Abstract
Starry stonewort (Nitellopsis obtusa) is an alga that has emerged as an aquatic invasive species of concern in the United States. Where established, starry stonewort can interfere with recreational uses of water bodies and potentially have ecological impacts. Incipient invasion of starry stonewort in Minnesota provides an opportunity to predict future expansion in order to target early detection and strategic management. We used ecological niche models to identify suitable areas for starry stonewort in Minnesota based on global occurrence records and present-day and future climate conditions. We assessed sensitivity of forecasts to different parameters, using four emission scenarios (i.e., RCP 2.6, RCP 4.5, RCP 6, and RCP 8.5) from five future climate models (i.e., CCSM, GISS, IPSL, MIROC, and MRI). From our niche model analyses, we found that (i) occurrences from the entire range, instead of occurrences restricted to the invaded range, provide more informed models; (ii) default settings in Maxent did not provide the best model; (iii) the model calibration area and its background samples impact model performance; (iv) model projections to future climate conditions should be restricted to analogous environments; and (v) forecasts in future climate conditions should include different future climate models and model calibration areas to better capture uncertainty in forecasts. Under present climate, the most suitable areas for starry stonewort are predicted to be found in central and southeastern Minnesota. In the future, suitable areas for starry stonewort are predicted to shift in geographic range under some future climate models and to shrink under others, with most permutations indicating a net decrease of the species’ suitable range. Our suitability maps can serve to design short-term plans for surveillance and education, while future climate models suggest a plausible reduction of starry stonewort spread in the long-term if the trends in climate warming remain.
Highlights
Starry stonewort (Nitellopsis obtusa, Characeae) is a species of concern for both its endangered status and its invasive status
Our evaluations revealed that 10,000 background points provided good model fit and performance for the three model calibration regions explored
Logistic suitability values of starry stonewort models based on Mg vs. Mi were significantly different (t = 1098, df = 544500, p < 0.001), with higher suitability predicted when Mg was considered (Fig 3)
Summary
Starry stonewort (Nitellopsis obtusa, Characeae) is a species of concern for both its endangered status (in parts of its native range in Europe and Asia) and its invasive status (in North America). In North America, female individuals of this species have not been detected to date [2]. It has a higher ecological plasticity than other charophytes [1,3]. Starry stonewort can grow densely, which may lead to displacement of native aquatic plant species and could have consequences for habitat quality [2]. Populations of starry stonewort in their native distribution in Europe and Japan have been declining [5,6,7], the species has shown great capacity to spread as an aquatic invasive species in North America [3,8,9]
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