Increased dispersal explains increasing local diversity with global biodiversity declines

Area of Science:

• Ecology
• Biodiversity Science
• Community Ecology

Background:

• Biodiversity decline narratives are often simplistic, as different biodiversity facets exhibit varied responses to human impacts across spatial scales.
• The long-term effects of human-induced biodiversity changes on ecological communities, such as cascading extinctions or increased robustness, remain debated.
• Mechanistic models are crucial for understanding and reconciling diverse biodiversity changes and assessing community resilience.

Purpose of the Study:

• To develop and analyze a trophically structured, mainland-archipelago metacommunity model.
• To investigate how local alpha diversity and regional gamma diversity are influenced by extirpation and dispersal rates.
• To explore the relationship between biodiversity changes, community robustness, and invasibility.

Main Methods:

• A mainland-archipelago metacommunity model incorporating trophic structure was developed.
• Model parameters were varied to simulate different scenarios of extirpation and dispersal.
• Local and regional diversity metrics (alpha, gamma, beta diversity) were analyzed in relation to model parameters.

Main Results:

• Local alpha diversity increased with higher dispersal and island heterogeneity, while regional gamma diversity decreased due to biotic homogenization (reduced beta diversity).
• Empirical observations of increased local diversity and decreased global diversity with human-assisted species transfers were mirrored in model outcomes.
• High-dispersal, high local-diversity communities demonstrated resistance to subsequent invasions, forming robust networks, unless dispersal was extremely high.

Conclusions:

• Biodiversity responses to human impacts are scale-dependent, with potential for homogenization and loss of endemic species.
• Despite potential species loss, resulting ecological communities can exhibit increased robustness and resistance to further invasions.
• Understanding metacommunity dynamics is key to predicting biodiversity trajectories and community stability in a changing world.