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Surviving environmental change: when increasing population size can increase extinction risk.

Mark M Tanaka1, Lindi M Wahl2

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Populations may face extinction risk at intermediate sizes when survival genes are slightly harmful. Evolutionary rescue, crucial for adapting to environmental change, is unexpectedly hindered in these populations.

Keywords:
evolutionary rescueextinctionmathematical modelstanding variation

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Area of Science:

  • Evolutionary biology
  • Population genetics
  • Ecology

Background:

  • Environmental changes pose extinction risks to populations.
  • Survival depends on genetic adaptation, either pre-existing or newly evolved.
  • Evolutionary rescue describes population survival through adaptation.

Purpose of the Study:

  • To investigate how population size affects extinction risk during environmental change.
  • To explore the role of pre-existing genotypes in evolutionary rescue.
  • To determine the impact of mildly deleterious mutations on population survival.

Main Methods:

  • Theoretical modeling of population dynamics.
  • Analysis of genotype frequencies and fitness effects.
  • Simulation of environmental change scenarios.

Main Results:

  • Extinction risk is lowest in very small or very large populations.
  • Intermediate population sizes exhibit the highest extinction risk.
  • This pattern is pronounced when the survival genotype is mildly deleterious before environmental change.

Conclusions:

  • Population size influences the success of evolutionary rescue.
  • Intermediate population sizes may be paradoxically more vulnerable to extinction.
  • Mildly deleterious mutations can significantly impact a population's ability to adapt to environmental change.