Combining genetic diversity data with demographic information more reliably reveals extinction risks of natural populations

Genetic diversity, a key pillar of biodiversity, is crucial for conservation. But can snapshot estimates of genetic diversity reliably indicate population extinction risk? New research shows that genome-wide genetic diversity is a strong predictor of extinction risk, but only when confounding, demographic, factors are accounted for.

As species face increasing environmental pressures, their populations often decline, leading to a loss of genetic diversity. This reduction in genetic variation can have serious consequences, including increased inbreeding and a diminished capacity to adapt to changing conditions. Genome-wide genetic diversity is often used as an indicator of species' vulnerability to extinction. However, recent studies have suggested that genetic diversity does not always predict population viability.

The collaborative research sought to clarify under what circumstances genetic diversity can accurately predict extinction risk. The findings suggest that while genetic diversity is indeed linked to extinction risk, the strength of this relationship varies depending on other factors such as population size and the potential for rescue through dispersal.

The importance of integrating demographic data

The study highlights the dangers of relying solely on genetic data to assess population viability. "Our research demonstrates that inferences about the role of genetic diversity in extinction risk must be informed by demographic and environmental data," explains Professor Marjo Saastamoinen, senior author of the paper.

 "For instance, we observed a strong negative relationship between genetic diversity and extinction risk, but this correlation was largely driven by underlying population size. Without accounting for demographic factors, we would have drawn misleading conclusions."

Dr. Michelle DiLeo, the leading author of the study, further cautions against oversimplification: "Had we focused only on genetic diversity, we might have incorrectly assumed its effects on extinction risk were uniform across different populations and environments. Conversely, ignoring the interactions between genetics and demographics would have led us to underestimate the importance of genetic diversity in explaining extinction risk. Our results suggest that both genetic diversity and demographic factors, such as population size, population trends and immigration, must be considered in conservation strategies.”

“Not all populations with low genetic diversity were doomed to extinction, as they were rescued by dispersal from other populations." continues DiLeo. 

Recommendations for conservation

Given that most species are data-deficient, the researchers emphasize the need for strategic data collection to inform conservation efforts. They recommend focusing on three key pieces of information: estimates of genome-wide or neutral genetic diversity, population size trends, and the potential for rescue via dispersal. Population size trends and population connectivity are already used in some global biodiversity frameworks, but more work is needed to integrate these metrics with genetic data for a comprehensive assessment of species vulnerability. The study also underscores the importance of maintaining connectivity among populations to mitigate the risks associated with low genetic diversity in the face of environmental change.

Utilizing long-term monitoring data of the Glanville fritillary butterfly

Assessing the relationship between genetic diversity and extinction risk in natural populations is not trivial as it requires high resolution population level genetic and demographic data. The researchers utilized the well-known ecological model system of the Glanville fritillary butterfly metapopulation in the Åland islands, SW Finland. For this system the survival of thousands of local populations and overwintering larval nests have been systematically monitored across over 30 years, data which has been more recently been accompanied with genetic data. 

In this study genetic data from 7,501 individuals with extinction data from 279 meadows and mortality of 1,742 larval nests in a butterfly metapopulation were analyzed. This allowed researchers to assess the effect of genetic diversity on extinction rates across years and under different conditions such as between small and large populations, in populations with longer history of decline and when extinctions could not be rescued by dispersal from nearby populations.