1. Predictions of the identities and ecological impacts of invasive alien species are critical for risk assessment, but presently we lack universal and standardized metrics that reliably predict the ...likelihood and degree of impact of such invaders (i.e. measurable changes in populations of affected species). This need is especially pressing for emerging and potential future invaders that have no invasion history. Such a metric would also ideally apply across diverse taxonomic and trophic groups. 2. We derive a new metric of invader ecological impact that blends: (i) the classic Functional Response (FR; consumer per capita effect) and Numerical Response (NR; consumer population response) approaches to determining consumer impact, that is, the Total Response (TR = FR × NR), with; (ii) the Tarker-Lonsdale equation' for invader impact, where Impact = Range × Abundance × Effect (per capita effect), into; (iii) a new metric, Relative Impact Potential (RIP), where RIP = FR × Abundance. The RIP metric is an invader/native ratio, where values > 1 predict that invader ecological impact will occur, and increasing values above 1 indicate increasing impact. In addition, the invader/invader RIP ratio allows comparisons of the ecological impacts of different invaders. 3. Across a diverse range of trophic and taxonomic groups, including predators, herbivores, animals and plants (22 invader/native systems with 47 individual comparisons), high-impact invaders were significantly associated with higher FRs compared to native trophic analogues. However, the RIP metric substantially improves this association, with 100% predictive power of high-impact invaders. 4. Further, RIP scores were significantly and positively correlated with two independent ecological impact scores for invaders, allowing prediction of the degree of impact of invasive alien species with the RIP metric. Finally, invader/invader RIP scores were also successful in identifying and associating with higher impacting invasive alien species. 5. Synthesis and applications. The Relative Impact Potential metric combines the per capita effects of invaders with their abundances, relative to trophically analogous natives, and is successful in predicting the likelihood and degree of ecological impact caused by invasive alien species. As the metric constitutes readily measurable features of individuals, populations and species across abiotic and biotic context-dependencies, even emerging and potential future invasive alien species can be assessed. The Relative Impact Potential metric can be rapidly utilized by scientists and practitioners and could inform policy and management of invasive alien species across diverse taxonomic and trophic groups.
Invasive non-native species (INNS) are key drivers of global biodiversity loss. This is particularly evident in freshwater ecosystems, where the rates of both vertebrate biodiversity loss and ...biological invasion exceed those of marine and terrestrial systems. Aotearoa New Zealand (henceforth Aotearoa) like many other island nations, has a troubled history with NNS. However, it is also unique, as the main islands were the last major landmasses on Earth to remain uninhabited by humans. The endemic fauna had evolved in isolation from any anthropogenic influence or introduced NNS, until the mid-thirteenth century with the arrival of Māori, the first people to inhabit Aotearoa. Centuries later, following European colonisation, many non-native freshwater fish were deliberately introduced by acclimatisation societies. Currently, most of the native freshwater fish species of Aotearoa are at risk of extinction, despite almost 90% of these being found nowhere else on earth. Many of these species are highly valued by the indigenous people of Aotearoa, who have repeatedly highlighted biases towards NNS in freshwater fish management. With the rate of biological invasions increasing, it is timely to address interconnected issues concerning the history, impacts, management and current / future policy directions, including those involving biosecurity, for non-native freshwater fish in Aotearoa. We do this by applying a social-ecological systems (SES) lens, with a focus on causal-loop relationships and feedbacks to improve understanding of the dynamics of drivers, mechanisms and impacts of such invasions. We highlight the tensions that have resulted from managing some NNS as ‘pests’ threatening native biodiversity, while simultaneously promoting a tourism and recreational fishery resource for specific NNS. This has generated extremely polarized views on the ‘status’ of non-native freshwater fish species and given rise to contradictory and divergent goals for their management. We show how a disjointed and often incoherent policy landscape has contributed to legal ‘anomalies’ for NNS, including policy misalignments and gaps, hampering effective use of resources, while also entrenching contradictory management programmes for different stakeholders. Our study shows how these interconnected issues have been manifested in social-ecological feedback loops on core aspects of NNS policy and management, past and present. Consequently, there is a need for increased comprehension of the diverse array of potential impacts of NNS for different environments, stakeholders and Māori while developing coherent and practical management methods to reduce such impacts and improve social-ecological resilience. We conclude that adopting a SES approach will aid this endeavour.
Metaphor, defined as the linguistic substitution of one phenomenon for another, is ubiquitous in environmental science and policy. In science, when used well, metaphors help to make complex and ideas ...familiar and relatable, while also helping people orient ethically to the natural world. In freshwater science, metaphors structure many aspects of scientific and lay understanding.
Yet, while metaphors are often used in environmental science and advocacy, there is a need to join up our currently diffuse understandings about how metaphors can help achieve social transformation for sustainability. Here, we focus on how metaphors are enshrined into institutions, giving them permanence and force as tools for social transformation.
We explore three examples of metaphors in environmental science and activism that have ‘gone public’ to shape freshwater politics and governance in Aotearoa New Zealand (henceforth Aotearoa NZ). We focus on the origins, strategic purposes and limitations of the metaphors, the ways they have been institutionalised, and the roles that scientists in particular have played in shaping metaphorical meanings.
Metaphors perform diverse political tasks, from mobilising popular support for species removal, to reorienting human obligations to rivers, through to expanding the scope of vision for river management. Scientists play key roles in shaping both regulatory institutions as well as informal norms that affect metaphor implementation. Finally, what makes a ‘good’ metaphor needs to be evaluated in context of who is mobilising the metaphor and what their broader sustainability values and objectives are.
Read the free Plain Language Summary for this article on the Journal blog.
Read the free Plain Language Summary for this article on the Journal blog.
The Ponto-Caspian amphipod
Dikerogammarus villosus
has invaded Central European and British freshwaters and its arrival is associated with biodiversity decline, as
D. villosus
is predatory towards ...many macroinvertebrate taxa, including resident amphipods such as
Crangonyx pseudogracilis
and isopods such as
Asellus aquaticus
. I investigated how differential physiological tolerance, habitat use and predation may drive coexistence or exclusion among
D. villosus
and resident ‘supertramp’ prey such as
C. pseudogracilis
. Experiments revealed that
D. villosus
could not survive 12 h in the extremely poor water qualities that
C. pseudogracilis
and
A. aquaticus
commonly live. Experiments manipulating oxygen levels, revealed low survivorship of
C. pseudogracilis
and
A. aquaticus
in the presence of
D. villosus
at higher oxygen levels but this survivorship increased significantly as oxygen levels fell. Predation of
C. pseudogracilis
by a resident amphipod
Gammarus pulex
followed a similar pattern but was much less severe and
A. aquaticus
appeared resistant to
G. pulex
predation. Mesocosm experiments showed that
C. pseudogracilis
survivorship in the presence of
D. villosus
increased when dense vegetation was present compared to bare substrate. Survivorship of
A. aquaticus
was uniformly poor in all habitats. Taxa with high environmental tolerance and adaptability may be resistant to this invader’s worst impacts.
It has been hypothesised that freshwater pollution may favour the establishment of tolerant invaders at the expense of less-tolerant residents. To test this, this study capitalises on the aftermath ...of a farm pollution incident, a slurry discharge to a small British stream, which eliminated the resident macroinvertebrate assemblage. Stream transplant bioassay experiments at the discharge site revealed a higher pollution tolerance of the invasive amphipod
Crangonyx pseudogracilis
and the isopod
Asellus aquaticus
than that of the native amphipod
Gammarus duebeni celticus
and the invasive
Gammarus pulex
.
A. aquaticus
recolonised the stream up to the discharge point within days, followed by
C. pseudogracilis
, then
G. pulex
, with
G. duebeni celticus
undetected after a month. Values of a macroinvertebrate-derived biotic index of organic water quality, the Average Score Per Taxon (ASPT), gradually increased up to the discharge point in the 30 days following the incident. In a larger-scale survey (72 river and 12 pond sites), inclusion/exclusion of
Gammarus
spp. had no effect on ASPT values, while inclusion of
C. pseudogracilis
increased values, despite an assumed equivalence of these amphipods in the index. Pollution could facilitate the establishment of tolerant invaders, and this has implications for biomonitoring.
Vertical transmission (VT) and associated manipulation of host reproduction are widely reported among prokaryotic endosymbionts. Here, we present evidence for widespread use of VT and associated ...sex-ratio distortion in a eukaryotic phylum. The Microspora are an unusual and diverse group of eukaryotic parasites that infect all animal phyla. Following our initial description of a microsporidian that feminizes its crustacean host, we survey the diversity and distribution of VT within the Microspora. We find that vertically transmitted microsporidia are ubiquitous in the amphipod hosts sampled and that they are also diverse, with 11 species of microsporidia detected within 16 host species. We found that infections were more common in females than males, suggesting that host sex-ratio distortion occurs in five out of eight parasite species tested. Phylogenetic reconstruction demonstrates that VT occurs in all major lineages of the phylum Microspora and that sex-ratio distorters are found on multiple branches of the phylogenetic tree. We propose that VT is either an ancestral trait or evolves with peculiar frequency in this phylum. If the association observed here between VT and host sex-ratio distortion holds true across other host taxa, these eukaryotic parasites may join the bacterial endosymbionts in their importance as sex-ratio distorters.
Single-author papers are the lowest relative contributors to the research output of international open access journals BioInvasions Records (BIR), Aquatic Invasions (AI) and Management of Biological ...Invasions (MBI), accounting for 5% or less of published papers. In contrast, papers by four or more authors are the highest contributors, accounting for over half of the research output for the three journals. Papers by two or three authors are intermediate between these extremes, accounting for 15–23% of research ouputs. The relative contributions of research papers by single-authors to the output of AI and MBI has also significantly declined over time, while concurrently those by four or more authors has significantly increased. Although not significant, a similar pattern is also evident in BIR. Considering invasion ecology research, factors such as increasing globalisation, the increasing use of transboundary data-sets for invasive species and the proliferation of collaborative multidisciplinary author teams with multiple skill-sets, may be driving single-author papers to extinction.
Non-consumptive effects (NCEs) of predators – so called ‘fear’ responses – encompass costly antipredator behaviours, such as reduced feeding efficiency. NCEs can influence prey population dynamics ...and community structure, if prey are ‘keystone’ species such as Gammarus spp. amphipod ‘shrimps’. These freshwater macroinvertebrates have the ecosystem functional role of shredding fallen leaf litter, making it accessible to other taxa. Across Europe, the invasive predatory ‘killer shrimp’ Dikerogammarus villosus is replacing resident Gammarus spp., potentially threatening this vital ecosystem function. While predation (consumptive effects (CEs)) of this invader has been well studied, for the first time we test whether NCEs can be evident in prey only exposed to D. villosus presence and whether this could potentially impact on the prey's functional role. In mesocosms, exposure to constrained D. villosus did not result in mortalities of any of three Gammarus prey species but the leaf shredding efficiencies of all prey were significantly reduced compared to a control treatment. This clear NCE has the potential to propagate through the ecological community via decreased energy processing. This study demonstrates the potential for fear of invasive predator presence alone to impact on ecosystem function.
•The invasive ‘killer shrimp’ Dikerogammarus villosus preys on Gammarus freshwater shrimp.•The mere presence of D. villosus reduces leaf shredding efficiencies of Gammarus prey species.•Non-consumptive effects of invasive predators or ‘fear’ responses impact on ecosystem function.
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