Demographic response of Rana uenoi to land use near breeding sites: A case study from the Gayasan region, South Korea

Abstract

Amphibians are highly sensitive to habitat disturbance because of their permeable skin and reliance on both aquatic and terrestrial environments. To evaluate how human-driven land-use change affects a forest-stream amphibian, we analysed long-term population dynamics of Rana uenoi in the Gayasan region of South Korea, with a focus on breeding habitats. Between 2007 and 2023, annual egg-mass surveys were conducted at 14 breeding sites, and land-use composition was extracted each year within a 500 m buffer from national geospatial databases. Land-use categories were reclassified into ecologically relevant groups (breeding, high-quality, low-quality and non-living/high-mortality habitats) and their areas were quantified for use in regression models. Breeding populations persisted at four focal sites, where annual egg-mass counts declined by up to 98.5 % over 17 years and breeding ceased entirely at the remaining ten sites. At the four persistent sites, a multiple regression model relating log10-transformed egg-mass counts to habitat composition and site identity explained a large proportion of the variation in reproductive output. Breeding habitats (wetlands and rice paddies) and high-quality habitats (forests) were positively associated with egg-mass production, whereas non-living/high-mortality habitats (roads, urban and barren land) tended to have negative or non-significant effects once other covariates were included. Low-quality habitats (cultivated fields and artificial grasslands) showed weaker and context-dependent associations. Model comparisons indicated that land-use variables alone provided stronger explanatory power than models including breeding-season climate, and time-series analyses showed no strong directional trend in temperature or precipitation over the study period. Although other unmeasured factors may also contribute to declines, our results underscore the predictive value of habitat-specific land-use metrics and highlight the importance of maintaining wetland-forest mosaics and limiting new road and urban development within a few hundred metres of breeding sites to support R. uenoi populations.