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The European eel (Anguilla anguilla) is endangered due to its peculiar life-history cycle, fishing pressure and difficulty in global population management. To improve our understanding of the population dynamics and refine conservation policies, an extended mark and recapture experiment and glass eel stocking were conducted in the River Rhône Delta (France) over 8 years. Around 1100 yellow eels were PIT-tagged and released in 2007, 2.5 kg of glass eels were released each year from 2008 to 2012, and the population was monitored using fishing between 2007 and 2015. After capture or recapture, the body parameters, sex and maturity were assessed. Age was estimated from otolith growth rings. At the end of the experiment, silver eels were between 352 and 875 mm long (age 17 to 185 months) and yellow eels between 170 and 868 mm long (age 12 to 123 months). Age estimates were validated using mark and recapture and showed 16% age underestimates and 5% inaccurate ages. The growth rates were extremely variable with lengths ranged by 2-fold at a given age. These results highlight the difficulty of eel population management, at least in the Mediterranean area.

North American cambarid crayfish have been highly successful in establishing and spreading across Europe and are now over-invading earlier arrivals in many water bodies. Parthenogenetic marbled crayfish (Procambarus virginalis), which originated from aquarium stocks, are relatively recent invaders and have established in lakes previously invaded by spiny-cheek crayfish (Faxonius limosus). However, the feeding ecology of marbled crayfish and consequential impacts on the non-native species’ coexistence are largely unexplored. By combining laboratory experiments with stable isotope analyses of field samples, we were able to (1) determine food preferences of both species under controlled conditions and (2) explore their trophic niches in three lakes where both species co-occur. In the food-choice laboratory experiments, the two species showed similar food preferences and consumption rates. Consistently, the stable isotope analyses (δ13C and δ15N) highlighted the intermediate trophic position of both species. Marbled crayfish and spiny-cheek crayfish occupied a wide range of trophic positions corresponding to a very generalist diet. However, marbled crayfish were more relying on arthropod prey than spiny-cheek crayfish which fed more on mollusks. This is the first work providing evidence for trophic plasticity of marbled crayfish in lake food webs. Our results suggest that the addition of marbled crayfish increases grazing pressure on macrophytes and macrophyte-dependent organisms and the allochthonous detritus decomposition in ecosystems already invaded by spiny-cheek crayfish. Since both species are listed as invasive alien species of EU concern, further assessments of potentially endangered food organisms are needed.

Changes in land use and agricultural intensification threaten biodiversity and ecosystem functioning of small water bodies. We studied 67 kettle holes (KH) in an agricultural landscape in northeastern Germany using landscape-scale metatranscriptomics, to understand the responses of active communities across the three domains of life, Bacteria, Archaea, and eukaryotes, to land use. These KH are proxies of the millions of small standing water bodies of glacial origin spread across the northern hemisphere. Like other landscapes in Europe, the study area has been used for intensive agriculture since the 1950s. In contrast to a parallel eDNA study which revealed the homogenization of biodiversity across KH conceivably resulting from long-lasting intensive agriculture, land-use type affected the structure of the active KH communities during spring crop fertilization, but not a month later. This effect was more pronounced in eukaryotes than in bacteria. In contrast, gene expression patterns did not differ between months or across land-use type, suggesting a high degree of functional redundancy across the KH communities. Variability in gene expression was best explained by active community structure, suggesting that these changes in functioning are primarily driven by interactions between organisms. Our results show that influences of the surrounding landscape result in temporary changes in the activity of different community members. Thus, even in KH where biodiversity has been homogenized, communities continue to respond to land management. This needs to be considered when developing sustainable management options for restoration purposes and for successful mitigation of further biodiversity loss in agricultural landscapes.

The diversity and composition of biological communities in ecosystems is typically linked to land use. Consequently, intensive agriculture has a strong influence on these patterns, including a reduction and homogenization of species diversity. Kettle holes (KH; also known as potholes) are small water bodies (2. They often function as drainage centers, linking various landscape elements in their surroundings and are hotspots of aquatic biodiversity in terrestrial landscapes. In the 1950s, the land use surrounding KH in Europe (e.g., Germany, Poland, The Netherlands) and North America (USA and Canada) shifted towards intensive agriculture, likely affecting the local and regional biodiversity of the KH. Reports on the biodiversity of ponds in agricultural landscapes are scarce, and mostly focus on single taxa. We used deep eDNA amplicon sequencing of eukaryotic, bacterial, and archaeal SSU rRNA genes to assess effects of land use on the overall species biodiversity of 67 KH in either arable fields, grasslands, or forests, all embedded in a landscape subjected to intensive agriculture for decades. These were later contrasted with Berlin city ponds. Metatranscriptomic analyses were conducted in parallel to investigate the taxonomic diversity and functionality of the active communities. The amplicon data, >300 million reads, were analyzed with phyloFlash and Kraken2 using the SILVA_SSU_Ref database. Subsequently, the sequences were grouped based on taxonomy. The use of different annotation pipelines resulted in similar patterns. A subset of the data was analyzed using DADA2, generating amplicon sequence variants. Clustering the sequences as variants or according to taxonomy resulted in identical patterns, suggesting that broad taxonomical groupings provide sufficient resolution for general overviews. Annotation of the eukaryotic community was challenging, as none of the currently available databases contains sufficient high-quality sequences to cover the entire phylogenetic breadth. To overcome this limitation, we used the SILVA_SSU_Parc database, which also contains short sequences excluded from SILVA_SSU_Ref, thus extending the taxonomic base of the analysis. The curated, high-quality PR2 eukaryotic database did not provide better results than the SILVA_SSU_Ref database. An incompatibility between the SILVA and classical taxonomic nomenclature resulted in a ‘language barrier,’ which could be partly resolved by using the parallel EMBL taxonomy provided in the SILVA databases. Nevertheless, we propose that short-read SSU-based eukaryotic taxonomic annotations should be validated by other means. Despite such methodological limitations, our study demonstrates that deep amplicon sequencing of eDNA return a reliable picture of the biodiversity in complex ecosystems. Such information is sufficient to identify biodiversity patterns across the three domains of life and can serve to pinpoint taxonomic groups which should be investigated by a more detailed approach. Our study concluded that long-term exposure to intensive agriculture results in biodiversity homogenization across diverse taxonomic groups, removing most differences in biodiversity patterns among land-use types. This outcome contrasts with biodiversity patterns associated with sediments of the KH, where temporal coverage by the eDNA analyses extends back to at least the onset of intensive agriculture. However, metatranscriptomic analyses, reflecting the distribution of activities rather than relative abundance, revealed temporal differences in the structure of the active community in KH of the investigated land-use types, matching times of field fertilization. Thus, even in a landscape where biodiversity has been homogenized, inputs from the surroundings result in short-term activity changes of different organisms. This needs to be considered when developing new management schemes needed to counteract the current biodiversity loss.

Understanding the influence of environmental and spatial factors on the structure of aquatic communities remains a major challenge in community ecology. This study aims to identify main drivers of rotifer abundance and diversity in ponds embedded in an intensive agricultural landscape in Northeast Germany. We studied 42 ponds of glacial origin (kettle holes) covering a wide range of environmental parameters. The predominant factors structuring the rotifer metacommunity shifted from abiotic environmental filtering in spring to unstudied factors in autumn, while spatial factors remained less important. Fertilizer-driven salinization, internal nutrient recycling, primary productivity and sediment phosphorus release were the prevalent biogeochemical processes in the ponds. Both fertilizer-driven salinization and primary productivity negatively affected rotifer alpha diversity, and positively affected beta diversity. This impact was lower in forest ponds than in those surrounded by arable fields or grassland. However, rotifer diversity did not significantly differ among land-use categories. Our results indicate that the long-term impact of intensive agriculture in the region and the associated widespread eutrophication overrides the direct influence of land use on rotifer diversity but point to an indirect effect via fertilizer-driven salinization. Furthermore, this study highlights the role of ponds in enhancing regional biodiversity in agricultural landscapes.

Commonly used in the literature to refer to the "attractiveness", "appeal", or "beauty" of a species, charisma can be defined as a set of characteristics - and the perception thereof - that affect people's attitudes and behaviors toward a species. It is a highly relevant concept for invasion science, with implications across all stages of the invasion process. However, the concept of invasive alien species (IAS) charisma has not yet been systematically investigated. We discuss this concept in detail, provide a set of recommendations for further research, and highlight management implications. We review how charisma affects the processes associated with biological invasions andIASmanagement, including species introductions and spread, media portrayals, public perceptions of species management, research attention, and active public involvement in research and management. Explicit consideration ofIAScharisma is critical for understanding the factors that shape people's attitudes toward particular species, planning management measures and strategies, and implementing a combination of education programs, awareness raising, and public involvement campaigns.

Background and aims Since its emergence in the mid‐20th century, invasion biology has matured into a productive research field addressing questions of fundamental and applied importance. Not only has the number of empirical studies increased through time, but also has the number of competing, overlapping and, in some cases, contradictory hypotheses about biological invasions. To make these contradictions and redundancies explicit, and to gain insight into the field’s current theoretical structure, we developed and applied a Delphi approach to create a consensus network of 39 existing invasion hypotheses. Results The resulting network was analysed with a link‐clustering algorithm that revealed five concept clusters (resource availability, biotic interaction, propagule, trait and Darwin’s clusters) representing complementary areas in the theory of invasion biology. The network also displays hypotheses that link two or more clusters, called connecting hypotheses , which are important in determining network structure. The network indicates hypotheses that are logically linked either positively (77 connections of support) or negatively (that is, they contradict each other; 6 connections). Significance The network visually synthesizes how invasion biology’s predominant hypotheses are conceptually related to each other, and thus, reveals an emergent structure – a conceptual map – that can serve as a navigation tool for scholars, practitioners and students, both inside and outside of the field of invasion biology, and guide the development of a more coherent foundation of theory. Additionally, the outlined approach can be more widely applied to create a conceptual map for the larger fields of ecology and biogeography., Global Ecology and Biogeography, 29 (6), ISSN:1466-822X, ISSN:1466-8238

Publisher's version (útgefin grein), Managing the impacts of invasive alien species (IAS) is a great societal challenge. A wide variety of terms have been used to describe the management of invasive alien species and the sequence in which they might be applied. This variety and lack of consistency creates uncertainty in the presentation and description of management in policy, science and practice. Here we expand on the existing description of the invasion process to develop an IAS management framework. We define the different forms of active management using a novel approach based on changes in species status, avoiding the need for stand-alone descriptions of management types, and provide a complete set of potential management activities. We propose a standardised set of management terminology as an emergent feature of this framework. We identified eight key forms of management: (1) pathway management, (2) interception, (3) limits to keeping, (4) secure keeping, (5) eradication, (6) complete reproductive removal, (7) containment and (8) suppression. We recognise four associated terms: prevention; captive management; rapid eradication; and long-term management, and note the use of impact mitigation and restoration as associated forms of management. We discuss the wider use of this framework and the supporting activities required to ensure management is well-targeted, cost-effective and makes best use of limited resources., This paper arose from a workshop of the Invasion Dynamics Network (InDyNet) in Berlin in 2018, funded by the Deutsche Forschungsgemeinschaft (DFG) Grant JE 288/8-1, which included a Mercator Fellowship for DLS. Additional support was received through DFG Grants JE 288/9-1 and JE 288/9-2 to JMJ, the G.E. Hutchinson Chair to DLS and the project “Capacity Building Neobiota” (Austrian Federal Ministry for Sustainability and Tourism) to WR. AN, PP and JP were supported by long-term research development project no. RVO 67985939, project 17-19025S and EXPRO grant 19-28807X (Czech Science Foundation). IJ was supported by the J. E. Purkyně Fellowship of the Czech Academy of Sciences. We also thank the referees for this paper for their critical and constructive comments.

Introduced and allopatric populations of brown trout Salmo trutta and rainbow trout Oncorhynchus mykiss were sampled in Slovenia for stable isotope analysis to assess dietary niche shifts through ontogeny and estimate the propensity for cannibalism. Both S. trutta and O. mykiss are cannibals, with higher average relative contribution of conspecific assimilated energy for S. trutta (27·9%) compared with O. mykiss (7·7%). The smallest cannibal was 166 mm in the S. trutta population and 247 mm in the O. mykiss population.

International audience; Intraspecific trait variability (ITV) maintains functional diversity in populations and communities, and plays a crucial role in ecological and evolutionary processes such as trophic cascades or speciation. Furthermore, functional variation within a species and its populations can help buffer against harmful environmental changes. Trait variability within species can be observed from differences among populations, and between‐ and within individuals. In animals, ITV can be driven by ontogeny, the environment in which populations live and by within‐individual specialization or variation unrelated to growth. However, we still know little about the relative strength of these drivers in determining ITV variation in natural populations. Here, we aimed to (a) measure the relative strength of between‐ and within‐individual effects of body size on ITV over time, and (b) disentangle the trophic changes due to ontogeny from other sources of variability, such as the environment experienced by populations and individual preferences at varying temporal and spatial scales. We used as a model system the endangered marble trout Salmo marmoratus, a freshwater fish living in a restricted geographical area (

International audience

SUMMARY 1. Invasive species may have strong negative impacts on ecosystems. Invasive crayfish are well known to cause ecological imbalances in freshwater systems and have become targets in eradication programmes. 2. The red swamp crayfish (Procambarus clarkii) is vulnerable to predation by several fish species. The European eel (Anguilla anguilla) appears to be a very good candidate given its benthic feeding activity and ability to recognise prey by odour. 3. Our study took place from 2009 to 2013 in a closed system in south-eastern France in which ponds were sampled twice a year by passive capture methods to evaluate trends in populations of potential prey. Eel population dynamics were assessed by means of a multistate capture–recapture model, and diet assessment was performed using stable isotope analysis in October 2010 and October 2012. 4. Our results show that the invasive crayfish was the most important prey in the eel diet, and every size-class of crayfish was preyed upon by the predator. 5. A high predator density, approaching carrying capacity for the European eel in this system, strongly affects P. clarkii populations, leading them to their collapse, but not eradication.

Niche-based hypotheses have been proposed to explain processes and mechanisms of success in the establishment of non-native species into native communities. Competition due to niche overlap may lead to native species niche shift and to native species replacement. To understand the ecological consequences of trophic interactions between non-native rainbow trout and native and endangered marble trout, we used as model system the Idrijca river (Western Slovenia) in which marble trout occurs either in allopatry (MTa) or in sympatry (MTs) with rainbow trout (RTs). We focused on different metrics of niche change such as centroid shift, niche overlap and trophic niche breadth using stable isotope analysis (δ15N and δ13C). Our results showed plasticity in niche overlap between MTs and RTs and niche shift of marble trout when occurring in sympatry with RTs, but not due to a niche replacement of MTs by RTs. Niche breadth of marble trout increases in sympatry and the trophic position during the growth period was higher for MTs than MTa.