Management of biological invasions: a review
Phil Hulme, Head of Ecosystem Dynamics at NERC Centre for Ecology and Hydrology (Scotland) and editor of the Journal of applied ecology develops his ideas on the management of biological invasions.
Although Government Departments, environmental managers and conservationists are facing practical management questions for resolving invasive alien species (IAS) problems, to date, research is more focussed on describing biological invasions than in delivering robust solutions to address all stages of the process of invasion, and only a few studies embrace the ecosystem approach.
Prevention, eradication and control form the cornerstones of recommended best practices aimed at managing IAS, prevention being considered the more cost-effective and environmentally desirable strategy. Prevention consists of assessing the risk of entry and establishment of a species in a given area. One approach is to use climate prediction tools to analyse the likelihood and extent of IAS establishment in a new region, using knowledge of the environmental constraints in its native range. Thus, caution must be applied when interpreting predictions based on climate matching alone. An alternative to the individual species approach is the “neural network”, which models entire IAS assemblages under the assumption that these are likely to be non-random species groupings that contain hidden predictive information. The advantage of this approach is that it integrates species and bio-geographical information in a single analysis, uses widely available data on species presence-absence rather than less-accessible climate and species trait information, and can be used at regional and global scales.
Nevertheless, the high number of candidate IAS, the expense of individual risk assessment, and the investment required in inspection capacities may act against measures aiming to prevent the introduction of IAS. In this context, species-centred approaches may require revision and moving the focus instead to modelling pathways of introduction (for example, intentional introduction of species for ornamental purposes, unintentional introduction of species with consignments of soils) may prove a valuable way forward.
However, even where the tools are appropriate and available, implementation of prevention measures requires action through voluntary codes of practice.
Rapid response should be consequent on early detection, but, when IAS are rare, it is both difficult to detect them and to assess the risk they represent. Vigilance is often focused at the sites of likely entry (e.g. ports and airports), where the probability of interception is expected to be highest. But most of the time, sampling protocols are not implemented in a consistent and statistically designed manner. An assessment of inspection protocols and the scope for extending them to cover a wider range of IAS threats (in order to protect the natural environment and not only plant and health) would help provide guidance for future interception strategies at places of entry. Improvements in remote sensing (such as hyperspectral imagery at spatial resolution of 2 m) may play an important role in large-scale surveys of relatively visible, recognizable and immobile IAS.
Rather than responding to rare incursions, action could be mobilized at a higher abundance threshold, at which the power of detection is increased. Developing a composite indicator that tracks trends in the relative abundance of a suite of IAS with similar life histories, shared pathways and/or habitat preferences may help in taking decisions.
Concerning management, strategic models that identify the optimum manner in which to deploy limited resources available for management can generate valuable empirical rules. For instance, one of the earliest empirical rules emphasized the importance of targeting small, isolated populations or ‘satellites’ rather than a larger core IAS population because many satellites will contribute proportionally more to population expansion than a large core population.
Moreover, the assessment of management options has to be done within an ecosystem perspective, taking into account the use of native competitors, consumers and mutualists, to reviewing existing management practices as well as mitigating other environmental pressures and addressing indirect effects on community diversity and structure.
In conclusion, a comprehensive approach to IAS management should include consideration of the following: expected impacts, technical options available, ease with which the species can be targeted, risks associated with management, likelihood of success, and extent of public concern and stakeholder interest.
Sources
Hulme PE (2006) Beyond control: wider implications for the management of biological invasions. Journal of applied ecology 43, 835-847