Negative density dependence characterizes mutualistic interactions between birds and fruiting plants across latitudes

Area of Science:

• Ecology
• Community Ecology
• Biodiversity

Background:

• Negative density dependence (NDD) mechanisms like competition and herbivory are known drivers of species coexistence.
• The role of mutualistic interactions, specifically frugivory and seed dispersal, in NDD remains less understood.
• Investigating NDD in frugivore-plant interactions can reveal novel mechanisms promoting plant diversity.

Purpose of the Study:

• To investigate the generality of negative density dependence (NDD) in mutualistic frugivore-plant interactions.
• To determine if birds select rare fruit resources or under-utilize abundant ones across diverse communities.
• To assess the contribution of frugivore-driven NDD to plant species coexistence and diversity.

Main Methods:

• Community-wide frugivory interactions were sampled across multiple sites in Pennsylvania, Puerto Rico, Peru, Brazil, and Argentina.
• Interaction frequencies between birds and fruit resources were compared against expectations based on relative fruit abundance.
• Models incorporated temporal scales of fruit availability, bird phylogeny, and dietary guilds.

Main Results:

• Negative density dependence (NDD) was found to characterize frugivory across diverse plant and bird communities.
• Birds consistently selected fruits from plant species that were proportionally rare or became rare due to phenological changes.
• Abundant fruit resources were generally under-utilized by frugivores, irrespective of bird taxa or dietary guild.

Conclusions:

• Negative density dependence in frugivore-plant interactions acts as a significant equalizing mechanism for seed dispersal.
• This mechanism contributes to the maintenance and building of plant species diversity in both temperate and tropical regions.
• Frugivore-mediated NDD is a crucial factor in sustaining diverse plant communities worldwide.