No abstract

Research on biological invasions has traditionally focused on the ecological component of invasive alien species, either without considering or by considering in a restringing way, the knowledge of the social component. Understanding the human dimension of invasions is critical to effectively tackling the problems associated with invasive species. We used questionnaires to evaluate the social perceptions and attitudes of different stakeholder groups affected by invasive alien species in the Doñana social-ecological system (SW Spain). Characteristics of respondents regarding their knowledge and attitudes toward biological invasions were categorized using hierarchical cluster and principal component analyses; while their potential support of eradication programs was assessed with a contingent valuation approach. Five stakeholder groups were recognized, differing in their degree of knowledge, perceptions, attitudes and willingness to pay for eradication. The fact that different stakeholders have remarkably different attitudes and perceptions about the impacts and benefits caused by alien invasive species should be considered in any decision-making process regarding their management, particularly for developing appropriate educational and informative programs.Public consultation with different stakeholders should also be encouraged from the beginning to avoid potential misunderstandings and to facilitate the implementation of management practices.

Based on a review and our own data, we present an overview of the ecological impacts on the trophic web of Mediterranean wetlands by an introduced Decapod Crustacean, the red swamp crayfish (Procambarus clarkii). P. clarkii lacks efficient dispersal mechanisms but is very well adapted to the ecological conditions of Mediterranean wetlands (fluctuating hydroperiods with regular intervals of drought). As an opportunistic, omnivorous species, which adapts its ecology and life history characteristics, such as timing and size at reproduction to changing environmental conditions, it became readily established in most of the Mediterranean wetland environments. High reproductive output, short development time and a flexible feeding strategy are responsible for its success as an invader. Like most crayfish, it occupies a keystone position in the trophic web of the invaded system and interacts strongly with various trophic levels. It efficiently grazes on macrophytes and is one of the main factors, besides the impact of flamingos, cattle and introduced fish, of the change of many water bodies from a macrophyte dominated, clear water equilibrium to a phytoplankton driven turbid water balance. Juveniles feed on protein rich animal food with the corresponding impact on the macroinvertebrate community in competition with other crayfish or fish species. At the same time, it serves as a prey for mammals, birds and fish. Due to its predatory and grazing activity, it efficiently canalises energy pathways reducing food web complexity and structure. Feeding also on detritus it opens, especially in marshlands, the detritic food chain to higher trophic levels which results in an increase of crayfish predators. As a vector of diseases, it has a severe impact on the preservation and reintroduction of native crayfish. P. clarkii accumulates heavy metals and other pollutants in its organs and body tissues and transmits them to higher trophic levels. Due to the long history of its presence, the complex interactions it established within the invaded ecosystems and the socio-economic benefits it provides to humans, prevention and control seem the most promising management measures to reduce the negative impact of this crayfish species. Biological Invasions (2005) 7: 49-73 Ó Springer 2005 ) High fecundity ++ Short generation and juvenile development times ++ Fast adaptation to environmental stress +++ High tolerance to environmental heterogeneity +++ Desirability to and association with humans (edibility, game species) +++ Additional features Omnivory +++ Brood care +++

Many of the world's wetlands may be profoundly affected by climate change over the coming decades. Although wetland managers may have little control over the causes of climate change, they can help to counteract its effects through local measures. This is because direct anthropogenic impacts, such as water extraction and nutrient loading, work in concert with climate change to damage wetlands. Control of these local stressors may therefore ameliorate undesired effects of climate change, such as a shift towards dominance by invasive floating plants, increasingly frequent cyanobacteria blooms, or extinction of key species. Using the iconic Doñana wetlands in Spain as a case study, we illustrate how the concept of creating a "safe operating space" may be implemented to better ensure that ecosystems do not surpass thresholds for collapse during an era of global change.