Population decline at distribution margins: Assessing extinction risk in the last glacial relictual but still functional metapopulation of a European butterfly

Abstract

Aim:To determine the interplay between climate and land use changes in driving population dynamics in a butterfly species, Coenonympha hero, at the southern limit of its distribution.Location: French Jura massif and Europe. Methods:We analysed patterns of genetic diversity distribution at 817 loci in 136 butterflies from 31 sites using NGS to infer the genetic structure and population size changes over time, using two methods of demographic inference (SNP frequency spectrum analyses and coalescent ABC inferences). We then characterized the climate and land use descriptors of C. hero geographic distribution using species distribution modelling (SDM) and ordination method and compared demographic changes to changes in climatically suitable areas. Results: Coenonympha hero persists in the Jura massif as three core populations that share a common history of decline in two steps: an old decline and a more recent decline that resulted in population fragmentation, the southernmost sites being the most threatened (lowest genetic diversity). Climate change during the Würm glaciation is presumably the main factor explaining the first demographic decline. The second decline started 2000 years ago possibly under increased human pressure as suggested by recent extinctions in several sites nowadays characterized by urban and agricultural surfaces. Both climate and land use variables are important descriptors of C. hero distribution, as SDM predictions were improved by adding aridity index, altitude and land use to bioclimatic predictors. Its habitats include forests in northeastern Europe and grasslands in the Jura massif.Main conclusions: Using SDM and genetic demographic inferences, we identified a persistent glacial refuge for the species in Europe. We show that although this relictual population has declined and fragmented under the combined effects of climate warming and anthropization, the metapopulation is still functional but requires

Living on the edge—Genomic and ecological delineation of cryptic lineages in the high‐elevation specialist Erebia nivalis

“…These low values are in line with our assumption of recent changes in effective population size, showing steep population declines over the last 500 years and a likely rapid bottleneck event in Grindelwald about 80 years ago (Figure 4a). Other studies on demographic trends in butterflies report similar gradual population declines as for E. nivalis during historical ages (Figure 4b; Sherpa et al, 2022) and sharp bottlenecks in more recent years (Després et al, 2019). The Swiss bottleneck event also fits within an inferred window of general butterfly decline around the 1960s that may be related to the intensification of agricultural and/or touristic practices (Habel et al, 2022).…”

Insights from the past: Invasion trajectory and niche trends of a global freshwater invader

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“…The higher the output values, the better the model performance (i.e., values close to 1 corresponding to perfect discrimination). To reduce uncertainties associated with a single SDM algorithm, an ensemble modelling approach (Araújo & New, 2007) was used weighting the model replicates by their predictive performance with a threshold of true skill statistic (TSS) > 0.7 (EMwmeanByTSS following Sherpa et al., 2022). This is a widely used approach in contemporary species distribution modelling (Jourdan et al., 2021; Sherpa et al., 2022).…”

Incorporating genomics into insect conservation: Butterflies as a model group

“…The inference of demographic trends using genome‐wide data is another potential contribution of genomics to insect conservation. For example, Sherpa et al (2022) evaluated the connectivity of populations of Coenonympha hero (Linnaeus, 1761) in the French Jura Mountains using ddRADseq loci. The authors identified severe demographic declines in pre‐historical times but also more recently possibly because of increased human pressure.…”