The Conditioned Environmental Center-Periphery Hypothesis of Biogeography: Statistical Evidence From Tree Species

Area of Science:

• Ecology
• Biogeography
• Environmental Science

Background:

• The distribution of species along environmental gradients has long been debated, with focus shifting from geographic centers to environmental niche centers.
• Understanding species' optimal environmental conditions is crucial for ecological and biogeographical studies.

Purpose of the Study:

• To analyze the ecological niche of 12 Mexican tree species across 16 abiotic environmental gradients.
• To determine if species occurrences are centered within their environmental gradients and assess the symmetry of their distribution.

Main Methods:

• Species occurrences were analyzed using probability density functions and grouped into histograms along environmental gradients.
• Logistic regression was employed to fit polynomial equations, and highest-probability intervals (25% of individuals) were determined.
• The relative distance of these intervals from the gradient midpoint was calculated to assess symmetry.

Main Results:

• Only 12.0% of species-variable combinations showed highest-probability intervals including the environmental gradient's midpoint.
• Natural truncation of environmental gradients prevented symmetrical expansion of the range in 55% of cases, leading to asymmetry.
• The classical environmental center-periphery hypothesis was found to be incorrect for many species-variable combinations due to this asymmetry.

Conclusions:

• Species distributions are frequently asymmetrical along environmental gradients, challenging the assumption of centered niches.
• A new conditioned environmental center-periphery hypothesis is proposed, accounting for gradient truncation.
• Findings have significant implications for conservation strategies and predicting climate change impacts on species distribution.