A comparison of univariate and multivariate methods for analyzing clinal variation in an invasive species

Abstract

The evolution of clinal variation has become a topic widely studied for invasive species. Most studies of this kind have found significant correlations between latitude and various plant traits, usually using univariate analytic methods. However, plants are composed of multiple, interacting traits, and it is this correlation among traits that can affect how quickly or even whether the populations of invasive plants adapt to their local climatic conditions. We used data from a common garden experiment to determine the possible formation of latitudinal clines in invasive North American populations of Lythrum salicaria L. (purple loosestrife) from the central portion of its invasive range. Analyses were conducted using the more common univariate approach (nested and oneway ANOVAs; linear regression) on individual plant traits (e.g., time to flowering, plant height, various mass measures, and growth rate) and then a multivariate approach (principle components analysis followed by redundancy analysis). Significant among-population differences (P \ 0.01) were noted when using both the nested and oneway ANOVAs, and multivariate techniques. However, there were no significant relationships between individual plants traits to latitude when using linear regressions, most likely as a result of the small number of populations used in the study (n = 4). On the contrary, the multivariate analyses showed a significant effect of latitude (P \ 0.001) on the invasive populations, but this explained only 4% of the variance; latitude explained 8% of the variance when both invasive and native populations were analyzed. Because of the integrated nature of plant phenotypes, a multivariate approach should provide a clearer and deeper understanding of population responses to changing conditions than univariate techniques.

Latitudinal trait variation and responses to drought in Arabidopsis lyrata

“…Plants from the north grew to a larger size and were more likely to switch to flowering. the latter result agrees with a pattern observed in other studies, that reproductive development is the one trait that is consistently slower at low latitude in herbaceous plant and grass species (etterson 2004;griffith and Watson 2005;De Frenne et al 2011;edwards et al 2011;Woods et al 2012;novy et al 2013). two Arabidopsis species may be exceptions.…”

“…studies comparing populations from different latitudes in common environments observe that phenological, physiological, morphological, and life history traits can correlate with latitude. In herbaceous plant and grass species, the most consistent variation occurs in reproductive development: plants from lower compared to higher latitudes often have a slower reproductive development (etterson 2004;griffith and Watson 2005;De Frenne et al 2011;edwards et al 2011;Woods et al 2012;novy et al 2013). In two Arabidopsis species, the trend is reported to be the opposite, with generally slower development in northern populations (stinchcombe et al 2004; riihimäki et al 2005).…”

Preface: Restoration, biogeochemistry and ecological services of wetlands

“…The correlation among these traits can affect how quickly or even whether populations of invasive plants adapt to their local climatic conditions. It has been shown that multivariate techniques represent a more useful approach when investigating the formation of latitudinal clines in invasive populations of Lythrum salicaria (purple loosestrife) than using univariate methods alone (Edwards et al, 2011).…”