Ecological Indicators 15 (2012) 76–84 Contents lists available at SciVerse ScienceDirect Ecological Indicators jo ur n al homep ag e: www.elsevier.com/locate/ecolind Plant community changes as ecological indicator of seabird colonies’ impacts on Mediterranean Islands Teddy Baumberger ∗ , Laurence Affre, Franck Torre, Eric Vidal, Pierre-Jean Dumas, Thierry Tatoni Institut Méditerranéen d’Ecologie et de Paléoécologie UMR 6116, Université Paul Cézanne, Aix-Marseille III, Faculté des Sciences et Techniques de Saint Jérôme, Case 421, F-13397 Marseille Cedex 20, France a r t i c l e i n f o Article history: Received 11 February 2011 Received in revised form 17 June 2011 Accepted 14 September 2011 Keywords: Diachronic Fine-scale study Urbanization Plant functional types GLM STATICO a b s t r a c t The aim of this study is to investigate vegetation changes on small Mediterranean islands under the impact of the drastic expansion of the gull colony, at local scale over eleven years using a set of permanent plots. First, we focused on functional aspects of vegetation in addition to its specific composition with regard to the plant functional types (Raunkiaer growth forms and Grime life strategies) as indicators of vegetation changes. Second, we used STATICO analysis to investigate patterns of change in the relationship between environmental variables and floristic composition. Third, we quantified the changes in the abundance of plant functional types by applying a simple comparison test between the two observation dates. Fourth, we investigated the relationship between vegetation changes (species turnover, plant functional type dynamics, and species richness) and gull density by performing simple linear regression. Our results show that gull density did not evolve equally for all plots. For areas where gull density increased, we recorded ruderalization of the vegetation. Surprisingly, in areas where there was a decrease in gull density, no clear pattern of vegetation change was apparent. We observed a statistically significant increase in the number of plant species due only to the increase in ruderal and stress ruderal and geophyte species. Gull colonies were responsible for high species turnover between 1997 and 2008. The higher the density of gulls, the lower the species number in 1997 and 2008. For high gull nest densities, we observed a high proportion of ruderal plant species and a low proportion of stress tolerant species. Gulls induced an increase of stress-ruderal species. We show that nest density recorded in 1997 is mainly responsible for the changes in vegetation composition, species turnover and proportions of plant functional types. We noted that a decrease in gull nest density does not necessarily induce a return to previous vegetation composition patterns. This may be seen as evidence of the inertial nature of the changes in island vegetation in the face of strong changes in environmental conditions such as the recent drastic expansion of gull colonies. Garbage management policy can have a strong and long-term impact on remote ecosystems. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction Global changes, mainly resulting from human activities, have had a strong negative impact on biodiversity (Vié et al., 2009). The Mediterranean Basin has been designated as one of the 34 world biodiversity hotspots (Mittermeier et al., 2005), because of its very high plant diversity (10% of the world’s vascular plants on 1.6% of the Earth’s surface) and endemism (50% of the total flora) (Médail and Quézel, 1997). Furthermore, the Mediterranean Basin, with thousands islands and islets (Delanoe et al., 1996), comprises one of the largest groups of islands in the world, and the flora on Mediter- ranean islands represents an important part of Mediterranean plant diversity as a whole. Even if the Mediterranean Basin has been ∗ Corresponding author. Tel.: +33 0 491288537; fax: +33 0 491288668. E-mail address: teddy.baumberger@univ-cezanne.fr (T. Baumberger). inhabited by humans since antiquity (Blondel, 2006), human activ- ities have recently reached unprecedented intensity and range, especially in the coastal areas (UNEP/MAP, 2009). However, human activities can also indirectly affect these ecosystems, especially when a biotic factor is altered (Chapin et al., 1997). The recent appearance and strong demographic expansion of seabird colonies on many Mediterranean islands, due to changes in the availability of food resulting from dumping and trawling, is a typical exam- ple of the indirect effects of human disturbances (Oro et al., 2004; Duhem et al., 2008). Seabird colonies have a very strong impact on ecosystem functioning and vegetation structure (Ellis, 2005) by affecting nutrient fluxes from marine to terrestrial ecosystems (Anderson and Polis, 1999), changing soil chemistry and vegetation productivity (García et al., 2002; Wait et al., 2005), altering plant population dynamics (Mulder and Keall, 2001; Calvi ˜ no-Cancela, 2002), improving invasion success of plant species by dispersal (Padrón et al., 2010) or by driving plant species turnover at island 1470-160X/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.ecolind.2011.09.009