Population demography maintains biogeographic boundaries.

Area of Science:

• Ecology
• Evolutionary Biology
• Biogeography

Background:

• Global biodiversity is organized into distinct biogeographic regions with unique species assemblages.
• Contemporary factors maintaining these regional differences are not well understood.
• Unexpectedly low species homogenization across regions suggests limiting factors on inter-regional expansion.

Purpose of the Study:

• To investigate the role of reduced adaptive capacity at biogeographic boundaries in maintaining regional biodiversity.
• To empirically test theoretical predictions of limited expansion due to demographic variation along environmental gradients.

Main Methods:

• Utilized three independently curated datasets on continental mammalian demography and population genetics.
• Analyzed patterns of effective population size, genetic diversity, and genetic differentiation near biogeographic boundaries.

Main Results:

• Populations situated near biogeographic boundaries showed significantly lower effective population sizes.
• These populations also exhibited reduced genetic diversity and increased genetic differentiation.
• These patterns were consistent across multiple mammalian datasets, suggesting generality.

Conclusions:

• Reduced adaptive capacity at biogeographic transition zones limits species homogenization.
• These findings highlight stable, generalizable processes that maintain global biodiversity patterns.
• Understanding these contemporary processes is crucial for predicting future biodiversity organization.