Background

Invasive species have been reported as one of the leading causes of species extinction. However, the evidence to support or contest their effects on the decline and/or extinction of threatened species has been largely unavailable and few efforts have been made to collate such information. In order to develop national and international policies addressing the loss of threatened species, and to prioritise research and mitigation efforts, the evidence needs to be systematically reviewed and mapped to determine the importance of such effects.

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 US species under threat. 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 will be analysed for relevance and quality using a pre-defined scoring system. A systematic map will be produced, summarising information from individual studies. Where possible, data will be extracted from included studies and synthesised using meta-analysis.