Institution: | 1. Biology Department - Washington University in Saint Louis, 1 Brookings Drive, St. Louis, MO, 63130 U.S.A.;2. Pennsylvania Natural Heritage Program and the Western Pennsylvania Conservancy, 400 Market Street, Harrisburg, PA, 17105 U.S.A.
Chicago Botanic Garden - Department of Plant Science and Conservation, 1000 Lake Cook Road, Glencoe, IL, 60022 U.S.A.;3. Chicago Botanic Garden - Department of Plant Science and Conservation, 1000 Lake Cook Road, Glencoe, IL, 60022 U.S.A.;4. Institute of Biology/Geobotany and Botanical Garden, Martin-Luther-University, Universitätsplatz 10, Halle-Wittenberg, 06108 Germany
Department of Community Ecology, UFZ, Helmholtz Centre for Environmental Research, Permoserstraße 15, Halle-Leipzig, 0438 Germany
German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, Deutscher Platz 5e, Leipzig, 04103 Germany |
Abstract: | The current loss of biodiversity has put 50,000 plant species at an elevated risk of extinction worldwide. Conserving at-risk species is often complicated by covariance or nonadditivity among threats, which makes it difficult to determine optimal management strategies. We sought to demographically quantify covariance and nonadditive effects of more threats on more rare plant species than ever attempted in a single analysis. We used 1082 population reports from 186 populations across 3 U.S. states of 27 rare, herbaceous plant species collected over 15 years by citizen scientists. We used a linear mixed-effects model with 4 threats and their interactions as fixed predictors, species as a random predictor, and annual growth rates as the response. We found a significant 3-way interaction on annual growth rates; rare plant population sizes were reduced by 46% during the time immediately after disturbance when populations were also browsed by deer (Odocoileus virginianus) and had high levels of encroachment by woody species. This nonadditive effect should be considered a major threat to the persistence of rare plant species. Our results highlight the need for comprehensive, multithreat assessments to determine optimal conservation actions. |