No abstract

Accurate estimations of population size and space-use are critical issues, for assessing population trends and extinction risk. In this study, we applied spatially explicit capture-recapture (SECR) modelling customized for linear habitats to a three-year Capture-Mark-Recapture (CMR) monitoring of three populations of stream-dwelling Pyrenean brook newt (Calotriton asper), an endemic species of the Pyrenean mountain range. Our aim was to explore (1) spatial and temporal variation in population densities, home range size and individual detection probability during breeding season between populations and years, and (2) the influence of water temperature and flow on activity of newts. Estimates of population density range from 3044 to 4641 individuals/km of stream across the three years of the study. Linear home range along the stream was estimated to be 13.31 m from the home range centre on average over the three years. All detection probability estimates were similar, both between years and between sites, with a mean probability of 0.09, except in Fougax in 2020 where detection probability was 0.03. Activity of the Pyrenean brook newt was influenced by water temperature and flow, but these factors acted at different time scales. Overall, population densities are locally high in both populations but home range of the Pyrenean brook newt during breeding season is very small indicating a strong site attachment. The importance of water temperature and flow on activity emphasizes the sensitivity of the species to these factors that are forecasted to change in coming decades.

To forecast species responses to environmental changes, it is crucial to understand drivers of species distribution acting at multiple spatial and temporal scales. While hydrology is acknowledged as a key driver for freshwater species, most studies have been limited to perennial river flow regimes when exploring species distribution in rivers. We developed a method to characterize stream flow to subsequently account for flow intermittence in species distribution models (SDMs). First, we used the hydrological Soil and Water Assessment Tool (SWAT) to simulate flow in the French Pyrenees at fine spatial grain and large spatial extent. Several metrics characterizing flow intermittence were subsequently included in a SDM along with topographic, hydrographic, climatic and land use variables. We applied this methodology to an extensive data set of the Pyrenean brook newt (Calotriton asper) presence in France.This amphibian is highly dependent on aquatic habitats, and its distribution could be mainly driven by hydrological and climatic variables. We found that 60% of the stream network of the study area is intermittent. Maximum air temperature and proportion of agricultural areas contribution in explaining species distribution were the most important (26.3% and 21.2%, respectively). Both variables negatively influenced the probability of presence of the Pyrenean brook newt. We also found a negative correlation with the frequency of zero-flow events (13%), emphasizing the role of flow intermittence in driving aquatic species distribution. Our study provides new insights into fine-grained hydrology in the Pyrenees and illustrates intermittence characterization and mapping methods that could be applied elsewhere.