan leaves. and hunt by listening and waiting for insects to fly by their feeding perches. Horseshoe bats feed on a wide variety of insects, especially moths, and were among the bats excluded in this study.
The Philippine horseshoe bat (Rhinolophus philippinensis) ranges from Australia through the Philippines and into Southeast Asia. It feeds both in dense vegetation and in open areas, often in rainforests. It is one of several horseshoe bat species likely to have been excluded.
Common Asian Ghost Bats (Megaderma spasma) are found throughout most of Southeast Asia, Indonesia and the Philippines. They form small groups, mostly consisting of a male and several females and their young, in caves, hollow trees, road culverts and buildings. Their large ears help detect prey sounds as they move through foliage. Prey consist mostly of large insects but also can include small vertebrates. This is one of many bat species most likely to have been excluded.

 

References

 

Maas, B. 2013. Bats and birds increase crop yield in tropical agroforestry landscapes. Ecology Letters 16:1480-1487.

Maas, B. and T. Tscharntke, A. Tjoa, S. Saleh, N. Edy, A. Anshary and M. Muhammad Basir. 2018. Effects of Ecosystem Services Provided by Birds and Bats in Smallholder Cacao Plantations of Central Sulawesi. Gottingen Univ. Press.

 

 

 

2 thoughts on “Bats and Chocolate Production

  1. Puzzled a bit by a lingering question, “What types of arthropods were, call it, controlled by bats and birds?” The inference is, of course, herbivore insects, but the article, that I could see, does not comment on this. Further reading, however, does confirm that herbivore insects do damage trees; for example: http://www.scirp.org/(S(i43dyn45teexjx455qlt3d2q))/reference/ReferencesPapers.aspx?ReferenceID=1357983

    Thanks for the report, Mr. Tuttle

    1. Hi Bill, thank you for your interest and inquiry. There is more detailed information within the cited publications and I recommend that anyone interested in further details contact Bea personally.

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