Negative density dependence mediates biodiversity-productivity relationships across scales

Area of Science:

• Ecology
• Biodiversity Science
• Community Ecology

Background:

• Global species diversity typically rises with primary productivity, but local diversity-productivity links are inconsistent.
• Understanding beta-diversity (β-diversity), or variation in species composition among local communities, is crucial for explaining these scale-dependent patterns.
• Existing hypotheses involve multiple local and regional mechanisms, but their relative importance remains unclear.

Purpose of the Study:

• To investigate the mechanisms driving changes in beta-diversity across a broad productivity gradient.
• To determine the relative roles of local density-dependent interactions versus regional processes in shaping community composition.
• To elucidate how species interactions influence biodiversity patterns at different scales.

Main Methods:

• Examined tree species communities across a subcontinental productivity gradient.
• Assessed the strength of negative density dependence (conspecific vs. heterospecific) within local communities.
• Quantified beta-diversity, habitat partitioning (species sorting), and local diversity.

Main Results:

• Changes in the strength of local density-dependent interactions explained variations in beta-diversity.
• Stronger negative density dependence (conspecific vs. heterospecific) in high-productivity areas correlated with higher local diversity.
• This led to weaker habitat partitioning and reduced community compositional differences among sites (lower beta-diversity).

Conclusions:

• Local density-dependent interactions, particularly the balance between conspecific and heterospecific negative density dependence, are key drivers of beta-diversity.
• Regional processes influencing species pools had minimal impact on observed beta-diversity patterns.
• Shifts in local species interactions may broadly explain prominent, yet poorly understood, global biodiversity gradients.