Wildlife Research Wildlife Research Society
Ecology, management and conservation in natural and modified habitats

Determinants of establishment success for introduced exotic mammals

Mary Bomford A , Rebecca O. Darbyshire A B and Lucy Randall A
+ Author Affiliations
- Author Affiliations

A Bureau of Rural Sciences, GPO Box 858, Canberra, ACT 2601, Australia.

B Corresponding author. Email: rebecca.darbyshire@brs.gov.au

Wildlife Research 36(3) 192-202 https://doi.org/10.1071/WR08055
Submitted: 11 April 2008  Accepted: 10 February 2009   Published: 15 April 2009


We conducted comparisons for exotic mammal species introduced to New Zealand (28 successful, 4 failed), Australia (24, 17) and Britain (15, 16). Modelling of variables associated with establishment success was constrained by small sample sizes and phylogenetic dependence, so our results should be interpreted with caution. Successful species were subject to more release events, had higher climate matches between their overseas geographic range and their country of introduction, had larger overseas geographic range sizes and were more likely to have established an exotic population elsewhere than was the case for failed species. Of the mammals introduced to New Zealand, successful species also had larger areas of suitable habitat than did failed species. Our findings may guide risk assessments for the import of live mammals to reduce the rate new species establish in the wild.


Funding was provided by the Australian Invasive Animals Cooperative Research Centre. L. Walter assisted with climate matching and calculating overseas range sizes. B. Raphael and L. Brown and three anonymous referees provided constructive comments. C. M. King provided advice on mammals established in New Zealand. S. Barry (CSIRO) and E. Lawrence (BRS) provided advice on statistical analyses.


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Appendix 1.  Exotic mammal species introduced to New Zealand, Australia and Great Britain
The following species were excluded from the analyses: NEW ZEALAND: Axis axis established a small self-sustaining wild population that was eradicated by hunting (Thomson 1922); an unknown Dasyurus sp. was unsuccessfully introduced to New Zealand (Thomson 1922); Pseudocheirus perigrinus and Lama vicugna were imported; however, it is uncertain whether they were released (Thomson 1922); Procyon lotor, Spermophilus beecheyi and Tamais striatus were also imported and it is unclear whether there was a release event of two or more animals for these species (Thomson 1922); AUSTRALIA: Canis aureus was reported being released in Victoria as a substitute for foxes for sport hunting (Fitzpatrick 1878); probably these jackals were released singly and hunted and killed soon after their release; Myers (1986) reported that zebra (Equus sp.) was released; however, we were unable to confirm the species or whether more than one individual was released; Long (2003) reported unconfirmed releases of Alces alces and Vicugna vicugna; BRITAIN: Lepus europaeus, Castor fibre, Sus scrofa, Micromys minutus, Canis lupus, Mustela putorius, Rangifer tarandus, Capreolus capreolus and Dama dama may all have been originally native (Yalden 1999); Mesocricetus auratus has established many times; however, populations have always been eradicated before becoming widespread (Long 2003), so its potential status is uncertain; Hystrix brachyura established a small breeding population that was eradicated by trapping (Baker 1990; Long 2003); Nyctomys sumichrasti is ‘not infrequently found in consignments of bananas in London, the Welsh ports, and no doubt elsewhere’ according to Fitter (1959); however, it is uncertain whether this species has ever been released from containment; Baker (1990) lists the following three escaped species that were present in the wild only for less than 10 days before being killed or caught: Papio hamadryas; Panthera tigris; Neofelis nebulosa. The following three species that are not now present or are uncommon in the wild were included as successful: NEW ZEALAND: feral dog (Canis lupus) packs were present in the 19th century (Thomson 1922) and are still not wholly restricted to human settlements (Atkinson 2006); BRITAIN: Myocastor coypus and Ondatra zibethicus were included because both exotic species were so widespread before their intentional eradication that it is clear they could have sustained wild populations. Outcome: 1 = successfully established; 0 = released but failed to establish. Climate match scores are presented as percentages of the total number of grid squares (or meteorological stations for Britain) in the country being assessed. Establishment success elsewhere score: 0 = introduced and failed; 1 = established overseas on small islands (<50 000 km-2); 2 = established overseas on larger islands (≥50 000 km-2) or a continent; NI = never introduced elsewhere; U = introduced elsewhere but success uncertain. Release events score: 0 = 1–4; 1 = >4 recorded release events of the species in country being assessed (after Forsyth et al. 2004). A single release event may be of any number of individual animals. World-range size (millions of km2), excluding range in country being assessed. For species introduced to New Zealand from Australia, we included their former distribution at the time of European settlement (Strahan 1995). Migration score: 0 = non-migratory; 1 = migratory
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Appendix 2.  Appendix 2. Habitats exotic mammal species introduced to New Zealand use in their overseas ranges
Outcome: 1 = successfully established; 0 = released but failed to establish. Habitat area indicates area of suitable habitat in New Zealand (×1000 km2). Habitats commonly used in overseas range: 1 = present; – = absent
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