Future of the small blue butterfly (Cupido minimus) in Scotland: a study of habitat suitability and change

Abstract

Climate change and coastal erosion are critical threats to species with specialised habitat requirements, such as the Small Blue butterfly (Cupido minimus), which relies on the larval host plant Kidney Vetch (Anthyllis vulneraria) and is largely confined to narrow coastal grasslands and dunes in Scotland. This study investigates how climate change affects the future habitat suitability of the endangered Small Blue butterfly in Scotland, using an integrative species distribution modelling approach with a particular focus on the role of biotic interactions and coastal erosion. MaxEnt models were developed to project habitat suitability under current and future climate scenarios, incorporating climatic, environmental, and biotic predictors as well as coastal erosion risk. Results suggest a significant inland shift in suitable habitats, with a marked decline in coastal suitability by the end of the century. Incorporating biotic predictors produced more fragmented and constrained suitability estimates, highlighting the importance of host plant availability.

Additionally, integrating coastal erosion risk layers revealed further habitat loss in vulnerable coastal regions, even where climatic and environmental conditions remained suitable. This study demonstrates an integrative approach combining climate, biotic interactions, and coastal erosion modelling, offering more realistic assessments of future habitat suitability for coastal species. The uncertainties in the current models highlight the need for careful interpretation of model outputs and further field validation. Adaptive conservation strategies are essential to support the Small Blue’s long-term persistence.