The influence of landscape change on population genetic structure of wild species has gained increasing attention as our landscapes are being increasingly fragmented by human activities, leaving natural habitats confined to small, isolated islands, posing increasing threat to wild species. Meanwhile, population genetic structure provides valuable insights into species persistence and, consequently, the overall biodiversity over the long term. This general pattern is also evident in temperate European agricultural landscapes, where forest specialists are constrained in small forest patches with complex land use histories, while their population genetic responses is largely understudied. Furthermore, much like many community-level responses to landscape change, population genetic structure often exhibits a delayed response to habitat loss, fragmentation, and landscape change, yet the magnitude of the delay and the key factors influencing it remain poorly understood. In this study, we investigated population genetic responses to habitat loss, fragmentation, and landscape change, with particular emphasis on the temporal dimension by integrating two centuries of land-use history in temperate Europe. We focused on three typical forest specialists with limited dispersal capacity (Anemone nemorosa, Oxalis acetosella, and Polygonatum multiflorum) that differ in life-history traits, such as generation time and mating strategy. The aim was to assess (a) the effect of population age on forest herb population genetic structure, with a focus on forest habitats; (b) the delayed responses of forest herb population genetic structure to changes in landscape composition and configuration, with a focus on the surrounding landscape matrix beyond the habitat; and (c) the role and relative importance of life-history traits in shaping their temporal genetic responses of forest herbs. We found that all three species responded to reduced population size with decreased allelic richness and increased among-population genetic differentiation. With increasing spatial isolation, all three species experienced increased genetic differentiation. These results confirmed that all three species are sensitive to habitat loss and fragmentation (Chapter I). Meanwhile, younger populations, compared to older populations, showed a similar level of allelic richness but lower observed heterozygosity and a stronger dependence on spatial connectivity (Chapter II), indicating that forest herb specialists rely on time and spatial connectivity to develop genetic structures suited for long-term persistence. The population genetic structure of these forest herb species was also influenced by many landscape elements outside their forest habitats, with the direction and strength of species responses to landscape change varying according to their traits, especially their pollen- or seed dispersal vectors (Chapter III). Moreover, the population genetic structure of older populations still reflected past landscape composition and configuration. The length of these lags varied with the landscape metrics considered and was linked to species traits, with species with longer generation times exhibiting longer lags, in some cases up to 220 years (Chapter IV‒V). Differences in associated pollinators may help explain the different importance of landscape elements in shaping genetic structure over the long term, while long-distance dispersal may help to shorten the time lags (Chapter V).
Siyu Huang (Thu,) studied this question.