Environmental impact classification for alien insects: a review of mechanisms and their biodiversity outcomes
Introduction
The impacts of alien species on native biodiversity and ecosystems are significant [1]. Understanding the form and size of these impacts is essential for prioritising species for prevention, early warning and control efforts [2]. This is recognised by global targets for reducing the pressure on biodiversity, specifically Aichi Target 9 of the Strategic Plan for Biodiversity 2011–2020, which includes that by 2020 ‘Invasive alien species … are identified and prioritized, priority species are controlled or eradicated …’ [3]. The range of ways in which invasive alien species impact biodiversity are well appreciated [1]. However, until recently there has been no widely accepted approach for assessing the impacts of a broad suite of alien taxa that enables the comparison and prioritisation of the size of their impacts [4••]. A common approach to assessing impact is essential for evaluating and tracking biological invasion and the success of intervention efforts.
Invasive alien insects, like other taxa, have a range of ecological impacts, although comparatively few invasive insect species have been studied, particularly under field conditions [5]. The literature is also strongly biased to a handful of species, a narrow range of ecological mechanisms of impact and those with socio-economic consequences; ecosystem structural changes and its consequences have, for example, received little attention [5]. Although invasive insects impact biodiversity in multiple ways, their impacts on native insect biodiversity, particularly closely related insect families, are often especially significant [6, 7, 8••]. A standardised approach for classifying alien insect species is needed. This should be based on the nature and size of their environmental impacts, and be able to accommodate data rich and data poor species. It would improve rapid decision-support schemes for policy and management, contribute to achieving Aichi Target 9, and accelerate efforts to fill some of the important information gaps on alien insect species and the consequences of their invasion [9, 10].
Recently, a standardised system was proposed that classifies alien species, based on a suite of impact mechanisms, according to the size of their environmental impacts [4••]. This system is being advocated for adoption as the standard scheme by which the IUCN classifies the negative impacts of species of all taxa that have become invasive [11]. The approach relies heavily on a standard set of impact mechanisms, and their environmental and socio-economic outcomes. The relevance and sufficiency of this scheme has yet to be reviewed for alien insects. Such a review is essential prior to application and widespread adoption of the system; to ensure that the outcomes are equally robust and comparable across the higher level taxa for which its adoption is intended, including the Insecta.
In this review we examine the appropriateness and relevance, for alien and invasive insects, of the impact mechanisms and their environmental outcomes that underpin this proposed method for classifying the environmental impact of alien taxa. The review more broadly outlines and assesses a scheme for describing the direct and indirect impacts of invasive alien insects, upon which the magnitude of these impacts and their relative importance can be classified.
Section snippets
Which alien insect species are invasive?
Identifying which alien insects are invasive forms the first task specified by Aichi Target 9. The number of alien insects known to be invasive, that is, to have negative impacts on biodiversity and ecosystems, is considered to be significantly underestimated [12]. Kenis et al. [5] found published evidence of ecological impacts for only 72 insect species, and found strong bias in the literature towards North America and ants (Table S2). As a contribution to Aichi Target 9, and more specifically
Mechanisms of impact
Four of the 10 impact mechanisms, that is, competition, predation, disease transmission and herbivory, are well-known, relevant and direct mechanisms by which alien insects impact biodiversity (scoring positively for between 15% and 61% of the invasive alien insects examined; HIGH, Table 1).
There is clear evidence for three other mechanisms, although evidence of their relevance is limited to a more narrow range of orders, families or cases than the above mechanisms, and may also be
Adequacy of 10 impact mechanisms
We have shown that the proposed standard mechanisms by which invasive species impact the environment are largely appropriate for application to insects, with a range in their relevance from high, relevant but probably underestimated, to low relevance. In some instances a more narrow definition of the mechanism applies (herbivory), and in others an expanded definition would better capture the nature of the mechanism (parasitism) for insects. In these cases we have suggested some refinement to
Conclusion
This assessment provides a basis for future adoption of the environmental impact classification scheme for alien taxa. Well known, direct mechanisms of alien insect impacts are well captured by the proposed standard alien classification scheme. Novel and indirect interactions, and their ecosystem outcomes, are critical mechanisms by which alien invasive insects impact the environment, supported by a growing body of evidence. A scheme that does not explicitly consider these often higher-order
References and recommended reading
Papers of particular interest, published within the period of review, have been highlighted as:
•• of outstanding interest
Acknowledgements
This work was supported in part by Australian Research Council grant DP150103017. We thank Akane Uesugi for commenting on the manuscript.
References (38)
- et al.
Impacts of biological invasions: what's what and the way forward
Trends Ecol Evol
(2013) - et al.
Comparing impacts of alien plants and animals in Europe using a standard scoring system
J Appl Ecol
(2015) - McGeoch MA, Genovesi P, Bellingham PJ, Costello MJ, McGrannachan C, Sheppard A: Prioritizing species, pathways, and...
The Strategic Plan for Biodiversity 2011–2020 and the Aichi Biodiversity Targets. UNEP/CBD/COP/DEC/X/2, 29 October 2010, Nagoya, Japan. COP CBD Tenth Meeting
(2011)- et al.
A unified classification of alien species based on the magnitude of their environmental impacts
PLoS Biol
(2014) - et al.
Ecological effects of invasive alien insects
Biol Invasions
(2009) - et al.
Interference competition by Argentine ants displaces native ants: implications for biotic resistance to invasion
Biol Invasions
(2007) - et al.
Testing the effects of ant invasions on non-arthropods with high-resolution taxonomic data
Ecol Appl
(2015) - et al.
Ten years of invasion: Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) in Britain
Ecol Entomol
(2015) - et al.
Environmental and economic impact of alien terrestrial arthropods in Europe
NeoBiota
(2014)