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      Parsing propagule pressure: Number, not size, of introductions drives colonization success in a novel environment


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          Predicting whether individuals will colonize a novel habitat is of fundamental ecological interest and is crucial to conservation efforts. A consistently supported predictor of colonization success is the number of individuals introduced, also called propagule pressure. Propagule pressure increases with the number of introductions and the number of individuals per introduction (the size of the introduction), but it is unresolved which process is a stronger driver of colonization success. Furthermore, their relative importance may depend upon the environment, with multiple introductions potentially enhancing colonization of fluctuating environments. To evaluate the relative importance of the number and size of introductions and its dependence upon environmental variability, we paired demographic simulations with a microcosm experiment. Using Tribolium flour beetles as a model system, we introduced a fixed number of individuals into replicated novel habitats of stable or fluctuating quality, varying the number of introductions through time and size of each introduction. We evaluated establishment probability and the size of extant populations through seven generations. We found that establishment probability generally increased with more, smaller introductions, but was not affected by biologically realistic fluctuations in environmental quality. Population size was not significantly affected by environmental variability in the simulations, but populations in the microcosms grew larger in a stable environment, especially with more introduction events. In general, the microcosm experiment yielded higher establishment probability and larger populations than the demographic simulations. We suggest that genetic mechanisms likely underlie these differences and thus deserve more attention in efforts to parse propagule pressure. Our results highlight the importance of preventing further introductions of undesirable species to invaded sites and suggest conservation efforts should focus on increasing the number of introductions or reintroductions of desirable species rather than increasing the size of those introduction events into harsh environments.

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          Most cited references32

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            Biological invasions: Lessons for ecology.

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            Anthropogenic introduction of species is homogenizing the earth's biota. Consequences of introductions are sometimes great, and are directly related to global climate change, biodiversity AND release of genetically engineered organisms. Progress in invasion studies hinges on the following research trends: realization that species' ranges are naturally dynamic; recognition that colonist species and target communities cannot be studied independently, but that species-community interactions determine invasion success; increasingly quantitative tests of how species and habitat characteristics relate to invasibility and impact; recognition from paleobiological, experimental and modeling studies that history, chance and determinism together shape community invasibility. Copyright © 1993. Published by Elsevier Ltd.
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              Genetic rescue to the rescue.

              Genetic rescue can increase the fitness of small, imperiled populations via immigration. A suite of studies from the past decade highlights the value of genetic rescue in increasing population fitness. Nonetheless, genetic rescue has not been widely applied to conserve many of the threatened populations that it could benefit. In this review, we highlight recent studies of genetic rescue and place it in the larger context of theoretical and empirical developments in evolutionary and conservation biology. We also propose directions to help shape future research on genetic rescue. Genetic rescue is a tool that can stem biodiversity loss more than has been appreciated, provides population resilience, and will become increasingly useful if integrated with molecular advances in population genomics.

                Author and article information

                Ecol Evol
                Ecol Evol
                Ecology and Evolution
                John Wiley and Sons Inc. (Hoboken )
                20 July 2018
                August 2018
                : 8
                : 16 ( doiID: 10.1002/ece3.2018.8.issue-16 )
                : 8043-8054
                [ 1 ] Graduate Group in Ecology University of California Davis California
                [ 2 ] Graduate Degree Program in Ecology Colorado State University Fort Collins Colorado
                [ 3 ] Department of Bioagricultural Science and Pest Management Colorado State University Fort Collins Colorado
                [ 4 ] Department of Integrative Biology University of California Berkeley California
                [ 5 ] Department of Ecology and Evolutionary Biology University of Colorado Boulder Colorado
                Author notes
                [*] [* ] Correspondence

                Michael J. Koontz, Graduate Group in Ecology, University of California, Davis, California.

                Email: mkoontz@ 123456ucdavis.edu

                Author information
                © 2018 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.

                This is an open access article under the terms of the http://creativecommons.org/licenses/by/4.0/ License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

                : 22 October 2017
                : 18 April 2018
                Page count
                Figures: 4, Tables: 0, Pages: 12, Words: 9874
                Funded by: NSF Graduate Research Fellowship
                Award ID: DGE‐1321845
                Award ID: DGE‐1106400
                Funded by: NSF
                Award ID: DEB‐0949619
                Award ID: DEB‐0949595
                Funded by: University of California Davis Libraries Open Access Fund
                Funded by: Colorado State University Libraries Open Access Research and Scholarship Fund
                Original Research
                Original Research
                Custom metadata
                August 2018
                Converter:WILEY_ML3GV2_TO_NLMPMC version:version=5.4.9 mode:remove_FC converted:19.09.2018

                Evolutionary Biology
                biocontrol,conservation,invasion,microcosm,population dynamics,propagule pressure,reintroduction,simulation,stochasticity


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