A global test of Eltonian and Grinellian niche conservatism: implications for forecasting species responses to climate change

Lise Comte (1), Julien Cucherousset (2), Julian D. Olden (3)

1 School of Aquatic and Fishery Sciences, University of Washington, 1122 NE Boat St, Seattle WA 98195,  lcomte@uw.edu

2 Laboratoire Evolution & Diversite Biologique, CNRS, Université Toulouse III Paul Sabatier, 118 route de Narbonne, F-31062 Toulouse, France,  julien.cucherousset@univ-tlse3.fr

3 School of Aquatic and Fishery Sciences, University of Washington, 1122 NE Boat St, Seattle WA 98195,  olden@uw.edu

Non-native species provide a unique opportunity to understand the mechanisms shaping current species ranges and how and when these limits may shift in response to rapid anthropogenic changes. For example, contemporary biological introductions are valuable replicated experiments that can be used to test for the existence of niche conservatism across a broad range of environmental conditions. We combine a global database of stable isotope data characterizing species trophic (Eltonian) niches with data describing climatic (Grinellian) niches and a species-level phylogeny to assess the degree of niche conservatism of 32 freshwater fish species between their native and introduced ranges. We asked three fundamental questions: (1) Do introduced species conserved their native niches or displayed rapid niche shifts when introduced into new environments? (2) Are niche shifts more likely to occur along some axes in niche space than along other? (3) Are these differences likely to be explained by their past rate of niche evolution? We found evidence of complex shifts along both the Eltonian and Grinellian niche axes for the majority of the evaluated species, but no clear relationship between past niche evolution and contemporary niche shifts. In particular, we documented a consistent shift towards intermediate trophic strategies, independently from the context of introduction or species evolutionary history. In conclusion, our findings suggest that more accurate predictions for species responses to climate change will benefit from acknowledging that both Grinellian and Eltonian niches may shift in space and time, and that invasive species provide powerful insight into these processes.