Determinants of plant species invasions in an arid island: evidence from Socotra Island (Yemen) Ali S. Senan • Federico Tomasetto • Alessio Farcomeni • Rayasamuda K. Somashekar • Fabio Attorre Received: 17 March 2012 / Accepted: 6 July 2012 / Published online: 15 July 2012 Ó Springer Science+Business Media B.V. 2012 Abstract Understanding the factors which affect the distribution of alien plants in arid islands is compli- cated by the complex and stochastic nature of the invasion process per se, the harsh environmental conditions, and the low number of researchers and sampling effort. We present the results of the most comprehensive inventory to date of alien vascular plant species occurring in Socotra Island, a global biodiversity hotspot just beginning to be developed. A floristic survey was conducted between 2006 and 2008 in 36 grid cells of 10 9 10 km. We integrated this data from this survey with those from scientific literature. We recorded 88 alien plant species. Tree and herbaceous species were the most common growth forms. Species from Asia and edible species were prevalent. We identified 80 species considered weeds worldwide with[ 50 % adapted to arid conditions. We used a two-part model to analyze the spatial distribu- tion of naturalized and alien plant species in relation to environmental and anthropogenic factors. Altitude and human-related factors play a significant role in the distribution of both naturalized and invasive species. Notably, the latter can potentially spread mainly in the alluvial basal areas. This study underpins the knowl- edge about alien species and their spatial distribution in Socotra Island. It provides a baseline for plant invasion management and contributes data for the analyses of invasion processes on islands worldwide. Keywords Alien plants Á Invasion Á Islands Á Naturalization Á Species distribution models Á Weeds Introduction Invasive alien plant species (IAPs) are widely recog- nized as one of the major threats to native biodiversity, particularly on oceanic islands (Denslow et al. 2009; Kueffer et al. 2010). Islands may be vulnerable to biologic invasion for two main reasons. The first may be related to the geographic and historic isolation (Denslow 2003). This has led to the low diversity of resident biota, which is relatively less competitive because of the limited biotic interaction and adaptation Electronic supplementary material The online version of this article (doi:10.1007/s11258-012-0098-1) contains supplementary material, which is available to authorized users. A. S. Senan Á R. K. Somashekar Department of Environmental Science, Bangalore University, Bangalore, India F. Tomasetto Bio-Protection Research Centre, Lincoln University, Lincoln, New Zealand A. Farcomeni Department of Public Health and Infectious Diseases, Sapienza University of Rome, Rome, Italy F. Attorre (&) Department of Environmental Biology, Sapienza University of Rome, P.le A. Moro 5, 00185 Rome, Italy e-mail: fabio.attorre@uniroma1.it 123 Plant Ecol (2012) 213:1381–1392 DOI 10.1007/s11258-012-0098-1