What Is Demographic Lability and When Might We Expect to See It?

Area of Science:

• Ecology
• Evolutionary Biology
• Population Dynamics

Background:

• Temporal variation in vital rates can theoretically increase stochastic fitness, a phenomenon termed demographic lability.
• Despite theoretical support, empirical evidence for demographic lability remains undocumented.

Purpose of the Study:

• To outline criteria for documenting demographic lability.
• To review existing literature for evidence of lability.
• To investigate conditions under which natural selection might favor or erode lability.

Main Methods:

• Defining three essential steps: estimating vital rate responses to environmental drivers, quantifying driver distributions, and comparing fitness effects against a no-variation baseline.
• Systematically reviewing studies for documented cases of demographic lability.
• Analyzing theoretical conditions for adaptive lability and its potential erosion by selection.

Main Results:

• No empirical studies fully documented demographic lability.
• Selection to exploit frequent environmental states may counteract lability.
• Lability is hypothesized to be less likely with abiotic than biotic drivers.

Conclusions:

• Demographic lability requires rigorous documentation, including specific methodological steps.
• Environmental variation's impact on fitness is complex, influenced by selection pressures and environmental characteristics.
• Further research is needed to establish the ecological and evolutionary significance of demographic lability.