Small populations, big challenges: Genetic, demographic, and landscape context collectively shape population performance of a perennial herb

Abstract

Habitat loss and fragmentation have led to smaller and more isolated plant populations, impacting population performance through changes in genetic processes, demographic structure, and pollinator availability. Understanding the interactive effects of these factors is crucial for sustaining and restoring viable populations. This study analysed the genetic structure of natural populations of the long-lived herb Primula elatior and investigated plant and population reproductive performance in relation to population size, floral morph type ratios, genetic diversity, pollinator abundance, and landscape context. Plant reproductive performance was measured in 33 natural populations in the Netherlands and related to population size and genetic diversity. Additionally, the landscape context, i.e., surface cover estimates of different land-use types, was assessed. Pollinator surveys were performed in a subset of 15 populations. Genetic divergence increased with geographic distance between populations. Structure analysis identified five genetic clusters corresponding to geographic regions. Genetic diversity was strongly positively correlated with population size but was not significantly associated with plant reproductive performance measures. Plant reproductive performance was however affected by floral morph ratio, pollinator abundance, and forest cover within 1000 m. Seed production increased with a more balanced floral morph ratio and higher pollinator abundance, and showed a unimodal relationship with the percentage of forest cover within 1000 m around the survey site. This study demonstrates that both floral morph ratio and landscape context simultaneously influence population performance and impose pressures particularly on small populations. This study underscores the need to adopt a landscape-oriented perspective to fully comprehend population performance.