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.

Species charisma, understood as a set of species characteristics and their perception that affect people's attitudes and behaviors, 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. Here, we discuss this concept, provide a set of recommendations for further research and highlight management implications. We review how charisma affects the processes associated with biological invasions and IAS management, including: effects on species introductions and spread, media portrayals, public perceptions of species management, research attention, and active public involvement in research and management. Explicit consideration of IAS charisma is critical to improve understanding of the drivers of people's attitudes towards particular IAS and planned management measures and strategies, and to implement programs aiming to influence stakeholder perceptions and behavior and to strengthen public engagement. In a nutshell • We discuss the concept of charismatic invasive alien species (IAS), highlight management implications and provide a set of recommendations for further research. • The charisma of IAS might influence all stages of the invasion process, and both charisma and its influence can vary over time and space. • It is a potential hindrance to management actions by affecting public support and contributing to conflicts. • We explore the concept of IAS charisma and its effects on biological invasions and management, including species introductions, media portrayal, public perceptions, opposition to management, research effort and public participation in research and management.

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)

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Dietary plasticity of populations can be associated to ontogenetic diet preferences and depends on the size-structure of populations. Dietary niche characterizes the functional role of organisms in a food web, as it reflects both resources' diversity used by a consumer and trophic interactions in the system. Dietary niches are controlled both by biotic and abiotic factors, but their interactions in natural systems remain poorly studied. Here, we investigated the variability of dietary niche in salmonid wild populations focusing both on inter-population and intra-population (through time) trophic changes, using marble trout (Salmo marmoratus) living in Slovenian headwater streams as a model system. Stable isotope analysis showed high variability of dietary niche and trophic diversity among six of the seven remnant marble trout populations. We observed substantial differences in dietary niche width among populations and within populations through time. Results of partial least square path modelling highlighted opposite effects of immature and mature trout on trophic niche structure. Direct effects of temperature and slope (stream and watershed) were opposite; temperature narrowed dietary niches while slope increased them. Environmental factors (e.g., temperature, stream and watershed slope) had indirect effects on trophic niches after accounting for fish density. Our results showed that size-distribution and sexual maturity are key determinants of the dietary niche width in a population. Increasing density of immature trout tended to widen the dietary niche while increasing density of mature trout tended to narrow it. Environmental factors had direct effects both on resources and consumers densities and indirect effects. Direct and indirect effects were often antagonistic

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The non-native rainbow trout (Oncorhynchus mykiss) has been introduced worldwide for angling purposes and has established self-reproducing populations in many parts of the world. Introduced rainbow trout often have negative effects on the native salmonid species, ranging from decrease abundance, growth and survival, to their local extinction. Assessing the effects of introduced rainbow trout on the native species is thus crucial to better set up conservation programmes. In this study, we investigated the effects of non-native rainbow trout on the diet of native marble trout (Salmo marmoratus) living in the Idrijca River (Slovenia). An impassable waterfall separates the stream in two sectors only a few hundred metres apart: a downstream sector (treatment) in which marble trout live in sympatry (MTs) with rainbow trout (RTs) and an upstream sector (control) in which marble trout live in allopatry (MTa). Specifically, we investigated using stable isotopes the effects of rainbow trout on dietary niche, diet composition, body condition, and lipid content of marble trout. We found dietary niche expansion and niche shift in marble trout living in sympatry with rainbow trout.Compared to MTa, MTs had higher piscivory rate and showed higher body condition and prereproduction lipid content. Our results indicate that the presence of rainbow trout did not have negative effects on marble trout diet and condition and that changes in dietary niche of marble trout are likely to be an adaptive response to the presence of rainbow trout, and further research is needed to better understand. K E Y W O R D Sbiological invasions, body condition, lipid content, niche segregation, stable isotope analysis, trophic niche breadth

Summary 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. 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. 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. 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. 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.