| Summary: | Introduced commensal rodents have had a major impact on the biota of island communities worldwide; the ship rat (Rattus rattus) and the house mouse (Mus domesticus) have a long history in the Galapagos islands, while the larger, more aggressive brown rat (Rattus norvegicus) was identified only in 1983 on one island, Santa Cruz. By 1988 it had spread into the agricultural zone but was still restricted to human habitation. In 1993 the cross-island road and village communities in the agricultural zone of Santa Cruz were sampled using a standard trap line of break-back traps. House surveys were also carried out, where appropriate. The brown rat was found to occur at all sites sampled on the south side of the island, including sites independent of human habitations, and is now the dominant commensal rat in houses. The impact of the brown rat on the ship rat and the conservation implications of its spread are discussed.
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