Invasive plants as drivers of regime shifts: identifying high-priority invaders that alter feedback relationships

Authors

  • Mirijam Gaertner,

    Corresponding author
    1. Centre for Invasion Biology, Department of Botany and Zoology, Stellenbosch University, Matieland, South Africa
    2. Environmental Resource Management Department (ERMD), Westlake Conservation Office, Tokai, Cape Town, South Africa
    • Correspondence: Mirijam Gaertner, Centre for Invasion Biology, Department of Botany and Zoology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa.

      E-mail: gaertnem@gmail.com

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  • Reinette Biggs,

    1. Stockholm Resilience Centre, Stockholm University, Stockholm, Sweden
    2. Stellenbosch Institute for Advanced Study (STIAS), Wallenberg Research Centre at Stellenbosch University, Stellenbosch, South Africa
    3. Centre for Studies in Complexity, Stellenbosch University, Matieland, South Africa
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  • Mariska Te Beest,

    1. Department of Ecology and Environmental Science, Umeå University, Umeå, Sweden
    2. Department of Conservation Ecology and Entomology and Centre for Invasion Biology, Department of Botany and Zoology, Stellenbosch University, Matieland, South Africa
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  • Cang Hui,

    1. Centre for Invasion Biology, Department of Botany and Zoology, Stellenbosch University, Matieland, South Africa
    2. Centre for Invasion Biology, Department of Mathematical Sciences, Stellenbosch University, Matieland 7602, South Africa; African Institute for Mathematical Sciences, Muizenberg 7945, VT, South Africa
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  • Jane Molofsky,

    1. Department of Plant Biology, University of Vermont, Burlington, VT, USA
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  • David M. Richardson

    1. Centre for Invasion Biology, Department of Botany and Zoology, Stellenbosch University, Matieland, South Africa
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Abstract

Aim

A major challenge for invasion ecology is to identify high-impact invaders to guide prioritization of management interventions. We argue that species with the potential to cause regime shifts (altered states of ecosystem structure and function that are difficult or impossible to reverse) should be prioritized. These are species that modify ecosystems in ways that enhance their own persistence and suppress that of native species through reinforcing feedback processes.

Methods

Using both systems analysis and meta-analysis approaches, we synthesized changes to ecosystems caused by 173 invasive plant species. For the systems analysis, we examined published studies of impacts of invasive plants to determine which presented evidence consistent with a reinforcement of feedback processes. For the meta-analysis, we calculated the effect size ratio between standardized changes in recipient ecosystem and in the status of introduced species as an indication of a reinforcing feedback in particular species-environment combinations. The systems analysis approach allowed us to conceptualize regime shifts in invader-dominated landscapes and to estimate the likelihood of such changes occurring. The meta-analysis allowed us to quantitatively verify the conceptual model and the key invader-context feedbacks and to detect the strength and direction of feedbacks.

Results

Most reinforcing feedbacks involve impacts on soil-nutrient cycling by shrub and tree invaders in forests and herbaceous invaders in wetlands. Feedbacks resulting in regime shifts were most likely related to processes associated with seed banks, fire and nutrient cycling. Results were used to derive a key for identifying high-impact invaders.

Main conclusions

Identifying combinations of plant life-forms and ecosystems most likely to result in regime shifts is a robust approach for predicting high-impact invasions and therefore for prioritizing management interventions. The meta-analysis revealed the need for more quantitative studies, including manipulative experiments, on ecosystem feedbacks.

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