Genetic Allee effects and their interaction with ecological Allee effects

Area of Science:

• Population Genetics
• Conservation Biology
• Ecological Dynamics

Background:

• Small populations face extinction risks from genetic factors like inbreeding depression and loss of genetic variation.
• It remains unclear if extinction risk from genetic causes escalates gradually or exhibits a sharp threshold with decreasing population size, akin to strong Allee effects.

Purpose of the Study:

• Define a 'strong genetic Allee effect' and identify conditions for its occurrence due to inbreeding depression from recessive deleterious mutations.
• Quantify the interplay between genetic Allee effects and the established mate-finding Allee effect.

Main Methods:

• Developed stochastic models analyzing the ecology and genetics of small populations.
• Defined a strong genetic Allee effect by a sigmoid relationship between initial population size and survival probability.
• Identified the critical population size as the inflection point of this sigmoid curve.

Main Results:

• Inbreeding depression can cause a strong genetic Allee effect if individuals carry a sufficient number of deleterious mutations (lethal equivalents).
• Populations may initially grow, then decline due to inbreeding, and potentially recover through purging of mutations.
• Interactions between ecological and genetic Allee effects can be additive or even superadditive.

Conclusions:

• Strong genetic Allee effects are expected within the range of lethal equivalents commonly found in birds and mammals.
• Extinction risks from genetic Allee effects can be underestimated due to initial population growth followed by a crash.
• Interactions between ecological and genetic Allee effects are significant and must be considered for population viability assessments.