When bats, birds and insects are united, More chocolate is provided

    Do you know what makes good quality chocolate? It all starts in the field where cacao plants are cultivated and harvested to be processed later into the worldwide loved sweet treat. Cacao is a tropical crop that is highly benefited by agroforestry systems that allow for greater interaction between organisms and the plantation than traditional agricultural methods. In agroforests, animals provide services such as pollination and pest control, but they can also provide disservices by harming or eating the crops. Therefore, understanding how services and disservices are balanced out is important for enhancing sustainable management practices in those biodiversity-friendly farms.

Image: Cacao agroforestry.

Google images. Accessed on Oct 02, 2022.

    In 2019, a group of researchers conducted a one-year field experiment in 12 cacao agroforests in northwestern Peru to better understand those associations. They assessed how three main productivity indicators: fruit set, fruit loss and marketable yield (yield value in dry weight of cacao fruits) were impacted by excluding flying insects, ants, birds and bats.

    They employed four different treatments to cacao plants in all the 12 agroforests:

- Control group: two plants for each site were open and accessible to all vertebrates and insects all the time;

- Bird exclusion: a cage was kept around two cacao trees during the day (6am to 6pm) and opened during the night;

- Bat exclusion: a cage was kept around two cacao trees during the night, but opened during the day;

- Full exclusion: a cage was permanently kept around two cacao trees.

    Flowers of the treatment groups were covered against flying insects, and one of the two trees in those groups received an “ant exclusion treatment” as well. To analyze the productivity indicators in each treatment, generalized linear mixed effect models – fancy statistics! – were created.

    In the results that came out, removing flying insects caused fruit set to drop from 1.3% to 0.5%, showing how pollinators are key in assisting crops to thrive. Intriguingly, in agroforests with intermediate canopy density of the non-cacao trees surrounding cacaos, the benefit gained from insects was greater compared to the ones with very dense canopy cover. Think about it: if you were a bee, how would you find cacao flowers if the cover above them was too dense? Exactly, it would be much harder!

    Birds and bats also increased fruit set, possibly because they predate on arthropods and reduce herbivory. In other words, they help plants produce more flowers and fruits because cacao trees can use their precious energy to flourish instead of using it to regrow structures eaten by herbivores. In addition, cacao yielded much more when both birds and bats were present than in any exclusion groups.

Figures: found in Vansynghel et al., 2022.

    Ants, on the other hand, demonstrated both positive and negative impacts. They collaborated on fruit loss, but in agroforests close to forests they accounted for an increase in cacao yield, which would need to be studied further. Lastly, researchers found that squirrels were among the main agents driving fruit loss in the experiment, and they also reduced annual cacao yield.

Figure: found in Vansynghel et al., 2022.

    In summary, this study demonstrates the essential role of pollinators, bats and birds in increasing and keeping great levels of cacao productivity. And what other crops would also benefit from interactions with them? Certainly, global agriculture would be enhanced if we started including biodiversity services in our soil cultivation practices. And what about ants and squirrels’ disservice to plantations? Well, everything in nature is a balance of trade-offs. Developing biodiversity-friendly management strategies to minimize their impacts would be important for farmers. But because the biodiversity services were greater than the disservices, agroforestry systems are still a great method of production where cacao yield is improved, and nature protected simultaneously.

References:

Vansynghel, Justine, Carolina Ocampo-Ariza, Bea Maas, Emily A. Martin, Evert Thomas, Tara Hanf-Dressler, Nils-Christian Schumacher, et al. “Quantifying Services and Disservices Provided by Insects and Vertebrates in Cacao Agroforestry Landscapes.” Proceedings of the Royal Society B: Biological Sciences 289, no. 1982 (September 14, 2022): 20221309. https://doi.org/10.1098/rspb.2022.1309.