Gaertner, M., Biggs, R., Te Beest, M., Hui, C., Molofsky, J. and Richardson, D.M. (2014), Invasive plants as drivers of regime shifts: identifying high-priority invaders that alter feedback relationships. Diversity Distrib., 20: 733-744. https://doi-org.colorado.idm.oclc.org/10.1111/ddi.12182
Regime shifts are defined here as large, abrupt shifts in the structure and function of an ecosystem and are caused by the change in and/or new introduction of feedback mechanisms - internal shifts in the system that bring the system closer or farther away from a steady state. Some invasive species cause small, community-level changes while other invaders cause large ecosystem-level changes through positive reinforcement mechanisms that enhance the invader’s dominance over native species. Gaertner and colleagues argue that invasive species that have the potential to cause ecosystem-level changes should be prioritized in management practices. A systematic literature review and a quantitative meta-analysis (calculating effect size ratio) were used to compile a list of 173 invasive species, from 443 studies, that have potential to cause ecosystem-level changes. From this analysis, 5 types of reinforcing feedbacks that sustain invasions were identified as changes in: 1) seed bank composition; 2) fire regime; 3) soil nutrients; 4) litter quantity and/or quality; and 5) soil biota structure and function. These mechanisms increase the competitive ability of the invaders and out of the 5, the soil–nutrient feedback seems to be the most prevalent and seed-bank-composition and litter feedbacks were less common. It was also found that invasive species were more commonly associated with a single reinforcing feedback rather than multiple. Lastly, Gaertner and colleagues found variation in effect size ratios across specific combinations of invaders and landscapes. Grass invaders in forests—which lead to altered fire regimes and soil-nutrient-structures—were found to have the highest degree of ecosystem alteration with positive feedback favoring the invasive species. Overall, identifying and prioritizing high-risk invaders that have the potential to cause regime shifts by using the framework outlined in this study could prove beneficial for management of ecosystems, especially in grass-invaded areas where the effect on native ecosystems was found to be the highest.
Take Home Points:
- Invasions can cause large regime shifts of an ecosystem through positive feedback mechanisms which sustain the invader’s dominance over native species.
- Grass invasions in forest ecosystems, which alter fire regimes and the soil-nutrient feedbacks, have the highest potential to cause large ecosystem regime shifts.
- To improve management efficiency, invasive species that have the potential to cause regime shifts should be prioritized so that valuable resources aren’t being used on invasives that cause little to no impact on the ecosystem.
- Invasions are “sticky”, meaning that once the feedback mechanisms are altered, the invasives can persist in the ecosystem even after the initial drivers are eliminated, which further demonstrates the urgency to prioritize invasive species with high potential for alteration.