Abstract
Little is known about how an introduced species may expand its ecological range, i.e. the set of local environmental conditions in which it can successfully establish populations. Delimiting this range of conditions is a methodological challenge, because it is impossible to sample all potential field locations for any species in a given region. Developing approaches to track ecological range over time could substantially contribute to understanding invasion dynamics. In this study, we use a previously established sampling strategy to document apparent changes across a 15-year time interval in the ecological range of the Asian annual Polygonum cespitosum Blume in northeastern North America, where the species has recently become invasive. Using a structured sample drawn from a large set of field populations, we determined the range of light, soil moisture and soil nutrient conditions that the species currently occupies in this region and the proportional distribution of individuals in differing types of microsite, and compared them with field measurements that were similarly determined 15 years earlier. Although in 1994 the species was absent from both high-light and flooded habitats, in 2009 P. cespitosum occurred in open as well as shaded habitats, across a wide range of moisture conditions. In 2009 the species also occupied a greater proportion of high-light microsites within field sites than in 1994. These findings suggest an expanded ecological range that, intriguingly, is consistent with the recent evolution in North American P. cespitosum populations of adaptive plasticity in response to high light. Possible non-evolutionary explanations for the change in field distribution are also considered.
Highlights
A non-indigenous species’ transition from introduced to invasive is usually marked by the onset of aggressive range expansion (Theoharides and Dukes 2007; Valery et al 2008)
A study of comparable multi-population field datasets indicates that in the 15 years between 1994 and 2009, the introduced Asian annual P. cespitosum measurably expanded its ecological range in northeastern North America
The newly colonized high-light habitats span the range of moisture environments inhabited by P. cespitosum
Summary
A non-indigenous species’ transition from introduced to invasive is usually marked by the onset of aggressive range expansion (Theoharides and Dukes 2007; Valery et al 2008). Despite the abundance of research documenting geographic range expansion in introduced species, little is known about how an introduced species may expand its ecological range, i.e. the Published by Oxford University Press on behalf of the Annals of Botany Company.
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