Fact and value in invasion biology

Functional traits-not nativeness-shape the effects of large mammalian herbivores on plant communities

Large mammalian herbivores (megafauna) have experienced extinctions and declines since prehistory. Introduced megafauna have partly counteracted these losses yet are thought to have unusually negative effects on plants compared with native megafauna. Using a meta-analysis of 3995 plot-scale plant abundance and diversity responses from 221 studies, we found no evidence that megafauna impacts were shaped by nativeness, "invasiveness," "feralness," coevolutionary history, or functional and phylogenetic novelty. Nor was there evidence that introduced megafauna facilitate introduced plants more than native megafauna. Instead, we found strong evidence that functional traits shaped megafauna impacts, with larger-bodied and bulk-feeding megafauna promoting plant diversity. Our work suggests that trait-based ecology provides better insight into interactions between megafauna and plants than do concepts of nativeness.

Concurrent invasions of European starlings in Australia and North America reveal population-specific differentiation in shared genomic regions

A species' success during the invasion of new areas hinges on an interplay between the demographic processes common to invasions and the specific ecological context of the novel environment. Evolutionary genetic studies of invasive species can investigate how genetic bottlenecks and ecological conditions shape genetic variation in invasions, and our study pairs two invasive populations that are hypothesized to be from the same source population to compare how each population evolved during and after introduction. Invasive European starlings (Sturnus vulgaris) established populations in both Australia and North America in the 19th century. Here, we compare whole-genome sequences among native and independently introduced European starling populations to determine how demographic processes interact with rapid evolution to generate similar genetic patterns in these recent and replicated invasions. Demographic models indicate that both invasive populations experienced genetic bottlenecks as expected based on invasion history, and we find that specific genomic regions have differentiated even on this short evolutionary timescale. Despite genetic bottlenecks, we suggest that genetic drift alone cannot explain differentiation in at least two of these regions. The demographic boom intrinsic to many invasions as well as potential inversions may have led to high population-specific differentiation, although the patterns of genetic variation are also consistent with the hypothesis that this infamous and highly mobile invader adapted to novel selection (e.g., extrinsic factors). We use targeted sampling of replicated invasions to identify and evaluate support for multiple, interacting evolutionary mechanisms that lead to differentiation during the invasion process.

Recent advances in availability and synthesis of the economic costs of biological invasions

Biological invasions are a global challenge that has received insufficient attention. Recently available cost syntheses have provided policy- and decision makers with reliable and up-to-date information on the economic impacts of biological invasions, aiming to motivate effective management. The resultant InvaCost database is now publicly and freely accessible and enables rapid extraction of monetary cost information. This has facilitated knowledge sharing, developed a more integrated and multidisciplinary network of researchers, and forged multidisciplinary collaborations among diverse organizations and stakeholders. Over 50 scientific publications so far have used the database and have provided detailed assessments of invasion costs across geographic, taxonomic, and spatiotemporal scales. These studies have provided important information that can guide future policy and legislative decisions on the management of biological invasions while simultaneously attracting public and media attention. We provide an overview of the improved availability, reliability, standardization, and defragmentation of monetary costs; discuss how this has enhanced invasion science as a discipline; and outline directions for future development.

Scaling up qualitative research to harness the capacity of lay people in invasive plant management

Successful management of invasive plants (IPs) requires the active participation of diverse communities across land tenures. This can be challenging because communities do not always share the views of scientists and managers. They may directly disagree, have alternative views, or be unwilling to manage IPs. Reviews of IP social science identify opportunities to better understand the role of cultural processes and everyday practices to address these challenges. To scale up and leverage the insights of existing qualitative social science IP research, we used meta-ethnography to unlock accounts and interpretations of lay perspectives. Meta-ethnography is a form of qualitative research synthesis increasingly used beyond its origins in health and education to produce interpretive syntheses of an area of research. In the 7 phases of meta-ethnography, we systematically identified and synthesized 19 qualitative articles pertinent to lay experience and knowledge of IPs in diverse settings. Action and meaning regarding IPs were influenced by 6 meta-themes in personal and social life: dissonance, priorities, difference, agency, responsibility, and future orientations. Through descriptions and examples of each meta-theme, we demonstrated how the meta-themes are higher level structuring concepts across the qualitative research that we analyzed and we retained grounding in the in-depth qualitative research. We characterized the meta-themes as leverage points and tensions by which we reframed lay people in terms of capacity for reflective IP management rather than as obstacles. The meta-ethnography synthesis shows how leverage points and tensions emerge from everyday life and can frame alternative and meaningful starting points for both research and public engagement and deliberation regarding IP management. These insights are not a panacea, but open up new space for reflective and mutual consideration of how to effectively navigate often complex IP problems and address conservation and social and livelihood issues in dynamic social and physical environments.

Defining invasive species and demonstrating impacts of biological invasions: a scientometric analysis of studies on invasive alien plants in Brazil over the past 20 years

Despite biological invasions being widely recognised as an important driver of environmental change, lack of consensus regarding the definition of invasive alien species (IAS) and vagueness around the demonstration of their impacts limits knowledge and research in this field. In this study, a scientometric approach was used to analyse academic documents published between 2002 and 2021 in three databases with reference to invasive alien plants in Brazil. Despite the growing body of scientific literature in the area, only 10% of the publications provided some definition of invasive species. Of the 398 publications analysed, 23.6% found some type of damage caused by the invader and, of these, only 5% addressed economic or social damage. Only 17% of the publications proposed a method for controlling and/or mitigating biological invasions. The absence of clear terminology and the lack of focus on impacts limits understanding of IAS of plants in Brazil. Based on the present findings, future studies on IAS of plants should move towards a consensus on the definition of biological invasion, as well as understand the impact caused by these species. In addition, it is recommended that further scientometric studies should guide future efforts to support objective measures for management and decision-making.

Consensus and controversy in the discipline of invasion science

Approaches, values, and perceptions in invasion science are highly dynamic, and like in other disciplines, views among different people can diverge. This has led to debate in the field specifically surrounding the core themes of values, management, impacts, and terminology. Considering these debates, we surveyed 698 scientists and practitioners globally to assess levels of polarization (opposing views) on core and contentious topics. The survey was distributed online (via Google Forms) and promoted through listservs and social media. Although there were generally high levels of consensus among respondents, there was some polarization (scores of ≥0.39 [top quartile]). Relating to values, there was high polarization regarding claims of invasive species denialism, whether invasive species contribute to biodiversity, and how biodiversity reporting should be conducted. With regard to management, there were polarized views on banning the commercial use of beneficial invasive species, the extent to which stakeholders' perceptions should influence management, whether invasive species use alone is an appropriate control strategy, and whether eradication of invasive plants is possible. For impacts, there was high polarization concerning whether invasive species drive or are a side effect of degradation and whether invasive species benefits are understated. For terminology, polarized views related to defining invasive species based only on spread, whether species can be labeled as invasive in their native ranges, and whether language used is too xenophobic. Factor and regression analysis revealed that views were particularly divergent between people working on different invasive taxa (plants and mammals) and in different disciplines (between biologists and social scientists), between academics and practitioners, and between world regions (between Africa and the Global North). Unlike in other studies, age and gender had a limited influence on response patterns. Better integration globally and between disciplines, taxa, and sectors (e.g., academic vs. practitioners) could help build broader understanding and consensus.

From anti-science to environmental nihilism: the Fata Morgana of invasive species denialism

Invasive species denialism (ISD) is a controversial and hitherto underexplored topic, particularly with regard to its potential impacts on stakeholder engagement in support of invasive species management and policy. We examined how ISD is framed within the Great Lakes invasive species community, as well as the impacts of excluding and including those perceived as denialists in engagement efforts. We interviewed key informants in the region to gain an understanding of their framings of ISD, as well as focus groups allowing participants to discuss the impacts of exclusion and inclusion of stakeholders during the engagement process. ISD discussions were organised into three framings: 1) invasive species denialism; 2) invasive species cynicism; 3) invasive species nihilism. Participants raised concerns about outright exclusion of stakeholders and offered recommendations for mitigation of the impacts of inclusion of proponents of ISD in during stakeholder engagement. Our results have shown that a better understanding of the different framings of ISD is crucial to improve communication with stakeholders and to better inform responses and mitigation efforts. The newly defined framings of invasive species cynicism and invasive species nihilism demonstrate that more targeted responses to specific forms of ISD are needed to improve stakeholder engagement outcomes.

Stakeholders Perceptions of Non-indigenous Freshwater Fish Species: A Case Study from a Mediterranean Biodiversity Hotspot

Even though the ecological impacts of invasive alien species (IAS) have been well studied, social aspects of IAS in freshwater ecosystems are still poorly explored. This study aimed to assess the perceptions associated with non-indigenous freshwater fish species (NIFS) among environmental-related professional and non-professional stakeholders in a Mediterranean country that displays high levels of fish species endemism, by using a questionnaire survey approach. Overall, 203 individuals participated, from which, the majority (n = 144) were related to environmental sciences. Most of the respondents perceived NIFS to be a threat of national importance, possibly attributed to the emotional effect of the term non-indigenous (conceived as intruder). However, NIFS were indicated as the least important threat affecting aquatic ecosystems when compared with other pressures. This contrasting perception could be explained by the fact that broad-scale impacts (i.e., climate change) exert stronger reactions compared to NIFS. Interestingly, non-professionals were more successful in identifying NIFS and native species compared to professionals, however both indicated low overall identification success. The majority of the respondents, both professionals and non-professionals, considered that: (a) the official authorities do not implement actions for NIFS management, (b) government spending should be increased to manage NIFS even if it should be reduced for other needs, and (c) early detection is the best way to manage NIFS. The establishment of a nationwide network consisting of all related stakeholders on NIFS issues, aiming to public awareness and preventive management actions to limit the spread and impacts of NIFS should be set as a priority.

Invasion costs, impacts, and human agency: response to Sagoff 2020

Article impact statement: In an era of profound biodiversity crisis, invasion costs, invader impacts, and human agency should not be dismissed.