A post 2020 target on invasive alien species (IAS) - IUCN

A post 2020 target on invasive alien species (IAS)

An IUCN & IUCN SSC Invasive Species Specialist Group proposal for a global target to
address IAS, which is made without prejudice to IUCNs final position on the post-2020
framework

Rationale for proposed 2030 target
Invasive alien species (IAS) are known to be one of the major drivers of biodiversity loss
(Maxwell et al. 2016, IPBES 2019), and are the primary cause of recent extinctions in most
taxonomic groups, especially on islands (e.g. Bellard et al. 2016, Spatz et al. 2017, Butchart et
al. 2018). IAS also cause substantial negative impacts to human health (Mazza et al. 2014,
Maza & Tricarico 2018), livelihoods (Pratt et al. 2017), and economies (Bradshaw et al. 2016).

The number of new introductions of species to areas outside their natural range is growing at an
unprecedented pace, among all taxonomic groups and in all biomes, with no sign of a saturation
effect (Seebens et al. 2017). Alarmingly, a high proportion of recent introductions are of species
that have never been recorded as alien before, meaning that the number of IAS is forecast to
increase in the future among all taxonomic groups (Seebens et al. 2018). In addition, due to
climate change many regions will become more suitable for a greater number of IAS (Bellard et
al. 2013), and an increase in extreme weather events will likely facilitate their spread (Diez et al.
2012). As a result, the impacts caused by IAS are expected to continue to increase.

Pathways
The transport and introduction of IAS can be intentional, e.g. for hunting or ornamental
purposes, or accidental (unintentional), e.g. as transport on, in, or with ships, airplanes, and
vehicles or with the commercial products carried by these conveyances. The management of
these ‘pathways’ of introduction is critical if we are to reduce future introductions of IAS.
Intentional movements of species can be effectively addressed by regulating trade, import,
possession and/or transport, whereas unintentional movements require the identification of the
most relevant pathways of introduction and effectively managing them in order to prevent the
arrival of IAS posing significant risks. The most appropriate intervention will depend on the
taxon or environment considered. Prevention by addressing pathways of introduction is
particularly critical for the marine environments, both because most IAS introduced arrive via
accidental means of transport such as ballast waters and biofouling, and because once

established marine IAS in almost all cases cannot be eradicated or controlled. It is important to
stress that addressing key pathways of introduction of marine IAS is a realistic goal; in fact, the
(UN-IMO) International Convention for the Control and Management of Ships' Ballast Water and
Sediments (BWM)1 entered into force on September 8, 2017 already includes targets (e.g.
target of full global implementation by 2024) whose fulfilment would be a significant progress in
this direction. Relative to biofouling there is encouraging progress, such as the GEF, UNDP,
UN-IMO GloFouling Project launched on November 20182, that could permit significant
advancements in the prevention of IAS introductions via this specific pathway. Prevention by
addressing pathways of introduction is similarly critical important for microbial invasions
(predominantly accidentally introduced, difficult to identify, manage post-border). For example,
“nearly 70% of damaging forest insects and pathogens established in the US between 1860 and
2006 most likely entered on imported live plants” (Liebhold et al. 2012), these risks need to be
understood and regulated in partnership with the stakeholders involved.

Species
However, to simply address future impacts through the prevention of IAS introductions is not
enough. It is essential that we control including secondary spread, and eradicate if possible, the
most harmful established IAS if we are to abate their impacts to biodiversity.

To enhance effective management it is also essential to promote an improvement of the tools
and strategies to predict, prevent, control or eradicate the most damaging IAS.

Areas
Finally, there is a need to identify and prioritise vulnerable areas, such as sites or ecosystems,
that are sensitive and susceptible to the impacts from IAS, in particular those that are important
for the persistence of biodiversity if we are to effectively mitigate against current and future
impacts from IAS (McGeoch et al. 2016). The removal of IAS from many islands, stands as a
significant global example that eradications are one of the most successful conservation
outcomes, effectively protecting native species, and preventing extinctions (Jones et al. 2016).
Further, by eradicating invasive mammals from 100-200 high priority islands around the world
has significant opportunity to improve the survival prospects of high numbers of threatened
species (e.g. Brooke et al. 2007, Dawson et al. 2015, Holmes et al. 2019).

This geographic prioritisation for mitigating impacts from IAS is not incorporated into Aichi
Target 9, which states: “By 2020, invasive alien species and pathways are identified and

1
  http://www.imo.org/en/About/Conventions/ListOfConventions/Pages/International-Convention-for-the-
Control-and-Management-of-Ships%27-Ballast-Water-and-Sediments-(BWM).aspx
2
  http://www.imo.org/en/mediacentre/pressbriefings/pages/20-biofouling.aspx

prioritized, priority species are controlled or eradicated, and measures are in place to manage
pathways to prevent their introduction and establishment”.

Proposal for 2030 invasive alien species target
In the last few years, substantial progress has been made in assessing the global patterns and
underlying causes of biological invasions – in particular by developing globally applicable tools
for assessing the environmental and socio-economic impacts of alien species (Blackburn et al.
2014, Bacher et al. 2018), by compiling global databases on the spatial distribution of alien
species of various taxonomic groups (e.g. mammals, birds, reptiles, amphibians, freshwater
fish, vascular plants, ants, spiders; (van Kleunen et al. 2015; Dyer et al. 2016; Capinha et al.
2017; Dawson et al. 2017; Pagad et al. 2018), and the temporal trajectories of alien species
accumulation (Seebens et al. 2017, 2018). This significant and sophisticated progress in
invasion science now permits establishing evidence-based targets to be derived for the post-
2020 period, that are scientifically sound, politically attainable, and for which progress can be
assessed by existing IAS indicators (Latombe et al. 2017).

Proposed IAS target for 2030 the % may need refining based on new data, and alignment with
other targets.

 Halting the loss of biodiversity caused by invasive alien species by 2030, by
 preventing their impacts in [100% of] the most vulnerable areas, regulating [50%
 of] the most harmful invasive alien species, and effectively managing [50% of] the
 most significant pathways of introduction, such that their impacts are reversed
 through restoration and recovery by 2050.

The overall goal of the proposed target is twofold:

1. Abate the impacts upon biodiversity from currently established IAS by 2030, this includes
alien species that have the potential to become invasive due to climate change.

2. Reduce the rate of introductions of alien species, preventing future impacts from IAS upon
biodiversity.

The quantitative elements suggested for 2030 are seen as a ‘stepping stone’ for 2040 and 2050,
where by 2040 all harmful invasive alien species are regulated, and all significant pathways of
introduction are effectively managed.

Actions needed to meet the target
To meet this target actions need to be developed and implemented by multiple stakeholder
groups, including government and private sector, civil society organisations, and local and
indigenous peoples. Primary actors in relation to the responsibility of implementation of actions
are governments and the private sector.

Actions needed at a national or regional level, involving all stakeholders

The actions highlighted below should be developed through a National Invasive Alien Species
Strategy and Action Plan (NISSAP), or through regional plans when appropriate.

1) Identify alien species that are currently present and those that are likely to be introduced in
the near future, along with their known and potential impacts, and pathways of introduction.

2) Identify vulnerable areas susceptible to introductions and sensitive to the impacts from
invasive alien species, especially those important for the persistence of biodiversity.

3) Prioritise invasive alien species for prevention, eradication, early warning rapid response,
long-term control, and monitoring, and implement effective and well-resourced measures.

4) Develop regulation(s) in order to prevent intentional introductions of priority species,
screened by risk analyses.

5) Implement effective and well-resourced management measures for priority pathways of
introduction to reduce unintentional introductions (e.g. risk analyses, biosecurity capacity and
practices) and the secondary spread of priority invasive species.

6) Implement effective and well-resourced early detection and rapid response capability.

7) Ensure the compilation and circulation of information on invasive species, the impacts they
cause, the pathways of introduction and the most vulnerable areas, to enable effective
prevention and management.

8) Monitor the status of biological invasions and the effectiveness of regulatory and
management interventions.

9) Develop and implement techniques to restore or recover sites affected by invasions.

Actions needed within private sector bodies

It must be stressed that the movement of invasive alien species is directly linked to human
activities and behaviours, and that it is essential that all relevant sectors of the society are

aware of the problem and are encouraged to adopt responsible behaviours, reducing the risk of
intentionally or unintentionally moving invasive alien species. An integrated approach, based on
the adoption of voluntary codes of conduct and on more regulatory approaches is needed.

The actions highlighted below are an example of a possible approach by the private sector
thatshould be developed through an expert-informed plan, and part of a broader environmental
safeguard strategy.

1) Identify areas of business that involve the movement of goods, materials, machinery, or
people, in particular over long distances.

2) Understand what invasive alien species are present in and near areas and sites of operation.

3) Implement biosecurity standards and best practices to prevent the uptake, transport, and
introduction of species to areas outside their native range. This is particularly important for
areas or sites of operation that are known to harbour invasive alien species.

4) Implement effective and well-resourced early detection and rapid response capability within
and around areas or sites of operation that are susceptible to the introduction of alien species.

Definitions of terms used
- Vulnerable areas - are geographically defined areas that are important for the persistence of
biodiversity and sensitive and susceptible to impacts from IAS. For example, islands, protected
areas, and Key Biodiversity Areas.

- Effectively preventing impacts in vulnerable areas – refers to the establishment of effective
management programmes that control, or where feasible eradicate IAS, and prevent their
introduction.

- Regulated - refers to the adoption and enforcement of national or regional legislation that
results in the prevention and effective management of IAS. In particular by restricting the import,
transport, possession and put on the market of a list of IAS, and establishes a biosecurity
framework and introduces an obligation to control and/or eradicate priority IAS.

- Harmful IAS - refers to IAS that cause, or have the potential to cause, substantial
environmental and/or socio-economic impacts within a countries boundaries. These can be
identified using existing impact assessment schemes, such as the Environmental Impact
Classification of Alien Taxa (EICAT), and the Socio-economic Impact Classification of Alien
Taxa (SEICAT) developed by the IUCN ISSG (as requested by Parties to the CBD). Potential
IAS not yet present within a country, but may be introduced soon, need be identified (e.g. using
a horizon scanning approach, see Roy et al. 2014). Impacts based on future climatic conditions
also need to be considered.

- Significant pathways of introduction, are those pathways that facilitate the introduction of
known and potential harmful IAS within national or subnational boundaries.

- Effectively managed pathways of introduction, refers to measures that are put in place that
successfully prevent the introduction of these IAS that cause significant impacts. For example
treatment of ballast water, biosecurity, and rapid detection and eradication capacity.

- Control, refers to management measures that are applied to established IAS over the long
term that successfully reduce the impacts from the IAS to desired (and measurable?) levels.

- Introduction, refers to the introduction of alien species into the wild and does not include
species that may already be alien and introduced within a country but are not currently
established in the wild, e.g. are only in captivity or found in gardens etc.

- Eradicate, refers to management measures that are applied to established IAS that remove all
individuals from an area, where there is no chance of re-introduction.

Scientific basis for the quantitative targets
The percentages proposed in the 2030 IAS target still needs to be refined based on ongoing
research by members of the ISSG, and alignment with other targets.

Existing indicators, used for Aichi Target 9
1) Trends in the impact of invasive alien species on extinction risk

The IUCN Red List Index on impacts of invasive alien species, is used as an indicator for Aichi
Target 9, and shows trends in the conservation status (IUCN Red List) of all birds worldwide
driven only by the negative impacts of invasive alien species or the positive impacts of their
control. For a 2030 target, this indicator will be broadened out to additional taxonomic groups
(e.g. mammals, amphibians) that have now undergone multiple IUCN Red List assessments.

2) Trends in invasive alien species vertebrate eradications

The Database of Islands and Invasive Species Eradication (DIISE) compiles all of the historical
and current invasive vertebrate (bird and mammal) eradications on islands, and is used to track
progress on IAS eradications.

3) Proportion of countries adopting relevant national legislation for the prevention or
control of invasive alien species

This indicator measures the adoption of national legislation relevant to the prevention or control
of invasive alien species. Note this indicator is also the official indicator used to track progress
for the UN Sustainable Development Goals Target 15.83.

New indicators for 2030 target
1) Rate of introductions of alien species

For monitoring the rate of introductions of alien species, the now available time series of alien
species richness for various taxonomic groups (Seebens et al. 2017, 2018) provide an important
first step for the development of global indicators of alien species accumulation across
taxonomic groups (McGeoch & Jetz 2019). But as indicators are required to be unbiased and
comprehensive, further research is needed to account for sampling biases in space and time. In
addition, aspects of invasion dynamics such as spatial extent, invasiveness or impacts have to
be covered as well. Currently, new global indicators of biological invasions are under
development, which aim at obtaining unbiased estimates of global and national alien and
invasive species richness, spatial extents of invasive species and their degree of impact. A
restricted dataset of IAS introductions for just 21 countries were used as an indicator for Aichi
Target 9.

2) Trends in the numbers of invasive species in countries

The IUCN SSC Invasive Species Specialist Group working with partners under a mandate
provided by Parties to the CBD, has developed the Global Register of Introduced and Invasive
Species that will form a global baseline to develop trends in the numbers of invasive species in
countries where demonstrated impact has been recorded.

3) Proportion of countries adopting relevant national legislation and adequately
resourcing the prevention or control of invasive alien species

This indicator, builds on the national legislation indicator already developed and collates data on
the resourcing allocated by countries to address IAS. This achieved through surveys on the
existence of government departments/agencies with a mandate for addressing IAS, and if they
have allocated budgets for this effort. A sub-global dataset (81 countries) for this indicator has
been used to track progress for the UN Sustainable Development Goals Target 15.8, for a 2030
Target this would be expanded to cover all countries.

3
  SDG Indicator 15.8.1: Proportion of countries adopting relevant national legislation and adequately
resourcing the prevention or control of invasive alien species

References
 Bacher, S., Blackburn, T.M., Essl, F., Genovesi, P., Heikkilä, J., Jeschke, J.M., Jones, G.,
   Keller, R., Kenis, M., Kueffer, C., Martinou, A.F., Nentwig, W., Pergl, J., Pyšek, P.,
   Rabitsch, W., Richardson, D.M., Roy, H.E., Saul, W.-C., Scalera, R., Vilà, M., Wilson,
   J.R.U. & Kumschick, S. (2018). Socio-economic impact classification of alien taxa
   (SEICAT). Methods Ecol. Evol., 9.

 Bellard C., Cassey P., & Blackburn T.M. (2016) Alien species as a driver of recent
   extinctions. Biology Letters, 12, .

 Bellard C., Thuiller W., Leroy B., Genovesi P., Bakkenes M., & Courchamp F. (2013) Will
   climate change promote future invasions? Global change biology, 1–9.

 Blackburn, T.M., Essl, F., Evans, T., Hulme, P.E., Jeschke, J.M., Kühn, I., Kumschick, S.,
    Marková, Z., Mrugała, A., Nentwig, W., Pergl, J., Pyšek, P., Rabitsch, W., Ricciardi, A.,
    Richardson, D.M., Sendek, A., Vilà, M., Wilson, J.R.U., Winter, M., Genovesi, P. &
    Bacher, S. (2014). A Unified Classification of Alien Species Based on the Magnitude of
    their Environmental Impacts. PLoS Biol., 12.

 Bradshaw, C.J.A., Leroy, B., Bellard, C., Roiz, D., Albert, C., Fournier, A., Barbet-Massin, M.,
   Salles, J-M., Simard, F. & Courchamp, F. (2016). Massive yet grossly underestimated
   global costs of invasive insects. Nature Communications, DOI

 Brooke MdeL, Hilton GM, Martins TLF. (2007). Prioritizing the world's islands for vertebrate-
   eradication programmes. Animal Conservation. 10(3):380-90.

 Butchart S.H.M., Lowe S., Martin R.W., Symes A., Westrip J.R.S., & Wheatley H. (2018)
   Which bird species have gone extinct? A novel quantitative classification approach.
   Biological Conservation, 227, 9–18.

 Capinha, C., Seebens, H., Cassey, P., García-Díaz, P., Lenzner, B., Mang, T., Moser, D.,
   Pyšek, P., Rödder, D., Scalera, R., Winter, M., Dullinger, S. & Essl, F. (2017). Diversity,
   biogeography and the global flows of alien amphibians and reptiles. Divers. Distrib., 23.

 Dawson, W., Moser, D., Van Kleunen, M., Kreft, H., Pergl, J., Pyšek, P., Weigelt, P., Winter,
   M., Lenzner, B., Blackburn, T.M., Dyer, E.E., Cassey, P., Scrivens, S.L., Economo, E.P.,
   Guénard, B., Capinha, C., Seebens, H., García-Díaz, P., Nentwig, W., García-Berthou, E.,
   Casal, C., Mandrak, N.E., Fuller, P., Meyer, C. & Essl, F. (2017). Global hotspots and
   correlates of alien species richness across taxonomic groups. Nat. Ecol. Evol., 1.

 Dawson J, Oppel S, Cuthbert RJ, Holmes N, Bird JP, Butchart SHM, et al. (2015). Prioritizing
   islands for the eradication of invasive vertebrates in the United Kingdom Overseas
   Territories. Conservation Biology. 29:143-53.

Diez et al. 2012. Will extreme climatic events facilitate biological invasions? Frontiers in
   Ecology & Environment, 10(5):249-257

Dyer, E.E., Redding, D.W. & Blackburn, T.M. (2016). The Global Avian Invasions Atlas - A
  database of alien bird distributions worldwide. bioRxiv.

IPBES. 2019. Summary for policymakers of the global assessment report on biodiversity and
  ecosystem services of the Intergovernmental Science-Policy Platform on Biodiversity and
  Ecosystem Services. S. Díaz, J. Settele, E. S. Brondizio E.S., H. T. Ngo, M. Guèze, J.
  Agard, A. Arneth, P. Balvanera, K. A. Brauman, S. H. M. Butchart, K. M. A. Chan, L. A.
  Garibaldi, K. Ichii, J. Liu, S. M. Subramanian, G. F. Midgley, P. Miloslavich, Z. Molnár, D.
  Obura, A. Pfaff, S. Polasky, A. Purvis, J. Razzaque, B. Reyers, R. Roy Chowdhury, Y. J.
  Shin, I. J. Visseren-Hamakers, K. J. Willis, and C. N. Zayas (eds.). IPBES secretariat,
  Bonn, Germany. 45 pages.

Jones H.P., Holmes N.D., Butchart S.H.M., Tershy B.R., Kappes P.J., Corkery I., Aguirre-
  muñoz A., Armstrong D.P., Bonnaud E., Burbidge A.A., Campbell K., Courchamp F.,
  Cowan P.E., Cuthbert R.J., Ebbert S., Genovesi P., Howald G., Keitt B.S., Kress S.W.,
  Miskelly C.M., Oppen S., Poncet S., Rauzon M.J., Rocamora G., Russell J.C., Samaniego
  A., Seddon P.J., Spatz D.R., Towns D.R., & Croll D.A. (2016) Invasive mammal
  eradication on islands results in substantial conservation gains. Proceedings of the
  National Academy of Sciences, 1–6.

van Kleunen, M., Dawson, W., Essl, F., Pergl, J., Winter, M., Weber, E., Kreft, H., Weigelt,
  P., Kartesz, J.T., Nishino, M., Antonova, L.A., Barcelona, J.F., Cabezas, F.J., Cárdenas,
  D., Cárdenas-Toro, J., Castaño, N., Chacón, E., Chatelain, C., Ebel, A.L., Figueiredo, E.,
  Fuentes, N., Groom, Q.J., Henderson, L., Inderjit, Kupriyanov, A., Masciadri, S.,
  Meerman, J., Morozova, O., Moser, D., Nickrent, D.L., Patzelt, A., Pelser, P.B., Baptiste,
  M.P., Poopath, M., Schulze, M., Seebens, H., Shu, W., Thomas, J., Velayos, M.,
  Wieringa, J.J. & Pyšek, P. (2015). Global exchange and accumulation of non-native
  plants. Nature, 525, 100–103.

Latombe, G., Pyšek, P., Jeschke, J.M., Blackburn, T.M., Bacher, S., Capinha, C., Costello,
   M.J., Fernández, M., Gregory, R.D., Hobern, D., Hui, C., Jetz, W., Kumschick, S.,
   McGrannachan, C., Pergl, J., Roy, H.E., Scalera, R., Squires, Z.E., Wilson, J.R.U., Winter,
   M., Genovesi, P. & McGeoch, M.A. (2017). A vision for global monitoring of biological
   invasions. Biol. Conserv., 213, 295–308.

Liebhold, A.M., Brockerhoff, E.G., Garrett, L.J., Parke, J.L. & Britton, K.O. (2012) Live plant
   imports: the major pathway for forest insect and pathogen invasions of the US. Frontiers in
   Ecology and the Environment, 10, 135-143.

Mazza G., & E. Tricarico (eds) 2018. Invasive species and human health. CABI, Wallingford.

Mazza G., Tricarico E., Genovesi P., & Gherardi F. (2014) Ethology Ecology & Evolution
    Biological invaders are threats to human health: an overview. Ethology, Ecology &
    Evolution, 26, 112–119.

  Maxwell, S.L., Fuller, R.A., Brook, T.M. & Watson, J.E.M. (2016). The ravages of gunds nets
    and bulldozers. Nature, 563, 143-145.

  McGeoch, M.A., Genovesi, P., Bellingham, P.J., Costello, M.J., McGrannachan, C. &
    Sheppard, A. (2016). Biological Invasions, 18, 299-314

  McGeoch, M.A. & Jetz W. (2019) Commentary Measure and Reduce the Harm Caused by
    Biological Invasions. One Earth, 1, 171–174.

   Pagad S, Genovesi P, Carnevali L, Schigel D and McGeoch M A 2018 Introducing the global
register of introduced and invasive species Sci. Data 5 170202

  Paini D.R., Sheppard A.W., Cook D.C., De Barro P.J., Worner S.P., & Thomas M.B. (2016)
    Global threat to agriculture from invasive species. Proceedings of the National Academy
    of Sciences, 113, 7575–7579.

  Pratt, C.F., Constantine, K.L. & Murphy, S.T. (2017). Economic impacts of invasive alien
    species on African smallholder livelihoods. Global Food Security, 14, 31-37.

  Roy, H.E., Peyton, J., Aldridge, D.C., Bantock, T., Blackburn, T.M., Britton, R., Clark, P.,
    Cook, E., Dehnen-Schmutz, K., Dines, T., Dobson, M., Edwards, F., Harrower, C., Harvey,
    M.C., Minchin, D., Noble, D.G., Parrott, D., Pocock, M.J.O., Preston, C.D., Roy, S.,
    Salisbury, A., Schönrogge, K., Sewell, J., Shaw, R.H., Stebbing, P., Stewart, A.J.A. &
    Walker, K.J. (2014). Horizon scanning for invasive alien species with the potential to
    threaten biodiversity in Great Britain. Glob. Chang. Biol., 20, 3859–3871.

  Seebens, H., Blackburn, T.M., Dyer, E.E., Genovesi, P., Hulme, P.E., Jeschke, J.M., Pagad,
    S., Pyšek, P., van Kleunen, M., Winter, M., Ansong, M., Arianoutsou, M., Bacher, S.,
    Blasius, B., Brockerhoff, E.G., Brundu, G., Capinha, C., Causton, C.E., Celesti-Grapow,
    L., Dawson, W., Dullinger, S., Economo, E.P., Fuentes, N., Guénard, B., Jäger, H.,
    Kartesz, J., Kenis, M., Kühn, I., Lenzner, B., Liebhold, A.M., Mosena, A., Moser, D.,
    Nentwig, W., Nishino, M., Pearman, D., Pergl, J., Rabitsch, W., Rojas-Sandoval, J.,
    Roques, A., Rorke, S., Rossinelli, S., Roy, H.E., Scalera, R., Schindler, S., Štajerová, K.,
    Tokarska-Guzik, B., Walker, K., Ward, D.F., Yamanaka, T. & Essl, F. (2018). Global rise in
    emerging alien species results from increased accessibility of new source pools. Proc.
    Natl. Acad. Sci., 115, E2264–E2273.

  Seebens, H., Blackburn, T.M., Dyer, E.E., Genovesi, P., Hulme, P.E., Jeschke, J.M., Pagad,
    S., Pyšek, P., Winter, M., Arianoutsou, M., Bacher, S., Blasius, B., Brundu, G., Capinha,
    C., Celesti-Grapow, L., Dawson, W., Dullinger, S., Fuentes, N., Jäger, H., Kartesz, J.,

Kenis, M., Kreft, H., Kühn, I., Lenzner, B., Liebhold, A., Mosena, A., Moser, D., Nishino,
   M., Pearman, D., Pergl, J., Rabitsch, W., Rojas-Sandoval, J., Roques, A., Rorke, S.,
   Rossinelli, S., Roy, H.E., Scalera, R., Schindler, S., Štajerová, K., Tokarska-Guzik, B., van
   Kleunen, M., Walker, K., Weigelt, P., Yamanaka, T. & Essl, F. (2017). No saturation in the
   accumulation of alien species worldwide. Nat. Commun., 8, 14435.

Spatz, D.R., Zilliacus, K.M., Holmes, N.D., Butchart, S.H.M., Genovesi, P., Cellabos, G.,
  Tershy, B.R. & Croll, D.A. 2017. Globally threatened vertebrates on islands with invasive
  species. Science Advances, 3 e1

Vilà, M., Espinar, J.L., Hejda, M., Hulme, P.E., Jarošík, V., Maron, J.L., Pergl, J., Schaffner,
   U., Sun, Y. & Pyšek, P. (2011). Ecological impacts of invasive alien plants: a meta-
   analysis of their effects on species, communities and ecosystems. Ecol. Lett., 14, 702–
   708.