AOBPreview originally published online on April 13, 2006
Annals of Botany 2006 97(6):1055-1062; doi:10.1093/aob/mcl052
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Demography of the Invasive Geophyte Oxalis pes-caprae Across a Mediterranean Island
1 CREAF (Center for Ecological Research and Forestry Applications) and Unit of Ecology, Department of Animal and Plant Biology and Ecology, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Barcelona, Spain and 2 Institut Mediterrani d'Estudis Avançats (CSIC-UIB), University of the Balearic Islands, Miquel Marquès, 21, 07190 Esporles (Mallorca), Spain
* For correspondence. E-mail montse.vila{at}uab.es
Received: 8 November 2005 Returned for revision: 13 December 2005 Accepted: 31 January 2006 Published electronically: 13 April 2006
• Background and Aims Success during the early stages of the life-history of alien plants is essential for invasion to occur. The reproductive components of plant invaders have mostly been studied in species reproducing sexually but little is known about invaders that depend exclusively on vegetative reproduction. In this paper, the importance of the different recruitment stages on population growth is quantified and, thus, the invasion potential of the South African annual geophyte Oxalis pes-caprae invading Mediterranean ecosystems is assessed.
• Methods Tests and experiments were conducted across Menorca (Balearic Islands) to analyse the spatial variability of Oxalis pes-caprae reproductive components (i.e. bulb production, bulb bank, bulb predation, bulb mortality, bulb dormancy, bulb germination, plant establishment and survival).
• Key Results Oxalis pes-caprae has a transient bulb bank that remains dormant in the soil during summer. High levels of bulb predation after dispersal, followed by bulb mortality during summer or a failure to germinate in autumn were the most critical factors limiting plant establishment. Bulb germination was high. However, plant establishment and bulb production is constrained by intraspecific competition, but is not affected by soil disturbance. No symptoms of spatial discordance could be found between recruitment stages because the spatial variability of the life cycle was extremely low at all the scales examined (i.e. among populations, habitats and microsites). It was estimated that, on average, 4 % of bulbs can become plants the following year and the field rate of population increase (
) to be 0·08.
• Conclusions The results suggest that invasion is constrained by post-dispersal bulb predation, loss of viability of the propagule bank due to summer drought and high intraspecific competition. However, a high spatial concordance between recruitment stages and probably a high propagule pressure due to human and livestock bulb dispersal determine the success of this invader across Menorca Island.
Key words: Alien plant, asexual reproduction, Bermuda butter-cup (soursob), bulb production, disturbance, geophyte, Menorca Island, microsite, Oxalis pes-caprae, post-dispersal bulb predation, plant establishment and survival
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