Trait-demography relationships underlying small mammal population fluctuations

Area of Science:

• Ecology
• Population Dynamics
• Animal Behavior

Background:

• Small mammal populations exhibit large-scale fluctuations in abundance.
• These fluctuations are often linked to changes in average individual body mass (the Chitty effect).
• Empirical data on the coupled dynamics of body mass and population growth have been limited.

Purpose of the Study:

• To investigate the relationship between body mass and demography in a fluctuating small mammal population.
• To examine how trait-demography relationships and body mass distributions change across population fluctuation phases.
• To determine the consequences of these changes for trait and population dynamics.

Main Methods:

• Utilized long-term life-history data from a 25-year study of male prairie voles (Microtus ochrogaster).
• Employed a trait-based demographic approach to analyze body mass and population dynamics.
• Compared trait distributions and life-history processes across different population fluctuation phases.

Main Results:

• Observed phase-specific changes in male adult body mass distribution, driven by ontogenetic growth variation, not selection.
• Body mass changes influenced life-history processes, with effects varying across population phases.
• Body mass did not significantly affect population growth rate due to its small influence on vital rates compared to phase-specific differences.

Conclusions:

• Body size dynamics in prairie voles are decoupled from population dynamics, resulting from different life-history processes.
• Population increase was driven by enhanced juvenile survival and fecundity; decline by reduced fecundity, survival, and maturation.
• This study provides a mechanism for trait changes accompanying population fluctuations and clarifies drivers of small mammal population dynamics.