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Although one of the most evident effects of biological invasions is the loss of native taxonomic diversity, contrasting views exist on the consequences of biological invasions on native functional diversity. We investigated this topic using Mediterranean stream, river and canal fish communities as a test case, at 3734 sites in Italy, and distinguishing between exotic and translocated species invasion in three different faunal districts. Our results clearly confirmed that introduced species were widespread and in many cases the invasion was severe (130 communities were completely composed by introduced species). Exotic and translocated fish species had substantially different geographical distribution patterns, perhaps arising from their differences in introduction timing, spread and invasion mechanisms. We also found a clear decreasing trend of functional dispersion along an invasion gradient, confirming our hypothesis that the invasion process can diminish the relative diversity of ecofunctional traits of host fish communities. Furthermore, our results suggested that exotic species might have a greater negative effect than translocated species on the relative diversity of ecofunctional traits of fish communities. This could also be linked to the fact that translocated species are more ecofunctionally similar to native ones, compared to the exotics. Our multivariate analysis of site-specific combinations of ecofunctional traits highlighted some traits characteristic of all invaded communities, while our discriminant analysis underlined how there was a substantial ecofunctional overlap between native, exotic and translocated species groups in most areas.
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... Our results provide evidence that niche processes (i.e., habitat filtering and interspecific interaction) had greater effects than neutral processes on the maintenance of forest vegetation diversity across climatic regions of China. This may be mainly because the species in these communities are not functionally equivalent, and therefore, random processes may play a role at the regional scale [42]. We found that the functional diversity of cold temperate forest vegetation was higher than that of random communities, and that the functional diversity of tropical and subtropical forest vegetation tended to be divergent. ...
... We found that interspecific interactions gradually intensified from cold temperate to tropical forest communities, which may be due to the differentiation of functional traits in species during long-term evolution and phenotypic plasticity [34]. Functional trait divergence can reduce niche overlap, therefore allowing species to be more evenly distributed along resource axes [19] and improving resource utilization [42]. Our results show that the overall similarity of functional traits among all species in cold temperate forest communities was higher, which may be because the community structure of the cold temperate forest is single and the dominant species are obvious, while the functional traits in the community are determined by the species with greater abundance. ...
... In tropical and subtropical forest communities, limited similarity plays a more important role in increasing variability in community functional traits [34]. We confirmed that habitat modification only acted on the functional traits or relatedness of the species rather than the species itself [4,19,42]. ...
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Community assembly research has mostly focused on areas with single vegetation types; however, the abiotic and biotic factors affecting community assembly act across regions. Integrating biotic and abiotic factors into “compound” habitats has gained attention as an emerging strategy to analyze spatial and temporal patterns of biodiversity. We used a compound habitat approach to explore the relative roles of habitat filtering, biotic competition, and stochastic processes in the forest community assembly of four climatic zones (tropical, subtropical, temperate, and cold temperate forests). Specifically, we combined biotic and abiotic factors in four compound ecological gradients by principal component analysis (PCA), which we used to assess the geographic and phylogenetic distribution of multiple woody plant functional traits. We found that forest functional and phylogenetic diversity shifted from clustered to overdispersed along the first compound habitat gradient (PC1) across climate zones. This finding indicates that competitive exclusion strongly affected the community assembly in tropical and subtropical forests, while habitat filtering played a key role in cold temperate forests; these mechanisms may both exist and interact in temperate forests. We also found that both habitat filtering and biotic competition affected forest community assembly across climatic regions in China. Our results elucidate the underlying mechanisms driving geographical differentiation of forest vegetation across climatic zones, and bolster empirical evidence for the conservation of forest biodiversity in China. Further research is also needed to explore whether the patterns found in this paper are prevalent in different locations in different climatic zones in China.
... In many other circumstances they can comprise a relevant number of functionally unique species, which lower their redundancy and increase their sensitivity to species loss (Comte et al., 2016;Teichert et al., 2017), especially in areas affected by Pleistocene glaciations, or rich in endemisms as in the Mediterranean basin (Côte et al., 2019). It is also expected that impacted fish communities will show an increase of functional homogenization (Buisson et al., 2013;Milardi et al., 2020b;Toussaint et al., 2016), but observed or forecasted outcomes are not always straightforward in this direction and are probably scale-dependent (e.g. Shuai et al., 2018;Toussaint et al., 2018). ...
... We found no apparent detrimental effects of exotic species invasion on functional richness, rather, this pressure increased significantly SESF dis . On the other hand, studies at different scale (Matsuzaki et al., 2016) even in the same biogeographic district covered by our study Milardi et al., 2020b), suggest a significant detrimental role for this pressure on functional diversity. It is important to emphasize how: 1) the impact of exotic fish was quantified differently in the cited studies (i.e. from presence/absence and biomass averaged abundance, to individual abundance in this study), 2) metrics were partially different (i.e. ...
... Indeed, at local spatial scale, competitive interactions or resource opportunisms resulted the prevalent process increasing invasion likelihood (Carboni et al., 2013), while at large spatial scale environmental filtering (i.e. the co-occurrence of native and exotic species with similar adaptations to the prevalent environmental local conditions), propagule pressure or residence time operate additively (Ma et al., 2016). This could explain the discrepancy between the low functional niche overlap between exotic and native fish species found in the present case respect to the study by Milardi et al. (2020b), which found extensive sharing of traits when species assemblages were analyzed on a biogeographic district scale. Again, in this latter study different traits parameters were used to calculate functional indices, and a direct comparison between the results of the two studies could be misleading, since functional spaces have been defined under different criteria. ...
Article
Freshwater fish communities are impacted by multiple pressures, determining loss of functional diversity and redundancy. Our aim was to disentangle the roles and relevancies of different pressures in shaping fish communities in small streams of the Po plain (North Italy). Long term trend (1998–2018) of functional diversity of 31 fish communities was assessed and modeled in respect to three potential pressures: temperature increase, intensity of exotic fish invasion, and habitat quality degradation. Ecological traits mostly influenced by the pressures were also identified. Reduction of functional richness mostly due to local extinction or contraction of cold adapted predators, such as salmonids, was linked to increasing temperatures. Warming probably also led to a shift of generalist and dominant species, which became more abundant in streams hosting mixed communities of salmonids and cyprinids, and determined the increase of functional dispersion and uniqueness. Reduction of functional redundancy and increasing functional dispersion were both also related to the introduction of new ecological traits brought by expanding exotic species. Low functional overlap was found among native and exotic species, indicating that the invasion process was mainly controlled by competitive interactions and/or resource opportunism. Functional response to habitat quality was not clearly evident. In conclusion, the impact of temperature increase and exotic species on fish functional diversity was effective, idiosyncratic and mediated by the scale of analysis and by the intensity of pressures.
... leniusculus) and Demon shrimp (Dikerogammarus haemobaphes) within British rivers (Mathers et al., 2020;Guareschi et al., 2021a) and have been shown to be useful complementary tools to detect biological invasion consequences in riverine communities. Similarly focussing on fish communities, functional diversity measures have identified impacts of non-native species in numerous geographic areas including effects on species-poor freshwater fish assemblages in Spain (Colin et al., 2018), the temperate and Mediterranean rivers of Italy (Milardi et al., 2020) and a large subtropical river in China (Shuai et al., 2018). However, in some contexts invasive species may bring new functional and morphological traits to the recipient community. ...
... Most research tends to concentrate on single species and short study periods, with a lack of studies focussing on long-term observational data, multiple IAS, implications upon communities beyond that directly affected (inter-community implications) or physiological and behavioral effects (e.g., Crystal-Ornelas and Lockwood, 2020). Multiple invasions have become common in rivers (e.g., fish: Milardi et al., 2020;invertebrates: Guareschi et al., 2021b) and an increase of interactions among introduced species, already detected in terrestrial ecosystems, is likely but has not been widely explored in riverine systems thus far. In addition, how invaders respond to environmental stressors, the interactions among invaders (e.g., synergic, antagonist) and their wider ecosystem effects require more research and may vary depending on the starting biotic and abiotic conditions of the recipient ecosystem. ...
Chapter
This article provides an overview of biological invasion of rivers and associated ecosystems. River ecosystems are among the most endangered ecosystems globally, with biological invasions representing one of the main contemporary pressures on their floral and faunal communities, resulting in varied and sometimes unexpected effects on the local economy, human wellbeing, biodiversity, water chemistry or riverbank stability. Moreover, river networks represent critically important ecological corridors in the landscape and their physical structure may affect both the distribution of organisms and inadvertently facilitate the invasion and dispersal of alien species. Following a review of the history and general concepts of biological invasions associated with riverine ecosystems, a range of contemporary examples, pathways of introduction, ecosystem effects and challenges regarding future management and conservation are provided and discussed from around the world. Specific consideration is also given to the implications of invasive species on river biomonitoring activities. We conclude with a discussion regarding future research challenges, opportunities, and new perspectives for gaining a better understanding of biological invasions within riverine ecosystems.
... non-significant, * < 0.1, ** < 0.5, *** < 0.001 with the appearence of non-native species in some habitat types, especially in highland and lowland streams (Fig. 7). These native, but not type-specific and accidentally-escaped species present an additional problem in the conservation management of freshwaters, and can negatively impact taxonomic and functional diversity of fish communities (Economidis et al. 2000;Perdikaris et al. 2016;Milardi et al. 2020). Moreover, we also note the negative impact of intentional releases, since economically exploited native species are often introduced into various habitats. ...
... However, they did not observe any specific relationships between species richness and the intensity of invasion. Milardi et al. (2020) Fig. 7 Relationships between A species richness (S), B functional richness (Fric), C Shannon diversity (H'), and D RaoQ of native fish communities in the studied six habitat types, based on generalized additive models (GAM, trend line from the smooth function ± SE). n.s. non-significant, * < 0.1, ** < 0.5, *** < 0.001. ...
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Recent researches suggest that functional diversity represents the response of communities to environmental alterations better than taxonomic diversity. However, there is scarce information about how the functional diversity of freshwater fishes is affected by habitat type and the dominance of non-native species. To address this question, we analysed a large database containing 15 morpho-functional traits of 61 fish species from the Pannon Biogeographic region (Hungary). Based on a fish faunistic list and relative abundance of taxa, we quantified the taxonomic and functional diversity of riverine communities for > 700 sites of six habitat types. We asked how non-native fishes affected the taxonomic and functional diversity in different river types and at the local scale (i.e. at the site level), and how the diversity measures of native fauna elements changes along the invasion gradient. Our results showed that both functional and taxonomic richness increases with habitat complexity, from small headwater streams to large rivers. Therefore taxonomic diversity served as a good proxy for functional diversity along the environmental gradient of river types. Non-natives showed considerable functional diversity relative to their species number in each habitat type. Diversity values of native fauna elements initially increased, and then showed a major decrease along the invasion gradient. River type-specific evaluations highlighted the importance of considering the proliferation of invasive species based on both taxonomic and functional diversity indices. We argue that type-specific action plans are needed in conservation management to preserve the taxonomic and functional diversity of native fishes in Hungary, but also elsewhere.
... In particular, our aims were as follows: (a) to characterize the geography of riverine fish invasions, focusing on species richness and life-history strategies that are under-and over-represented in non-native versus native species pools; (b) to quantify patterns of flow regime alteration, characterized by changes in ecologically relevant measures of flow variability, and propagule pressure, characterized by proxy metrics of human recreational and socioeconomic activity; and (c) to identify how fish invasion patterns can be explained by the unique and interactive effects of niche opportunities (as represented by hydrological alteration) and propagule pressure. Recognizing that the biogeographical origin of non-native species might influence the spatio-temporal patterns and mechanisms of invasion (Milardi et al., 2020), we also examined the generality of our conclusions by distinguishing non-natives originating outside of the continent (exotic species) from non-natives introduced to locations outside of their historical range within the continent (translocated species). Given the extensiveness of flow modification in the USA (Carlisle et al., 2019;Poff et al., 2007;Zimmerman et al., 2018) and strong dependence of native fish species on natural flow variability (Bunn & Arthington, 2002;Mims & Olden, 2012), we hypothesized that flow regime alteration is at least as important as propagule pressure in controlling the composition of fish assemblages. ...
... Here, we found that translocated and exotic species have substantially different life-history traits and distributions patterns across the U.S. watersheds, as has been reported in other geographical regions (e.g., Milardi et al., 2020). Although exotic species were less numerous than translocated ones, they were responsible for the most drastic changes in life-history composition because of marked differences in life-history strategies relative to the native species pool. ...
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Aim River flow regimes are changing globally as a consequence of human use of freshwater resources. Additionally, rivers are among the most invaded ecosystems. Invasion biology predicts that the establishment and spread of non‐native species might be favoured both by new environmental regimes (niche opportunities) and by human‐mediated dispersal (propagule pressure). Here, we expand on past research by asking whether these two mechanisms act in isolation or whether they interact to facilitate the spread of non‐natives. Location Conterminous USA. Time period 1987–2016. Major taxa studied Freshwater fishes. Methods First, we examined the geography of riverine fish invasions across 1,148 watersheds spanning the conterminous USA. We focused on species richness and the life‐history strategies of non‐native (both translocated and exotic) relative to native species pools. Second, we quantified flow regime alteration as the deviation between observed and expected contemporary flow regimes, using a combination of spectral analyses on long‐term discharge data and random forest models. We focused on two biologically relevant facets of the flow regime: flow variability and flow seasonality. We also estimated metrics of propagule pressure: recreational fishing pressure and socioeconomic activity. We then compared the strength of evidence associating riverine fish invasions with flow alteration, propagule pressure, and interactions between the two mechanisms. Results We found that alteration of flow variability and seasonality is widespread across the conterminous U.S. rivers, and has favoured invasions by filtering specific life‐history strategies. Importantly, high levels of flow stabilization and propagule pressure interacted: where co‐occurring, these two drivers were associated with higher fish invadedness levels than expected based on their individual effects. Main conclusions Our results underscore the need to consider different drivers of invasion concurrently. Otherwise, important synergistic interactions might be missed that could explain (and guide management strategies to mitigate) the high levels of invasion in fresh waters.
... In some Italian systems, entire fish communities have been completely substituted by NNS (e.g., Lanzoni et al., 2018;Haubrock et al., 2021). Information on the spread of NNS in main rivers and large lakes is available (Carosi et al., 2015;Volta et al., 2018;Milardi et al., 2020;Haubrock et al., 2021), but restricted knowledge is present for small water bodies. Similarly, no SIA studies have been carried out on fish assemblages of small and shallow lakes in Italy, leaving unexplored the quantification of the spread of NNS in these ecosystems and the quantification of the interspecific trophic interactions between NNS and NS. ...
Article
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The introduction and establishment of non-native fish species is a widespread phenomenon in freshwater ecosystems, including small and shallow lakes. However, these ecosystems are often not considered in conservation and ecological studies and a few information is available on their fish communities and the impacts of biological invasions. Here, standardized fish surveys (gillnetting and electrofishing) and stable isotopes analysis (SIA) of carbon and nitrogen (δ¹³C and δ¹⁵N) were combined to assess fish community composition, trophic structure and trophic diversity, and to characterize the interspecific trophic interactions (as isotopic niches and their relative asymmetric overlap) of the native and non-native species (NS and NNS, respectively) found in two protected small and shallow lakes, San Michele and Campagna (northern Italy). In San Michele, 92 % of the fish caught were NNS and both the individual and biomass per unit effort were dominated by NNS, particularly by the invasive Lepomis gibbosus L. and Ictalurus punctatus (Rafinesque, 1818). In Campagna, 5.6 % of the fish in the total catches belonged to NNS and the numeric and biomass abundances of the assemblage were dominated by the NS Alburnus alborella (Bonaparte, 1841). SIA revealed that NNS had greater trophic structure and were exploiting a wider range of resources (as per Layman metrics) and had a higher asymmetric overlap than NS assemblages in both lakes. This was also evident when species-specific isotopic ecology was considered, underlining that, in both lakes, NNS (particularly the NNS Ameiurus melas (Rafinesque, 1820)) may have a competitive advantage over NS in case of limiting resources. The results thus pointed to a worrying conservation status of these lakes that may mirror the condition of other Italian shallow and small lakes highlighting the need to implement management actions to preserve these valuable ecosystems.
... Where present, it tends to dominate the community of predator fishes (~ 30% of the whole fish community biomass, M. Milardi, unpublished data). Wels catfish and other introduced fish species are a major problem also for native fish diversity in Italian freshwaters (Milardi et al. 2018(Milardi et al. , 2019a(Milardi et al. , 2020a(Milardi et al. , 2020b(Milardi et al. , 2020c, but to date, little has been done to address this problem. A recent review by Cucherousset et al. (2018) underlined how the species is widespread and abundant also in the rest of its introduced range (e.g. ...
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Predatory fish have occasionally been observed preying on birds, sometimes repeatedly, but few studies were able to unravel the overall significance of avian prey in fish diet and the predation impacts on bird populations. We used a control/impact study setup, using a Nature Reserve in northern Italy and a nearby control area, to determine: 1) the contribution of waterbirds to wels catfish diet in the Reserve, 2) the population density of wels catfish in the Reserve and control area and 3) the potential impacts of waterbird depredation by wels catfish on waterbird population trends. Our stable isotope Bayesian mixing model indicated that birds contributed 12.2% (5-27.9%, 50% confidence interval) of the diet of large wels catfish (> 98 cm in total length). Large individuals constituted the majority of the population in the shoreline areas of the reserve in 2013-2019, where the population was stable despite control efforts. Numbers were below detectable levels in the control area. Large wels catfish consumed an average of 224, 148 and 187 kg of birds during the 2019 chick growing period, as estimated through three different bioenergetic models. Compared to the control area, mallard reproductive success was diminished in the Reserve, likely due to higher rates of fish predation, although effects were variable in different years. Overall, our data suggest that high densities of invasive wels catfish might impact waterbird reproductive success through predation on bird chicks, but further studies would be needed to reduce uncertainties related to the intrinsic variability of field ecology data. Our study constitutes a preliminary attempt to assess the potential of introduced wels catfish to affect the conservation value of waterbird protection areas, and should be repeated at broader spatial and temporal scales.
... They become invasive when they manage to establish and reproduce in the new area generating an alien population, which can cause strong ecological pressures on the local biodiversity, especially in mega-diverse countries (Mooney & Hobbs, 2000;Frehse et al., 2016). The effects caused by the action of invasive species include the migration of local species, the transmission of pathogens, and the local extinctions, among others (Clavero & García-Berthou, 2005; Díaz et al., Milardi et al., 2020). This problem has increased in recent years due to cargo shipments associated with market globalization (Levine & D'Antonio, 2003;Meyerson & Mooney, 2007) and human migrations (Veitch & Clout, 2001;Hulme, 2009;Lockwood, et al., 2013) evidencing the strong relationship between industrial development and the establishment of foreign species with clear examples in Asia and America (Lin, et al., 2007;Mayerson & Mooney, 2007;Ramírez-Albores, et al., 2019). ...
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The study of the introduction of exotic species in Colombia has been a trending topic in the last decade due to their effects on local diversity. The records of exotic reptile species of the genus Hemidactylus have increased based on museum vouchers and fieldwork. However, there are still plenty of information gaps regarding their current distribution in the country. Similarly, there is limited information on unusual reptile distributions caused by human transport inside the country. Here, we present an update to the distribution of the exotic house geckos Hemidactylus frenatus, H. garnotii, and H. mabouia based on several new localities and historical records. We also present an atypical record of the golden spectacled tegu Gymnophthalmus speciosus in paramo ecosystems from the Central Andes of Colombia, almost 2000 meters above the upper elevational known limit for this species. The distribution update shows that H. frenatus is widely distributed in 30 of the 32 departments of Colombia with no records for Chocó and Guainía. H. garnotii is currently known only from the Cauca River basin of the departments of Antioquia, Caldas, and Risaralda, while H. mabouia, previously known from the Amazon basin of the country, is now reported for the Andean region. Finally, Gymnophthalmus speciosus presence in a paramo ecosystem, considered unusual as it is not part of its distribution area, was probably the result of an accidental transport from a typical lowland locality (below 1000 meters above sea level.
... For macroinvertebrates, we used 8 traits, including body size, descendant per reproductive cycles, dispersal capacity, habits, physiological sensitivity, reproduction type, respiration and functional feeding groups (Zhao et al., 2018;Bruno et al., 2019). For fish, we selected 6 traits: body size, descendant per reproductive cycles, habits, physiological sensitivity, reproduction and feeding habitats (Milardi et al., 2020). Codes of periphyton, macroinvertebrates and fish, and their functional traits are provided in Supplemental Table S4. ...
Article
Anthropogenic salinisation is becoming an increasing global issue for freshwater ecosystems, leading to serious biodiversity loss and ecosystem degradation. While the effect of anthropogenic salinisation on freshwater ecosystems has been intensively studied in recent years, most studies focus on salinisation effects on the individual or single groups of organisms without considering the effect on the ecosystem levels, such as diversity and trophic links. Therefore, we conducted a long-term field survey from May 2009 to August 2016 at 405 sites in northeast China to investigate the effect of a gradient of salinisation on community diversity, functional diversity and trophic links in mountain streams. Samples of water chemistry, periphyton, macroinvertebrates and fish were collected. Our results showed that as anthropogenic salinisation increased, Ca²⁺, Mg²⁺, HCO3⁻ and SO4²⁻ exhibited significant increases (p <0.05). These increased ions caused decreases in taxonomic evenness and biotic integrity, but an increase in the beta diversity for periphyton and macroinvertebrates, and a slight increase in the evenness of fish. The increased salinisation resulted in the extirpation of salt-sensitive taxa and declines in macroinvertebrate functional richness and functional redundancy, which consequently led to simplified trophic links. Our results implied that if salt-tolerant taxa in high salinisation sites were not functionally redundant with less tolerant taxa, alterations of their functional composition probably decrease the stability of ecosystem functions. Overall, our study suggests that the ongoing anthropogenic salinisation is posing serious threats to biodiversity and trophic links in river ecosystems, and should be considered in future river restoration and biodiversity conservation.
... Furthermore, it is not a target both of commercial and recreational fishing and, therefore, its exploitation is likely very low. Overall, as observed by Milardi et al., 2020, on Italian rivers, community homogenisation driven by non-native species can reduce the functional diversity of fish communities, increasing the risk of functional loss despite different lake morphology and origin. ...
Article
In European lakes, anthropogenic pressures have increased significantly since the 1950s, facilitating colonisation by non-native species and increasing the potential for further invasions. Here, we determined the effects of anthropogenic pressures (i.e., habitat alterations and introduction of nonnative species) on the fish communities of Italian sub-alpine lakes. We hypothesised that established non-native species would have more competitive traits against anthropogenic stressors, such as habitat alteration, than native species. Thus, we expected that non-native species would dominate lake communities and reduce native species occurrence and abundance depending on the degree of anthropogenic alterations. Overall, we predicted that the increase in anthropogenic pressures after the 1950s had led to homogenisation of the fish communities of the lakes in the region. We tested these hypotheses using data on 15 sub-alpine lakes, covering a broad geographical and morphological gradient, and compared the 2007-2014 fish community composition (sampled according to the CEN protocol plus point-abundance electrofishing) with variables of lake habitat and anthropogenic pressures (based on the Lake Habitat Survey, a method to evaluate the hydromorphological conditions of lakes according to the European Water Framework Directive ) and fish communities before 1950, the latter based on bibliographic information. Following our hypothesis, non-native species showed higher prevalence of traits that increase their competitiveness against anthropogenic alterations (e.g., tolerance to pollution). In addition to lake morphology, the community composition of non-native fish determined as abundance (NPUE) and biomass (BPUE) was positively related to anthropogenic pressures. Since the 1950s, 19 non-native species have colonised the Italian sub-alpine lakes, and the occurrence of native species has decreased by ~ 27%. However, contrary to our expectation, these changes have increased the β-diversity of the fish communities in the lakes.
... In the studied canal network, human intervention continuously causes redistribution of fish species between different canals, thus likely increasing the spread and colonization of exotic species (Castaldelli et al. 2013). Our results suggested that exotic invasions might contribute to shape the spatial patterns of ecofunctional diversity in fish communities (see also Milardi et al. 2019 andMilardi et al. 2020). Clear water, rheophilic, intermediate migration, phytophylic, lithophylic and piscivorous species seem to contribute the most to the overall ecofunctional uniqueness of fish communities in the area, being typical traits of native species and most likely belonging to species with intermediate site occupancy. ...
Article
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We investigated the relationships between exotic freshwater fish invasions, environmental factors and ecofunctional diversity (i.e. the combination of ecological traits in communities) in streams. We used data from 335 stream sites, belonging to 105 watersheds and 3 basins in Italy, to test whether the exotic species invasion was dominated by species with generalist traits and whether the environment-ecofunctional trait relationships of exotic and native species would differ from each other. We also tested the hypothesis that ecofunctional uniqueness patterns between exotic and native species would be substantially different. We found that generalist traits were widespread in nearly all areas where exotic species occurred, but not all generalist traits were equally abundant in exotic communities. Only temperature tolerant, low oxygen tolerant and eurytopic traits were typically more dominant in exotic communities than native ones, suggesting that not all generalist traits are equally important in the invasion process and that more complex mechanisms of trait selection could take place. Environment-ecofunctional trait relationships of exotic and native species partly differed both in direction and magnitude, suggesting that invasion dynamics could decouple the linkage between environment and biotic communities, but also that this decoupling might decrease at later invasion stages (i.e. > 30 years after major invasions). Finally, site and trait ecofunctional uniqueness differed between exotic and native species. Exotic species ecofunctional diversity hotspots were located in human-disturbed areas, suggesting that human disturbance might play a strong role in invasion patterns. We advocate for a wider use of ecofunctional approaches in conservation studies in the future, as they could be a key to understand complex ecological processes such as exotic invasions.
... We also evaluated the spatial overlap and correlation between invasion degree and functional diversity (as expressed through the FDis metric calculated using ecofunctional traits, 65 ). First, we used linear kriging to represent functional diversity, based on the whole community, for invaded sites (i.e. ...
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Exotic species invasions often result in native biodiversity loss, i.e. a lower taxonomic diversity, but current knowledge on invasions effects underlined a potential increase of functional diversity. We thus explored the connections between functional diversity and exotic species invasions, while accounting for their environmental drivers, using a fine-resolution large dataset of Mediterranean stream fish communities. While functional diversity of native and exotic species responded similarly to most environmental constraints, we found significant differences in the effects of altitude and in the different ranking of constraints. These differences suggest that invasion dynamics could play a role in overriding some major environmental drivers. Our results also showed that a lower diversity of ecological traits in communities (about half of less disturbed communities) corresponded to a high invasion degree, and that the exotic component of communities had typically less diverse ecological traits than the native one, even when accounting for stream order and species richness. Overall, our results suggest that possible outcomes of severe exotic species invasions could include a reduced functional diversity of invaded communities, but analyzing data with finer ecological, temporal and spatial resolutions would be needed to pinpoint the causal relationship between invasions and functional diversity.
... Lanzoni et al., 2018) and their effects on biodiversity (e.g. Castaldelli et al., 2013a, Milardi et al., 2019a. We used this information to model aquatic vegetation production and standing crop, its denitrification potential, and its consumption by grass carp in the drainage network, with the aim to verify whether historical N loads were affected by grass carp or other changes in agricultural practices. ...
Article
Eutrophication has a profound impact on ecosystems worldwide. Grass carp Ctenopharyngodon idella, an herbivorous fish, has been introduced to control aquatic plant overgrowth caused by eutrophication, but could have other, potentially detrimental, effects. We used the Po di Volano basin (south of the Po River delta, northern Italy) as a test case to explore whether grass carp effects on canal aquatic vegetation could be at the root of historical changes in N loads exported from the basin to the Goro Lagoon. We modeled the aquatic vegetation production and standing crop, its denitrification potential, and its consumption by introduced grass carp. We then examined whether changes in historical nitrogen loads matched the modeled losses of the drainage network denitrification function or other changes in agricultural practices. Our results indicate that introduced grass carp could completely remove submerged vegetation in the Po di Volano canal network, which could – in turn – lead to substantial loss of the denitrification function of the system, causing in an increase in downstream nitrogen loads. A corresponding increase, matching both timing and magnitude, was detected in historical nitrogen loads to the Goro Lagoon, which were significantly different before and after the time of modeled collapse of the denitrification function. This increase was not clearly linked to watershed use or agricultural practices, which implies that the loss of the denitrification function through grass carp overgrazing could be a likely explanation of the increase in downstream nitrogen loads. Perhaps for the first time, we provide evidence that a freshwater fish introduction could have caused long-lasting changes in nutrient dynamics that are exported downstream to areas where the fish is not present.
Article
Invasive alien species often affect native ecosystems worldwide. In Japan, the channel catfish Ictalurus punctatus is an invasive species in rivers. However, information regarding its feeding habits in rivers around dam reservoirs is still scarce. Thus, in this study, we assessed the feeding habits of I. punctatus collected from the Nunome River, a secondary tributary of the Yodo River, downstream of the Nunome Dam reservoir. Standard length and weight of the collected individuals were measured, and their stomach contents were analyzed under a stereomicroscope to identify prey species. Moreover, stable isotope analysis was conducted to determine their trophic niche. Overall, I. punctatus was shown to feed on a variety of food resources derived from the riparian forest and river ecosystem; in particular, algae represented 78.8% of its stomach contents. However, stable isotope analysis suggested that I. punctatus depended on benthic insects and fish to ensure adequate body composition, whereas algae were not assimilated by I. punctatus. Among benthic insects, I. punctatus relied on trichopteran larvae such as Macrostemum radiatum, which appears downstream of the dam reservoir and utilizes plankton algae from the dam. In conclusion, these findings provide additional clues for a better understanding of I. punctatus feeding activity and its relationship with its surrounding ecosystem.
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We analyzed the large-scale drivers of biological invasions using freshwater fish in a Mediterranean country as a test case, and considering the contribution of single species to the overall invasion pattern. Using Boosted Regression Tree (BRT) models, variation partitioning and Redundancy Analysis (RDA), we found that human factors (especially eutrophication) and climate (especially temperature) were significant drivers of overall invasion. Geography was also relevant in BRT and RDA analysis, both at the overall invasion and the single species level. Only variation partitioning suggested that land use was the second most significant driver group, with considerable overlap between different invasion drivers and only land use and human factors standing out for single effects. There was general accordance both between different analyses, and between invasion outcomes at the overall and the species level, as most invasive species share similar ecological traits and prefer lowland river stretches. Human-mediated eutrophication was the most relevant invasion driver, but the role of geography and climate was at least equally important in explaining freshwater fish invasions. Overall, human factors were less prominent than natural factors in driving the spread and prevalence of invasion, and the species spearheading it.
Thesis
Understanding the geographic distribution of species across space and time is one of the long-standing challenges in ecology and evolution. Among the major components of species distribution, the species' geographic range size has been studied across several taxonomic groups and has been related to multiple ecological and evolutionary factors. The geographic range size of species is also of paramount importance in conservation strategies because it consistently emerges as a key correlate of extinction risk, where species occupying smaller geographic ranges are assumed to have a higher risk of extinction. Results concerning these fundamental and applied aspects of geographic range size have largely neglected freshwater fish, commonly focusing on the usual vertebrate groups (e.g. mammals, birds). However, freshwater fish, the most diverse vertebrate group, can provide novel insights about the geographic range size determinants and threats because of the unique dendritic shape and reduced amount of their habitat (i.e. river networks) compared to other terrestrial and marine ecosystems. In this PhD work, we analyzed for the first time the global patterns of geographic range size in freshwater fish species and tested previous hypotheses proposed to explain the variation of geographic range size in other taxonomic groups. Our findings showed that current and historical connectivity are the most important factors driving the geographic range size of freshwater fishes, contrasting with the main determinants reported for terrestrial and marine taxa. From an applied point of view, we focused on the usually observed macroecological relationship between the species' geographic range size and body size. This relationship would allow estimating the minimum geographic range size needed by species for long-term persistence. Based on ecological theory of species temporal fluctuations of abundances, we provide a mechanistic validation of this relationship, supporting its use to identify vulnerable species and their changes in extinction risk through reduced geographic ranges induced by anthropogenic factors. Using a tropical river basin as a case study, we used this macroecological relationship to quantify changes in species extinction risk due to the fragmentation of their ranges caused by hydropower development. The results and the data compiled in this thesis represent useful information to guide and inform conservation in freshwater fish and give the opportunity to continue filling theoretical gaps.
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Motivation: We compiled a global database of long-term riverine fish surveys from 46 regional and national monitoring programmes and from individual academic research efforts, with which numerous basic and applied questions in ecology and global change research can be explored. Such spatially and temporally extensive datasets have been lacking for freshwater systems in comparison to terrestrial ones. Main types of variables contained: The database includes 11,386 time-series of riverine fish community catch data, including 646,270 species-specific abundance records, together with metadata related to the geographical location and sampling methodology of each time-series. Spatial location and grain: The database contains 11,072 unique sampling locations (stream reach), spanning 19 countries, five biogeographical realms and 402 hydrographical basins world-wide. Time period and grain: The database encompasses the period 1951–2019. Each timeseries is composed of a minimum of two yearly surveys (mean = 8 years) and represents a minimum time span of 10 years (mean = 19 years). Major taxa and level of measurement: The database includes 944 species of rayfinned fishes (Class Actinopterygii). Software format: csv. Main conclusion: Our collective effort provides the most comprehensive long-term community database of riverine fishes to date. This unique database should interest ecologists who seek to understand the impacts of human activities on riverine fish biodiversity and to model and predict how fish communities will respond to future environmental change. Together, we hope it will promote advances in macroecological research in the freshwater realm.
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The aim of this study was to determine the food webs structure of a large Patagonian river in two river sections (Upstream and Midstream) and to evaluate isotopic overlap between native and introduced species. We used stable isotope analyses of δ15N and δ13C and stomach content. The Upstream section had a more complex food webs structure with a greater richness of macroinvertebrates and fish species than Midstream. Upstream basal resources were dominated by filamentous algae. Lake Trout were found to have a higher trophic position than all other fish species in that area although, the most abundant fish species, were Rainbow Trout. Depending on the life stage, Rainbow Trout shifted from prey to competitor/predator. In the Midstream section, the base of the food webs was dominated by coarse particulate organic matter, and adult Rainbow Trout had the highest trophic level. Isotopic values changed among macroinvertebrates and fish for both areas. The two most abundant native and invasive species — Puyen and Rainbow Trout — showed an isotopic separation in Midstream but did not in Upstream areas. The presence of invasive fish that occupy top trophic levels can have a significant impact on native fish populations that have great ecological importance in the region.
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Exotic species invasions often result in native biodiversity loss, i.e. a lower taxonomic diversity, but current knowledge on invasions effects underlined a potential increase of functional diversity. We thus explored the connections between functional diversity and exotic species invasions, while accounting for their environmental drivers, using a fine-resolution large dataset of Mediterranean stream fish communities. While functional diversity of native and exotic species responded similarly to most environmental constraints, we found significant differences in the effects of altitude and in the different ranking of constraints. These differences suggest that invasion dynamics could play a role in overriding some major environmental drivers. Our results also showed that a lower diversity of ecological traits in communities (about half of less disturbed communities) corresponded to a high invasion degree, and that the exotic component of communities had typically less diverse ecological traits than the native one, even when accounting for stream order and species richness. Overall, our results suggest that possible outcomes of severe exotic species invasions could include a reduced functional diversity of invaded communities, but analyzing data with finer ecological, temporal and spatial resolutions would be needed to pinpoint the causal relationship between invasions and functional diversity.
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We investigated whether the introduction of fish (brown trout, Salmo trutta) in previously fishless boreal lakes could alter the aquatic insect subsidy and affect the nesting population of insectivorous migratory birds, with a particular focus on the pied flycatcher, Ficedula hypoleuca, which is the most represented species. According to our paleolimnological data and bioenergetic model, introduced trout increased the adult midge biomass output from 18.6 to 28.7 kg (+54.6%), which was energetically significant and could have theoretically supported an increase in insectivorous birds nesting around the lake. While the long-term series of insectivorous birds nesting around the lake seemed to increase according to the modeled fish effects, we could not establish a clear link with changes in food availability. Our control (pied flycatchers) showed similar patterns as our treatment, suggesting that this species' abundance was affected by factors other than fish presence in the lake. The demographic fluctuations and trends of the pied flycatcher at the regional scale seemed to override cascading effects linking introduced fish, emerging midges, and insectivorous birds. We conclude that further studies will be needed to investigate this topic and propose some areas for future research.
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Aim Exotic species are a major threat to biodiversity and have modified native communities worldwide. Invasion processes have been extensively studied, but studies on species richness and beta diversity patterns of exotic and native species are rare. We investigate such patterns among exotic and native fish communities in upland and lowland rivers to explore their relationship with environmental drivers. Location Northern Italy. Methods Exotic and native fish beta diversity patterns were investigated separately in lowland and upland sites using Local Contribution to Beta Diversity (LCBD) and Species Contribution to Beta Diversity (SCBD) analyses. To examine the main environmental variables affecting the LCBD, a Boosted Regression Trees (BRT) method was used. Community dispersion among and within stream orders was investigated with the PERMDISP test. Results In lowland sites, exotic species richness was higher than native species richness, especially in large rivers and drainage canals. An opposite trend was found in upland sites, where native species richness was higher than exotic species richness, especially in large rivers. No clear LCBD patterns were found along stream orders in the lowland, whereas higher stream orders in the upland showed the highest LCBD. Its patterns in upland and lowland sites were related to a number of factors, such as total suspended solids and total phosphorus. Community dispersion among stream orders did not show a relationship with environmental heterogeneity. SCBD values were positively correlated with species occupancy in the study area, and native species showed higher SCBD values than exotic species only in the uplands. Main conclusions Large rivers in the uplands are important in maintaining native fish diversity and should be protected against invasive fish. In contrast, most lowland rivers have suffered from biological homogenization. Some rare native species can show low contribution to beta diversity, but still need conservation actions due to their risk of local extinction.
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In order to mitigate the ecological impact of alien species there is a need to control or eradicate those species that are causing a loss of biodiversity. However, such conservation actions can lack public support. In their editorial to The European Zoological Journal (Vol. 85, pp. 227-228), Fenoglio and co-authors observe that public opinion is little concerned about fish welfare and, therefore, is less likely to oppose alien fish than alien bird and mammal eradications. Alien fish management is presented as a science-driven model to which the management of alien birds and mammals should aspire, and public education is identified as a solution for the social conflicts inherent to alien species management. This reflects the authors' opinion that a unitary, integrally scientific strategy would be the best one to counter biological invasions. However, a more flexible strategy including societal inclinations might be considered too, to avoid sabotage of the conservation actions by several predictable opponents, including animal rights movements. Moving from the latter opinion, the present reply aims at providing additional examples and argumentations on (i) why double or multiple management standards could be the only viable strategy to counter alien species, (ii) why alien fish management is not a good model, and (iii) why education cannot be the only solution for social conflicts inherent to alien species management.
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The search for traits associated with plant invasiveness has yielded contradictory results, in part because most previous studies have failed to recognize that different traits are important at different stages along the introduction–naturalization–invasion continuum. Here we show that across six different habitat types in temperate Central Europe, naturalized non-invasive species are functionally similar to native species occurring in the same habitat type, but invasive species are different as they occupy the edge of the plant functional trait space represented in each habitat. This pattern was driven mainly by the greater average height of invasive species. These results suggest that the primary determinant of successful establishment of alien species in resident plant communities is environmental filtering, which is expressed in similar trait distributions. However, to become invasive, established alien species need to be different enough to occupy novel niche space, i.e. the edge of trait space.
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Global spread of non‐native species profoundly changed the world biodiversity patterns, but how it translates into functional changes remains unanswered at the world scale. We here show that while in two centuries the number of fish species per river increased on average by 15% in 1569 basins worldwide, the diversity of their functional attributes (i.e. functional richness) increased on average by 150%. The inflation of functional richness was paired with changes in the functional structure of assemblages, with shifts of species position toward the border of the functional space of assemblages (i.e. increased functional divergence). Non‐native species moreover caused shifts in functional identity toward higher body sized and less elongated species for most of assemblages throughout the world. Although varying between rivers and biogeographic realms, such changes in the different facets of functional diversity might still increase in the future through increasing species invasion and may further modify ecosystem functioning.
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Estimates of recent biodiversity change remain inconsistent, debated, and infrequently assessed for their functional implications. Here, we report that spatial scale and type of biodiversity measurement influence evidence of temporal biodiversity change. We show a pervasive scale dependence of temporal trends in taxonomic (TD) and functional (FD) diversity for an ~50-year record of avian assemblages from North American Breeding Bird Survey and a record of global extinctions. Average TD and FD increased at all but the global scale. Change in TD exceeded change in FD toward large scales, signaling functional resilience. Assemblage temporal dissimilarity and turnover (replacement of species or functions) declined, while nestedness (tendency of assemblages to be subsets of one another) increased with scale. Patterns of FD change varied strongly among diet and foraging guilds. We suggest that monitoring, policy, and conservation require a scale-explicit framework to account for the pervasive effect that scale has on perceived biodiversity change.
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Biological invasions are considered to be one of the main threats to biodiversity. Invasions lead to a loss of native species, changes to species composition, and a shift in the functioning and stability of ecosystems. In this study, derived from nine consecutive years of monitoring data and based on morphological functional trait values measured at the individual-level, we quantified the functional differences between native and non-native fish species and further assessed how biological invasions impact on species richness and functional diversity in the large subtropical Pearl River in southern China. Specifically, we differentiated intraspecific functional variability by separating individuals of a species according to their different life stages. Our results provided strong evidence that native and non-native fish were significantly different in their functional attributes. Invasion caused no obvious change in species richness; however, the yearly increase in non-native populations was accompanied by a significant decrease in functional niches of native species and change in several aspects of functional diversity in the fish community. Decreasing functional richness, and increasing functional divergence and specialization, indicated that most native species had been replaced by non-native species with different specific functional traits, which may affect ecosystem stability. Notably, this study provided empirical evidence that functional diversity was more sensitive to biological invasions than species richness. Our results show that control of non-native aquatic species is both necessary and urgent in the Pearl River. An understanding of the processes described in this study can form the basis of conservation in fish community, which is critical to sustainable and successful fisheries.
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Padogobius nigricans and Padogobius bonelli are two gobies native to Italy and characterized by an allopatric distribution: P. nigricans is endemic to the Tyrrhenian catchment of central Italy, while P. bonelli is endemic to the Adriatic catchment of Northern Italy. In the past two decades P. bonelli has successfully established in central Italy outside of its original area of distribution, coming into contact with populations of P. nigricans. The superiority of P. bonelli in competition for breeding sites is well documented by laboratory studies; however, little evidence from the field has been provided. In this study, the occurrence and abundance of the two gobies were investigated in the River Tiber basin (central Italy) to assess the impacts of P. bonelli expansion on P. nigricans populations. Moreover, to investigate nest interference by P. bonelli towards P. nigricans, shelter occupancy of the two Italian gobies was investigated in the field with respect to individual density. Sampling was conducted by electrofishing in 77 sites throughout the upper River Tiber basin and nest occupation was analyzed in 8 river stretches. Padogobius bonelli has further expanded its distribution in recent years, following both natural and human-mediated dispersal patterns. It is numerically dominant over P. nigricans and fewer P. nigricans juveniles were found in the invaded than the uninvaded areas. Depending on adult density, P. bonelli can occupy up to 97% of nest sites and can seize a significant percentage of shelters even at low adult abundance. The expansion of P. bonelli into newly colonized areas in recent years has increased concern for the conservation of P. nigricans. In the invaded areas, the survival of P. nigricans populations is mostly through migration of individuals from the uninvaded areas located upstream of weirs, allowing isolated populations of this vulnerable and endangered species to persist.
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The invasion of exotic species is one of the main threats to worldwide biodiversity and can be aided by changes in environmental conditions. We hypothesized that a temporal trend of decreasing discharge and increasing temperature might have favored the invasion of warm-adapted, lentic exotic fish species in the lower Po River, northern Italy. We used presence/absence data over a long-term period (over 20 years) to investigate the dynamics of exotic fish invasion along water temperature and discharge gradients. Mean annual discharge and temperature did not show a clear trend and did not affect exotic fish species invasion, which progressed with time irrespective of these factors. The total number of species fluctuated without a clear trend, which underlined a progressive substitution of native species with exotic ones. Perhaps surprisingly, the community composition changed over time towards more temperature tolerant but also rheophilic, benthivore and generalist fish species. These results highlight how species interactions could be one of the main factors driving the invasion. Furthermore, our data underlines a continuously rising tide of exotics, which questions the success of past control strategies. Considering the current conservation resources limitations, priority should be given to the development of prevention strategies in order to avoid new species introductions.
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Trait-based ecology has been developed for decades to infer ecosystem responses to stressors based on the functional structure of communities, yet its value in species-poor systems is largely unknown. Here, we used an extensive dataset in a Spanish region highly prone to non-native fish invasions (15 catchments, N = 389 sites) to assess for the first time how species-poor communities respond to large-scale environmental gradients using a taxonomic and functional trait-based approach in riverine fish. We examined total species richness and three functional trait-based indices available when many sites have ≤ 3 species (specialization, FSpe; originality, FOri and entropy, FEnt). We assessed the responses of these taxonomic and functional indices along gradients of altitude, water pollution, physical habitat degradation and non-native fish biomass. Whilst species richness was relatively sensitive to spatial effects, functional diversity indices were responsive across natural and anthropogenic gradients. All four diversity measures declined with altitude but this decline was modulated by physical habitat degradation (richness, FSpe and FEnt) and the non-native:total fish biomass ratio (FSpe and FOri) in ways that varied between indices. Furthermore, FSpe and FOri were significantly correlated with Total Nitrogen. Non-native fish were a major component of the taxonomic and functional structure of fish communities, raising concerns about potential misdiagnosis between invaded and environmentally-degraded river reaches. Such misdiagnosis was evident in a regional fish index widely used in official monitoring programs. We recommend the application of FSpe and FOri to extensive datasets from monitoring programs in order to generate valuable cross-system information about the impacts of non-native species and habitat degradation, even in species-poor systems. Scoring non-native species apart from habitat degradation in the indices used to determine ecosystem health is essential to develop better management strategies.
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We assessed the prevalence of alien species as a driver of recent extinctions in five major taxa (plants, amphibians, reptiles, birds and mammals), using data from the IUCN Red List. Our results show that alien species are the second most common threat associated with species that have gone completely extinct from these taxa since AD 1500. Aliens are the most common threat associated with extinctions in three of the five taxa analysed, and for vertebrate extinctions overall. © 2016 The Author(s) Published by the Royal Society. All rights reserved.
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The introduction of invasive species, which often differ functionally from the components of the recipient community, generates ecological impacts that propagate along the food web. This review aims to determine how consistent the impacts of aquatic invasions are across taxa and habitats. To that end, we present a global meta-analysis from 151 publications (733 cases), covering a wide range of invaders (primary producers, filter collectors, omnivores and predators), resident aquatic community components (macrophytes, phytoplankton, zooplankton, benthic invertebrates and fish) and habitats (rivers, lakes and estuaries). Our synthesis suggests a strong negative influence of invasive species on the abundance of aquatic communities, particularly macrophytes, zooplankton and fish. In contrast, there was no general evidence for a decrease in species diversity in invaded habitats, suggesting a time lag between rapid abundance changes and local extinctions. Invaded habitats showed increased water turbidity, nitrogen and organic matter concentration, which are related to the capacity of invaders to transform habitats and increase eutrophication. The expansion of invasive macrophytes caused the largest decrease in fish abundance, the filtering activity of filter collectors depleted planktonic communities, omnivores (including both facultative and obligate herbivores) were responsible for the greatest decline in macrophyte abundance, and benthic invertebrates were most negatively affected by the introduction of new predators. These impacts were relatively consistent across habitats and experimental approaches. Based on our results, we propose a framework of positive and negative links between invasive species at four trophic positions and the five different components of recipient communities. This framework incorporates both direct biotic interactions (predation, competition, grazing) and indirect changes to the water physicochemical conditions mediated by invaders (habitat alteration). Considering the strong trophic links that characterize aquatic ecosystems, this framework is relevant to anticipate the far-reaching consequences of biological invasions on the structure and functionality of aquatic ecosystems. © 2015 John Wiley & Sons Ltd.
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Collections were made of fishes occurring in the streams of the Sierra Nevada foothills in Central California. Environmental factors associated with each collection were recorded. Correlation analyses indicated which environmental factors affected the distribution of 11 of the 21 species collected: Micropterus salmoides, Lepomis cyanellus, L. macrochirus, Gambusia affinis, Notemigonus crysoleucas, Lavinia exilicauda, Ptychocheilus grandis, Mylopharodon conocephalus, Hesperoleucus symmetricus, Catostomus occidentalis and Salmo gairdneri. The fishes were found to belong to four distinct fish associations, each found in a distinctive set of environmental conditions. The Rainbow Trout Association was found in the cold, clear permanent streams of the higher elevations. The California Roach Association was found in the small, warm intermittent tributaries to the larger streams. The Native Cyprinid-Catostomid Association was found in the larger low elevation streams. The Introduced Fishes Association was found in low elevation intermittent streams that had been highly modified by man's activities.
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Understanding, modeling, and predicting the impact of global change on ecosystem functioning across biogeographical gradients can benefit from enhanced capacity to represent biota as a continuous distribution of traits. However, this is a challenge for the field of biogeography historically grounded on the species concept. Here we focus on the newly emergent field of functional biogeography: the study of the geographic distribution of trait diversity across organizational levels. We show how functional biogeography bridges species-based biogeography and earth science to provide ideas and tools to help explain gradients in multifaceted diversity (including species, functional, and phylogenetic diversities), predict ecosystem functioning and services worldwide, and infuse regional and global conservation programs with a functional basis. Although much recent progress has been made possible because of the rising of multiple data streams, new developments in ecoinformatics, and new methodological advances, future directions should provide a theoretical and comprehensive framework for the scaling of biotic interactions across trophic levels and its ecological implications.
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Freshwater ecosystems worldwide are experiencing native fish losses with severe threats to the conservation of freshwater biodiversity and ecosystem functioning, and the debate on whether the cause is biotic or abiotic disturbance is still open. Temporal variation in fish assemblages was analysed over an 18 year period in 14 waterways of the lowland backwaters of the Po River in north-eastern Italy, which are important feeding, spawning and nursery sites for native fish. In 1991, 14 native and eight exotic species were collected. In less than 20 years 10 native species underwent local extinction, three of which – Rutilus pigus, Rutilus aula, and Chondrostoma soetta – were endemic to the Padano-Veneto District in northern Italy. Ordination of the data (MDS, CLUSTER, ANOSIM, SIMPER) showed a clear temporal gradient in fish community structure. After the establishment of the exotic predator Silurus glanis, some native species significantly declined in abundance and biomass (i.e. Alburnus arborella and Scardinius erythrophthalmus) or disappeared (i.e. Rutilus aula and Tinca tinca). Moreover, exotic species Cyprinus carpio, Ameiurus melas, and Carassius auratus from previous introductions, underwent significant changes in their abundance and biomass. No correlation was found between fish community structure and water quality parameters (BIOENV). The success of exotic species, particularly S. glanis which thrived in this degraded habitat, seems to have led to the decline of native fish fauna in the canals of the lower portion of the Po River basin. Conservation strategies focusing on the containment of exotic species and habitat restoration are recommended.
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Biological invasions are a widespread and significant component of human-caused global environmental change. The extent of invasions of oceanic islands, and their consequences for native biological diversity, have long been recognized. However, invasions of continental regions also are substantial. For example, more than 2,000 species of alien plants are established in the continental United States. These invasions represent a human-caused breakdown of the regional distinctiveness of Earth's flora and fauna - a substantial global change in and of itself. Moreover, there are well-documented examples of invading species that degrade human health and wealth, alter the structure and functioning of otherwise undisturbed ecosystems, and/or threaten native biological diversity. Invasions also interact synergistically with other components of global change, notably land use change. People and institutions working to understand, prevent, and control invasions are carrying out some of the most important - and potentially most effective - work on global environmental change.
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The use of species traits to characterize the functional composition of benthic invertebrate communities has become well established in the ecological literature. This approach holds much potential for predicting changes of both species and species assemblages along environmental gradients in terms of traits that are sensitive to local environmental conditions. Further, in the burgeoning field of biomonitoring, a functional approach provides a predictive basis for understanding community-level responses along gradients of environmental alteration caused by humans. Despite much progress in recent years, the full potential of the functional traits-based approach is currently limited by several factors, both conceptual and methodological. Most notably, we lack adequate understanding of how individual traits are intercorrelated and how this lack of independence among traits reflects phylogenetic (evolutionary) constraint. A better understanding is needed if we are to make the transition from a largely univariate approach that considers single-trait responses along single environmental gradients to a multivariate one that more realistically accounts for the responses of many traits across multiple environmental gradients characteristic of most human-dominated landscapes. Our primary objective in this paper is to explore the issue of inter-trait correlations for lotic insects and to identify opportunities and challenges for advancing the theory and application of traits-based approaches in stream community ecology. We created a new database on species-trait composition of North American lotic insects. Using published accounts and expert opinion, we collected information on 20 species traits (in 59 trait states) that fell into 4 broad categories: life-history, morphological, mobility, and ecological. First, we demonstrate the importance of considering how the linkage of specific trait states within a taxon is critical to developing a more-robust traits-based community ecology. Second, we examine the statistical correlations among traits and trait states for the 311 taxa to identify trait syndromes and specify which traits provide unique (uncorrelated) information that can be used to guide trait selection in ecological studies. Third, we examine the evolutionary associations among traits by mapping trait states onto a phylogentic tree derived from morphological and molecular analyses and classifications from the literature. We examine the evolutionary lability of individual traits by assessing the extent to which they are unconstrained by phylogenic relationships across the taxa. By focusing on the lability of traits within lotic genera of Ephemeroptera, Plecoptera, and Trichoptera, taxa often used as water-quality indicators, we show how a traits-based approach can allow a priori expectations of the differential response of these taxa to specific environmental gradients. We conclude with some ideas about how specific trait linkages, statistical correlations among traits, and evolutionary lability of traits can be used in combination with a mechanistic understanding of trait response along environmental gradients to select robust traits useful for a more predictive community ecology. We indicate how these new insights can direct the research in statistical modeling that is necessary to achieve the full potential of models that can predict how multiple traits will respond along multiple environmental gradients.
Article
Eutrophication has a profound impact on ecosystems worldwide. Grass carp Ctenopharyngodon idella, an herbivorous fish, has been introduced to control aquatic plant overgrowth caused by eutrophication, but could have other, potentially detrimental, effects. We used the Po di Volano basin (south of the Po River delta, northern Italy) as a test case to explore whether grass carp effects on canal aquatic vegetation could be at the root of historical changes in N loads exported from the basin to the Goro Lagoon. We modeled the aquatic vegetation production and standing crop, its denitrification potential, and its consumption by introduced grass carp. We then examined whether changes in historical nitrogen loads matched the modeled losses of the drainage network denitrification function or other changes in agricultural practices. Our results indicate that introduced grass carp could completely remove submerged vegetation in the Po di Volano canal network, which could – in turn – lead to substantial loss of the denitrification function of the system, causing in an increase in downstream nitrogen loads. A corresponding increase, matching both timing and magnitude, was detected in historical nitrogen loads to the Goro Lagoon, which were significantly different before and after the time of modeled collapse of the denitrification function. This increase was not clearly linked to watershed use or agricultural practices, which implies that the loss of the denitrification function through grass carp overgrazing could be a likely explanation of the increase in downstream nitrogen loads. Perhaps for the first time, we provide evidence that a freshwater fish introduction could have caused long-lasting changes in nutrient dynamics that are exported downstream to areas where the fish is not present.
Article
We present the most updated list of non-native freshwater fauna established in Portugal, including the Azores and Madeira archipelagos. This list includes 67 species at national level but corresponds to 84 species records, of which 53 are in the mainland, 23 in the Azores and 8 in Madeira archipelagos. We also discuss the progression of the cumulative number of introductions since 1800 and identify the most probable vectors of introduction, main taxonomic groups and their regions of origin. Furthermore, we review the existing knowledge about ecological and economic impacts, invasion risk and potential distribution of invaders, under present and future climatic conditions, and the applied management actions, including the production of legislation. Along the 20th century the number of successful introductions increased at an approximate rate of two new species per decade until the beginning of 1970s. Since then, this rate increased to about 14 new species per decade. These introductions were mainly a result of fisheries, as contaminants or for ornamental purposes. Fish and mollusks are the taxonomic groups with more established species, representing more than half of the total. Most species (>70%) are native from other regions of Europe and North America. Studies about ecological or socioeconomic impacts are more common for fish, crustaceans and mollusks. Impacts for most amphibians, reptiles and mammals are not thoroughly studied. A few studies on the impacts and management actions of health-threatening mosquitoes are also available. The potential distribution in the Portuguese territory was modelled for 26 species. Only a minority of these models provides projections of distributions under scenarios of future climate change. A comparison of the Portuguese and EU legislation shows large discrepancies in the invasive species lists. Using the EU list and a ranking procedure for the national context, we identify freshwater species of high national concern for which actions are urgently needed.
Article
Rivers worldwide are impacted by human activities such as habitat degradation, habitat fragmentation, waterway flow regulation, and introduction of exotic species, which are responsible for the reduction or the disappearance of native species in many parts of the world. The Oglio River, a tributary of the Po River in Northern Italy, is a good example of a river with a long history of human alteration and where exotic invasions are present. We used data on water parameters and fish communities along the watercourse to investigate whether low flow conditions, degraded water quality, abundant exotic species, and the presence of migration barriers could be a disadvantage for native species. We used ordination methods (redundancy analysis), variance partitioning analysis, and the threshold indicator taxa analysis to explore changes in community composition and ecofunctional traits along an altitude gradient. We found that exotic species affected native ones more than water quality and hydromorphological parameters. Native species were most abundant in the upper reach of the Oglio River, despite low flow and shallow depth. Moreover, rheophilic and clear water native fish decreased rapidly in the lower reach of the river, where exotic species increased. This distribution could be explained by the presence of barriers in the middle reach, which block exotic species migrating upstream from the highly invaded Po River, and by a lower suitability of the upper reach for some exotic species. Our results provide a general description of the fish fauna of a strongly regulated river and can contribute to develop more effective fish and water management practices.
Article
The implementation of the European Water Framework Directive, especially regarding the establishment of fish indexes for riverine habitats, has taken different paths in different countries. For example, in Italy previous efforts have been directed towards a taxonomy-based index, contrarily to most other European countries where an ecofunctional approach took place. Taxonomical indexes are particularly hard to apply to Mediterranean countries, where fish taxonomy is often revised causing problems in practical implementation. Alternatively, ecofunctional characteristics of fish communities could be exploited to inform on river habitat quality and to detect anthropogenic impacts, thus reducing the index sensitivity to the taxonomical variability of the fish fauna. We therefore proposed a new, multimetric index based on ecofunctional traits of fish species (EFFI, EcoFunctional Fish Index) and tested it on 208 river sampling stations of the Emilia-Romagna region, northern Italy. Using theoretical reference communities, ecological quality ratios were estimated for the whole area expressing the ecological distance of each site from reference conditions. Perhaps unsurprisingly, this work underlined how fish communities were more degraded at lower altitudes than at higher ones. EFFI scores were remarkably close to two already-established indexes for chemical (LIM) and macrozoobenthos communities (IBE) alteration. Further work should explore the validity of this approach over a wider geographical range as well as investigate the definition of environmental class boundaries and its potential intercalibration with other indexes.
Article
While the significance of anthropogenic pressures in shaping species distributions and abundances is undeniable, some ambiguity still remains on their relative magnitude and interplay with natural environmental factors. In our study, we examined 91 late-invasion-stage river locations in Northern Italy using ordination methods and variance partitioning (partial-CCA), as well as an assessment of environmental thresholds (TITAN), to attempt to disentangle the effects of eutrophication and exotic species on native species. We found that exotic species, jointly with water quality (primarily eutrophication) and geomorphology, are the main drivers of the distribution of native species and that native species suffer more joint effects than exotic species. We also found that water temperature clearly separates species distributions and that some native species, like Italian bleak (Alburnus alborella) and Italian rudd (Scardinius hesperidicus), seem to be the most resilient to exotic fish species. We also analyzed the dataset for nestedness (BINMATNEST) to identify priority targets of conservation. As a result, we confirmed that altitude correlated negatively with eutrophication and nestedness of exotic species and positively with native species. Overall, our analysis was able to detect the effects of species invasions even at a late invasion stage, although reciprocal effects seemed comparable at this stage. Exotic species have pushed most native species on the edge of local extinction in several sites and displaced most of them on the rim of their natural distribution. Any potential site- and species-specific conservation action aimed at improving this situation could benefit from a carefully considered prioritization to yield the highest results-per-effort and success rate. However, we encourage future research to update the information available before singling out specific sites for conservation or outlining conservation actions.
Book
S-Plus is a powerful environment for statistical and graphical analysis of data. It provides the tools to implement many statistical ideas which have been made possible by the widespread availability of workstations having good graphics and computational capabilities. This book is a guide to using S-Plus to perform statistical analyses and provides both an introduction to the use of S-Plus and a course in modern statistical methods. The aim of the book is to show how to use S-Plus as a powerful and graphical system. Readers are assumed to have a basic grounding in statistics, and so the book is intended for would-be users of S-Plus, and both students and researchers using statistics. Throughout, the emphasis is on presenting practical problems and full analyses of real data sets.
Article
Mediterranean shallow lakes support high biodiversity but suffer many anthropogenic threats, including introductions of alien fish. We studied the impact of introduction of common carp (Cyprinus carpio) to Medina and Zoñar lakes in SW Spain. Both lakes were protected as Ramsar sites because of their importance for waterbirds, particularly the globally threatened white-headed duck (Oxyura leucocephala IUCN Endangered) and common pochard (Aythya ferina IUCN Vulnerable). Two carp introduction events in Medina lake, with total eradication of carp in between, provided a unique opportunity to study the impacts of carp on the waterbird community (counted monthly from 2001 to 2013, with up to 69 species) and submerged macrophyte cover (quantified with satellite images). A comparison of waterbird abundance before and after carp eradication in the smaller Zoñar lake supported the results from Medina lake. Carp consistently led to the destruction of macrophyte beds and a radical change in the waterbird community. After controlling for the influence of depth fluctuations, the numbers and species richness of diving ducks were significantly reduced by carp, whilst the opposite effect was observed for piscivores such as herons. Negative impacts on O. leucocephala, A. ferina, red-crested pochard (Netta rufina) and herbivorous coots (Fulica spp.) were particularly pronounced. A significant negative impact of carp was also recorded on greater flamingos (Phoenicopterus ruber), black-necked grebes (Podiceps nigricollis), little grebes (Tachybaptus ruficollis) and gadwall (Anas strepera). In contrast, carp presence had a positive impact on grey herons (Ardea cinerea). The ongoing expansion of alien cyprinids in the Mediterranean region constitutes a major threat for waterbirds and particularly for sedentary, threatened taxa such as the white-headed duck and red-knobbed coot (F. cristata). Of 22 key sites for the isolated Iberian population of white-headed duck identified in a European action plan in 1996, at least 14 have since suffered carp invasions. Further development of successful control methods for carp populations is urgently required to support the conservation of waterbirds in the Mediterranean region.
Article
Protecting the worlds freshwater resources requires diagnosing threats over a broad range of scales, from global to local. Here we present the first worldwide synthesis to jointly consider human and biodiversity perspectives on water security using a spatial framework that quantifies multiple stressors and accounts for downstream impacts. We find that nearly 80% of the worlds population is exposed to high levels of threat to water security. Massive investment in water technology enables rich nations to offset high stressor levels without remedying their underlying causes, whereas less wealthy nations remain vulnerable. A similar lack of precautionary investment jeopardizes biodiversity, with habitats associated with 65% of continental discharge classified as moderately to highly threatened. The cumulative threat framework offers a tool for prioritizing policy and management responses to this crisis, and underscores the necessity of limiting threats at their source instead of through costly remediation of symptoms in order to assure global water security for both humans and freshwater biodiversity.
Article
Practical approaches to measuring biodiversity are reviewed in relation to the present debate on systematic approaches to conservation, to fulfil the goal of representativeness: to identify and include the broadest possible sample of components that make up the biota of a given region. Rather than adapting earlier measures that had been developed for other purposes, the most recent measures result from a fresh look at what exactly is of value to conservationists. Although debate will continue as to where precisely these values lie, more of the discussion has been devoted to ways of estimating values in the absence of ideal information. We discuss the current principles by assuming that the currency of biodiversity is characters, that models of character distribution among organisms are required for comparisons of character diversity, and that character diversity measures can be calculated using taxonomic and environmental surrogates. Full text at: www.vliz.be/imisdocs/publications/125660.pdf
Article
Introduction of the exotic Nile perch (Lates niloticus) into Africa's Lake Victoria accelerated decline of the diverse, endemic ichthyofauna, altered food web structure, and created valuable fisheries. As the Nile perch population expanded and predation rates increased, many of the endemic fish species disappeared, total fishery yield increased nearly fourfold, and fishery-related employment approximately doubled. Ecological changes in this system now occur rapidly, are due largely to human actions, and have profound socioeconomic effects. We used a bioenergetics model of Nile perch predation rates to evaluate the consequences of previous, current, and future fishery exploitation patterns and their ecological implications. The analysis produced three main conclusions: (1) Development of fisheries based on large-mesh gill nets reduced total predation by Nile perch to ≃40% of that estimated during the late 1970s, when Nile perch densities were greatest. (2) Expansion of recent intensive beach seine and small-mesh gill net fisheries for juvenile Nile perch could reduce total predation to ≃25%. (3) The combination of fishing methods could reduce total predation to ≃10% of previous levels. Reduction in estimated predatory impact corresponds with recent reports of recovery by haplochromine populations and increased fish species diversity in regions (e.g., Napoleon Gulf, Mwanza Gulf, and Winam Gulf) where fisheries are locally intense.
Article
Brown trout Salmo trutta were introduced to New Zealand in 1867. Successful establishment was broadly predictable in terms both of the characteristics of brown trout and of the receiving community. There is evidence of impacts of brown trout on the abundance of some native fish and invertebrates, and brown trout have been responsible for the local extinction and fragmentation of certain species. An intensive study of the Taieri River has revealed that several native galaxiid fishes are now restricted to headwaters above large waterfalls that prevent the upstream migration of brown trout. Brown trout may profoundly affect the functioning of stream communities, reducing the abundance of grazing invertebrates and altering their grazing behaviour so that algal biomass increases. A trophic cascade was predictable on the basis of the attributes of the invader and of the stream community. Brown trout seem to have been responsible for the evolution among invertebrates of novel anti-predator behaviours with far-reaching community consequences. The ecological and evolutionary consequences of the introduction of brown trout to New Zealand are probably reversible.
Article
The functional ecological guild approach is the cornerstone for the development of Indices of Biotic Integrity and multi-metric indices to assess the ecological status of aquatic systems. These indices combine metrics (unit-specific measures of a functional component of the fish community known to respond to degradation) into a single measure of ecological assessment. The guild approach provides an operational unit linking individual species characteristics with the community as a whole. Species are grouped into guilds based on some degree of overlap in their ecological niches, regardless of taxonomic relationships. Despite European fish species having been classified into ecological guilds, classification has not been standardised Europe-wide or within the context of classifying species into guilds from which metrics can be developed for ecological assessment purposes. This paper examines the approach used by the EU project FAME to classify European fish species into consistent ecological guilds and to identify suitable metrics as basic tools for the development of a standardised ecological assessment method for European rivers to meet the requirements of the Water Framework Directive.
Article
Understanding the processes shaping biological communities under multiple disturbances is a core challenge in ecology and conservation science. Traditionally, ecologists have explored linkages between the severity and type of disturbance and the taxonomic structure of communities. Recent advances in the application of species traits, to assess the functional structure of communities, have provided an alternative approach that responds rapidly and consistently across taxa and ecosystems to multiple disturbances. Importantly, trait-based metrics may provide advanced warning of disturbance to ecosystems because they do not need species loss to be reactive. Here, we synthesize empirical evidence and present a theoretical framework, based on species positions in a functional space, as a tool to reveal the complex nature of change in disturbed ecosystems.
Article
In this paper, we respond to Gozlan’s views of the introduction of freshwater fish, as we strongly disagree with his view and approach. We demonstrate that many real-world examples of freshwater fish introductions have catastrophic ecological consequences. We detail a few noteworthy examples, such as those of the Nile perch, carp, tilapias, catfishes, and the zebra mussel. We discuss within-nation introductions, and we explore several related problems, such as hybridization and spread of pathogens and parasites. We propose that Gozlan’s analysis is biased, as more reliable data on impacts that are already widespread are urgently needed, mainly in the biologically richest areas of the world. Thus, we continue to advocate the precautionary principle, because species introductions, once established, are largely irreversible.
Article
Genetic diversity was analysed in brown trout Salmo trutta populations living in an area of central Italy using RFLP analysis of two mtDNA segments and of the nuclear locus LDH-C1*. The data indicated a genetic structure profoundly altered by repeated stockings with allochthonous material of Atlantic origin. In fact, four and 11 of the haplotypes detected were, respectively, identical or genetically very close to haplotypes found in Danish populations, the putative source of stocked brown trout. Furthermore, the LDH-C1*90 allele, typical of north-western Europe, was widespread among the samples studied. Nonetheless, four populations are characterized by a high frequency of both putative autochthonous haplotypes and the LDH-C1*100 allele, common in the Mediterranean basin. These populations, sampled in areas where S. trutta is documented historically, might represent a remnant of the species’ indigenous biodiversity, showing the scope for improving the management of brown trout in central Italy.
Article
Due to the current species extinction crisis, there is an urgent need to identify the most threatened areas of ex-ceptionally high biodiversity and rates of endemism (i.e., "hotspots"; Mittermeier et al. 1998; Myers 1988; Reid 1998). Conservation strategies represent a crucial issue in the mediterranean biome because this area, which represents only 2% of the world's surface, houses 20% of the world's total floristic richness (Médail & Quézel 1997). Myers initially (1988, 1990) defined 14 hotspots in the tropical biome and four in mediterranean biocli-mates (southwestern Australia, Cape Region of South Af-rica, California, and part of Chile). Like the four other mediterranean areas, the Mediterranean Basin is one of the world's major centers for plant diversity, where 10% of the world's higher plants can be found in an area rep-resenting only 1.6% of the Earth's surface (Médail & Quézel 1997). The prominent role played by these areas as reservoirs for plant biodiversity has been emphasized by Myers (1990). He hesitated, however, to group the whole Mediterranean Basin into one single hotspot be-cause it covers such a large surface area, and insufficient data were available for certain regions. In this context, Médail and Quézel (1997) performed a global survey of plant richness and endemism to more precisely define hotspots in the Mediterranean Basin; they identified 10 hotspots. Three main approaches, however, have been taken in recent studies performed by international con-servation organizations to define priority conservation areas in the Mediterranean Basin. The first approach, the "megadiversity countries" project (Mittermeier et al. 1997), defined 17 megadiverse countries based primarily on plant endemism, species richness, and political boundaries. The top countries listed were Indonesia, Colombia, Brazil, Australia, Mex-ico, and Madagascar, but the Mediterranean Basin was completely left out, although, as some authors have re-cently pointed out (Heywood 1995; Médail & Quézel 1997), several tropical or subtropical countries have lower plant diversity than the Mediterranean Basin. For example, all of tropical Africa has the same plant rich-ness (30,000 taxa) as the circum-Mediterranean region in a surface area four times larger. Furthermore, the Mediterranean Basin possesses 10.8 species/1000 km 2 , which is higher than the 3.1 species/1000 km 2 in China, 4.7 in Zaire and in India, and 6.5 in Brazil, but lower than the 40 in Colombia and 90 in Panama (Médail & Quézel 1997). In the second approach, on the opposite extreme, some recent conservation strategies treat the Mediterra-nean Basin as a unique hotspot. The Global 200 project, performed by Olson and Dinerstein (1997, 1998), included the whole area in one large ecoregion defined by one rare major habitat type (i.e., Mediterranean shrublands and woodlands). These authors emphasized that "more-detailed, fine-scale analyses are essential to identify im-portant targets within ecoregions." In a recent work, Mittermeier et al. (1998) defined 24 hotspots in which, based on plant endemism, the whole Mediterranean Ba-sin was listed second after tropical Andes. Nevertheless, including all the different parts of the Mediterranean Ba-sin in one unique hotspot seems to oversimplify the situ-ation, even on a global scale. In fact, this area has many highly differentiated biogeographical patterns and land-use practices in space and time within its complex and heterogenous landscapes. The Mediterranean region constitutes both a refuge area and one that encourages floral exchange and active plant speciation (Quézel 1978, 1985). In the western ba-sin, high-endemism areas are related to the age of the geological platform and relict endemics prevail, whereas in the east, vicariant endemism is high due to the moder-ate role of glaciations and the presence of ultramafic rocks (Verlaque et al. 1997). Between the northern and southern coasts, human effects have created two differ-ent situations (Barbero et al. 1990). The collapse of the * email f.medail@botmed.u-3mrs.fr Paper submitted September 22, 1998; revised manuscript accepted June 9, 1999.