Synthesis reveals approximately balanced biotic differentiation and homogenization

Area of Science:

• Ecology
• Biodiversity Science
• Conservation Biology

Background:

• The biodiversity crisis is often characterized by biotic homogenization, a decline in spatial variation of species composition.
• Understanding biotic homogenization and differentiation requires examining local and regional diversity changes across scales.

Purpose of the Study:

• To synthesize patterns of biotic homogenization and differentiation across diverse ecological datasets.
• To investigate the scale-dependent drivers of changes in species composition.

Main Methods:

• Analysis of 461 metacommunities (10-91 years) and 64 species checklists (13-500+ years).
• Application of a typology linking homogenization and differentiation to local and regional diversity dynamics.
• Examination of species occupancy and distribution patterns.

Main Results:

• No significant change in species composition was the most frequent outcome across datasets.
• Biotic homogenization and differentiation were observed in numerous instances.
• A weak average homogenizing trend (0.3% increase in shared species/year) was driven by widespread species, particularly in long-term, large-scale studies.
• At smaller spatial and temporal scales, changes in rare and common species distributions influenced homogenization and differentiation.

Conclusions:

• Biotic homogenization and differentiation are complex, scale-dependent phenomena.
• Longer durations and larger spatial scales favor homogenization, driven by widespread species.
• Understanding multiscale dynamics is crucial for identifying drivers of biotic changes and informing conservation strategies.