Global Change Ecology


, Volume 142, Issue 3, pp 474-479

First online:

Evidence for the enemy release hypothesis in Hypericum perforatum

  • Montserrat VilàAffiliated withCentre de Recerca Ecològica i Aplicacions Forestals, Universitat Autònoma de Barcelona Email author 
  • , John L. MaronAffiliated withDivision of Biological Sciences, University of Montana
  • , Laia MarcoAffiliated withCentre de Recerca Ecològica i Aplicacions Forestals, Universitat Autònoma de Barcelona

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The enemy release hypothesis (ERH), which has been the theoretical basis for classic biological control, predicts that the success of invaders in the introduced range is due to their release from co-evolved natural enemies (i.e. herbivores, pathogens and predators) left behind in the native range. We tested this prediction by comparing herbivore pressure on native European and introduced North American populations of Hypericum perforatum (St John’s Wort). We found that introduced populations occur at larger densities, are less damaged by insect herbivory and suffer less mortality than populations in the native range. However, overall population size was not significantly different between ranges. Moreover, on average plants were significantly smaller in the introduced range than in the native range. Our survey supports the contention that plants from the introduced range experience less herbivore damage than plants from the native range. While this may lead to denser populations, it does not result in larger plant size in the introduced versus native range as postulated by the ERH.


Biological control Herbivory Plant invasions Natural enemies hypothesis St John’s Wort