Network analysis of the plant and bird species underpinning Nature’s Contributions to People on Kilimanjaro

Understanding how biodiversity underpins Nature’s Contributions to People (NCP) is key to assessing nature’s role in human well-being. However, identifying the species involved in NCP supply is challenging, as many species indirectly affect NCP supply through ecological interactions. The network cascade framework addresses this complexity by linking NCP to the individual organisms that directly supply them (providers), and to the organisms that interact with these providers (regulators). Here, we use this framework to determine the diversity of tree and bird species that directly and indirectly contribute to six regulating and material NCP on Kilimanjaro.

We quantified NCP supply by trees using functional traits, species abundances and ethnobotanical data. To capture the role of avian seed dispersers for NCP, we estimated the probability of seed-dispersal interactions between NCP providers (103 tree species) and NCP regulators (46 frugivorous birds species) using abundance weighted and presence-absence trait-matching models. We further tested whether key provider and regulator species exhibited phylogenetic clustering.

We found that NCP differed in the number of species involved. Regulating NCP, such as habitat creation, depended on more species than material NCP like food provision. The diversity of provider and regulator species increased when multiple NCP were considered simultaneously. When factoring in species abundances, the reliance of regulating NCP on biodiversity decreased sharply, highlighting the importance of dominant species for these NCP. Phylogenetic analyses revealed that key tree species were clustered within particular clades (e.g., Lauraceae and Fabaceae), whereas important avian seed dispersers were spread across the entire bird phylogeny.

Our results show that ecological networks provide insights into NCP supply in biodiverse ecosystems. They highlight that NCP require a high taxonomic and phylogenetic diversity of provider and regulator species, and that dominant species play a particularly important role for certain NCP.