Invasion dynamics of two alien Carpobrotus (Aizoaceae) taxa on a Mediterranean island: II. Reproductive strategies.

This study compares sexually and asexually produced fruit set, seed production, biomass, germination, and seedling size in Carpobrotus acinaciformis and C. edulis following controlled pollination experiments in order to evaluate the potential role of reproductive traits with respect to the invasive potential of these taxa. C. edulis is slightly agamospermic, completely self-fertile, slightly preferentially self-compatible, experiences no inbreeding depression, and has low hybrid vigour. In contrast, C. acinaciformis does not have reliable agamospermy, is only slightly self-fertile and self-compatible, experiences a slight inbreeding depression, and has a strong hybrid vigour. Both taxa have relatively low, although significantly different germination frequencies, and insignificantly different seedling sizes. Owing to the high performance in hybridisation as compared to all other controlled pollinations in C. acinaciformis, as well as a large amount of previously demonstrated introgression, we refer to the population studied on the island of Bagaud (France) as C. affine acinaciformis. We conclude that both C. edulis and C. affine acinaciformis should be considered as harmful invasive plants in the Mediterranean Basin, the former because of the flexibility of its mating system and high seed production, and the latter because of its strong clonality, high hybrid vigour, and potential for continued introgression from C. edulis genes. These differences require different control strategies, while the avoidance of sympatry is a distinct priority.

Invasion dynamics of two alien Carpobrotus (Aizoaceae) taxa on a Mediterranean island: I. Genetic diversity and introgression.

This study, based on morphological and isozyme analysis, clearly discriminates two invasive Carpobrotus taxa, C. edulis and C. acinaciformis, in the Hyères archipelago off the southeastern coast of France. However, three different allelic combinations demonstrate the presence of intermediate individuals resulting from an introgression of part of the C. edulis genome into that of C. acinaciformis. Both taxa have higher than average genetic (C. edulis: P(0.95)=62.5%, A=2.25+/-0.70, H(o)=0.329+/-0.324; C. acinaciformis: P(0.95)=75%, A=2.38+/-0.42, H(o)=0.645+/-0.109) and clonal diversities (C. edulis: IP=0.37; C. acinaciformis: IP=0.48). Furthermore, C. acinaciformis has an excess of heterozygotes (F=-0.585+/-0.217), probably due to introgression. The relationship between the probability of clonal identity for two individuals and distance indicates that C. acinaciformis relies more on clonal reproduction than on sexual recruitment (seed recruitment/vegetative propagation=u/v=0.027), in contrast to C. edulis, whose probability of clonal identity did not vary with distance. The overwhelming clonal growth and high genetic diversities of C. acinaciformis and the previously recorded invasion potential for C. edulis raises concern for intensified invasion via hybridisation.

[Predictive value of biological species for plant conservation in the Mediterranean area]. / Valeur prédictive des types biologiques pour la conservation de la flore méditerranéenne.

The validity of Raunkiaer's biological types (or life-forms) was tested on native Corsican flora, using criteria of altitudinal distribution and rarity. The biological basis of this classification has been widely confirmed. The analysis of floras from Corsica and Provence revealed the major role played by both altitude and human impact, and also demonstrated the importance of the predictive value of life-forms to plant conservation. In Southeastern France, there are no clear proportional relationships between rarity and extinction percentages. With increasing levels of human activity, rarity percentages are seen to increase for nearly all types. Conversely, extinction percentages exhibit a clear progression only for the most threatened life-forms: bulb and tuber geophytes, therophytes, parasites and especially hydrophytes. Thus, priority should be given to the protection of these 4 herbaceous types, which are found at low altitudes and lack visible vegetative organs during the unfavourable season.

Seabirds drive plant species turnover on small Mediterranean islands at the expense of native taxa.

The analysis of long-term floristic changes was conducted on nine west-Mediterranean limestone islands (size range: 2-95 ha) which have recently undergone a severe demographic explosion in their yellow-legged gull Larus cachinnans colonies. A comparison of past and present plant inventories was used to quantify extinction-colonization events, both from a classical biogeographical perspective (per island approach) and a metapopulational perspective (per species approach). In the first approach, floristic turnover intensity was negatively related to island area and positively to gull nesting density, but was independent of island isolation. In the second, species turnover rate was compared with a set of plant species life history traits (dispersal mode, Grime CSR strategy, growth form, biogeographical type). Plants which exhibited the highest turnover rate were primarily ruderal, annual, wind-dispersed species with a wide geographic range. The severe disturbance induced by seabird activities has tended to select and favour some adapted plant species groups at the expense of indigenous island taxa. The relationships between specific turnover intensity and plant life history traits justify using the metapopulation approach and point to the importance of interspecific variations in extinction-colonization patterns.