Invasive Species Systematic Review, March 2015 What is the evidence that invasive species are a significant contributor to the decline or loss of threatened species? Philip D. Roberts, Hilda Diaz-Soltero, David J. Hemming, Martin J. Parr, Richard H. Shaw, Nicola Wakefield, Holly J. Wright, Arne B.R. Witt www.cabi.org KNOWLEDGE FOR LIFE Contents Contents .................................................................................................................................. 1 Abstract .................................................................................................................................... 3 Keywords ................................................................................................................................. 4 Definitions ................................................................................................................................ 4 Background .............................................................................................................................. 5 Objective of the review ............................................................................................................ 7 The primary review question: ....................................................................................... 7 Secondary question 1: ................................................................................................. 7 Secondary question 2: ................................................................................................. 7 Methods ................................................................................................................................... 8 Results ................................................................................................................................... 13 Search results ............................................................................................................ 13 Scope ......................................................................................................................... 13 Results secondary questions 1 .................................................................................. 17 Results secondary question 2 .................................................................................... 19 Discussion ............................................................................................................................. 21 Discussion secondary question 1 .............................................................................. 21 Discussion secondary question 2 .............................................................................. 22 Review limitations ...................................................................................................... 23 Recommendations for further development of the map ............................................. 26 Review Conclusions ................................................................................................... 26 Implications for Research .......................................................................................... 29 Conclusion ............................................................................................................................. 31 Competing interests ............................................................................................................... 31 Acknowledgments .................................................................................................................. 31 References ............................................................................................................................ 32 Appendix 1: Species list of the review for secondary question 1 ........................................... 33 Appendix 2: Quality coding tool ............................................................................................. 43 Appendix 3: Data presented by invasive species .................................................................. 44 Appendix 4: Data presented by Threatened species ............................................................. 66 Appendix 5: Still visuals of the taxonomic species pair data ................................................. 88 Appendix 6: List of references included in the final review from which data was extracted from. ....................................................................................................................................... 93 1 Authors Philip D. Roberts [email protected] David J. Hemming [email protected] Martin J. Parr [email protected] Nicola Wakefield [email protected] Holly J. Wright [email protected] CABI Head Office Nosworthy Way Wallingford OX108DE United Kingdom Hilda Diaz-Soltero [email protected] USDA, National Invasive Species Council, 1201 Eye Street, NW., 5th Floor, Washington, DC, USA Richard H. Shaw [email protected] CABI, Bakeham Lane, Egham, Surrey, TW209TY, United Kingdom Arne B.R. Witt [email protected] CABI Canary Bird, 673 Limuru Road, Muthaiga, PO Box 633-00621, Nairobi, KENYA 2 Abstract Background: The Convention on Biological Diversity has reported invasive species as 2nd greatest cause of species extinction (COP10). However few efforts have been made to collate the evidence to support or contest the impact of invasive species on the decline and/or extinction of threatened species across large taxonomic or geographical scales. This Systematic Review was commissioned by the United States Department for Agriculture (USDA) Invasives Causing Extinction (ICE) programme to determine if the COP10 statement was based on scientific evidence. The evidence needs to be systematically reviewed and mapped to determine the importance and relevance of any such effects in order to develop national and international policies addressing the loss of threatened species, and to prioritise research and mitigation efforts. Methods/design: The searching of online publication databases, grey literature and other resources, such as recovery plans of endangered species, aims to gather existing evidence on whether invasive species are a significant contributor to the decline and/or extinction of threatened species. This study focuses on species under threat in the United States of America (USA). The methods used to carry out the Systematic Review will address the following two fundamental questions: (a) what proportion of threatened species have an invasive species as a significant contributor to their decline?, and (b) through what mechanisms do invasive species contribute towards the decline of native species? The pool of resources gathered has been analysed for relevance and quality using a pre-defined scoring system. A systematic map has been produced, summarising information from individual studies. Results: This systematic review found broad scientific consensus that invasive species are likely to play a crucial and devastating role in driving species extinctions. The review found that the topic has been vastly understudied. Despite the level of concern raised in the COP10 statement, when considering all US FWS ‘threatened species’, for only 6.5% have studies of the impact of invasive species been conducted and published. The reasons for this lack of evidence will be explored subsequently. What is most striking, is that, despite the limited number of studies, where evidence does exist it was overwhelmingly negative. Of all studies that investigated the impact of invasive species on US ‘threatened species’ 80% reported a negative impact. To maximise the practical use of the of this systematic review map the mechanisms of impact were recorded to help provide points of management intervention. The most common mechanisms of impact reported were predation, competition for resources and herbivory. Conclusions: There is broad scientific consensus that invasive species are likely to play a crucial and devastating role in driving species extinctions. This Systematic Review set out to collect all of the available evidence relating to this claim for US FWS ‘threatened species’. This is the first time all evidence has been collated at such a large taxonomic or geographical scale. The review found that the topic has been vastly understudied. Despite the level of concern raised in the COP10 statement, when considering all US FWS ‘threatened species’, for only 6.5% have studies of the impact of invasive species been conducted and published. The reasons for this lack of evidence will be explored subsequently. What is most striking, is that, despite the limited number of studies, where evidence does exist it was overwhelmingly negative. Of all studies that investigated the impact of invasive species on US ‘threatened species’ 80% (158 cases of evidence) reported a negative impact. This dominance of negative interactions is a clear evidence-based message to policy makers and land managers of the importance of the impact that invasive species are having on already imperilled species. 3 Keywords • Invasive species • Alien species • Threatened species • Impact, Decline • Extinction, Mechanism Definitions Invasive species: As defined by the United States of America (USA) Presidential Executive Order 13112 of February 3, 1999 is being used. It states that an “Alien species” means, with respect to a particular ecosystem, any species, including its seeds, eggs, spores, or other biological material capable of propagating that species, that is not native to that ecosystem. It also states that “Invasive species” means