title: Evaluating early-warning indicators of critical transitions in natural aquatic ecosystems.
abstract: Ecosystems can show sudden and persistent changes in state despite only incremental changes in drivers. Such critical transitions are difficult to predict, because the state of the system often shows little change before the transition. Early-warning indicators (EWIs) are hypothesized to signal the loss of system resilience and have been shown to precede critical transitions in theoretical models, paleo-climate time series, and in laboratory as well as whole lake experiments. The generalizability of EWIs for detecting critical transitions in empirical time series of natural aquatic ecosystems remains largely untested, however. Here we assessed four commonly used EWIs on long-term datasets of five freshwater ecosystems that have experienced sudden, persistent transitions and for which the relevant ecological mechanisms and drivers are well understood. These case studies were categorized by three mechanisms that can generate critical transitions between alternative states: competition, trophic cascade, and intraguild predation. Although EWIs could be detected in most of the case studies, agreement among the four indicators was low. In some cases, EWIs were detected considerably ahead of the transition. Nonetheless, our results show that at present, EWIs do not provide reliable and consistent signals of impending critical transitions despite using some of the best routinely monitored freshwater ecosystems. Our analysis strongly suggests that a priori knowledge of the underlying mechanisms driving ecosystem transitions is necessary to identify relevant state variables for successfully monitoring EWIs.
authors.affiliation: Ecosystem Research, Leibniz Institute of Freshwater Ecology and Inland Fisheries, 12587 Berlin, Germany; a.gsell@nioo.knaw.nl.|Aquatic Ecology, Netherlands Institute of Ecology, 6708 PB Wageningen, The Netherlands.
authors.forename: Alena Sonia
authors.identifier: 0000-0001-7795-1996
authors.initials: AS
authors.lastname: Gsell
authors.affiliation: Ecosystem Research, Leibniz Institute of Freshwater Ecology and Inland Fisheries, 12587 Berlin, Germany.|Department of Biology, Chemistry, and Pharmacy, Free University of Berlin, 14195 Berlin, Germany.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Scharfenberger
authors.affiliation: Waikato Regional Council, 3216 Hamilton, New Zealand.
authors.forename: Deniz
authors.initials: D
authors.lastname: Özkundakci
authors.affiliation: Wyoming Cooperative Fish and Wildlife Research Unit, US Geological Survey, Laramie, WY 82071.
authors.forename: Annika
authors.initials: A
authors.lastname: Walters
authors.affiliation: Department of Biology, Lund University, 223 62 Lund, Sweden.
authors.forename: Lars-Anders
authors.initials: LA
authors.lastname: Hansson
authors.affiliation: Aquatic Ecology, Netherlands Institute of Ecology, 6708 PB Wageningen, The Netherlands.|Department of Aquatic Ecology and Water Quality Management, Wageningen University, Wageningen, The Netherlands.
authors.forename: Annette B G
authors.initials: AB
authors.lastname: Janssen
authors.affiliation: Centre for Limnology, Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, 61117 Tartumaa, Estonia.
authors.forename: Peeter
authors.initials: P
authors.lastname: Nõges
authors.affiliation: The Laboratory, Sir Alister Hardy Foundation for Ocean Science, Plymouth PL1 2PB, United Kingdom.|Marine Institute, Plymouth University, Plymouth PL4 8AA, United Kingdom.|The Laboratory, Marine Biological Association of the United Kingdom, Plymouth PL1 2PB, United Kingdom.
authors.forename: Philip C
authors.initials: PC
authors.lastname: Reid
authors.affiliation: School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA 98195.
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Schindler
authors.affiliation: Aquatic Ecology, Netherlands Institute of Ecology, 6708 PB Wageningen, The Netherlands.
authors.forename: Ellen
authors.initials: E
authors.lastname: Van Donk
authors.affiliation: Institute of Integrative Biology, Center for Adaptation to a Changing Environment, ETH Zürich, 8092 Zürich, Switzerland.
authors.forename: Vasilis
authors.initials: V
authors.lastname: Dakos
authors.affiliation: Ecosystem Research, Leibniz Institute of Freshwater Ecology and Inland Fisheries, 12587 Berlin, Germany.|Department of Biology, Chemistry, and Pharmacy, Free University of Berlin, 14195 Berlin, Germany.
authors.forename: Rita
authors.initials: R
authors.lastname: Adrian
mesh_terms: D000818:Animals; D056808:Biostatistics; D002980:Climate; D017753:Ecosystem; D005068:Eutrophication; D020387:Food Chain; D005618:Fresh Water; D060106:Lakes; D008954:Models, Biological; D011235:Predatory Behavior; D013997:Time Factors
keywords: competition; intraguild predation; resilience indicators; time series; trophic cascade