# Conservation paradoxes and challenges in invasive alien species with economic costs

Marine Robuchon, Camille Bernery, Ana Cristina Cardoso, Cheikh Abdou Khadre Mbacké Dia, Franck Courchamp, Christophe Diagne, Eugenio Gervasini, Gustavo Heringer, Sandrine Pavoine, David Renault, et al.

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## To cite this version:

Marine Robuchon, Camille Bernery, Ana Cristina Cardoso, Cheikh Abdou Khadre Mbacké Dia, Franck Courchamp, et al. Conservation paradoxes and challenges in invasive alien species with economic costs. Biological Conservation, 2025, 305, pp.111041. 10.1016/j.biocon.2025.111041. hal-04993757

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Submitted on 17 Mar 2025

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# Conservation paradoxes and challenges in invasive alien species with economic costs

Marine Robuchon<sup>a,*</sup>, Camille Bernery<sup>b</sup>, Ana Cristina Cardoso<sup>a</sup>, Cheikh A.K.M. Dia<sup>c</sup>, Franck Courchamp<sup>b</sup>, Christophe Diagne<sup>d</sup>, Eugenio Gervasini<sup>a</sup>, Gustavo Heringer<sup>e,f,g</sup>, Sandrine Pavoine<sup>h</sup>, David Renault<sup>i</sup>, Vanessa Rezende<sup>e,j</sup>, Anne-Charlotte Vaissière<sup>b,i</sup>, Céline Bellard<sup>b</sup>

## ARTICLE INFO

Keywords:

Coordinated management

Functional distinctiveness

InvaCost

Phylogenetic distinctiveness

Threat category

## ABSTRACT

Several studies have revealed species that constitute conservation paradoxes because they are invasive in some areas and threatened in others. However, those studies only considered ecological impacts of invasions and species' threat category as a criterion that makes them conservation priorities. Here, our aim was to highlight further species that cause economic costs because of their invasiveness in some areas while being in need of priority protection in their native ranges. We used the InvaCost database to calculate an economic cost for each invasive alien species (IAS) in this database and explored the threat category, as well as the phylogenetic and functional distinctiveness of these IAS. We also focused on the costliest IAS to reveal their threat category and distinctiveness. Among the 355 species of mammals, birds, and plants constituting IAS with sufficient data on economic costs, we found that 10 species are also conservation priorities because they are threatened in their native range, therefore constituting conservation paradoxes. We further found that 27 IAS with economic costs are also conservation priorities because they are among the most phylogenetically or functionally distinctive, thus constituting conservation challenges. One IAS with economic costs is a conservation priority both because it is threatened in its native range and phylogenetically distinctive: the koala. Finally, we found three conservation paradoxes or challenges among the costliest IAS. Our work stresses to an unprecedented level that some species simultaneously need to be controlled in their invasive range and protected in their native range.

## 1. Introduction

When species establish outside of their native areas, some of them can have dramatic negative impacts on local biodiversity and consequently on ecosystem functioning and possibly on nature's contribution to people (or ecosystem services) (e.g. Blackburn et al., 2004; Katsanevakis et al., 2014; Magliozzi et al., 2020; Simberloff et al., 2013). They

can also cause substantial losses and damages to human health and economic activities (e.g., Bradshaw et al., 2016; Mazza et al., 2014; Paini et al., 2016; Polce et al., 2023). Such species established outside of their native areas that have negative impacts are referred to as invasive alien species (IAS) (Russell and Blackburn, 2017). To mitigate the negative impacts of IAS, funds can be mobilised to implement management measures to prevent, control, or even eradicate IAS populations

<footnote><sup>a</sup> European Commission, Joint Research Centre (JRC), Ispra, Italy</footnote>

<footnote><sup>b</sup> Université Paris-Saclay, CNRS, AgroParisTech, Ecologie Société Evolution, 91190, Gif sur Yvette, France</footnote>

<footnote><sup>c</sup> Department of Parasitology - Mycology, Faculty of Medicine, University Cheikh Anta DIOP of Dakar, B.P. 5005 Dakar, Senegal</footnote>

<footnote><sup>d</sup> CBGP, IRD, Université de Montpellier, CIRAD, INRAE, Institut Agro, 34988 Montferrier-sur-Lez, France</footnote>

<footnote><sup>e</sup> Programa de Pós-Graduação em Ecologia Aplicada, Departamento de Ecologia e Conservação, Instituto de Ciências Naturais, Universidade Federal de Lavras - UFLA, CEP 37200-900, Lavras, MG, Brazil</footnote>

<footnote><sup>f</sup> Nürtingen-Geislingen University (HfWU), Schelmenwasen 4-8, 72622 Nürtingen, Germany</footnote>

<footnote><sup>g</sup> Thünen Institute, Institute of Biodiversity, Bundesallee 65, 38116 Braunschweig, Germany</footnote>

<footnote><sup>h</sup> Centre d'Ecologie et des Sciences de la Conservation (CESCO), Muséum National d'Histoire Naturelle, CNRS, Sorbonne Université, 75005 Paris, France</footnote>

<footnote><sup>i</sup> ECOBIO (Ecosystèmes, biodiversité, évolution) - UMR 6553, University of Rennes, CNRS, Rennes, France</footnote>

<footnote><sup>j</sup> Departamento de Biociências, Universidade do Estado de Minas Gerais, Passos, MG 37900-106, Brazil</footnote>

<footnote>* Corresponding author.
E-mail address: marine.robuchon@ec.europa.eu (M. Robuchon).</footnote>
in the invaded area and/or repair the damages caused by the invasive populations (Pyšek et al., 2020). For example, nearly 600 terrestrial populations of native island species benefited from eradication plans of invasive mammals (Jones et al., 2016).

However, the negative impacts of IAS do not necessarily trigger a management response. For example, the recent IPBES report on IAS estimated that almost half of countries do not invest financial resources to mitigate the impact of IAS (IPBES, 2023). This is because the decision to manage - or not - the negative effects of an IAS in a certain area is the result of a trade-off between the preferences of the various players involved, who may have different perceptions of the IAS in question. Such decision further depends on financial resources available. Therefore, management measures to contain IAS can be delayed or even discarded when IAS are socially accepted, thanks to e.g., their charisma (Jarić et al., 2020), the economic benefits they generate (Kourantidou et al., BirdLife, 2022), or the ecological services they provide (Linders et al., 2021). In such situations, the societal attention to IAS conflicts with the need to control them on ecological grounds.

The picture can become even more complex when IAS that have negative effects in the introduced ecosystems they invade are at the same time threatened and consequently needing protection in their native area. One such case is the wattle-necked turtle (*Palea steindachneri*). On the one hand, this species is considered critically endangered in its native range in China and Vietnam due to its high value in food trade (Marchetti and Engstrom, 2016). On the other hand, it has been introduced and probably farmed into Hawaiian Islands, Honk Kong, and Mauritius, where it causes severe alterations of the native freshwater species, which are often unique and endemic (Marchetti and Engstrom, 2016). This issue emphasizes the complexity of managing by controlling or eradicating IAS populations from species whose native populations face threats in their native range. In fact, invasive populations within alien ranges can provide valuable information on ecological and life history traits, as well as a genetic pool that can be used as insurance for species survival in their native area. In other words, while controlling or eradicating these populations would help protect invaded ecosystems and the local community, it may concomitantly further jeopardise the future of the species at the global scale. Such IAS for which the management of invasive populations conflicts with the protection of threatened native populations have been designated as conservation paradoxes by Marchetti and Engstrom (2016). They provided a dozen other examples of this kind of species, including the notorious European wild rabbit *Oryctolagus cuniculus*, which is invasive in many areas but endangered in Iberian Peninsula (Lees and Bell, 2008). All of those examples are conservation paradoxes as defined by Marchetti and Engstrom (2016). Additionally, the way they are managed within their native and alien ranges results from a trade-off between different sociocological constraints. For example, the European wild rabbit within its native range is documented both as a crucial game species for hunters and as a pest species for farmers, as it causes agricultural damages (Virgós et al., 2007). However, it is also an important prey item for many endangered predators in Spain and its populations are currently in decline, emphasizing the importance of its conservation (Lees and Bell, 2008).

Recent efforts have comprehensively revealed conservation paradoxes at continental scale (Baquero et al., 2023), or in specific taxonomic groups at global scale (Gibson and Yong, 2017; Tedeschi et al., 2024). However, these studies focused only on the negative ecological impacts of IAS, overlooking the economic burden they could also generate. Given the huge cost of IAS management amounting to $66.3 billion for the 1970–2017 period (Diagne et al., 2021) and which continues to rise (Ahmed et al., 2023), it seems even more crucial to ensure coherence between money spent in management actions to control invasive populations and money spent in conservation actions to protect threatened, native populations of the same species. We acknowledge that, although cost estimates for conservation actions at species level enabling such comparisons are not yet available, several studies have estimated the cost of meeting conservation targets (e.g., Barbier et al., 2018; McCarthy et al., 2012). Yet, identifying the most expensive situations, in terms of management and/or damage costs due to IAS, is also informative to help prioritise and reallocate spending on conservation and control measures.

The high degree of threat that species experience globally is one of the main criteria that is being used to prioritise species conservation: protecting species threatened on a global scale is a way to avoid irreversible species extinctions, which has been suggested as the main criterion to define biodiversity targets in public policies (Rounsevell et al., 2020). However, protecting species that are already threatened is a reactive conservation approach (Brooks et al., 2006). Indeed, conservation actions happen while the species is already under threat, and therefore imply huge recovery efforts with unknown chances of success. While such conservation approaches have proved effective to save some species from extinction (e.g., Al Rawahi et al., 2022), focusing on them alone to effectively protect biodiversity is a risky strategy. On the other hand, proactive conservation approaches that target non-threatened species require less effort and have more chance of success in maintaining the species unthreatened (Possingham et al., 2002), therefore complementing reactive conservation approaches. Several studies have proposed such proactive approaches targeting non-threatened but yet irreplaceable species, whether in terms of evolutionary history (Faith, 2015; Robuchon et al., 2021) or ecological functions (Cooke et al., 2020). Protecting species that exhibit a unique evolutionary history (i.e., phylogenetically distinctive species) is a way to conserve the evolutionary heritage of our planet as well as the evolutionary potential of these species. In addition to its intrinsic value, such evolutionary heritage, measured as phylogenetic diversity, represents option values, i.e., a reservoir of yet-to-be discovered benefits for humanity (Faith, 1992; IPBES, 2019). Additionally, protecting species exhibiting unique ecological functions (i.e., functionally distinctive species) is a way to preserve the integrity of ecological processes and functions (Cooke et al., 2020). Furthermore, some species can be threatened and irreplaceable at the same time, and several studies have highlighted the need for urgent conservation attention for these species, cumulating several conservation criteria (e.g., Loiseau et al., 2020; Sfair et al., 2022). We have therefore adopted a plural definition of conservation priorities in our work (Box 1).

In this study, we investigated the situations where IAS for which we

**Box 1**

Definition of key concepts used in this study

* **Conservation priorities (or species in need of priority protection):** Species that constitute priorities for conservation at global scale because they are documented as globally threatened by the IUCN Red List of Threatened Species (hereafter referred to as 'Red List'), and/or among the most evolutionarily and/or functionally distinctive species of their taxonomic group.

* **Conservation paradoxes:** Species that are simultaneously invasive in some areas and documented as globally threatened by the Red List.

* **Conservation challenges:** Species that are simultaneously invasive in some areas while being among the most evolutionarily and/or functionally distinctive species of their taxonomic group.
could calculate an economic cost of invasion (so not all invasive species) are also conservation priorities. Our first objective was to identify the IAS with economic costs that are threatened in their native range and happen to be invasive in other areas, therefore representing conservation paradoxes (Box 1). Second, because being threatened in its native range is not the only criterion to consider to prioritise species conservation, we wanted to investigate whether some IAS with economic costs also exhibit high evolutionary and/or functionally distinctiveness – respectively defined here as the species overall contribution to phylogenetic and functional diversities (Kondratyeva et al., 2019; Pavoine et al., 2017) – therefore representing conservation challenges (Box 1). We focused on mammals, birds, and plants, as they were the only taxonomic groups having sufficient data in the four areas of concern: economic costs caused in invaded areas, threat category, phylogeny, and functional traits. These analyses allowed us to highlight IAS with economic costs that are both threatened in their native areas (conservation paradoxes) and evolutionary and/or functionally distinctive (conservation challenges). Finally, we focused our attention on the costliest IAS to reveal whether conservation paradoxes and challenges occur in this subset of species that entail the highest economic costs.

# 2. Material and methods

## 2.1. Economic cost collection

We used the InvaCost database to calculate the economic cost associated with invasive alien mammals, birds, and plants over the 1960–2020 period and identified IAS with economic costs. InvaCost is a live and publicly available database that compiles the monetary losses incurred by IAS worldwide. The database was generated following a systematic, standardised methodology to collect information from scientific articles, grey literature, stakeholders and expert elicitation (Diagne et al., 2020). Each cost estimate collated was standardised to a common and up-to-date currency (that is, 2017 US dollars). The version used of this database (version 4.1) is available here: https://doi.org/10.6084/m9.fishshare.12668570. We filtered out entries that: (i) were not attributed to a single species, including those associated with different subspecies, or mix of species, (ii) did not have cost information in an up-to-date currency, (iii) corresponded to potential costs or costs from unreliable sources, and (iv) had no information on starting and ending years for cost estimation.

## 2.2. Estimation of the average costs per species

We obtained average costs for each species by aggregating cost entries over time and space following Diagne et al. (2020). First, we homogenised costs on an annual basis using the *expandYearlyCosts* function of the ‘invacost’ R package (Leroy et al., 2022). Hence, costs spanning over multiple years (for example, $20 million between 2006 and 2010) were divided according to their duration (for example, $4 million for each year between 2006 and 2010). Second, we calculated the average annual cost for each species by dividing the annualised costs by the number of cost entries in the expanded database where costs were homogenised annually. Note that we focused on average annual costs (rather than total cumulated costs) over time to weigh the differences in both number and temporal coverage of cost entries across recorded species in the database. We estimated this average annual cost separately for the two main types of cost in the InvaCost database: ‘economic damages’ caused by IAS (hereafter ‘damage costs’) and ‘management investments’ to mitigate their impacts (hereafter ‘management costs’). Finally, for each taxonomic group and based on the calculated costs, we further identified the top 5 costliest species both in terms of damage and management cost. We carried out a sensitivity analysis to compare the identity of these top 5 costliest species using average annual costs versus cumulated costs in the Supplementary Material.

## 2.3. Conservation metrics: threat category, phylogenetic distinctiveness, and functional distinctiveness

To identify conservation paradoxes, we relied on the threat category of each IAS with economic costs within its native range. We collected the global threat category of bird, mammal, and plant species from the version 2022–1 of the Red List (IUCN, 2022). Importantly, the Red List threat category is assigned to ‘wild populations inside their natural range’, and to ‘populations resulting from benign introductions’ (IUCN, 2012), thus excluding IAS populations.

Furthermore, we also downloaded phylogenies and traits for bird and mammal species from VertLife (https://vertlife.org/data/). Specifically, we used the mammal phylogeny based on the tip-dated backbone tree published by Upham et al. (2019), the bird phylogeny based on the fossil-calibrated backbone tree by Ericson et al. (2006) published by Jetz et al. (2014), and the species-level foraging attributes of the world’s birds and mammals published by Wilman et al. (2014). The traits we used to calculate functional distinctiveness are described in Table 1. For mammals and birds, they include traits related to diet, activity and body mass. For diet-related traits, we completed missing information for three mammal species (*Myzopoda aurita*, *Mystacina robusta* and *Mystacina tuberculata*) with data from the Phylacine database (Faurby et al., 2018). Following previous studies (Fritz and Purvis, 2010; Pavoine and Ricotta 2023) and to avoid the spurious assumption that the biological impact of a given difference in body mass would be the same between two small species as between two large species, we use the cube-root transformation for body mass. For plant species, we chose the most comprehensive phylogeny of seed plants published by Smith and Brown (2018), and the ‘Global Inventory of Floras and Traits’ (GIFT) database for species traits (Weigelt et al., 2020). As the species coverage in GIFT varied greatly among traits, we selected the five traits with >50 % species coverage (Table 1).

## 2.4. Calculation of phylogenetic and functional distinctiveness

We calculated scores of phylogenetic and functional distinctiveness for all mammals, birds, and plants in the world for which we had phylogenetic and trait information thanks to the function ‘distinctTree’ from the R package adv (Pavoine, 2020) using the evolutionary distinctiveness metric as a parameter (Isaac et al., 2007; Redding, 2003). Such metric consists in dividing the total diversity of a clade among its members by applying a value to each branch of the (phylogenetic or functional) tree equal to its length divided by the number of species subtending the branch. The (phylogenetic or functional) distinctiveness of a species is simply the sum of these values for all branches from which the species is descended, to the root of the tree. For mammal and bird phylogenetic distinctiveness, following the approach of Robuchon et al. (2021) to take into account phylogenetic uncertainty, we calculated species scores on a subset of 100 phylogenetic trees from the available posterior distributions of phylogenetic trees and we calculated the median score. For plant phylogenetic distinctiveness, we calculated species scores based on the only tree available.

For mammal and bird functional distinctiveness, we started by calculating three distinct scores: diet distinctiveness using diet-related traits, activity distinctiveness using activity-related traits and mass distinctiveness using body mass (see Table 1 for trait categories). We chose this approach to better understand where the distinctiveness originates (i.e., diet, activity, or mass). For these first three scores, we calculated distances between species using the function ‘dist.ktab’ from the R package ade4 (Pavoine et al., 2009; Thioulouse et al., 2018) which generalizes Gower’s general coefficient of distance to calculate functional distances between species using any statistical type of traits (e.g., circular, fuzzy, ordinal). We further calculated an overall functional distinctiveness score corresponding to the mean over diet distinctiveness, activity distinctiveness, and mass distinctiveness (with equal weight). For plant functional distinctiveness, as the information on traits
<caption>**Table 1**</caption>

Description of the traits used to calculate functional distinctiveness for mammals, birds and plants. For mammals and birds, descriptions follow Wilman et al. (2014). For plants, descriptions follow Weigelt et al. (2020).

<table><thead><tr><th>Taxonomic group(s)</th><th>Trait variable</th><th>Trait description</th><th>Trait type</th><th>Trait category</th></tr></thead><tbody><tr><td>Mammals</td><td>ForStrat-Value</td><td>Assignment to one of five (possibly ordinal when excluding marine species) foraging stratum categories: M - marine, G - ground level including aquatic foraging, S - scansorial, Ar - arboreal, A - aerial</td><td>Categorical / Ordinal</td><td>Activity</td></tr><tr><td>Mammals</td><td>Activity-Nocturnal</td><td>Foraging activity at night</td><td>Binary</td><td>Activity</td></tr><tr><td>Mammals</td><td>Activity-Crepuscular</td><td>Foraging activity at twilight</td><td>Binary</td><td>Activity</td></tr><tr><td>Mammals</td><td>Activity-Diurnal</td><td>Foraging activity at day</td><td>Binary</td><td>Activity</td></tr><tr><td>Birds</td><td>ForStrat-watbelowsurf</td><td>Prevalence of: Foraging below the water surfaces</td><td>Integer</td><td>Activity</td></tr><tr><td>Birds</td><td>ForStrat-wataroundsurf</td><td>Prevalence of: Foraging on or just (&lt;5 in.) below water surface</td><td>Integer</td><td>Activity</td></tr><tr><td>Birds</td><td>ForStrat-ground</td><td>Prevalence of: Foraging on ground</td><td>Integer</td><td>Activity</td></tr><tr><td>Birds</td><td>ForStrat-understory</td><td>Prevalence of: Foraging below 2 m in understory in forest, forest edges, bushes or shrubs</td><td>Integer</td><td>Activity</td></tr><tr><td>Birds</td><td>ForStrat-midhigh</td><td>Prevalence of: Foraging in mid to high levels in trees or high bushes (2 m upward), but below canopy</td><td>Integer</td><td>Activity</td></tr><tr><td>Birds</td><td>ForStrat-canopy</td><td>Prevalence of: Foraging in or just above (from) tree canopy</td><td>Integer</td><td>Activity</td></tr><tr><td>Birds</td><td>ForStrat-aerial</td><td>Prevalence of: Foraging well above vegetation or any structures</td><td>Integer</td><td>Activity</td></tr><tr><td>Birds</td><td>PelagicSpecialist</td><td>Foraging predominantly pelagic</td><td>Binary</td><td>Activity</td></tr><tr><td>Birds</td><td>Nocturnal</td><td>Main foraging activity at night</td><td>Binary</td><td>Activity</td></tr><tr><td>Mammals and birds</td><td>Diet-Inv</td><td>Percent use of: Invertebrates-general, aquatic invertebrates, shrimp, krill, squid, crustaceans, molluscs, cephalapod, polychaetes, gastropods, orthoptera, terrestrial Invertebrates, ground insects, insect larvae, worms, orthopterans, flying insects</td><td>Integer</td><td>Diet</td></tr><tr><td>Mammals and birds</td><td>Diet-Vend</td><td>Percent use of: Mammals, Birds</td><td>Integer</td><td>Diet</td></tr><tr><td>Mammals and birds</td><td>Diet-Vect</td><td>Percent use of: Reptiles, snakes, amphibians, salamanders</td><td>Integer</td><td>Diet</td></tr><tr><td>Mammals and birds</td><td>Diet-Vfish</td><td>Percent use of: Fish</td><td>Integer</td><td>Diet</td></tr><tr><td>Mammals and birds</td><td>Diet-Vunk</td><td>Percent use of: Vertebrates-general or unknown</td><td>Integer</td><td>Diet</td></tr><tr><td>Mammals and birds</td><td>Diet-Scav</td><td>Percent use of: Scavenge, garbage, offal, carcasses, trawlers, carrion</td><td>Integer</td><td>Diet</td></tr><tr><td>Mammals and birds</td><td>Diet-Fruit</td><td>Percent use of: Fruit, drupes</td><td>Integer</td><td>Diet</td></tr><tr><td>Mammals and birds</td><td>Diet-Nect</td><td>Percent use of: Nectar, pollen, plant exudates, gums</td><td>Integer</td><td>Diet</td></tr><tr><td>Mammals and birds</td><td>Diet-Seed</td><td>Percent use of: Seed, maize, nuts, spores, wheat, grains</td><td>Integer</td><td>Diet</td></tr><tr><td>Mammals and birds</td><td>Diet-PlantO</td><td>Percent use of: Other plant material, Grass, ground vegetation, seedlings, weeds, lichen, moss, small plants, reeds, cultivated crops, forbs, vegetables, fungi, roots, tubers, legumes, bulbs, leaves, above ground vegetation, twigs, bark, shrubs, herbs, shoots, aquatic vegetation, aquatic plants</td><td>Integer</td><td>Diet</td></tr><tr><td>Mammals and birds</td><td>BodyMass-Value</td><td>Body mass (g)</td><td>Floating Point</td><td>Mass</td></tr><tr><td>Plants</td><td>Woodiness</td><td>Assignment to one of three categories: woody, non-woody, variable</td><td>Categorical</td><td>–</td></tr><tr><td>Plants</td><td>Growth form</td><td>Assignment to one of four categories: herb, shrub, tree, other</td><td>Categorical</td><td>–</td></tr><tr><td>Plants</td><td>Epiphyte</td><td>Assignment to one of three categories: obligatory, facultative, terrestrial</td><td>Categorical</td><td>–</td></tr><tr><td>Plants</td><td>Climber</td><td>Assignment to one of three categories: obligatory, facultative, self-supporting</td><td>Categorical</td><td>–</td></tr><tr><td>Plants</td><td>Parasite</td><td>Assignment to one of three categories: obligatory, facultative, independent</td><td>Categorical</td><td>–</td></tr></tbody></table>

was different and not organised into categories as for mammals and birds, we calculated a single overall score of functional distinctiveness based on the five selected traits (Table 1) using an in-house R function (Robuchon et al., 2025). This function was written as a fast way to calculate functional distances when only categorical traits are considered and was therefore more adapted to calculate functional distinctiveness over more 200,000 plant species based on nominal traits compared to the 'dist.ktab' function that can process many different types of traits but is more resource intensive.

## 2.5. Harmonisation of taxonomic names and description of the final data set

In order to merge datasets of economic costs, threat category, phylogenetic distinctiveness, and functional distinctiveness by species, we first harmonised species names across these different datasets. Such harmonisation is a way to identify synonyms, replace them with a single reference name for each individual species, and therefore avoid duplication of species that could otherwise occur due to name mismatch between datasets. We based this harmonisation work on the workflow 2

described by Grenié et al. (2023) where species names are first attributed to a higher taxonomic group (here mammals, birds, or plants) and then matched to taxon-specific databases. Specifically, we first pre-processed species names by getting a list of raw names and standardising their writing style across all datasets. We then split the standardised species names by taxon before matching them to different databases according to the taxon. For mammals, we used the 2022–1 version of the Red List as the taxonomic reference (IUCN, 2022), and further matched unmatched names to the Integrated Taxonomic Information System (ITIS, https://www.itis.gov) and the Mammal Diversity Database from the American Society of Mammalogists (MMD, https://www.mammaldiversity.org). For birds, we used the 2022–1 version of the Red List as the taxonomic reference (IUCN, 2022), and further matched unmatched names to the ITIS and the 2022 version of the eBird database (https://www.birds.cornell.edu/clementschecklist/introduction/updateindex/october-2022/). For plants, we used the Leipzig Plant Catalogue version 2.1.0 as the taxonomic reference (https://idiv-biodiversity.github.io/lcvplants/).

After these necessary steps of species name harmonisation, we merged economic costs, threat category, phylogenetic distinctiveness,
and functional distinctiveness by harmonised species names into a single dataset. From this dataset, we removed entries related to domestic, extinct, and extinct in the wild species to obtain the final dataset used for our analyses (described in Table 2).

## 2.6. Identification of conservation paradoxes and challenges

For each taxonomic group (mammals, birds, and plants) and type of cost (damage and management), we first identified conservation paradoxes in IAS with economic costs as the species for which we could calculate an economic cost based on InvaCost and that are simultaneously threatened according to the Red List (i.e., assessed as ‘vulnerable’, ‘endangered’ and ‘critically endangered’). Second, we identified conservation challenges in IAS with economic costs as the species belonging to the most phylogenetically distinctive species (hereafter ‘most phylogenetically distinctive’) or the most functionally distinctive species (hereafter ‘most functionally distinctive’) of their taxonomic group. In the main manuscript, we identified the most phylogenetically/ functionally distinctive species as those belonging to the top 5 % most phylogenetically/functionally distinctive species of their taxonomic group. To investigate how the number of conservation challenges changes with a broader definition of ‘most distinctive species’, we conducted a sensitivity analysis by identifying the most phylogenetically/functionally distinctive species as those belonging to the top 25 % most phylogenetically/functionally distinctive species of their taxonomic group in the Supplementary Material.

We further identified IAS with economic costs that are both conservation paradoxes and challenges as those IAS that are at the same time threatened and part of the most phylogenetically and/or functionally distinctive species. Finally, we examined whether conservation paradoxes and conservation challenges in IAS with economic costs occur among the top five costliest species for each taxonomic group and type of cost.

# 3. Results

## 3.1. Threat category of IAS with economic costs

Although most of the IAS with economic costs are least concern (for mammals and birds) or are not assessed (for plants), five mammals and five plants are threatened (Fig. 1A-C, Table 3, Table S1) and can therefore be considered as conservation paradoxes. They include two endangered species (the Przewalski horse *Equus ferus* and the European rabbit) and three vulnerable species (the aoudad *Ammotragus lervia*, the koala *Phascolarctos cinereus*, and the reindeer *Rangifer tarandus*) for mammals, as well as one critically endangered species (the Tatarian honeysuckle *Lonicera tatarica*), three endangered species (the Chinese privet *Ligustrum sinense*, the leafy spurge *Euphorbia esula* and the Mexican hat plant *Kalanchoe daigremontiana*) and one vulnerable species (the cow tree *Citharexylum gentryi*) for plants (Table S1). Among the five

threatened mammals documented in InvaCost, one species has damage costs and five species have management costs (as one species has both damage and management costs), and the same holds for the five threatened plants (Table 3).

## 3.2. Phylogenetic distinctiveness of IAS with economic costs

Although the phylogenetic distinctiveness of IAS with economic costs is very variable, one mammal and seven plants are among the most phylogenetically distinctive species of their taxonomic group and thus represent conservation challenges (Fig. 1D-F, Table 3, Table S1). These include the koala, which is phylogenetically distinctive from other mammal species as it is the oldest species of Vombatiformes, and the water lettuce *Pistia stratiotes*. The koala has only management costs, while among the seven IAS of plants with economic costs the most phylogenetically distinctive, two have damage costs and six have management costs (Table 3).

## 3.3. Functional distinctiveness of IAS with economic costs

The functional distinctiveness of IAS with economic costs is also very variable between species (Fig. 1G-I). We found that eight mammals, three birds, and eight plants of these IAS with economic costs are also among the most functionally distinctive species (Fig. 1G-I, Table 3, Table S1) and can therefore be considered as conservation challenges. These include the raccoon dog *Nyctereutes procyonoides*, which has a very distinct diet (dominated by reptiles, snakes, amphibians, salamanders, and fruits) compared to other mammal species, the common myna *Acridotheres tristis*, which also has a very distinct diet (omnivore dominated by invertebrates) compared to other bird species, and the wetland nightshade *Solanum tampicense* (see Table S1 for their respective rankings). Among the eight mammals, four species have damage costs and six species have management costs (Table 3), while among the three birds, one has damage costs and three have management costs (Table 3). Finally, among the eight plant species, two species have damage costs and seven have management costs (Table 3).

## 3.4. Multi-criteria conservation paradoxes and/or challenges in IAS with economic costs

We further investigated whether some of the IAS with economic costs cumulate several criteria that make them in need of priority protection in their native areas. We found that only one species, the koala, is an IAS with economic costs both threatened and among the most phylogenetically distinctive species (Fig. 2, Table S1), and therefore constitutes both a conservation paradox and a conservation challenge. On the contrary, we did not find any IAS with economic costs that was at the same time threatened and among the most functionally distinctive species, nor any that was at the same time among the most phylogenetically and functionally distinctive species (Fig. 2).

<caption>**Table 2**</caption>

Description of the final dataset showing the number of species by taxonomic group with an economic cost, a threat category, a phylogenetic distinctiveness score and a functional distinctiveness score. Note that species can have both damage and management costs.

<table><thead><tr><th>Taxonomic group</th><th>Overall mammals + birds + plants</th><th>Mammals out of the 5,911 living mammal species estimated by Upham et al. (2019)</th><th>Birds out of the 11,188 living bird species estimated by BirdLife in 2022</th><th>Plants out of the c.a. 400,000 living plant species estimated by Govaerts (2001)</th></tr></thead><tbody><tr><td>Economic costs</td><td>355 (82 damage costs +334 management costs)</td><td>36 (19 damage costs +33 management costs)</td><td>17 (10 damage costs +14 management costs)</td><td>302 (53 damage costs +287 management costs)</td></tr><tr><td>Threat category</td><td>76,280</td><td>5881</td><td>10,998</td><td>59,401</td></tr><tr><td>Phylogenetic distinctiveness score</td><td>302,730</td><td>5626</td><td>9758</td><td>287,346</td></tr><tr><td>Functional distinctiveness score</td><td>260,270</td><td>5107</td><td>9758</td><td>245,405</td></tr></tbody></table>
Invasive alien species with economic costs (black bars or dots) versus all the other species of their taxonomic groups (grey bars or violin plots)

<figure><img src="image_3.png" /><figcaption>**Fig. 1.** Distribution of threat category (A-C), phylogenetic distinctiveness (D-F), and functional distinctiveness (G-I) of invasive alien species with economic costs (black bars or dots) compared to other species of their taxonomic groups (grey bars or violin plots) for mammals (A, D, and G), birds (B, E, and H), and plants (C, F, and I). To ease visualisation, the scales of the y-axes have been transformed (square-root-transformed for panels A to C and log-transformed for panels D to I), but the values shown are the original ones. Plain, dot-dashed and dashed red lines represent, respectively, median, third quartile, and 95th percentile values of the taxonomic group. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>
<caption>**Table 3**</caption>

Number of invasive alien species with economic costs by type of costs (total number of species with costs, number of species with damage costs and number of species with management costs – note that species can have both damage and management costs) and by taxonomic group (mammals, birds, and plants) that are also conservation priorities because they (i) are threatened (‘Threatened’) and/or (ii) belong to the top 5 % most phylogenetically distinctive species of their taxonomic group (‘Phylogenetically distinctive’) and/or (iii) belong to the top 5 % most functionally distinctive species of their taxonomic group (‘Functionally distinctive’).

<table><thead><tr><th rowspan="2">Taxonomic group<br/>Type of costs</th><th colspan="3">Mammals</th><th colspan="3">Birds</th><th colspan="3">Plants</th></tr><tr><th>Total</th><th>Damage</th><th>Management</th><th>Total</th><th>Damage</th><th>Management</th><th>Total</th><th>Damage</th><th>Management</th></tr></thead><tbody><tr><td>Threatened</td><td>5</td><td>1</td><td>5</td><td>0</td><td>0</td><td>0</td><td>5</td><td>1</td><td>5</td></tr><tr><td>Phylogenetically distinctive</td><td>1</td><td>0</td><td>1</td><td>0</td><td>0</td><td>0</td><td>7</td><td>2</td><td>6</td></tr><tr><td>Functionally distinctive</td><td>8</td><td>4</td><td>6</td><td>3</td><td>1</td><td>3</td><td>8</td><td>2</td><td>7</td></tr></tbody></table>

### 3.5. Conservation paradoxes and/or challenges in the costliest IAS

We further found that, among the top 5 costliest IAS for each taxonomic group and for each type of cost (constituting a total of 24 species), only one species represents a conservation paradox: the European rabbit, associated with an average annual cost of 66.4 million US$ in terms of damage, and 1.8 million US$ in terms of management (Fig. S1, Table S1). Although none of the costliest IAS is among the most phylogenetically distinctive species (Fig. 3), two are among the most functionally distinctive ones (Fig. 4, Table S1). These are the American mink *Neovison vison*, functionally distinctive from other mammal species because of its specific diet (it eats mainly mammals and birds) and associated with an average annual damage cost of 0.4 million US$ and management cost of 8.1 million US$, and the common starling *Sturnus vulgaris*, also functionally distinctive from other bird species because of its diet (omnivore dominated by fruits) and associated with an average annual damage cost of 40.6 million US$ and management cost of 0.3 million US$.

### 4. Discussion

#### 4.1. Shedding light on conservation paradoxes and challenges from a new perspective: the economic costs associated with IAS

By definition, IAS with economic costs have negative ecological and economic impacts in the areas they invade. Such negative impacts may, however, eclipse the need of protection of their corresponding native populations, as this has been suggested for the European rabbit (Ward, 2005). As an attempt to systematically shed light on such situations, our work represents the first study investigating the number and identity of IAS with economic costs that are paradoxically also conservation priorities. Among the 355 species of mammals, birds, and plants representing IAS with economic costs, we found that a tenth of them (i.e. 36 species) are in need of priority protection in their native areas – either because they are threatened (i.e., conservation paradoxes) and/or belong to the most phylogenetically or functionally distinctive species (i.e., conservation challenges).

Ten IAS with economic costs are threatened in their native areas, representing 2.8 % of the mammals, birds, and plants documented in InvaCost. On the other hand, 27 IAS with economic costs belong to the

<figure><img src="image_4.png" /><figcaption>**Fig. 2.** Number of mammal, bird, and plant invasive alien species with economic costs that represent conservation paradoxes because they are threatened (‘Threatened’) and/or represent conservation challenges because they belong to the top 5 % most phylogenetically distinctive species of their taxonomic group (‘Phylogenetically distinctive’) or to the top 5 % most functionally distinctive species of their taxonomic group (‘Functionally distinctive’). The 10 threatened species (9 exclusively threatened +1 also phylogenetically distinctive) are in clockwise order: *Rangifer tarandus*, *Equus ferus*, *Oryctolagus cuniculus*, *Ammotragus lervia*, *Phascolarctos cinereus* (mammals), *Ligustrum sinense*, *Euphorbia esula*, *Citharexylum gentry*, *Lonicera tatarica*, *Kalanchoe daigremontiana* (plants). The 8 phylogenetically distinctive species (7 exclusively phylogenetically distinctive +1 also threatened) are in clockwise order: *Phascolarctos cinereus* (mammals), *Zantedeschia aethiopica*, *Pistia stratiotes*, *Rubus fruticosus*, *R. glaucus*, *R. adenotrichus*, *R. megalococcus*, *R. armeniacus* (plants). The 19 functionally distinctive species are in clockwise order: *Mustela erminea*, *Herpestes edwardsii*, *Neovison vison*, *Procyon lotor*, *Paguma larvata*, *Nyctereutes procyonoides*, *Eutamias sibiricus*, *Atelerix albiventris* (mammals), *Acrodothes tristis*, *Pycnonotus cafer*, *Sturnus vulgaris* (birds), *Striga asiatica*, *Orobanche aegyptiaca*, *O. ramosa*, *Araujia sericifera*, *Periploca graeca*, *Solanum tampicense*, *Senecio jacksonii*, *Centaurea affinis* (plants).</figcaption></figure>
most phylogenetically or functionally distinctive species, representing 7.6 % of the mammals, birds, and plants documented in InvaCost. We also found that an IAS with economic costs, the koala, is simultaneously threatened and is among the most phylogenetically distinctive mammals – as also recently highlighted by Yang and Pavoine (2023). This is not the first time that koala management has been described as challenging (Whisson and Ashman, 2020). Indeed, although the koala is threatened and one of Australia's most iconic endemic species, koalas have also been introduced outside of their historic range, and overabundant southern populations are now causing significant negative impacts on native ecosystems (for example on Kangaroo Island). The koala is therefore an emblematic example of the conservation paradoxes and

challenges that we revealed here, illustrating the fact that biological invasions are a population-level rather than a species-level phenomenon (Haubrock et al., 2024). For this species, the qualifier “invasive alien” only refers to those non-native populations with negative impacts on native ecosystems, in the South of Australia, that are outside the native range of koalas. Globally, the species remains threatened and among the most phylogenetically distinctive mammals.

By analysing the nature and amount of costs associated with these conservation paradoxes or challenges in IAS with economic costs, we further highlighted two interesting findings whose specific management implications are discussed in the next subsection. First, most of the conservation paradoxes and/or challenges that we revealed among IAS

<figure><img src="image_5.png" /><figcaption>**Fig. 3.** Phylogenetic distinctiveness scores (dots) and ranks (text on the right of the dots) of the top 5 costliest invasive species for mammals (A), birds (B), and plants (C) in terms of damage and management. For each taxonomic group, rank refers to the position of the species in terms of phylogenetic distinctiveness within all species of the taxonomic group for which phylogenetic distinctiveness was assessed. The plain, dot-dashed, and dashed red lines respectively indicate the median, the third quartile, and the 95th percentile values of phylogenetic distinctiveness for each taxonomic group. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>
<figure><img src="image_6.png" /><figcaption>Fig. 4. Functional distinctiveness scores (dots) and ranks (text on the right of the dots) of the top 5 costliest invasive species for mammals (A), birds (B), and plants (C) in terms of damage and management. For each taxonomic group, rank refers to the position of the species in terms of functional distinctiveness within all species of the taxonomic group for which functional distinctiveness was assessed. The plain, dot-dashed, and dashed red lines respectively indicate the median, the third quartile, and the 95th percentile values of functional distinctiveness for each taxonomic group. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

with economic costs have management costs. This holds true for all IAS with economic costs that are also threatened, with a total average annual cost of 4.25 million US$ - of which 40 % are due to the European rabbit and 33 % to the Tatarian honeysuckle. This also holds true for most IAS with economic costs that are among the most phylogenetically or functionally distinctive species, with a total average annual cost of almost 11.4 million US$, of which 71 % are due to the American mink. Second, we revealed that three of the identified conservation paradoxes or challenges – the European rabbit, the American mink, and the common starling – are also among the costliest IAS, therefore already incurring the highest economic costs in areas where they are invasive.

## 4.2. Management implications: conservation paradoxes versus conservation challenges

The 36 IAS with economic costs identified here as conservation paradoxes and/or challenges all have, by definition, negative ecological and economic impacts, in turn supporting the need for management efforts to protect invaded ecosystems. However, the nature of management measures needed may differ between conservation paradoxes and conservation challenges. On the one hand, for threatened IAS with economic costs, the control and/or eradication of invasive populations may jeopardise the survival of the species at global scale (Marchetti and Engstrom, 2016). Examples of such cases in our study include the
European rabbit (endangered in its native range and among the costliest invasive mammal species with a total average annual cost of 68.2 million US$), the aoudad (vulnerable in its native range and an IAS with economic costs threatening at least 8 native species - Global Invasive Species Database, 2022), the koala (vulnerable in its native range and an IAS with economic costs), and the cow tree (vulnerable in its native range and an IAS with economic costs). In such cases, particular attention should be paid to coordinate management between invasive and native ranges, so that control and/or eradication of invasive populations do not contribute to precipitate the global extinction of the species. Specifically, while control and/or eradication measures should be taken for invasive populations, conservation actions are needed to protect or restore native, threatened populations. In this context, using alien individuals as substitutes to help offset the demand for wild-caught organisms or by translocating them in an effort to reinforce threatened populations within their native ranges appear as strong coordinated management solutions (Gibson and Yong, 2017). Translocation of alien individuals could further contribute to *ex situ* conservation efforts, therefore complementing and reinforcing *in situ* conservation efforts (Conde et al., 2011; Pritchard et al., 2012). In both cases, relocating alien individuals should follow translocation guidelines (IUCN/SSC, 2013) to achieve its conservation objectives while avoiding unintended damage (Tedeschi et al., 2024). Currently, while some threatened IAS such as the European rabbit, the aoudad, and the koala are controlled in their invasive ranges and also benefit from intensive conservation efforts in their native ranges (Cassinello et al., 2021; Lees and Bell, 2008; Vilalbuarte and Delibes-Mateos, 2019; Woinarski and Burbidge, 2020), other threatened IAS such as the cow tree are only controlled in their invasive ranges without any recorded conservation effort in their native ranges (Santiana and Pitman, 2004).

On the other hand, for the IAS with economic costs belonging to the most phylogenetically or functionally distinctive species, control and/or eradication actions of invasive populations are fully compatible with preventive conservation actions for native, not-yet threatened populations. Examples of such cases in our study include the water lettuce (a phylogenetically distinctive plant), the raccoon dog (a functionally distinctive mammal), and the common myna (a functionally distinctive bird). Even if these distinctive IAS with economic costs are not threatened (yet), they are securing a large amount of evolutionary history and/or ecological functions, and each new human action in their native range that might damage them should therefore be avoided (Jono and Pavoine, 2012; Robuchon et al., 2021; Steel et al., 2007). In addition, should the native populations show any sign of decline, relocating alien individuals to reinforce native populations and/or for *ex situ* conservation could be relevant as a proactive, insurance conservation strategy to ensure the long-term persistence of those distinctive species at global scale, complementary to more reactive strategies seeking to reduce the pressures that threaten them. This strategy may become more relevant, with species in their native area that may be at risk of local extinctions with ongoing and future climate change and habitat losses, as it has been predicted for some important IAS such as *Miconia calvescens* (González-Muñoz et al., 2015).

Here, we demonstrated the existence and quantified the number of conservation paradoxes and/or challenges in IAS with economic costs. Since most of those IAS have management costs, the situation is even more paradoxical: on one side, national governments and non-governmental organisations spend money to limit the number of individuals and potential spread of the species where they are invasive, while on the other side, other governments or national institutions (already or may need to) spend money to protect the species where they are native. In such situations, two options are possible: keep decoupling conservation actions in the native ranges from management actions in the invaded ranges, or coordinate conservation and management efforts between countries that host native and alien ranges. The first option comprises an economic risk (overspending money due to lack of coordination) on top of the already mentioned ecological risk in the case of

conservation paradoxes (the control and/or eradication of invasive populations may jeopardise the survival of the species at global scale). We therefore argue that the second option, where the conservation of those conservation paradoxes and challenges is reinforced when needed in native areas, and if relevant the control in invaded areas is adapted (e. g., considering translocation), is more suitable. This coordinated option constitutes a cost-efficiency approach optimising human resources and costs across the range of the species, e.g., by sharing experience and knowledge between practitioners working at different locations or scales. Although such a coordinated management strategy is valid for all conservation paradoxes and challenges in IAS with economic costs identified here, it would be economically rational to start ensuring this is working for the IAS already incurring the highest economic costs in areas where they are invasive. This is particularly relevant when it comes to public spending, which must be legitimate and defended in a context of dwindling funds for conservation matters. More generally, it is true in situations of injustice, where the existence of significant costs borne by all or part of the society should speed up the identification and contribution of the actors or economic sectors favouring these invasions. Furthermore, since this coordinated management strategy can involve a lot of different countries and that existing regional policy instruments are not enough to tackle the issue of managing conservation paradoxes and challenges (Baquero et al., 2023), it would be best to use an inter-governmental instrument to implement it. The recent IPBES report on biological invasions (IPBES, 2023) synthesizes the threats posed by biological invasions and dedicates one if its chapters to their management (Sankaran et al., 2023). Yet, while this chapter highlights that managing IAS can be challenging in situations where indigenous peoples and local communities use them for practical, cultural, or spiritual purposes, it does not address the need of coordinating management between alien and native ranges for those which are also in need of priority protection in their native areas. We believe that this topic deserves special attention, either within an existing intergovernmental instrument that could be fine-tuned to that aim (e.g., the Convention on International Trade in Endangered Species of Wild Fauna and Flora) or a new, dedicated one to manage conservation paradoxes and challenges worldwide going beyond the IAS perspective.

### 4.3. *Limits and perspectives*

Our work focused on mammals, birds, and plants because these are the groups with the most available data over the four variables: threat category, phylogeny, functional traits, and economic costs. However, we did not have full taxonomic coverage for any of these variables, which may bias some of our results. First, regarding threat category, while we have a good taxonomic coverage for mammals (99.5 % of the mammal species estimated by Upham et al., 2019) and birds (98.3 % of the bird species estimated by BirdLife in BirdLife, 2022), only 14.9 % of the estimated seed plant species (Govaerts, 2001) have a threat category. This implies that we possibly underestimated the number of plant conservation paradoxes in IAS with economic costs. Phylogenetic distinctiveness is probably the least biased variable, since we have phylogenetic distinctiveness scores for 95.2 % of mammals, 87.2 % of birds, and 71.8 % of plants. We also have good taxonomic coverage for functional distinctiveness scores: 86.4 % of mammals, 87.2 % of birds, and 61.4 % of plants. However, concerning phylogenetic or functional distinctiveness, the lack of complete taxonomic coverage leads to an overestimation of distinctiveness (Robuchon et al., 2019). Finally, the economic costs represent the variable with the largest gap in terms of taxonomic coverage, since InvaCost does not include all costs of IAS but only those that have been reported. Typically, <10 % of IAS have economic costs recorded, while the >90 % without data are certainly not all without cost (Haubrock et al., 2021 and references therein). Therefore, our results are highly conservative in this regard, and it is more likely that more conservation paradoxes and challenges will be revealed in the future.
Additionally, while we were able to associate economic costs with IAS thanks to the InvaCost database, we were unable to trace the economic costs associated with conservation actions of the corresponding native populations. Indeed, although some initiatives have started to document the costs of conservation projects worldwide such as eConservation (https://econservation.jrc.ec.europa.eu/econservation), to our knowledge, no database exists yet compiling the economic costs of conservation actions by species. Such a database would permit us to extend our analyses to compare money spent in management actions to control invasive populations and money spent in conservation actions to protect native populations of the same species.

Finally, while we identified here conservation paradoxes in IAS with economic costs as those that are also globally threatened and conservation challenges in IAS with economic costs as those that are also among the most phylogenetically or functionally distinctive species, we argue that other focuses may apply, resulting in the identification of more conservation paradoxes and/or challenges. For example, other studies have stressed the challenges represented by IAS with both economic costs and economic benefits (Kourantidou et al., 2022). The koala, identified here as both a conservation paradox and challenge, is also part of such IAS being simultaneously a burden and a benefit: on the one hand, managing populations in invaded areas represents an economic burden, but on the other hand, it is generating billions of dollars in tourism revenue (Hundloe and Hamilton, 1997). Beyond the IAS with economic costs, all IAS have ecological impacts and therefore deserve special attention. Furthermore, we only considered globally threatened species, while some IAS are only regionally threatened, such as the popular bony fish (Arapaima gigas), invasive in Indonesia, not assessed globally because of a lack of data (World Conservation Monitoring Centre, 1996), but endangered in Brazil (Marková et al., 2020).

## 4.4. Conclusions

In this study, we highlight that a tenth of the examined invasive mammals, birds, and plants with economic costs are also conservation priorities based on ecological and/or evolutionary criteria. This stresses to an unprecedented level that some species simultaneously need to be controlled and/or eradicated in their invasive ranges and conserved in their native ranges. Management of such species must be tightly coordinated throughout their range to optimise cost-effective actions and maximise conservation benefits. Although our work fills a gap by revealing conservation paradoxes and challenges in IAS with economic costs based on ecological and/or evolutionary grounds, we acknowledge that IAS management depends on societal considerations that can also vary geographically. Therefore, we urge the scientific community to further investigate paradoxes and challenges in IAS management through the lens of societal attention. This would be crucial in defining management plans for those IAS that integrate ecological, evolutionary and social dimensions as well as their geographical variability, and, in turn, in better protecting biodiversity.

### CRediT authorship contribution statement

**Marine Robuchon:** Writing – review & editing, Writing – original draft, Validation, Methodology, Formal analysis, Conceptualization.
**Camille Bernery:** Writing – review & editing, Formal analysis.
**Ana Cristina Cardoso:** Writing – review & editing.
**Cheikh A.K.M. Dia:** Writing – review & editing, Formal analysis.
**Franck Courchamp:** Writing – review & editing, Funding acquisition, Conceptualization.
**Christophe Diagne:** Writing – review & editing.
**Eugenio Gervasini:** Writing – review & editing.
**Gustavo Heringer:** Writing – review & editing, Formal analysis.
**Sandrine Pavoine:** Writing – review & editing, Formal analysis.
**David Renault:** Writing – review & editing.
**Vanessa Rezende:** Writing – review & editing, Formal analysis.
**Anne-Charlotte Vaissière:** Writing – review & editing, Conceptualization.

**Céline**

## Authors' contributions

MR, FC, ACV and CBel designed the study, which was initially discussed in a workshop with all co-authors. MR, CBer, CAKMD, GH, SP, VR and CBel ran the analyses. MR led the writing of the manuscript with substantial contributions of CBel. All authors revised the manuscript.

## Declaration of competing interest

The authors have no competing interests to declare.

## Acknowledgements

The authors acknowledge the French National Research Agency (ANR-14-CE02-0021) and the BNP-Paribas Foundation Climate Initiative. The present work was conducted following a workshop funded by the AXA Research Fund Chair of Invasion Biology and is part of the AlienScenario project funded by BiodivERSA and Belmont-Forum call. MR work was supported by the institutional activities of the Directorate D (Sustainable Resources) at the Joint Research Centre of the European Commission, GH post-doctoral research by 'Coordenação de Aperfeiçoamento de Pessoal de Nível Superior' [Brasil (Capes) – Finance code 001] and Alexander von Humboldt Foundation, and CB work by her salary as French public servants. The authors thank Boris Leroy for fruitful discussions and its contribution to code development of the project. The authors also thank Patrick Weigelt, Christian König and Holger Kreft for providing early access to the GIFT database.

## Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.biocon.2025.111041.

## Data availability

The sources of the data used in this study are mentioned in the Material and Methods section. The data generated within this study and the code to generate them are publicly accessible on the following GitHub repository: https://github.com/MarineRobuchon/invacost_consparadox. This GitHub repository has been paired with a Zenodo repository (Robuchon et al., 2025).

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