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Keywords:

  • evolution;
  • history;
  • inbreeding;
  • invasion;
  • invasive plants;
  • pampas grass

Summary

  • 1
     The expansion histories of two South American species of Cortaderia, similar in morphology but differing profoundly in their breeding systems, were compared in California, USA.
  • 2
     Both species were introduced to California in the mid-1800s, but herbarium records indicate that the sexual C. selloana has expanded spatially at twice the rate of the asexual C. jubata.
  • 3
     The invasiveness of C. selloana has increased over time, whereas that of C. jubata has remained relatively constant. Populations of C. selloana now occupy more vegetation types and more non-ruderal habitats than C. jubata.
  • 4
     Populations of C. selloana have experienced directional morphological change, whereas the morphology of C. jubata has been constant over the 90 years for which preserved specimens are available.
  • 5
     The invasion of an alien species appears to be a malleable process, rather than a singular event. Species traits, such as inbreeding, can be advantageous at some stages but disadvantageous at others. Alien species also adjust over time to the novel and diverse selective regimes that they encounter as they expand spatially. Sexual species may have a greater ability to adjust to diverse selective landscapes relative to asexual species.