Elucidating pollination ecosystem services in Theobroma cacao agroforestry systems

Cacao production relies heavily on ecosystem services, particularly pollination and pest control, yet significant gaps remain in our understanding of the biodiversity and ecological dynamics underlying these services. This thesis investigates pollination ecology in cacao agroforestry systems in Cameroon through an interdisciplinary approach combining environmental DNA (eDNA) metabarcoding, vertebrate dietary analysis, and farmer interviews.
In Chapter 2, I develop and apply a methodological framework using eDNA metabarcoding to detect insect taxa associated with cacao flowers. By sampling and sequencing genetic traces from floral reproductive and non-reproductive structures, I detected a wide diversity of insect groups, with Diptera, Lepidoptera, and Coleoptera among the most prevalent. Detected taxa were compared with records of cacao flower visitors and assessed using geographic and morphological plausibility criteria to identify plausible flower visitors and candidate pollinators, although taxonomic uncertainty and database limitations posed challenges. The findings demonstrate the potential of eDNA approaches in tropical agroecosystems, especially where direct observation is impractical.
Chapter 3 assesses the potential ecosystem services and disservices associated with birds, bats, and amphibians through dietary metabarcoding of over 600 faecal and gut-content samples. These insectivores consumed both cacao pest taxa and flower-associated taxa, including potential pollinators. This indicates a possible trade-off between pest regulation and the consumption of insects that may contribute to pollination. However, the net effect of these interactions on cacao yield or ecosystem function was not directly measured.
Chapter 4 explores the perceptions of 33 smallholder cacao farmers regarding pollination and related ecosystem services. Interview analysis showed that pollination was rarely described as a named process or explicit biological mechanism before explanation, although farmers described several ecological processes through experiential observations. Farmers more readily discussed visible and immediate farm concerns, including pests, diseases, soil conditions, and water availability. These insights highlight the need for participatory approaches that build on farmers’ existing knowledge while making less visible ecosystem services, such as pollination, more explicit within cacao management.
Finally, Chapter 5 synthesises the biophysical and social findings, highlighting the importance of integrating molecular evidence, ecological interpretation, and farmer perceptions when studying ecosystem services in cacao agroforestry. Together, this thesis contributes methodological and empirical insights into the pollination ecology of cacao and the broader sustainability of tropical agroforestry systems.