Introducing AlienScenarios : a project to develop scenarios and models of biological invasions for the 21 st century

AlienScenarios, a three-year project starting in March 2019, will evaluate for the first time the range of plausible futures of biological invasions for the 21st century. AlienScenarios consists of seven project partners and seven integrated complementary subprojects. We will develop the qualitative narratives for plausible futures of global alien species richness and impacts in the 21st century – the Alien Species Narratives Copyright Franz Essl et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. NeoBiota 45: 1–17 (2019) doi: 10.3897/neobiota.45.33366 http://neobiota.pensoft.net NEW DEVELOPMENT Advancing research on alien species and biological invasions A peer-reviewed open-access journal


Introduction
Human agency has modified virtually every facet of the biophysical environment (Lewis and Maslin 2015) with profound implications for the status, distribution and resilience of biodiversity worldwide (Leadley et al. 2010).Several major drivers of biodiversity loss have been identified with climate change, land-use change and invasive alien species (IAS) being among the most important ones (Secretariat of the Convention on Biological Diversity 2014).Changes in climate and land use have received much attention during the last decades, which resulted in readily available scenarios (Lamarque et al. 2005;Moss et al. 2010;Hurtt et al. 2011;IPCC 2014;Popp et al. 2016).In contrast, comparable approaches are completely missing for biological invasions despite their importance in driving biodiversity losses (Simberloff et al. 2013;Blackburn et al. 2014), and causing substantial negative impacts on human livelihoods (Pejchar and Mooney 2009).Worryingly, recent research has shown that numbers of alien species are rising unabatedly in most taxonomic groups (Seebens et al. 2017(Seebens et al. , 2018)).Therefore, a thorough evaluation of plausible future trajectories of biological invasions is urgently needed to (i) enable comprehensive assessments of biodiversity changes for the decades to come, (ii) allow better-informed decisions of policy makers and stakeholders (Ferrier et al. 2016) and (iii) examine the future implications of different societal responses for biological invasions.

Objectives and approach
In AlienScenarios, we will close the knowledge gap outlined above by evaluating the range of plausible futures of biological invasions for the 21 st century at different spatial scales and for a range of taxonomic groups.We will use complementary data and approaches, and examine multiple measures of impacts.We will combine the strate-gic forward-looking methodology of scenario planning with advanced modelling approaches to construct plausible global mid-term (2050) and long-term (2100) futures of biological invasions and their impacts taking into account uncertainties.In this context, we will take advantage of several recently compiled large data sets of global alien species distributions, which have partly been compiled by members of the project team: vascular plants (GloNAF, (van Kleunen et al. 2015, 2018;Pyšek et al. 2017), amphibians and reptiles (Capinha et al. 2017), mammals (Dawson et al. 2017), birds (GAVIA, (Dyer et al. 2017), freshwater fish (Dawson et al. 2017) and selected invertebrates (ants, spiders, Bertelsmeier et al. 2013;Roura-Pascual et al. 2016;Dawson et al. 2017).In addition, we will use the Alien Species First Record Database (Seebens et al. 2017(Seebens et al. , 2018)), an exhaustive database of global historic alien species accumulation rates.Finally, for regional analyses AlienScenarios will make use of complementary alien species data for in depth-analyses.

Overview of the AlienScenarios project structure
AlienScenarios consists of seven work packages (WPs) (Figure 1) that are briefly described below.WP I builds on this preparatory work and transforms it into a conceptual framework for the development of scenarios on how alien species richness and impacts might change throughout the 21 st century.Based on the subset of the seven most relevant drivers of biological invasions, we will develop internally consistent storylines -the Alien Species Narratives (ASNs) (Figure 2) -that form the core elements of our scenario framework (Rounsevell and Metzger 2010).Given that we are developing biological invasion scenarios for the first time, and thus want to explore the full range of potential future alien species trajectories, we choose a descriptive approach (Priess and Hauck 2014;IPBES 2016) to come up with four to five ASNs.Further, we are going to construct the ASNs independent of other frameworks to ensure the greatest freedom in exploring different facets of the system more rigorously.This way we will avoid constraints held by pre-existing storylines that are likely too general for the specific needs in invasion science (Chytrý et al. 2012).The ASNs will then a posteriori be set into a broader context (see Spangenberg et al. 2012) (van Vuuren et al. 2014) combined with a "one-on-one" mapping of the scenario narratives (Zurek and Henrichs 2007) to assess the congruence between the RCP x SSP and the ASN frameworks.This way, we will identify the relationships of biological invasions to global socio-economic and environmental change scenarios.
The ASN framework developed here will serve as the overarching concept for the simulations of the global (WP II) models of biological invasions, for assessing the global impacts that future invasions may cause (WP III), and for developing continental (WP IV) and regional alien species scenarios and models (WPs V, VI).

WP II: Implementing global models of biological invasions (Lead: Senckenberg BiK-F, Hanno Seebens)
In this WP, a model of alien species accumulations on large spatial (global, continental) and temporal scales (centuries) will be developed and explored for various scenarios obtained from WP I.A common feature of existing invasion models (e.g.Leung et al. 2004;Costello et al. 2007;Brockerhoff et al. 2014) is that invasion dynamics were calculated based on trends of drivers such as import volumes of a country.While driver dynamics have been proven to be valuable predictors of invasion dynamics (Levine and D'Antonio 2003;Pyšek et al. 2010), it is essential to additionally consider potential constraints on the number of establishing species by the size of source pools (Liebhold et al. 2017;Seebens et al. 2018).
Here, we will combine the process-based extension of the statistical invasion model developed by Liebhold et al. (2017) with the modelling approach of Seebens et al. (2018) to estimate candidate species pools and to simulate the spread from these pools to alien ranges.The model will simulate the rate of invasion based on various drivers of invasion, while the total number of establishments will be constrained by the size of the source pools.The implementation of ASNs into the newly developed model will require adaptations of the model structure as well as refinements of the scenarios.
The model will be evaluated against long-term trends of alien species accumulations obtained from the recently established Alien Species First Record Database, which provides regional time series (1500-2005) of invasions for >17,000 established alien species from various taxonomic groups (Seebens et al. 2017(Seebens et al. , 2018).
An invasion model as proposed here will provide the ideal tool to reach our objectives of developing future projections, as it integrates the most important mechanisms of invasion dynamics and at the same time provides a simple framework to simulate alien species accumulations for the drivers for which data are available in future scenarios.At the end of the project, we will have a set of invasion trajectories for each taxonomic group considered here, spanning the full range of potential developments for the 21 st century.These results will also be used as baseline input for assessing future impacts (WPs III, V) and for discussing future pro-active policies and management options (WP VII).

WP III: Evaluating impacts on ecosystem services and human livelihoods (Lead: University of Paris Saclay, Franck Courchamp)
This WP focuses on evaluating impacts of the different global scenarios.Because the currency metrics is one that allows impact comparisons across different scales (time, space, taxonomy, category of impact, etc.), we will focus on economic costs as an output of most facets of this WP.
The WP will proceed with different, complementary approaches.The first one will use a meta-analysis of the state-of-the-art of current economic costs of IAS worldwide (in collaboration with environmental economists).This analysis will provide us with the first high-quality global map of costs, but also with a detailed description of current knowledge gaps, be they taxonomic, geographic or economic markets.These comprehensive current costs will then use the ASNs and results obtained by other WPs to assess (i) which species are likely to become (or remain) invasive in areas of interest and (ii) which areas on the globe are likely to become invaded by focal species, both for mid-term (2050) and long-term (2100) futures.The WP will focus on alien vertebrates, vascular plants and selected groups of insects (such as ants) for which the necessary global distribution data are available (e.g.van Kleunen et al. 2015van Kleunen et al. , 2018;;Capinha et al. 2017;Dawson et al. 2017;Dyer et al. 2017).We will then use local, current costs of selected alien species and project them to spatially explicit maps in order to obtain more quantitative estimates for different areas.
These invasion costs will be put in regards with costs of policies and biosecurity measures to provide an integrated scheme of prioritization according to the different ASNs developed in WP I.The approach will allow for evaluating and ranking different political and management options of biological invasions for the 21 st century according to climatic and socio-economic scenarios, regions and possibly economic markets.

WP IV: Developing scenarios and models of biological invasions at continental scale (Lead: University of Girona, Nuria Roura-Pascual)
Based on the global ASN framework developed in WP I, we will zoom in on a continental (Europe) scale and construct scenarios nested within the global ones.
The main objective is to assess the consequences of different levels of implementation of the European Union Regulation on IAS (Regulation No. 1143/2014, EU 2014).This regulation has become the key policy tool in coordinating and improving the efforts of EU member states to combat IAS.EU member states differ in policies and regulatory histories, risk assessment tools and data availability (Sonigo et al. 2011), but the ramification this heterogeneity has on IAS is unknown (Tollington et al. 2017).We will examine regulations, management capacities and other socio-ecological factors (e.g.environmental heterogeneity, length of common borders) across EU member states, integrate these into a spatially-explicit model along with human vector movement (i.e. the primary mechanism of alien species transport and dispersion; Leung et al. 2004;Della Venezia et al. 2018).
We will statistically relate these socio-ecological constraints and human-mediated pathways of spread to the patterns of alien species establishment and impact across the EU (in collaboration with WPs II and III).We will focus on the IAS of EU concern (currently 49 species) as listed in the EU regulation on IAS (EU 2014).Our analyses will allow us to unravel the effect that differing policy implementation and capacities may have on the studied IAS in each member state.Further, since member states are interconnected by transportation and trade in goods, we will also parse out their ramifications for other member states (i.e.what is the effect of a "weak link").We will also use this model to simulate the effect of alternative policies and capacities, based on a series of qualitative scenarios for managing IAS in Europe constructed by applying the methodology of scenario-planning following the premises of the conceptual framework.Such an integrated approach will give a scientific basis to quantitatively examine the consequences of the differing degrees of policy implementation across the EU.

WP V: Scenarios of alien species traits related to impact in selected regions (Lead: Helmholtz Centre for Environmental Research -UFZ, Ingolf Kühn)
There is a long history of analysing species traits that are related to the success of alien species (e.g.Pyšek and Richardson 2007;Küster et al. 2008).The impacts of alien species on ecosystem functions and services, though, are mediated through effect traits (Pyšek et al. 2012).Here, we will use the downscaled scenarios and model projections of the WPs I, II and IV to apply case studies on selected taxonomic groups (such as plants, birds, mammals) and regions (mountain regions).
In particular, we will extend the results from scenario development (WPs I, II, IV) to species traits, i.e. to the increase or decrease in specific traits.This means that we will not only consider the magnitude of change in terms of species richness (WPs II, IV), but will also consider which traits will benefit or suffer under the respective scenarios.We will applying both network analyses as well as already existing trait distribution models (e.g.Kühn et al. 2006Kühn et al. , 2009)), by combining the same environmental drivers as in WP III on land use, climate (and preferably traffic/trade routes) with traits and propagule pressure to project which trait compositions to expect under different ASN assumptions (from WP II).This will allow us to analyse alien species impacts under scenario conditions by regionalization and to recognize specific context sensitivity (Kueffer et al. 2013), but also quantify uncertainties.
Because trait information is not equally available throughout Europe, we will focus with the previous analysis on ecosystems in Europe that are highly sensitive to invasions, but not yet too heavily invaded, such as mountains (Pyšek et al. 2009).Further, these systems will have strong anticipated changes in climate and land use and an increase in trade and traffic, so that a massive transformation by alien species is likely (Alexander et al. 2016).This also means that the storylines and scenarios developed in WPs I and IV need to be extended regionally.The choice of analysed systems follows a hierarchical selection strategy, especially based on good data availability in Central Europe.By acquiring more data, this can be extended to other regions.Mountain ecosystems fulfil all requirements mentioned above and will serve as a model system to start with.
To this end, we will prioritize (i) regions and, within regions, ecosystems that are more sensitive than others, and (ii) traits that are more effective than others in causing an impact onto these systems.

WP VI: Integrating models of socio-ecological change with biological invasions in the Global South: Panama as a model system (Lead: McGill University, Brian Leung)
This WP focuses on a tropical region of particular importance for biological invasions, i.e.Panama.Panama is a tropical biodiversity hotspot (Ibáñez et al. 2002) and home to the Panama Canal, one of the major gateways of inter-oceanic marine alien species exchanges (Muirhead et al. 2015).Simultaneously, Panama faces rapid economic growth (10.6% in 2011) and population growth (>40% by 2050), and highly skewed wealth distribution (17/136 in the world).These factors influence the movement of goods and people, as well as societal values and choices (e.g.land use), which in turn, can affect biological invasions.Thus, Panama is an excellent model system of developing, tropical nations.In pursuing WP VI, we complement the global (WP II) and continental analyses (WP IV) by (1) scale: analyzing an indepth country-level analysis, (2) region: focusing on a tropical region in the Global South, which are under-represented in invasion biology studies, and (3) drivers: focusing on detailed socio-ecological models.
We will connect to an ongoing initiative, the Panama Research and Integrated Sustainability Model (PRISM, see http://prism.research.mcgill.ca),which is a firstgeneration nationwide spatially-explicit computational model of ecological and social components of sustainability.PRISM currently incorporates sub-models for physical processes linked to water availability and land use, and biological patterns for the biascorrected distributions of >6000 plant species across Panama.Further, socio-economic layers are currently being developed, including urban growth of Panama City, changes in shipping through the Panama Canal over the coming decades, and connectivity, which will influence the movement of alien species.PRISM will act as a foundation on which to explore the introduction, establishment, spread and impact of alien species.In turn, WP VI will contribute a biological invasions layer to PRISM.
In particular, WP VI will integrate quantitative socio-ecological models with the drivers of invasions identified in the ASN framework of WP I.In close collaboration with WPs IV and V, we will develop national alien species storylines nested in the global ASN framework.We will apply the general scenarios of driver changes from WP I to the context-rich knowledge of Panama, and use PRISM to actually quantify the interactions between those drivers (e.g.urban growth increases by x%, resulting in y% increase of material flow and human migration, which then results in z% land-use and biodiversity change).We will use the models from WP II as the global context, within which Panama exists (e.g.how will the invasions of trading partners change introduction pressure to Panama?).We will then model how future biological invasions in Panama quantitatively flow through the country to 2050, by combining PRISM's socio-ecological outputs with invasion models.

WP VII: Project synthesis and co-design, communication and outreach (Lead: University of Vienna, Franz Essl)
This integrative WP has three closely related goals: (i) it will use a participatory approach involving the AlienScenarios project team and an external Advisory Board for ensuring strong integration and co-design of the sub-projects and for monitoring project progress; (ii) building on the results of the other WPs, it develops a synthesis of the project results which will be discussed with the Advisory Board; and (iii) it ensures that the project and its results are communicated to stakeholders and the wider community using a range of different tools and formats.
AlienScenarios has an interdisciplinary Advisory Board of ca.20 leading representatives to end-users, decision makers and global change scientists.The Advisory Board serves several purposes: (i) to co-develop and discuss the planned implementation of project approaches and goals to maximize applicability and transferability to other relevant initiatives (e.g.IPBES, Future Earth, CBD, GEOBON), (ii) to discuss project results and their implications for alien species policies and management, (iii) to ensure that inputs and views of the wider community will fertilize the implementation of the project and (iv) to provide advice to the WPs on specific questions and problems.
The second goal of this WP is to provide a synthesis of developed methodological approaches and obtained results for different audiences.This will be done by producing (i) a leaflet (policy brief ) introducing the global ASNs, (ii) a scientific project synthesis on the implications of the project results for policy making, alien species management and science, and (iii) a short version aimed at a more general audience as a policy brief.For the scientific project synthesis, we plan to write this either as a dedicated book with an international publisher, or as a comprehensive review publication.This will also include an in-depth analysis of the advantages and weaknesses of the different model approaches in predicting biological invasions.We will also synthesise the results obtained for the different spatial scales, regions and taxa in an integrative analysis and assessment.Finally, we will apply network analysis tools developed by J. Jeschke's team to connect concepts and hypotheses that have been proposed to explain biological invasions with the scenarios (e.g.Enders et al. 2018).This will be done in a dedicated workshop hosted in Berlin in the final project year.

Outlook
The importance of scenarios on biological invasions for science, policy and biodiversity conservation While there has recently been substantial progress in many fields in invasion science, and while in particular modelling approaches that include projections into the future (e.g.Bradley et al. 2012;Seebens et al. 2015;Early et al. 2016), the long-term dynamics of biological invasions and the impacts they cause is still understudied.In particular, there a lack of understanding the interactions of biological invasions with other drivers of environmental change, and how different policies and trajectories of drivers may modify the future impacts of invasions.
The unabated rise in alien species numbers and their impacts on nature and human livelihood have been a growing global concern, which resulted in new regulations and initiatives attempting to tackle the alien species challenge (e.g. the new EU regulation or the likely forthcoming IPBES thematic assessment of IAS, IPBES 2016).Given the substantial impacts of biological invasions (e.g.Vilà et al. 2011;Bradshaw et al. 2016), this lack of long-term projections of biological invasions and their impacts is considered an important knowledge gap (Ferrier et al. 2016).AlienScenarios will address these questions and will thus provide results of high importance for environmental planning and policy advice (e.g.IPBES, Ferrier et al. 2016;Essential Biodiversity Variables in GEOBON, Latombe et al. 2017).

The contribution of AlienScenarios to synthesis initiatives and conservation agreements
AlienScenarios aims to deliver important contributions to several high-profile initiatives on biodiversity conservation, sustainable development and knowledge synthesis.The Convention on Biological Diversity CBD (https://www.cbd.int/) and the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services IPBES (https://www.ipbes.net/)are the two most prominent ones; both are crucial for formulating and advising global IAS policy, and improved information on potential longterm dynamics of alien species is highly relevant for this purpose.
On a continental level, the EU legislation on IAS (http://ec.europa.eu/environment/nature/invasivealien/index._en.htm) is one of the most ambitious laws for managing IAS worldwide.In particular, WP IV of AlienScenarios will deliver important insights on the potential impact of implementing this regulation on future alien species dynamics in Europe.
The Invasion Dynamics Network (InDyNet) (https://indynet.de)was launched 2015 and studies temporal changes in biological invasions and their impacts.It will highly benefit from the results of the AlienScenarios project.Further, a working group on "Theory and Workflows for Alien and Invasive Species Tracking (sTwist)" (https://www.idiv.de/sdiv/working_groups/wg_pool/stwist.html) has been funded by the German Biodiversity Synthesis Centre iDiv in 2018.sTwist brings together the knowledge, methods and data needed to track alien species globally and develops robust indicators for biological invasions.For elucidating the potential future trajectories of such indicators on biological invasions, AlienScenarios will deliver crucial insights.
Finally, AlienScenarios will provide results that will be useful for elucidating potential trajectories of invasions at different scales (from national to global), and for different purposes (e.g.impacts on the environment, human livelihood).

Conclusions
Formulating and applying scenarios and models of how biological invasions may unfold in the coming decades is a daunting task.AlienScenarios will be a crucial step towards this goal, but clearly, it will only be a first step on a long road to travel.Thus, future collaborative work will be needed to advance the understanding on future invasion dynamics refining and expanding the results of this project.This will need the expertise and commitment of different stakeholders ranging from scientists of different disciplines, biodiversity managers, politicians and funding institutions.
By providing the first coherent set of projections of how biological invasions may unfold in the 21 st century under different storylines of human behavior, we hope that AlienScenarios will initiate a process similar to work done in the climate change research community (IPCC 2014) and that has become hugely influential.

WP I :
Developing global storylines and scenarios of biological invasions in the 21 st century (Lead: University Vienna, Bernd Lenzner, Franz Essl) Alien species displacement and establishment are affected by a range of drivers.These drivers have been comprehensively assessed in a workshop on alien species scenarios coorganized by three partners of AlienScenarios (F.Essl, B. Leung, N. Roura-Pascual) in Vienna in October 2016.In this workshop, an interdisciplinary panel of c. 30 experts performed an elicitation of the existing literature, and assessed relevant mechanisms and pathways.The assessment identified the seven most relevant drivers for biological invasions in the 21 st century: land-use and land cover change, biodiversity change, climate change, human population development, international trade and transport, legislation, and agreements as well as scientific, technological and societal development (Roura-Pascual in prep.).

Figure 1 .
Figure 1.Project management structure and the interactions between the work packages of AlienScenarios.Shown are the seven work packages (WPs), the institution of the WP lead, the integration of the WPs within the project, the external Advisory Board, and the Steering Committee consisting of the WP leaders that is responsible for internal decision making.The arrows indicate the interconnectedness of the WPs in terms of data, idea and material exchange.

Figure 2 .
Figure 2. Conceptual figure showing the key elements and key steps for developing a framework for global scenarios (WP I) and models (WPs II, III) of biological invasions, from which continental and regional scenarios and models will be derived (WPs IV, V, VI).The figure is composed of a conceptual layer (boxes) that describes the stepwise scenario-and model-development process from initial data assessment and mobilisation to storyline construction, model quantification and, finally, to the synthesis of the full biological invasion scenarios and their communication.The position of the seven WPs of AlienScenarios along this scenario-and model-development axis is shown separately for global and regional scenarios.