Neonatives and translocated species: different terms are needed for different species categories in conservation policies
expand article infoFranz Essl, Petr Pyšek§|, David M. Richardson
‡ University Vienna, Vienna, Austria
§ Czech Academy of Sciences, Institute of Botany, Průhonice, Czech Republic
| Charles University, Prague, Czech Republic
¶ Stellenbosch University, Stellenbosch, South Africa
Open Access

Pervasive human-induced environmental changes are increasingly causing species to move, with profound implications for their conservation and survival (e.g. Chen et al. 2011; Dawson et al. 2011). In a recently published piece on “Global policy for assisted colonization of species”, Brodie et al. (2021) call for assisted colonisation (also called managed relocation) to be embraced as a viable management option in post-2020 global conservation policies. They suggest that species, deliberately introduced beyond their historic native range and species that expand their ranges on their own in response to climate changes, should be treated identically for the purposes of policy. They also suggest expanding the use of the term “neonative” – which we previously proposed for range-expanding species that track environmental changes without human assistance (Essl et al. 2019) – so that this term also applies to species targeted for assisted colonisation.

We recognise the need to proactively consider the opportunities and risks of species translocations as a key tool in policies and management in the Anthropocene. However, we agree with Ricciardi and Simberloff (2021) and consider it crucial to treat distinct phenomena and different categories of species of conservation concern differently in policies. Very careful attention must be given to the precise definition of core concepts and terminology. Human-induced translocations differ from range-expanding species (i.e. ‘neonatives’ as we defined them in Essl et al. 2019) in key aspects (Table 1), which makes lumping these two categories of species highly problematical with regard to fundamental features that relate to policy. These aspects include dispersal potential, the rate and direction of range expansions, the number and characteristics of species involved and the associated risks and uncertainties. Whereas species targeted for assisted colonisation are currently a limited number of charismatic taxa (Hällfors et al. 2017), range-expansions by “neonatives” (as in our definition) involve a wide range of biota (Essl et al. 2019), some of them with a great potential to spread. Additionally, the risks and benefits associated with the two phenomena differ (IUCN 2013; Ricciardi and Simberloff 2014). Finally, although human decisions on whether or not to move species are pivotal in assisted colonisation (Richardson et al. 2009), this is not the case for species undergoing range expansions independently of direct human action. For the latter, measures to preserve or restore connectivity are most relevant (e.g. Wessely et al. 2017). Consequently, these profoundly different key characteristics of range-expanding species tracking environmental change vs. those subject to assisted colonisation result in very different conservation challenges (Table 1).

Table 1.

Ten key features and associated differences between range-expanding species tracking environmental changes (= neonatives) and species moved purposefully to regions outside their native range in response to (anticipated) environmental changes (= assisted colonisation or managed relocation). The main conservation and challenges associated with the features are shown.

No Key features Neonatives Conservation challenges and implications Assisted colonisation Conservation challenges and implications
1 Number of individuals typically involved (Very) large No specific conservation challenges (Very) small Ensuring that founder populations do not go through genetic bottlenecks
2 Number of species involved Often large to very large Monitoring the effects of range-expanding species on resident biota One or few Selection of priority species (incl. the potential that translocated species might become invasive), monitoring the effects of translocated species on resident biota
3 Characteristics of species involved Wide range of species, particularly mobile species and generalists Applying management measures to ensure survival of less mobile species and of specialists Charismatic, large, conspicuous species Identification of alternative conservation options for the vast majority of biota that cannot be realistically translocated
4 Range expansion is reactive or proactive to environmental changes Always reactive, i.e. species are responding to environmental change that has already occurred No specific conservation challenges Reactive or proactive (in anticipation of expected environmental change) Taking uncertainty of future environmental changes into account
5 Source regions of individuals involved in range expansion Leading range edge No specific conservation challenges Anywhere, often current centres of occurrence Ensuring that suitable ecotypes of the translocated species are chosen
6 Form and distance of range expansion Wave-like range expansion from current leading edge to adjacent regions that have become suitable Improving landscape permeability Jump dispersal, places of translocations are often distant and disjunct to the native range Identifying suitable places of release with high likelihood of establishment and low risks of negative impacts
7 Velocity of range expansion Variable, depending on characteristics of the species, the landscape (e.g. permeability) and the velocity of environmental change Improving landscape permeability Abrupt, depending on human activity (i.e. introduction of individuals or propagules to the site of release) Apply an exhaustive ex ante risk-assessment prior to species translocation
8 Degree of ecological novelty associated with the range-expanding species Typically low, but with exceptions (e.g. if range-expanding species have novel traits) Monitoring the impacts on resident biota and potentially managing if negative impacts are observed Variable, but often high as distances to native range are often large Monitoring the impacts on resident biota, potentially managing if negative impacts are observed
9 Direct resources involved Low to non-existing Typically no resources are directly needed, but potentially for monitoring, or management (e.g. increasing landscape permeability) Medium to high The planning, execution and monitoring of translocations requires (substantial) resources
10 Connectivity of native range and newly colonised region High, newly colonised regions are usually adjacent to (leading edge of) native range No specific conservation challenge Low, places of translocations are usually distant from the native range and separated by unsuitable regions in between Identifying suitable places of release with a high likelihood of establishment and low risks of negative impacts

We call upon conservation bodies, such as the IUCN and the Convention of Biological Diversity (CBD), to evaluate the full range of conservation opportunities and risks created by species on the move. These efforts should recognise the profoundly different nature of translocated species and those undergoing range changes due to global change, but without direct human assistance. We are convinced that only such a nuanced approach will lead to appropriate conservation action to ensure species survival in the Anthropocene. We argue that species selected for assisted colonisation are a distinct category that should be subject to exactly the same classification as all other species. As they are introduced purposefully outside their natural range, they should be considered as aliens. The protocols for evaluating associated risks are well established (Richardson et al. 2009; Karasov-Olson et al. 2021). However, given that translocated species also differ in some important characteristics from other alien species, it may be warranted to classify these species in a distinct (sub)category.


FE appreciates funding from the Austrian Science Foundation FWF (grant I 3757-B29). PP was supported by EXPRO grant no. 19-28807X (Czech Science Foundation) and long-term research development project RVO 67985939 (Czech Academy of Sciences). DMR acknowledges the DSI-NRF Centre of Excellence for Invasion Biology. We thank the Handling Editor, Ingolf Kühn for helpful suggestions.


  • Brodie JF, Lieberman S, Moehrenschlager A, Redford KH, Rodriguez JP, Schwartz M, Seddon PJ, Watson JEM (2021) Global policy for assisted colonization of species. Science 372: 456–458.
  • Chen IC, Hill JK, Ohlemüller R, Roy DB, Thomas CD (2011) Rapid range shifts of species associated with high levels of climate warming. Science 333: 1024–1026.
  • Essl F, Dullinger S, Genovesi P, Hulme PE, Jeschke JM, Katsanevakis S, Kühn I, Lenzner B, Pauchard A, Pyšek P, Rabitsch W, Richardson DM, Seebens H, van Kleunen M, van der Puttten WH, Vilà M, Bacher S (2019) A conceptual framework for range-expanding species that track human-induced environmental change. Bioscience 69: 908–919.
  • Karasov-Olson A, Schwartz MW, Skikne SA, Hellmann JJ, Olden JD, Lawrence DJ, Morisette JT, Schuurman GW, Allen S, Brigham CA, Buttke D, Miller-Rushing AJ, Trammell M, Hawkins Hoffman C (2021) Co-development of a risk assessment strategy for managed relocation. Ecological Solutions and Evidence 2: e12092.
  • Richardson DM, Hellmann JJ, MacLachlan JS, Sax DF, Schwartz MW, Gonzalez P, Brennan EJ, Camacho A, Root TL, Sala OE, Schneider SH, Ashe DM, Clark JR, Early R, Etterson JR, Fielder ED, Gill JL, Minteer BA, Polasky S, Safford HD, Thompson AR, Vellend M (2009) Multidimensional evaluation of managed relocation. Proceedings of the National Academy of Sciences USA 106: 9721–9724.
  • Wessely J, Hülber K, Gattringer A, Kuttner M, Moser D, Rabitsch W, Schindler S, Dullinger S, Essl F (2017) Habitat-based conservation strategies cannot compensate for climate change-induced range loss. Nature Climate Change 7: 823–827.