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      Spatial heterogeneity in climate change effects decouples the long‐term dynamics of wild reindeer populations in the high Arctic

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          Abstract

          The ‘Moran effect’ predicts that dynamics of populations of a species are synchronized over similar distances as their environmental drivers. Strong population synchrony reduces species viability, but spatial heterogeneity in density dependence, the environment, or its ecological responses may decouple dynamics in space, preventing extinctions. How such heterogeneity buffers impacts of global change on large‐scale population dynamics is not well studied. Here, we show that spatially autocorrelated fluctuations in annual winter weather synchronize wild reindeer dynamics across high‐Arctic Svalbard, while, paradoxically, spatial variation in winter climate trends contribute to diverging local population trajectories. Warmer summers have improved the carrying capacity and apparently led to increased total reindeer abundance. However, fluctuations in population size seem mainly driven by negative effects of stochastic winter rain‐on‐snow (ROS) events causing icing, with strongest effects at high densities. Count data for 10 reindeer populations 8–324 km apart suggested that density‐dependent ROS effects contributed to synchrony in population dynamics, mainly through spatially autocorrelated mortality. By comparing one coastal and one ‘continental’ reindeer population over four decades, we show that locally contrasting abundance trends can arise from spatial differences in climate change and responses to weather. The coastal population experienced a larger increase in ROS, and a stronger density‐dependent ROS effect on population growth rates, than the continental population. In contrast, the latter experienced stronger summer warming and showed the strongest positive response to summer temperatures. Accordingly, contrasting net effects of a recent climate regime shift—with increased ROS and harsher winters, yet higher summer temperatures and improved carrying capacity—led to negative and positive abundance trends in the coastal and continental population respectively. Thus, synchronized population fluctuations by climatic drivers can be buffered by spatial heterogeneity in the same drivers, as well as in the ecological responses, averaging out climate change effects at larger spatial scales.

          Abstract

          Spatially autocorrelated weather and climate may cause population co‐fluctuations over large distances. We show that increasingly frequent rain‐on‐snow (ROS) and icing events in winter synchronize the annual dynamics of Svalbard reindeer populations, while, paradoxically, spatial variation in ROS trends and density‐dependent weather effects cause diverging local population trajectories in the long run. Such decoupling of population dynamics increases species viability under a rapidly warming high‐Arctic climate.

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          Ecological dynamics across the Arctic associated with recent climate change.

          At the close of the Fourth International Polar Year, we take stock of the ecological consequences of recent climate change in the Arctic, focusing on effects at population, community, and ecosystem scales. Despite the buffering effect of landscape heterogeneity, Arctic ecosystems and the trophic relationships that structure them have been severely perturbed. These rapid changes may be a bellwether of changes to come at lower latitudes and have the potential to affect ecosystem services related to natural resources, food production, climate regulation, and cultural integrity. We highlight areas of ecological research that deserve priority as the Arctic continues to warm.
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            Ecological Impacts of Deer Overabundance

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              Spatial population dynamics: analyzing patterns and processes of population synchrony.

              The search for mechanisms behind spatial population synchrony is currently a major issue in population ecology. Theoretical studies highlight how synchronizing mechanisms such as dispersal, regionally correlated climatic variables and mobile enemies might interact with local dynamics to produce different patterns of spatial covariance. Specialized statistical methods, applied to large-scale survey data, aid in testing the theoretical predictions with empirical estimates. Observational studies and experiments on the demography of local populations are paramount to identify the true ecological mechanisms. The recent achievements illustrate the power of combining theory, observation and/or experimentation and statistical modeling in the ecological research protocol.
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                Author and article information

                Contributors
                brage.b.hansen@ntnu.no
                Journal
                Glob Chang Biol
                Glob Chang Biol
                10.1111/(ISSN)1365-2486
                GCB
                Global Change Biology
                John Wiley and Sons Inc. (Hoboken )
                1354-1013
                1365-2486
                21 August 2019
                November 2019
                : 25
                : 11 ( doiID: 10.1111/gcb.v25.11 )
                : 3656-3668
                Affiliations
                [ 1 ] Centre for Biodiversity Dynamics (CBD) Department of Biology Norwegian University of Science and Technology (NTNU) Trondheim Norway
                [ 2 ] Norwegian Polar Institute (NPI) Fram Centre Tromsø Norway
                [ 3 ] James Hutton Institute Aberdeen UK
                Author notes
                [*] [* ] Correspondence

                Brage Bremset Hansen, Centre for Biodiversity Dynamics (CBD), Department of Biology, Norwegian University of Science and Technology (NTNU), N‐7491 Trondheim, Norway.

                Email: brage.b.hansen@ 123456ntnu.no

                Author information
                https://orcid.org/0000-0001-8763-4361
                https://orcid.org/0000-0002-2341-1035
                https://orcid.org/0000-0002-3290-7091
                https://orcid.org/0000-0002-5860-9252
                Article
                GCB14761
                10.1111/gcb.14761
                6851690
                31435996
                9940cef8-dfc9-40ff-a5e1-ac1943d5216d
                © 2019 The Authors. Global Change Biology Published by John Wiley & Sons Ltd

                This is an open access article under the terms of the http://creativecommons.org/licenses/by-nc/4.0/ License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

                History
                : 15 January 2019
                : 05 March 2019
                Page count
                Figures: 6, Tables: 0, Pages: 13, Words: 10187
                Funding
                Funded by: Norges Forskningsråd , open-funder-registry 10.13039/501100005416;
                Award ID: 223257
                Award ID: 244647
                Award ID: 276080
                Categories
                Primary Research Article
                Primary Research Articles
                Custom metadata
                2.0
                November 2019
                Converter:WILEY_ML3GV2_TO_JATSPMC version:5.7.1 mode:remove_FC converted:13.11.2019

                arctic,caribou and reindeer,climate change,meta‐population,population dynamics,spatial heterogeneity,spatial synchrony,ungulate

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