Long-Term Dynamics of a Cave Salamander Population in a Region under Changing Climate

Long-term effects of current climate on animal populations living in subterranean habitats are still poorly understood. In this study, we analyzed the variability of the demographic structure and abundance of a population of terrestrial plethodontid Strinati's Cave Salamanders (Speleomantes strinatii) (Aellen, 1958) living inside a northwestern Italian artificial cave over 27 yr from 1996 to 2022. The study site is situated in the Northern Apennines, where average air temperatures measured at two local weather stations were steadily increasing, whereas precipitation was relatively constant over the past 60 yr. Our objective was to evaluate whether the demographic traits of the population of Strinati's Cave Salamanders were showing detectable signs of directional shift during the 27 yr. Each year in July, the population abundance was estimated by a three-occasion removal experiment, salamanders' snout-vent length (SVL) was measured, and the population polymodal body-size distribution was decomposed into estimated age classes. The annual population abundance, adult sex ratio, recruitment, SVL, and growth increments of first- and second-year immature salamanders were analyzed. The Strinati's Cave Salamander time series was modeled by autoregressive moving average (ARMA) analysis, and demographic parameters were tested for temporal trends. There were no directional trends observed in any of the demographic parameters of the focal cave salamander population over the study period. The best autoregressive model describing the population variation was an ARMA (2,1). Results indicated that the salamander population had a complex fluctuating pattern in which the interaction of lagged density dependence and an external autocorrelated factor were influencing the population long-term dynamics. Our findings suggest that the population of this long-lived salamander species was probably buffered from external conditions by the thermal inertia of its subterranean habitat that is known to delay and reduce the amplitude of aboveground climatic signals.