Species attributes and invasion success by alien plants on Mediterranean islands

Abstract

Summary1 Species attributes have been used to explain invasion patterns assuming the prevalence of biological mechanisms, although this approach often suffers several methodological and conceptual limitations, such as local idiosyncrasies, differences among habitats, phylogenetic constraints and insufficient sample size. 2 The relative importance of 15 species traits for explaining the abundance over 350 naturalized alien plant species was assessed across five Mediterranean islands (Corsica, Crete, Majorca, Malta and Sardinia). A comparative analysis accounting for phylogeny was used to examine variation in semi-quantitative estimates of species abundance in comparable habitats across the five island floras. 3 Species were divided into those with affinity for semi-natural, agricultural and ruderal habitats. Both vegetative and reproductive attributes were evaluated for individual islands and averaged across all islands. 4 Vegetative propagation, large leaf size, summer flowering, long flowering period and dispersal by wind or vertebrates were positively associated with average alien abundance across all five islands. Fewer significant trends were found in island-specific patterns. 5 The relative importance of a few reproductive traits is reflected in over-representation of Caryophyllales, Asterales and Poales (late flowering, large seed size and anemochory). Although significant covariation in traits was found there was no evidence for welldefined invasive syndromes. 6 Succulence was important in ruderal habitats, long flowering period in agricultural habitats and vertebrate seed dispersal in semi-natural habitats, suggesting that empty niches, avoidance of competitors and exploitation of mutualists, respectively, are important. 7 The study highlights the importance of estimating invasion success across a wide region, but analyses of specific invasion stages are also needed. Reproductive traits, which may be more relevant for long-distance colonization, and vegetative traits, which determine local dominance and persistence, were, nevertheless, both related to abundance within islands.

The response of plant community diversity to alien invasion: evidence from a sand dune time series

“…Among perennials, geophytes such as A. psilostachya and S. versicolor grow more slowly and propagate mostly by way of below-ground organs. Although vegetative propagation does not guarantee long-distance spread, it ensures rapid establishment and maintenance within suitable habitats, and successful exclusion of any possible competition (Lloret et al 2005). Numerical supremacy and the frequency of herbaceous aliens, both within the plots and along the time series, testify to their successful strategy which, on the other hand, is that of native species.…”

“…Efforts to explain the ecological effects of invader species have primarily focussed on their functional attributes (and how they differ from those of the resident species) and their abundance (Lloret et al 2005;Stanisci et al 2010;Vitousek 1990) or, on the habitat properties responsible for inherent vulnerability to invasion, i.e. invasibility (Chytrý et al 2008b;Davis et al 2000;Rejmánek et al 2005).…”

Reproductive phenological pattern of Calotropis procera (Apocynaceae), an invasive species in Brazil: annual in native areas; continuous in invaded areas of caatinga

“…Nevertheless, none of those studies registered any species with continuous flowering, as observed for C. procera. Long flowering periods were found to be an important attribute for invasive species in Canada (Goodwin et al 1999) and in the Mediterranean, because they increased the chances of reproductive success (Lloret et al 2005). This is an advantage over native species that exhibit seasonal flowering and strong competition for pollinators.…”

“…In addition to the changes in the reproductive phenological pattern, C. procera showed a suite of traits that are associated with invasiveness in tropical ecosystems, such as large leaves (e.g., Lloret et al 2005), wind-dispersed seeds (e.g., Lake & Leishman 2004), hermaphrodite flowers (e.g., Reichard & Hamilton 1997), and attractiveness to humans (e.g., Cox 2004), initially as an ornamental and currently as a forage plant. The presence of all those life history attributes, combined with the observed reproductive phenological changes, might have facilitated the success of C. procera in the invasion process and reveal its potential to invade other ecosystems in the world.…”

Linking vegetation patterns to environmental gradients and human impacts in a mediterranean-type island ecosystem

“…Unfortunately, islands in the mediterranean-type climates of the world tend to be located near dense human populations, and so much of the scholarship surrounding mediterranean-type islands has focused on invasion ecology (e.g. Lloret et al 2005) or the conservation of rare or endangered island endemics (e.g. Morrison et al 2011).…”