Abstract
Nitellopsis obtusa (starry stonewort) is a dioecious green alga native to Europe and Asia that has emerged as an aquatic invasive species in North America. Nitellopsis obtusa is rare across large portions of its native range, but has spread rapidly in northern-tier lakes in the United States, where it can interfere with recreation and may displace native species. Little is known about the invasion ecology of N. obtusa, making it difficult to forecast future expansion. Using ecological niche modeling we investigated environmental variables associated with invasion risk. We used species records, climate data, and remotely sensed environmental variables to characterize the species’ multidimensional distribution. We found that N. obtusa is exploiting novel ecological niche space in its introduced range, which may help explain its invasiveness. While the fundamental niche of N. obtusa may be stable, there appears to have been a shift in its realized niche associated with invasion in North America. Large portions of the United States are predicted to constitute highly suitable habitat for N. obtusa. Our results can inform early detection and rapid response efforts targeting N. obtusa and provide testable estimates of the physiological tolerances of this species as a baseline for future empirical research.
Highlights
A recent example of a largely rare native species becoming an aggressive invasive species is the spread of Nitellopsis obtusa
In our niche model of N. obtusa, we focused on scenopoetic variables, defined as those abiotic environmental variables not consumed by the species and for which there is no competition among species[28,29]
We identified 2,255 occurrences for N. obtusa distributed across France (n = 1), Switzerland (1), the United Kingdom (5), Germany (7), Japan (46), Sweden (116), and the Netherlands (1,776), as well as the United States (US) (303; Supplementary Material S1)
Summary
A recent example of a largely rare native species becoming an aggressive invasive species is the spread of Nitellopsis obtusa Nitellopsis obtusa is of increasing concern in the Great Lakes region of North America It appears to spread readily via human-assisted movement of fragments and bulbils (only males have been found in North America to date, precluding sexual reproduction), with occurrences associated with boat accesses and high-use areas[17]. Where it invades, N. obtusa can spread rapidly, grow tall and dense, and form surface mats, interfering with boating and recreation and potentially displacing native plant species[17,24]. To estimate physiological tolerances (goal 4), we employed the binary ecological niche model and occurrence records as “masks” (i.e., spatial limits) to extract maximum and minimum values of climatic variables, and additional scenopoetic variables extracted from finer-scale, remotely sensed environmental data (Fig. 1)
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