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RESEARCH PRODUCT

Mutualistic tree-frugivore interactions in Afrotropical forests : from local ecological knowledge to the identification of network interaction patterns

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Frugivory in tropical forests is a major ecological process, as most tree species rely on frugivores for their dispersion, and numerous animal species used fruits as their principal sources of food. However, frugivory networks between plants and animals in Afrotropical forests are poorly described, and the mechanisms shaping them remain largely unexplored. This PhD thesis addresses a structural approach of the frugivory network, a plant-community approach and a methodological approach using local ecological knowledge and cameras.The first chapter describes the frugivory network of Afrotropical forests, based on a compilation of frugivory interactions from the literature that comprised >10,000 links, between 807 tree and 285 frugivore species. We analysed the network structure with a recent method for ecology, the latent block model that groups species with similar interaction patterns and estimates interaction probabilities among them. Larger frugivores were the main dispersers of most trees and larger and/or low wood density trees were the primary fruit sources of most frugivores. Our findings show the vulnerability of this frugivory network and the fragile integrity of Afrotropical forest composition, as large frugivores are largely threatened by defaunation and large trees by logging.The second chapter focused on the trait variations of tree communities within the Congo Basin forest in relation to frugivory interactions. Our findings showed differences in frugivory traits offered among the floristic type, with Atlantic forests offering larger fruits, while Northern forests presented a greater abundance of smaller fruits with smaller seeds. Moreover, we found that while chimpanzees and calaos interact with the fruits that are more abundant, elephants always consume the largest fruits and seeds offered by the community, while smaller birds consume the smallest fruits and seeds.The third chapter focused on local ecological knowledge on tree-frugivore interactions. We used a common set of trees and frugivores species, to compare information gathered by local people, academic knowledge. Local people had substantial knowledge on tree-frugivore relationships, with 39% of unique interactions. LEK also changed our understanding of the frugivory network, by assigning on average smaller frugivores to tree species and smaller seeded plants to frugivore species.In the chapter four, we used camera traps to monitor tree-frugivore information of the terrestrial frugivore forest community of the Moukalaba-Doudou National Park. We comparison of the records with the LEK and academic dataset, and showed that camera record added more than 30% of new interactions Most of these interactions concerned smaller frugivore like rodents, but also large mammals like elephants and gorillas. These results show the necessity to continue the investigation on tree-frugivore interactions but also to integrate other complementary sources to appreciate the complexity of mutualistic networks.This PhD work gave insight on the different mechanisms governing tree-frugivore interactions, regarding the importance of overlap in distribution areas and match between biological traits. We also highlighted biases concerning the dataset with most studies on emblematic species and certain areas, and concerning the different methods with cameras focus on ground frugivores, and LEK restricted by academic knowledge. These results allowed us to give recommendations to counteract these biases, and increase our knowledge on frugivory interactions. One of the recommendations was to diversify the methods to sample interactions, by collaborating with local people in diverse areas of the Afrotropical forests, or by using arboreal cameras to record smaller frugivores.