Forest fragmentation effects on mutualistic interactions: Frugivorous birds and fruiting trees

While many effects of forest fragmentation are reasonably well understood, knowledge of interspecific interactions in fragmented ecosystems is much more limited, particularly for high-diversity tropical forests. Using nearly 40 years of data from the Biological Dynamics of Forest Fragments Project in Central Amazonia, we assessed whether forest fragment area and time since isolation impact mutualistic interactions between frugivorous birds and their food resources. We used structural equation modeling to analyze the complex pathways between four main variables determining these interactions: fruiting tree abundance, frugivorous bird abundance, forest fragment area, and time since fragment isolation. Our results confirm that fragment area alters the abundance of some tree resources, with successional plant families increasing in abundance with decreasing fragment size. However, these changes do not drive alterations in the abundance of frugivorous birds. We also tested if bird species with a greater relative diet breadth are less vulnerable to forest fragmentation and found that specialist frugivores are more vulnerable to forest fragmentation immediately after isolation but are not differentially impacted within the long term. Collectively, our results demonstrate the need to further evaluate human-driven habitat change across multiple timescales to fully understand its impacts on complex species interactions.