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Island biogeography and the species richness of introduced mammals on New Zealand offshore islands

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Abstract Aim 

To investigate and establish the significance of various island biogeographic relationships (geographical, ecological and anthropological) with the species richness of introduced mammals on offshore islands. Location 

The 297 offshore islands of the New Zealand archipelago (latitude: 34–47°S; longitude: 166–179°E). Methods 

Data on New Zealand offshore islands and the introduced mammals on them were collated from published surveys and maps. The species richness of small and large introduced mammals were calculated for islands with complete censuses and regressed on island characteristics using a Poisson distributed error generalized linear model. To estimate the ‘z-value’ for introduced mammals on New Zealand islands, least-squares regression was used [log10 S vs. log10 A]. Results 

High collinearity was found between the area, habitat diversity and elevation of islands. The island characteristics related to the species richness of introduced mammals differed predictably between large and small mammals. The species richness of introduced large mammals was mostly related to human activities on islands, whereas species richness of introduced small mammals was mostly related to island biogeographical parameters. The ‘z-value’ for total species richness is found to be expectedly low for introduced mammals. Main conclusions 

Distance appears to have become ecologically trivial as a filter for introduced mammal presence on New Zealand offshore islands. There is strong evidence of a ‘small island’ effect on New Zealand offshore islands. The species richness of both small and large introduced mammals on these islands appears to be most predominantly related to human use, although there is some evidence of natural dispersal for smaller species. The ecological complexity of some islands appears to make them less invasible to introduced mammals. Some human activities have an interactive effect on species richness. A small number of islands have outlying species richness values above what the models predict, suggesting that the presence of some species may be related to events not accounted for in the models.
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Keywords: Island biogeography; New Zealand; introduced mammals; linear modelling; offshore islands

Document Type: Research Article

Affiliations: 1: School of Biological Sciences 2: Department of Statistics, University of Auckland, Auckland, New Zealand

Publication date: 2004-04-01

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