This novel approach based on changes in species status has a number of advantages over previous definitions of individual management terms. The different forms of management are defined by the start- and end-points of the changes in species status, rather than requiring stand-alone definitions of their own. This obviates the need for complex definitions of often overlapping management terms, which has led to many of the current problems of interpretation. This approach also brings an element of completeness, as all possible changes in species status are included. In this section, we describe each management term used in our framework and compare it with other terms used in the literature. Table 3 provides a published example of each form of management.
Pre-border pathway management
To reduce the uptake of the species and its transport outside the area of interest. This can be defined as changing status from In Transit to No Risk, or maintaining a species as No Risk, with the objective of preventing or reducing the uptake or transport of individuals. Pathway Management is already widely recognised as a key element of IAS management (Hulme et al. 2008). These include measures to reduce the uptake of individuals, such as requirements for clean shipping materials and packaging prior to the shipment of goods; regulations such as The Ballast Water Management Convention (Werschkun et al. 2014) or the management of horticultural supply chains (Hulme et al. 2018).
To intercept individuals when they first enter into the area of interest. This can be defined as maintaining status as In Transit. This includes established processes of surveillance of imports and border inspections to intercept new arrivals. Accepted definitions include ‘the detection of a pest during inspection or testing of an imported consignment’ and ‘the refusal or controlled entry of an imported consignment due to failure to comply with phytosanitary regulations’ (FAO 2018).
This is the overarching term to describe Pre-border Pathway Management and Interception. This primary stage of management has been described as ‘stop invasions before they happen, either by preventing high-risk species from entering the country or by intercepting individuals at the border’ (van Wilgen et al. 2014).
Limits to keeping
To limit the keeping or cultivation of individuals of the species within the area of interest. This can be defined as changing status from In Captivity/Cultivation to In Transit or No Risk. For example, the EU regulation provides the basis for listing Species of Union Concern and prohibits them being kept, bred, transported, sold, used or exchanged, allowed to reproduce, grown or cultivated, or released into the environment (EU 2014). In general, if all captive individuals are removed, then the only remaining risk of entry arises from individuals In Transit.
To ensure the security of individuals held in captivity/cultivation within the area of interest. Defined as maintaining status as In Captivity/Cultivation. Related terms include time–limited quarantine—the official confinement of regulated articles, pests or beneficial organisms for inspection, testing, treatment, observation or research (FAO 2018). Other examples include the ongoing management of biological collections such as zoos or gardens, or the holding of species under other controlled conditions (Cassey and Hogg 2015, EU 2015).
This is the overarching term to describe Limits to Keeping and Secure Keeping. These actions are rarely explicit in the current descriptions of IAS management (Table 1).
To remove the entire population from the area of interest—with no immediate risk of re-invasion. This can be defined as reducing status from either Surviving, Reproducing, Spreading or Widespread, to In Captivity/Cultivation or In Transit. Bomford and O’Brien (1995) provide a widely used definition of this term ‘The complete and permanent removal of all wild populations from a defined area by a time-limited campaign’, which is compatible with its use in this framework.
This is a specific form of Eradication, where the population is managed before it has begun to spread. This term is widely used (Table 1) and highlights a management priority. However, it is not a specific form of management in itself—‘rapid’ constitutes good advice rather than describing a change in status. Rapid Eradication does not cover all forms of Eradication, which has also been applied to species that have been long and widely established in an area. This is particularly the case for mammals (Keitt et al. 2011; Robertson et al. 2017) although the opportunities vary widely between taxa.
Complete reproductive removal
To remove the entire reproductive population from the area of interest—but with remaining risk of re-invasion or further reproduction if not managed, or the remaining presence of non-breeding forms. This can be defined as reducing status from either Reproducing, Spreading or Widespread to Surviving, or maintaining status as Surviving. Management of this sort requires an on-going effort to maintain the area clear in the face of dormant life stages such as seeds, or the continued influx of new individuals from neighbouring areas. This term does not feature explicitly in most of the existing descriptions of IAS management (Table 1) but is needed as there are a growing number of large-scale control programs (Bryce et al. 2011; Robertson et al. 2017) where the removal is not complete or permanent as required by the current definition of eradication (Bomford and O’Brien 1995; Robertson et al. 2019). However, the area of interest is effectively kept clear of the species, so it is different from Suppression. This form of management is likely to increase as more widespread species are managed at large scales.
To limit the spread of a reproducing population within the area of interest. This can be defined as maintaining status as Reproducing. This term is already widely used, for example ‘Any action aimed at creating barriers which minimises the risk of a population of an invasive alien species dispersing and spreading beyond the invaded area’ (EU 2014), or ‘Application of phytosanitary measures in and around an infested area to prevent spread of a pest’ (FAO 2018).
To reduce the distribution or abundance of a population within the area of interest. It can be defined as changing status from either Spreading or Widespread to either Reproducing or Spreading respectively with the objective of reducing the distribution or abundance of a population. Synonyms include reduction, control or population control, or ‘…Action…with the aim of keeping the number of individuals as low as possible so that …its invasive capacity and impacts…. are minimised’ (Population control, EU 2014). Reproducing populations remain after Suppression, so any management will typically need to be repeated indefinitely to maintain its effect. However, some forms of biological control can achieve effective suppression without ongoing management inputs and have particular value. Suppression is a widely used form of management, but its objectives in terms of the degree of suppression or the reduction of impact need to consider the context specific IAS density vs impact relationship (Norbury et al. 2015) if its effectiveness is to be assessed.
This is the overarching term which includes Containment, Suppression and Complete Reproductive Removal. This form of management requires the on-going input of management if the desired outcome is to be achieved and maintained.
For populations that are already widespread in an area and where there is no objective to reduce their abundance or extent, then no management is undertaken (Maintaining species status as Widespread). If a Widespread population is managed, then its abundance or distribution will be reduced—forming part of Suppression. No Management is synonymous with the concepts of ‘Tolerance’ or ‘Acceptance’. Even with No Management of the species, its impacts may still be reduced through Impact Adaptation.
When considering management to change the status of a species to be No Risk, in many cases no single method was considered able to achieve this, these cases were classed as Multiple Methods Required. For example, Eradication of a species from a particular area would need to be accompanied by effective Pathway Management to remove all risk of it returning. This is not to say that species cannot be managed to achieve this outcome, just that this would require multiple steps.
By being directly linked to the status of the population before and after management, these terms relate to the direct management of the species. However, management may also be motivated and directed to reduce the impact of an existing species, or one that has been removed from an area. We recognise two further terms, Impact Adaptation and Restoration. They are included here for completeness although they do not refer to changes in species status.
No change in the status of the species, but forms of management to reduce associated impacts. This includes payments to compensate for impact caused, changes in human behaviour to avoid situations where the impact might occur, operation of hatcheries or nurseries for native species, selection of resistant genotypes of species that may be impacted, control of nutrient inputs, placing protective covers or deterrents on young trees vulnerable to grazing, responding to increased erosion risk by mechanically stabilising habitats. These may also occur alongside the other direct forms of species management described here.
The management of the environment following the change in the status of an IAS. Related terms describing different forms and intensities of management include regeneration, revegetation, replacement, rehabilitation and remediation of a habitat favouring native communities (van Andel and Aronson 2012), with definitions including ‘restoring ecosystems following the removal of invasive species’ (van Wilgen et al. 2014) and ‘restore or rehabilitate degraded areas to their proper ecological function […] after invasive species removal’ (USDA 2004).