Ecological and evolutionary theories suggest different mechanisms of invasion success. We investigate phenotypic changes that distinguish successful invaders from native range con-specifics in the invasive weed, Centaurea diffusa. We examine phenotypic differences between populations from the native and invaded ranges, using common garden experiments. We also test for resource allocation trade-offs by comparing growth rate and fecundity in the presence of experimentally applied stresses. Results will indicate whether invasive populations of C. diffusa have higher growth rates than native populations, and if growth rate is correlated with stress tolerance. Previous work in many invasive species has been limited by the use of a single common garden in the invasive range, limited population sampling, and by the influence of maternal effects. We therefore conducted multiple common gardens to look at early life history differences between native and invasive C. diffusa. These include a greenhouse common garden using field collected seed from 50 populations across the native and invasive range, a smaller greenhouse common garden using greenhouse produced seed to control for maternal effects, and a field common garden conducted in the naturalized range of C. diffusa.
Data from all three common gardens experiments indicate that invasive individuals grow larger and/or have higher fitness than individuals from the native range across all three experimental environments, including a field experiment in the naturalized range of the species. The field experiment in particular demonstrates that phenotypic differences are also found when experiments are replicated in the non-invasive range, with a more realistic environment. This will allow interpretation of genetic differences found between the native and invaded ranges (in previous and ongoing genetic analyses). This consistent phenotypic divergence between the native and invasive ranges could indicate evolved differences which have allowed for invasion success in this species.