Demographic buffering in natural populations: A multi-level perspective

Area of Science:

• Ecology and Evolutionary Biology
• Population Dynamics
• Conservation Biology

Background:

• Environmental variability challenges population persistence.
• Demographic buffering, stabilizing population growth amidst fluctuations, is a proposed but empirically under-tested mechanism.
• Existing studies on demographic buffering yield conflicting results.

Purpose of the Study:

• To introduce an integrative demographic framework to identify demographic buffering.
• To test if populations with low stochastic elasticities (indicating buffering) show concave selection on vital rates.
• To assess the alignment between ecological buffering and evolutionary constraints across mammalian species.

Main Methods:

• Developed a framework combining stochastic elasticities (sensitivity of long-term growth rate to variance) and second-order derivatives of deterministic growth (indicating selection on vital rates).
• Applied the framework to 43 natural populations across 37 mammalian species.
• Analyzed variance in demographic processes and identified species exhibiting buffering and concave selection.

Main Results:

• Most primates and long-lived mammals showed evidence of demographic buffering (low stochastic elasticities).
• Only the Columbian ground squirrel demonstrated strong buffering with key vital rates under concave selection.
• Primates often exhibited convex or absent second-order effects, indicating a mismatch between ecological buffering and evolutionary constraint.

Conclusions:

• Demographic buffering is more dynamic and context-dependent than previously assumed.
• Selection does not consistently reduce vital rate variance, even in species with stable population growth.
• Ecological and evolutionary signals of buffering may be decoupled, necessitating integrated approaches to understand population resilience.