Report 372
Non-native species in UK Overseas Territories: a review
Varnham, K
The Overseas Territories and Crown Dependencies of the United Kingdom are comprised mostly of island environments and are notable for their numbers of endemic and globally threatened species.


Non-native species are a major cause of the loss of biodiversity globally and their impacts are especially severe on the island ecosystems and species typical of our Overseas Territories and Crown Dependencies.  The biodiversity found in the Territories contains many globally threatened and endemic species and also populations of species whose abundance is of regional or global significance.
This study was commissioned to investigate, through desk study, the occurrence of non-native species in the Overseas Territories and Crown Dependencies of the United Kingdom.
The review collated information gathered from the literature, individual experts and organisations, both in the UK and in the Territories or Dependencies themselves, and was guided by a workshop at JNCC in January 2004 involving representatives of the Foreign & Commonwealth Office, the Department for International Development and the UK Overseas Territories Conservation Forum.
A minimum of 2261 non-native species is recorded as occurring across the UK Overseas Territories & Crown Dependencies with a total of >2900 records of occurrence overall.  The review showed that Bermuda has the unfortunate distinction of topping the non-native species polls with 1139 species recorded – by contrast, the South Sandwich Islands have none. 
A number of species are recorded as causing problems in several Territories. The study collated records of rats (Rattus rattus, R. norvegicus and R. exulans) from 14 Territories and feral cats (Felis catus) and house mice (Mus musculus) each from 11. The mimosa Leucaena leucocephala is currently the most widely recorded introduced plant species with records from 10 territories, followed by Australian pine Casuarina equisetifolia from eight Territories and lantana Lantana camara from six Territories.  However, it only takes the presence of a single invasive species to have devastating consequences for some native wildlife.
In general, the number of non-native species recorded from a Territory is closely related to the amount of biological survey work carried out there in recent years. The number of species recorded in the database, therefore, does not necessarily reflect the true numbers of introduced species in many Territories.  Numbers in most Caribbean Territories are likely to be far higher than recorded here whereas numbers from the Falklands, Bermuda, Gough Island, Ascension and St. Helena are based on recent research.  This review should, therefore, be seen very much as work in progress.  The low numbers of non-native species recorded from the British Antarctic Territory and the South Sandwich Islands are thought to be genuine.
This audit, the first of its kind, will help to inform any measures aimed at eradicating, controlling and, more importantly, preventing the future establishment of, non-native species and conserving the native biodiversity they threaten.
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ISSN 0963 8091
Please cite as: Varnham, K, (2006), Non-native species in UK Overseas Territories: a review, JNCC Report 372, ISSN 0963 8091