Ecological thresholds and regime shifts: approaches to identification. Trends Ecol Evol

Department of Biology, University of Oslo, P.O. Box 1066, Blindern, N0316 Oslo, Norway.
Trends in Ecology & Evolution (Impact Factor: 16.2). 11/2008; 24(1):49-57. DOI: 10.1016/j.tree.2008.07.014
Source: PubMed


There is an apparent gap between the prominence of present theoretical frameworks involving ecological thresholds and regime shifts, and the paucity of efforts to conduct simple tests and quantitative inferences on the actual appearance of such phenomena in ecological data. A wide range of statistical methods and analytical techniques are now available that render these questions tractable, some of them even dating back half a century. Yet, their application has been sparse and confined within a narrow subset of cases of ecological regime shifts. Our objective is to raise awareness on the range of techniques available, and to their principles and limitations, to promote a more operational approach to the identification of ecological thresholds and regime shifts.

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Available from: Jacob Carstensen, Oct 01, 2015
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    • "This change point is consistent with the idea of a taxon-specific threshold response (sensu Groffman et al., 2006). A variety of statistical methods (including, e.g., nonparametric deviance reduction, piecewise regression, Bayesian changepoint, quantile piecewise constant, quantile piecewise linear approaches and significant zero crossings) have been used to detect and investigate ecological thresholds, whereas these thresholds have primarily been examined on the aggregate community level and not on the species level (Andersen et al., 2009; Brenden et al., 2008; Cardoso et al., 2013; Dodds et al., 2010; Sonderegger et al., 2009). A methodological approach to identify taxon-specific change points along environmental gradients was developed by Baker and King (2010). "
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    ABSTRACT: Freshwater organisms face numerous stressors, such as nutrient enrichment, contaminant pollution, sedimentation and alterations in stream hydrology and habitat structure. One of the most significant and widespread stressors in European freshwaters is expected to be water pollution from intensive land use. However, the information on critical threshold concentrations at which taxa decline or increase in frequency and abundance is missing for the large majority of river benthic invertebrate taxa. The main aim was to determine ecological change points for benthic invertebrate taxa at which rapid alterations in species frequency and abundance occur as a consequence of relatively small changes in the environmental gradient. These change points can be interpreted as critical threshold concentrations. A total of 468 river benthic invertebrate taxa and nine physico-chemical variables describing the daytime dissolved oxygen, chloride, nutrient concentrations and organic load were analyzed. We selected 751 river sites from a nationwide range of locations in Germany for this investigation. Depending on the physico-chemical variable, between 20.6% and 48.8% of the total number of tested taxa were assigned with a valid change point. All taxa were assigned to negative or positive response groups depending on the response direction. Except for daytime dissolved oxygen, negative responding taxa are referred to as decreasers and positive responding taxa as increasers, respectively. In total, 25.8–100% of the decreasers’ change points were below (and above in the case of daytime dissolved oxygen) the background values defined as quality criteria for German rivers by the water authorities. This indicates that stricter quality criteria may need to be set to reach the good ecological status according to the European Water Framework Directive. The calculated daytime dissolved oxygen change points were essentially in line with the species saprobic values and taxon-specific change points for physico-chemical variables fit well with the data provided in other international studies. We deliver valuable knowledge about the sensitivities and response schemes of river benthic invertebrate species. This information is especially useful for the development of efficient management and policy tools to predict the likelihood of occurrence of individual species under different levels of anthropogenic impact.
    Ecological Indicators 10/2015; 57:314-323. DOI:10.1016/j.ecolind.2015.04.043 · 3.44 Impact Factor
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    • "that we are passing 'tipping' points and exceeding ecological thresholds (Grebmeier et al. 2006, Wassmann et al. 2008, and Andersen et al 2009). In this new state, physical, chemical, and biological linkages and feedbacks within the ocean-ice-atmosphere system are to a large extent unknown. "
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    ABSTRACT: ART) is a proposed integrative, multi-disciplinary, long-term pan-Arctic program to study changes and feedbacks with respect to physical characteristics and biogeochemical cycles of the Arctic Ocean and its biological productive capacity.
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    • "Trees of different sizes and canopy status compete differently for water and light (Orwig and Abrams, 1997), particularly when growth becomes limited by these resources (Tilman, 1988). Thus, trees may have different growth responses to climate, depending on the stand structural attributes (Andersen et al., 2008). It is known that changes in stand structure, climate and local site conditions alter tree growth and, as a result, forest dynamics (Lebourgeois et al., 2014). "
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    ABSTRACT: Understanding the relative contributions of competition and climate on individual tree growth is critical to project realistic forest dynamics under projected climate scenarios. Furthermore, present competition levels may reflect legacies of past use. Here, we analyze the effects of climate, site conditions and competition on radial growth in three Scots pine stands located along an altitudinal gradient in central Spain. Current stand structure and retrospective analyses of radial growth (basal area increment, BAI) were used to model changes in tree growth as a function of a spatially-explicit competition index (CI) and climate. Linear mixed-effects models were employed to model BAI and to quantify the growth responses to climate of trees under low and high competition levels. Competition effects on growth were steady over time regardless of tree age. High competition levels negatively affected growth since negative exponential functions characterized the CI–BAI relationships. Tree growth sensitivity to climate increased with decreasing competition intensity. Growth at high elevations was mainly limited by low winter temperatures , whereas warm spring enhanced growth at middle elevations and warm late summer temperatures constrained growth at low elevation. Growth responsiveness to climate is enhanced under low competition levels. Overall, current competition is a more relevant driver of recent growth than climate. Proactive forest management should be adopted to reduce the vulnerability of Scots pine forests currently subjected to higher competition levels and warmer and drier conditions.
    Forest Ecology and Management 09/2015; 358:12-25. DOI:10.1016/j.foreco.2015.08.034 · 2.66 Impact Factor
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