Thermal niches are more conserved at cold than warm limits in arctic-alpine plant species.
OBJECTIVE
Understanding the stability of realized niches is crucial for predicting the responses of species to climate change. One approach is to evaluate the niche differences of populations of the same species that occupy regions that are geographically disconnected. Here, we assess niche conservatism along thermal gradients for 26 plant species with a disjunct distribution between the Alps and the Arctic.


METHODS
European Alps and Norwegian Finnmark.


METHODS
We collected a comprehensive dataset of 26 arctic-alpine plant occurrences in two regions. We assessed niche conservatism through a multispecies comparison and analysed species rankings at cold and warm thermal limits along two distinct gradients corresponding to (1) air temperatures at 2 m above ground level and (2) elevation distances to the tree line (TLD) for the two regions. We assessed whether observed relationships were close to those predicted under thermal limit conservatism.


RESULTS
We found a weak similarity in species ranking at the warm thermal limits. The range of warm thermal limits for the 26 species was much larger in the Alps than in Finnmark. We found a stronger similarity in species ranking and correspondence at the cold thermal limit along the gradients of 2-m temperature and TLD. Yet along the 2-m temperature gradient the cold thermal limits of species in the Alps were lower on average than those in Finnmark.


CONCLUSIONS
We found low conservatism of the warm thermal limits but a stronger conservatism of the cold thermal limits. We suggest that biotic interactions at the warm thermal limit are likely to modulate species responses more strongly than at the cold limit. The differing biotic context between the two regions is probably responsible for the observed differences in realized niches.
University of Lausanne, Department of Ecology and Evolution, CH-1015 Lausanne, Switzerland.
Loïc
L
Pellissier
Department of Arctic and Marine Biology, University of Tromsø, 9037 Tromsø, Norway.
Kari Anne
KA
Bråthen
University of Lausanne, Department of Ecology and Evolution, CH-1015 Lausanne, Switzerland ; University of Lausanne, Faculty of Geosciences and the Environment, CH-1015 Lausanne, Switzerland.
Pascal
P
Vittoz
Department of Arctic and Marine Biology, University of Tromsø, 9037 Tromsø, Norway.
Nigel G
NG
Yoccoz
University of Lausanne, Department of Ecology and Evolution, CH-1015 Lausanne, Switzerland.
Anne
A
Dubuis
Swiss Federal Research Institute WSL, Birmensdorf, CH-8903 Switzerland ; Research Station Agroscope Reckenholz-Taenikon ART, CH-8046 Zurich, Switzerland.
Eliane S
ES
Meier
Swiss Federal Research Institute WSL, Birmensdorf, CH-8903 Switzerland.
Niklaus E
NE
Zimmermann
University of Lausanne, Department of Ecology and Evolution, CH-1015 Lausanne, Switzerland.
Christophe F
CF
Randin
Laboratoire d'Ecologie Alpine, UMR CNRS 5553, Université Joseph Fourier, Grenoble I, BP53, 38041 Grenoble Cedex 9, France.
Wilfried
W
Thuiller
Conservatoire Botanique National Alpin, Domaine de Charance, 05000 GAP, France.
Luc
L
Garraud
Conservatoire Botanique National Alpin, Domaine de Charance, 05000 GAP, France.
Jérémie
J
Van Es
University of Lausanne, Department of Ecology and Evolution, CH-1015 Lausanne, Switzerland ; University of Lausanne, Faculty of Geosciences and the Environment, CH-1015 Lausanne, Switzerland.
Antoine
A
Guisan
Air–soil temperature; European Alps; Norwegian Finnmark; biotic interactions; disjunct distribution; distance to tree line; niche conservatism; realized niche; species distribution models