Abundance versus presence-absence in extinction debt: Time-lagged effects of land use change on salamander populations

Habitat loss and fragmentation have caused global biodiversity loss. It is important to understand the impact of past land use on biodiversity, not only in the present, but also to inform appropriate land-use strategies. Most studies on extinction debt, the concept that past land use drives present organism distribution, focus on species richness. However, when focusing on individual species, species richness is based on presence-absence data and does not reflect abundance. Therefore, extinction debt may not be clearly evident in presence-absence data. However, few studies have compared the effects of past land use on organism distribution using both abundance and presence-absence data. In this study, we compared the effects of past land use on the abundance and presence-absence of the ezo salamander Hynobius retardatus. We surveyed the aquatic areas of Ezo salamander egg sacs along a survey route in northern Japan. We measured the percentages of past and present forest areas, the physical environment, water quality, and waterbody type. The number of egg sacs was significantly associated with the percentage of past forest area, physical environment, water quality, and waterbody type. The presence or absence of egg sacs was significantly associated with the physical environment and water quality. Our results suggest that the effects of past land use on organism distribution are more evident in abundance data than in presence-absence data. Researchers and land managers may need to consider the time lag before extinction based on abundance data to assess extinction risk accurately.