Habitat patches for newts in the face of climate change: local scale assessment combining niche modelling and graph theory

Abstract

& francis isselin-nondedeu 3,6Triturus cristatus and Triturus marmoratus are two protected and declining newts occurring in the administrative department of Vienne, in France. They have limited dispersal abilities and rely on the connectivity between habitats and their suitability. In a warming climate, the locations of suitable habitats are expected to change, as is the connectivity. Here, we wondered how climate change might affect shifts in habitat suitability and connectivity of habitat patches, as connectivity is a key element enabling species to realize a potential range shift. We used ecological niche modelling (ENM), combining large-scale climate suitability with local scale, high-resolution habitat features, to identify suitable areas for the two species, under low and high warming scenarios (RCP 2.6 and RCP 8.5). We associated it with connectivity assessment through graph theory. The variable 'small ponds' contributed most to land cover-only ENMs for both species. Projections with climate change scenarios revealed a potential impact of warming on suitable habitat patches for newts, especially for T. cristatus. We observed a decrease in connectivity following a decrease in patch suitability. Our results highlight the important areas for newt habitat connectivity within the study area, and define those potentially threatened by climate warming. We provide information for prioritizing sites for acquisition, protection or restoration, and to advise landscape policies. Our framework is a useful and easily reproducible way to combine global climate requirements of the species with detailed information on species habitats and occurrence when available. open Scientific RepoRtS | (2020) 10:3570 | https://doi.org/10.1038/s41598-020-60479-4www.nature.com/scientificreports www.nature.com/scientificreports/ connected by "edges", which refer to ecological corridors. Landscape graphs can be used to represent ecological networks and to analyse connectivity between habitats, with, for instance, the purpose of prioritizing sites for protection, improving connectivity, or assessing potential effect of an urban development project 19,20 . In this approach, the landscape between habitat patches is represented by a "resistance" or "cost" which estimates the relationships between environmental variables and movement of the considered species 21 . Resistance surfaces can be categorical, with a cost associated with land cover types 22 ; continuous, for example from an output of ENM, where resistance increases when habitat suitability decreases 23,24 ; or binary, assuming that the influence of the matrix on species movement is homogenous between patches 25 . Ziółkowska et al. 26 have compared the efficiency of such resistance surface representation on landscape connectivity assessment and they recommend using continuous resistance surface whenever possible. Using a habitat suitability map from ENM helps to overcome a lack of sufficient data. The use of ENM output is also a way to explore predictions of changes in high habitat su...

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