Abstract
Invasive alien species are a major threat to biodiversity and human activities, providing a strong incentive to understand the processes by which alien invasion occurs. While it is important to understand the determinants of success at each of several invasion stages—transport, introduction, establishment, and spread—few studies have explored the first of these stages. Here, we quantify and analyze variation in the success of individual animals in surviving the transport stage, based on shipping records of European passerines destined for New Zealand. We mined the original documents of Acclimatisation Societies, established in New Zealand for the purpose of introducing supposedly beneficial alien species, in combination with recently digitized newspaper archives, to produce a unique dataset of 122 ships that carried passerines from Europe to New Zealand between 1850 and 1885. For 37 of these shipments, data on the survival of individual species were available. Using generalized linear mixed models, we explored how survival was related to characteristics of the shipments and the species. We show that species differed greatly in their survival, but none of the tested traits accounted for these differences. Yet, survival increased over time, which mirrors the switch from early haphazard shipments to larger organized shipments. Our results imply that it was the quality of care received by the birds that most affected success at this stage of the invasion process.
Highlights
The transportation and subsequent introduction of species to regions beyond their natural distribution, where they do not naturally occur, is one of the principal ways in which human activities are changing the natural world (e.g., Bellard, Genovesi, & Jeschke, 2016; Blackburn et al, 2011; Clavero & Garcia-Berthou, 2005; Lockwood & McKinney, 2001).[Correction added on 27 March 2020 after first publication: an error in the underlying data has been corrected
We did not find predictors of variation in the likelihood of passerine birds surviving the voyage to New Zealand, with the exception of an overall trend toward higher survival rates over time
This trend was probably driven by early failures, subsequently leading to improved policies, and by the fact that initial private endeavors (Canterbury Acclimatisation Society, 1866) were, in the late 1860s and in 1870s, replaced by large shipments organized by the Acclimatisation Societies, with very low mortality (e.g., Warrior Queen in 1868, 1870 and 1871 to Otago and Charlotte Gladstone in 1872, Tintern Abbey in 1875, and Waimate in 1880 to Canterbury)
Summary
The transportation and subsequent introduction of species to regions beyond their natural distribution, where they do not naturally occur (here termed aliens), is one of the principal ways in which human activities are changing the natural world (e.g., Bellard, Genovesi, & Jeschke, 2016; Blackburn et al, 2011; Clavero & Garcia-Berthou, 2005; Lockwood & McKinney, 2001). The several larger Societies founded in New Zealand were a rich source of information on the invasion process for alien birds in New Zealand (McDowall, 1994) They maintained detailed records of which species they introduced and which introductions resulted in established populations, and summaries of these records were subsequently collated and published in catalogue form (Drummond, 1906; Thomson, 1922). Some data are stored only in the newspapers, as shipments of birds commenced before Acclimatisation Societies were founded, some Society records were lost, and some shipments were private endeavors These sources allowed us to collate a unique dataset of ships for which there was reliable information both about the number of individual birds loaded at the ports of origin and the number that survived the journey to New Zealand. | 3946 due to higher mortality of males in sexually dimorphic species (Promislow, Montgomerie, & Martin, 1992) or migratory restlessness in the case of migrants
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