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.