Conservation of bird functional diversity and ecosystem services in tropical forest, agroforest, and agricultural ecosystems

Background/Question/Methods

Birds’ ecological functions cover a wide spectrum, from creating soil to shaping primate behavior, and many species play key ecological roles, such as decomposition, predation, pollination, nutrient deposition, and seed dispersal. From an ecosystem functional perspective, birds are mobile links that are crucial for maintaining ecosystem function, memory, and resilience. The three main types of mobile links, genetic, process, and resource linkers, encompass all major avian ecosystem services. Although most bird species avoid agricultural areas, nearly a third of all birds occasionally use such habitats, often providing important ecosystem services like pest control, pollination, and seed dispersal. Combining literature review with a meta-analysis of world’s birds, I compared tropical bird species that prefer forests, agricultural areas or both, with respect to body mass, diet, habitat and resource specialization.

Results/Conclusions

Compared to primary forests, in agro-forests species numbers of large frugivorous and insectivorous birds (especially terrestrial and understory species) often decline. In contrast, nectarivores, small-to-medium insectivores (especially migrants and canopy species), omnivores, and sometimes granivores and small frugivores do better, frequently by tracking seasonal resources. However, changes in guild species numbers do not necessarily translate to changes in relative abundance, biomass or function, and more studies are needed to quantify these important measures. The findings suggest that the replacement of forests and agro-forests with simplified agricultural systems can result in shifts towards less specialized bird communities with altered proportions of functional groups. These shifts can reduce avian ecosystem function, affect the ecosystem services provided by birds, and create further conservation problems in agricultural landscapes. Rapid losses of tropical bird species may cause substantial reductions in certain ecosystem processes before we have time to study and understand the underlying mechanisms.