Abstract
Intraspecific variation can have a major impact on plant community composition yet there is little information available on the extent that such variation by an already established species affects interspecific interactions of an invading species. The current research examined the competitiveness of clones of a globally rare but locally common native grass, Calamagrostis porteri ssp. insperata to invasion by Alliaria petiolata, a non-native invasive species. A greenhouse experiment was conducted twice over consecutive years in which 15 clones from three populations of Calamagrostis were paired with rosettes of Alliaria in pots containing native forest soil previously uninvaded by Alliaria. Both species showed a negative response to the presence of the other species, although Alliaria more so than Calamagrostis. Moreover, the effect of Calamagrostis depended upon population, and, to a lesser extent, the individual clone paired with Alliaria. Competitive effects were stronger in the first experiment compared with when the experiment was repeated in the second year. The influence of Calamagrostis clones on the outcome of the experiment varied among populations and among clones, but also between years. Clones from one of the three populations were more influential than clones from the other two populations. Only one of 15 clones, both from the same population, was influential in both experiments. This research supports a growing literature indicating that intraspecific variability among clones of a dominant species can affect interspecific interactions and that such variability in a native species can affect performance of an invading species.
Highlights
Understanding the importance of individual variation on population and community dynamics, and the upscaling of processes at the level of individuals to population scale patterns are key ecological challenges (Sutherland et al 2013)
Calamagrostis porteri ssp. insperata (Poaceae) is a coolseason, loosely clumped, perennial grass limited in its global distribution to approximately 80 populations in five US states where it is considered endangered in Arkansas, Illinois, Kentucky, Maryland, Ohio, and Tennessee, threatened in Indiana
Regardless of whether plants were competing with Alliaria or not, Calamagrostis clones and populations grew significantly different to each other in both years of the experiment (Table 1)
Summary
Understanding the importance of individual variation on population and community dynamics, and the upscaling of processes at the level of individuals to population scale patterns are key ecological challenges (Sutherland et al 2013) In this vein, intraspecific variation among competing neighbors is known to affect species diversity in plant communities (Booth and Grime 2003; Vellend 2006; Gibson et al 2012). A consequence of these interactions is that potential niche space availability may vary depending upon the presence or number of certain genotypes of dominant species in the community. These dominant species are those that make a substantial contribution to plant biomass in a community by virtue of their large relative size and high frequency of occurrence. If a dominant species in the community exhibits ecologically relevant intraspecific variability, the opportunity for establishment of a new species in a community may depend upon the particular genotypes of the dominant species that are present (Crutsinger et al 2010; Adams et al 2011)
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