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Risk assessment currently lacks reliable tools that can be applied across a range of environmental contexts to predict the success and impact of invasive species. A comparative functional response approach may offer insight and predictive power regarding the impacts of invasive bivalves. This could prove valuable in the management of invasive species that drive losses in ecosystem function and biodiversity. We conducted feeding experiments to assist in predicting the relative impact of two sympatric species of dreissenid mussel, the zebra and quagga (Dreissena polymorpha and D. rostiformis bugensis, respectively). Feeding rates and functional responses were calculated for each species under different 'contexts', including ranges of algal concentrations and temperatures. Clearance rates ranged from 10 to 44 ml/g mussel/h. Both species exhibited type I functional responses across all contexts studied. There were no differences in the clearance rates or functional responses between species at 4 °C and 12°C. Thus, the competitive exclusion of zebra mussels by quagga mussels seen in nature does not appear to be driven by disparities in feeding efficiencies. Both species demonstrated elevated functional responses at the highest temperature (24 °C) compared with the lowest temperature (4 °C). Zebra mussels showed a significantly higher clearance rate than quagga mussels at 24 °C. We conclude that total species abundance, rather than changes in species dominance, is likely to be more important for net species impact. Functional responses may offer considerable explanatory and predictive power under certain contexts; they are particularly fitting for sessile invasive bivalves due to their high feeding rates and the seasonal changes in algae abundance they experience. [ABSTRACT FROM AUTHOR]

Protected areas ( PAs) are intended to provide native biodiversity and habitats with a refuge against the impacts of global change, particularly acting as natural filters against biological invasions. In practice, however, it is unknown how effective PAs will be in shielding native species from invasions under projected climate change. Here, we investigate the current and future potential distributions of 100 of the most invasive terrestrial, freshwater, and marine species in Europe. We use this information to evaluate the combined threat posed by climate change and invasions to existing PAs and the most susceptible species they shelter. We found that only a quarter of Europe's marine and terrestrial areas protected over the last 100 years have been colonized by any of the invaders investigated, despite offering climatically suitable conditions for invasion. In addition, hotspots of invasive species and the most susceptible native species to their establishment do not match at large continental scales. Furthermore, the predicted richness of invaders is 11%-18% significantly lower inside PAs than outside them. Invasive species are rare in long-established national parks and nature reserves, which are actively protected and often located in remote and pristine regions with very low human density. In contrast, the richness of invasive species is high in the more recently designated Natura 2000 sites, which are subject to high human accessibility. This situation may change in the future, since our models anticipate important shifts in species ranges toward the north and east of Europe at unprecedented rates of 14-55 km/decade, depending on taxonomic group and scenario. This may seriously compromise the conservation of biodiversity and ecosystem services. This study is the first comprehensive assessment of the resistance that PAs provide against biological invasions and climate change on a continental scale and illustrates their strategic value in safeguarding native biodiversity. [ABSTRACT FROM AUTHOR]

Abstract: Climate change and invasive species are two major biodiversity threats expected to provoke extinctions of many species in the future. This study evaluates the joint threat posed by climate change and two invasive species: the zebra mussel (Dreissena polymorpha) and the signal crayfish (Pacifastacus leniusculus), on the distribution of two endangered freshwater species: the depressed river mussel (Pseudanodonta complanata) and the white-clawed crayfish (Austropotamobius pallipes), at the scale of Europe. We expected the native species to experience a gradual contraction over time in their geographic range size, while the invasive species would maintain or increase their spread; therefore, their overlap would increase, further threatening the conservation of the native species. To test these three hypotheses, ensemble species distribution models (SDMs) were calibrated with current distributions and projected onto present and 2050 future climatic scenarios. In agreement with our expectations, the 2050 scenarios suggested D. polymorpha may strongly benefit from climate changes (increase of 15–20% in range size), while the depressed river mussel would experience a considerable loss (14–36%), the overlap between both mussels increasing up to 24%. Although both crayfishes were predicted to be negatively affected by climate changes, the contraction was more severe for the invasive P. leniusculus (up to 32% decrease in range size). Moreover, the overlap between both crayfishes decreased by 13–16%, which may reduce the pressure upon the native A. pallipes. This study illustrates how SDMs can assist in management of endangered species over large spatial and temporal scales by identifying current and future areas of shared bioclimatic suitability and potential refugia. [Copyright &y& Elsevier]

Risk assessment currently lacks pliable tools that can be reliably applied across a range of environmental contexts to predict the success and impact of non‐native species (NNS). An approach adopting functional responses (FR) and the Relative Impact Potential (RIP) metric may offer considerable insight and predictive power regarding invader impacts, which may include losses in ecosystem function and biodiversity. We aim to evaluate the use of FRs and the RIP metric in predicting impact in non‐native, data‐deficient bivalves.Very little is known about the potential impacts of the Gulf wedge clam, Rangia cuneata outside of its native range, and as a rapidly spreading non‐native species, it is highly suitable for this study. Comparisons of feeding activity and abundance between non‐native species and functionally analogous native species may produce reliable impact predictions where significant disparity in these factors exists. We conducted field abundance surveys and laboratory feeding studies on R. cuneata, in order to quantify FRs and the RIP metric. Clearance rates and FRs were calculated for R. cuneata and the sympatric, native unionid duck mussel, Anodonta anatina, across a range of algal concentrations at 1.0 ppt salinity.Mean ± SE clearance rates (ml g DW−1 hr−1) were found to be significantly greater for R. cuneata (294.31 ± 65.17) than for A. anatina (125.99 ± 29.59) with both species exhibiting a type I functional response. As a result of far greater field abundance of R. cuneata compared with A. anatina (37.7 m−2 ± 6.1 versus 0.7 m−2 ± 0.4 at sympatric sites) and a significantly higher feeding rate, the RIP score for R. cuneata was high (11.61) signifying likely ecological impact. Calculating the probability density function for the RIP includes uncertainty in the metric and also yielded a very high value (38.14), and these results provide the first evidence that R. cuneata should be considered a high‐risk invasive species.The results of our analyses firmly support the assertion that R. cuneata will likely continue to have significant impact in its introduced range if management action is not taken. The rate of spread of R. cuneata, its established densities and RIP score are all comparable to severely invasive bivalves; therefore, R. cuneata may pose a significant threat to both freshwater and brackish water biodiversity and function. We conclude that FRs and the RIP metric may be extremely beneficial to making reliable impact predictions for non‐native species and are particularly well suited for estimating the potential impacts of data‐deficient novel and emerging non‐natives. [ABSTRACT FROM AUTHOR]

Freshwater mussels (Unionida) are globally endangered but perform crucial ecosystem services in temperate ecosystems. Their status and role in tropical regions are poorly understood, resulting in a nearly complete lack of effort toward their conservation. Understanding mussel functions in developing countries is particularly important because costly interventions to restore habitat functionality are often infeasible. We investigated the role of mussels in the nearshore zone of Dhanmondi Lake, a narrow, polluted lake in central Dhaka, Bangladesh, during the dry season. Sampling at 50 sites 1 to 3 m from the shore revealed dense mussel populations, averaging 218 individuals (ind)/m2 from 2 species (Lamellidens marginalis and Parreysia caerulea). Based on laboratory filtration rates and in-situ size-frequency distribution, we calculated that mussels filter the equivalent of the volume of the lake margins in 21 h. This filtration capacity appears to explain the lake's high water clarity (>2 m visibility during the dry season), despite copious nutrient availability for algal growth. Although it is heavily polluted, the near-shore zone of the lake has a diverse macroinvertebrate fauna, featuring up to 16 invertebrate families/0.25 m2. Strong positive correlations among mussel density, macroinvertebrate richness, and diversity were revealed through 2-min kick-samples, and indicate that mussels act as microhabitat engineers that promote localized biodiversity. Loss of mussel communities could result in further loss of ecosystem services, which would be costly to replace through other means. Moreover, our data suggest that mussel abundance may be used to identify sites of high macroinvertebrate biodiversity in tropical freshwaters and, thus, help to focus management efforts in the most cost-effective way. [ABSTRACT FROM AUTHOR]

Invasive alien species ( IAS) are considered one of the greatest threats to biodiversity, particularly through their interactions with other drivers of change. Horizon scanning, the systematic examination of future potential threats and opportunities, leading to prioritization of IAS threats is seen as an essential component of IAS management. Our aim was to consider IAS that were likely to impact on native biodiversity but were not yet established in the wild in Great Britain. To achieve this, we developed an approach which coupled consensus methods (which have previously been used for collaboratively identifying priorities in other contexts) with rapid risk assessment. The process involved two distinct phases: Preliminary consultation with experts within five groups (plants, terrestrial invertebrates, freshwater invertebrates, vertebrates and marine species) to derive ranked lists of potential IAS., Consensus-building across expert groups to compile and rank the entire list of potential IAS., Five hundred and ninety-one species not native to Great Britain were considered. Ninety-three of these species were agreed to constitute at least a medium risk (based on score and consensus) with respect to them arriving, establishing and posing a threat to native biodiversity. The quagga mussel, Dreissena rostriformis bugensis, received maximum scores for risk of arrival, establishment and impact; following discussions the unanimous consensus was to rank it in the top position. A further 29 species were considered to constitute a high risk and were grouped according to their ranked risk. The remaining 63 species were considered as medium risk, and included in an unranked long list. The information collated through this novel extension of the consensus method for horizon scanning provides evidence for underpinning and prioritizing management both for the species and, perhaps more importantly, their pathways of arrival. Although our study focused on Great Britain, we suggest that the methods adopted are applicable globally. [ABSTRACT FROM AUTHOR]

The European Union (EU) has recently published its first list of invasive alien species (IAS) of EU concern to which current legislation must apply. The list comprises species known to pose great threats to biodiversity and needs to be maintained and updated. Horizon scanning is seen as critical to identify the most threatening potential IAS that do not yet occur in Europe to be subsequently risk assessed for future listing. Accordingly, we present a systematic consensus horizon scanning procedure to derive a ranked list of potential IAS likely to arrive, establish, spread and have an impact on biodiversity in the region over the next decade. The approach is unique in the continental scale examined, the breadth of taxonomic groups and environments considered, and the methods and data sources used. International experts were brought together to address five broad thematic groups of potential IAS. For each thematic group the experts first independently assembled lists of potential IAS not yet established in the EU but potentially threatening biodiversity if introduced. Experts were asked to score the species within their thematic group for their separate likelihoods of i) arrival, ii) establishment, iii) spread, and iv) magnitude of the potential negative impact on biodiversity within the EU. Experts then convened for a 2‐day workshop applying consensus methods to compile a ranked list of potential IAS. From an initial working list of 329 species, a list of 66 species not yet established in the EU that were considered to be very high (8 species), high (40 species) or medium (18 species) risk species was derived. Here, we present these species highlighting the potential negative impacts and the most likely biogeographic regions to be affected by these potential IAS. We identified 66 species, that are currently absent from the EU, which pose a very high, high or medium threat to biodiversity and ecosystems. The species span a range of functional groups, with primary producers being numerically dominant. Escape from confinement is the pathway considered to be the most likely route of introduction for many species, particularly among plants and vertebrates. [ABSTRACT FROM AUTHOR]

Large river floodplains contain a high diversity of habitats and species but are highly threatened by human activities. River floodplain restoration is increasingly undertaken to reverse biodiversity loss and enhance ecosystem services., Few studies have examined the consequences on the biota of restoring lateral connectivity, a key variable that represents the exchange of materials and organisms between the river and its floodplain. We developed models to describe the richness and abundance of aquatic macroinvertebrates in 18 channels of the Rhône floodplain and predict how restoration (i.e. the increase in lateral connectivity of floodplain channels) should alter the native and alien communities., Models quantified how richness and abundance decrease for lentic taxa and increase for lotic and alien taxa with higher connectivity between the floodplain channels and the main channel. Predicted changes were weakly related to overall observed changes when all restored channels were combined, but consistent with observed changes when floodplain channels were grouped by restoration type. We highlighted that restoration interventions modifying lateral connectivity induced a change of lentic and lotic taxa richness in accordance with the predictions. Richness of alien taxa was favoured by restoration more than predicted; however, no interaction between alien species changes and native species was detected after restoration., Restoration of the ecosystem predictably transformed native communities and encouraged alien species, at least over the 4 years studied. Our findings demonstrate that lateral connectivity is a key variable driving macroinvertebrate communities in large river floodplains and that the response of macroinvertebrates to restoration of a disturbance-driven ecosystem can in part be predicted. Therefore, the outcome of restoration programmes can be optimised by quantifying lateral connectivity before and after restoration. [ABSTRACT FROM AUTHOR]

Rivers and floodplains are among the most threatened ecosystems. Hydroelectric power plants and embankments have reduced the hydrological connectivity between rivers and their floodplain channels, leading to loss of freshwater habitats and biological communities. To prevent and reverse such loss, numerous restoration programmes have aimed at rejuvenating the lateral hydrological connectivity between rivers and floodplain channels. Despite considerable global attention, we know remarkably little about the ecological benefits of floodplain restoration programmes., We analysed the functional diversity of different macroinvertebrate groups (natives and aliens) along a gradient of lateral hydrological connectivity on the Rhône river in France. We used 36 sampling sites to describe the functional diversity (Rao's quadratic entropy) before and after the enhancement of the lateral hydrological connectivity by restoration. The effects of restoration on functional diversity were tested for each macroinvertebrate group and at multiple spatial levels (alpha and beta)., Before restoration, alpha functional diversity of the entire macroinvertebrate community peaked in sites with a high lateral connectivity. The contribution of the native groups to functional diversity was higher than that of the alien group. The latter was not constrained by high values of lateral hydrological connectivity and reached a maximum in highly connected sites., After restoration, within-site functional diversity (alpha FD) declined linearly following the enhancement of lateral hydrological connectivity. The restoration operations increased the contribution of the aliens to functional diversity and reduced the contribution of a group of native taxa. In addition, among-sites functional diversity (beta FD) was successfully enlarged by restoration., Synthesis and applications. The lateral hydrological connectivity (LHC) represents a key parameter for explaining the functional diversity (FD) of macroinvertebrates in a floodplain ecosystem. Our results demonstrate that restoration-induced changes to functional diversity can be predicted. Controversially, restoration-induced enhancement of lateral hydrological connectivity increased the functional diversity of the alien macroinvertebrates. However, these species contributed only to a small part of the total macroinvertebrate functional diversity. We recommend that restoration programmes diversify the levels of lateral hydrological connectivity among the channels to ensure an optimal functional diversity at the floodplain scale. [ABSTRACT FROM AUTHOR]