The influence of fluctuating population densities on evolutionary dynamics

Area of Science:

• Ecology
• Population Genetics
• Evolutionary Biology

Background:

• Fluctuating population densities are a key ecological factor, but their impact on maintaining genetic variation in structured populations is understudied.
• Spatial structure and differing habitat selectivities influence population dynamics and allele frequency maintenance.

Purpose of the Study:

• To analyze the effects of differing demographic stability and selection trade-offs in two connected habitats on allele frequencies.
• To investigate how ecological feedback from fluctuating population sizes impacts genetic variation and local adaptation.

Main Methods:

• Analytic treatment of a continent-island model incorporating migration between two habitats.
• Examination of selection, immigration, and intergenerational population fluctuations.

Main Results:

• Locally fluctuating population sizes create ecological feedback, significantly altering equilibrium allele frequencies.
• Fluctuations introduce asymmetry in gene flow, decreasing the equilibrium frequency of locally adapted types.
• Strong recurrent fluctuations can lead to the extinction of types adapted to unstable niches, even if they are locally advantageous.

Conclusions:

• Fluctuating population densities disrupt the maintenance of genetic diversity by impacting selection and gene flow dynamics.
• Specialization in unstable habitats confers a disadvantage, increasing vulnerability to swamping by populations from stable habitats.
• The study extends classic models of diversity maintenance by incorporating demographic instability.