Invasive Species in Native and Non-native Ranges

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Studying germination in the native and non-native range of a species can provide unique insights into processes of range expansion and adaptation; however, traits related to germination have rarely been compared between native and nonnative populations. In a series of common garden experiments, we explored whether differences in the seasonality of precipitation, specifically, summer drought vs summer rain, and the amount and variation of annual and seasonal precipitation affect the germination responses of populations of an annual ruderal plant, Centaurea solstitialis, from its native range and from two non-native regions with different climates. We found that seeds from all native populations, irrespective of the precipitation seasonality of the region in which they occurred, and non-native populations from regions with dry summers displayed similarly high germination proportions and rates. In contrast, genotypes from the non-native region with predominantly summer rain exhibited much lower germination fractions and rates and ecology. Organisms transported by humans to regions where they are not native (exotics) commonly face novel selective forces, which given enough genetic variation, may trigger novel evolutionary responses. The worldwide distribution of this species encompasses environments with contrasting precipitation regimes within both native and non-native ranges. Specifically, some of the regions where C. solstitialis grows are characterized by a Mediterranean-type climate with wet winters and dry summers, whereas other regions have a precipitation regime in which most of the precipitation falls during the summer, and winters are substantially drier. In all regions, the species germinates primarily in autumn (Sheley and Larson 1994, Hierro et al. 2006, L. Khetsuriani, L. Janoian, and K. Andonian unpubl.); thus, winter conditions may affect its survival. Here, by conducting a series of common garden experiments in a growth chamber, we investigated whether contrasting differences in the seasonality of precipitation and changes in surrogates for environmental quality (e.g. precipitation totals) and risk (e.g. inter-annual variation in precipitation) affect germination responses of C. solstitialis populations occurring across its native range and in two climatically distinct non-native regions.

To investigate the potential effects of seasonality of precipitation on C. solstitialis germination, we conducted three successive seed collections from populations occurring in regions exepte France, Crete and Armenia, where seeds were pooled within populations. Mean cumulative germination percentages (91 SE) of pappus and non-pappus seeds of C. solstitialis populations plotted against the coefficient of variation of winter precipitation and the probability of occurring a good winter.

Full article available in  Oikos 118: 529_538, 2009

doi: 10.1111/j.1600-0706.2009.17283.x,

# 2009 The Authors. Journal compilation # 2009 Oikos

Subject Editor: Pia Mutikainen. Accepted 31 October 2008

“Germination responses of an invasive species in native and non-native ranges”

Jose´ L. Hierro, O¨zkan Eren, Liana Khetsuriani, Alecu Diaconu, Katalin To¨ro¨ k, Daniel Montesinos,

Krikor Andonian, David Kikodze, Levan Janoian, Diego Villarreal, Marı´a E. Estanga-Mollica and Ragan M. Callaway

Armenia, ECRC/AUA
USA, University of Montana, University of California
Argentina, Universidad Nacional de La Pamba
Turkey, Adnan Menderes University
Georgia, Institute of Botany
Romania, Institute Of Biological Research
Hungary, Institute of Ecology and Botany