The propagule pressure hypothesis asserts that the number of individuals released is the key determinant of whether an introduction will succeed or not. It remains to be shown whether propagule pressure is more important than either species-level or site-level factors in determining the fate of an introduction. Studies claiming to show that propagule pressure is the primary determinant of introduction success must assume that the historical record as reported by secondary sources is complete and accurate. Here, examine a widely introduced game bird, the Chukar (Alectoris chukar), to the USA. We compare the records reported by two secondary sources (Long, 1981; Lever, 1987) to those in a primary source (Christensen, 1970) and to a recent study by Sol et al. (2012). Numerous inconsistencies exist in the records reported by Sol et al. (2012), Long (1981) and Lever (1987) when compared to the primary record of Christensen (1970). As reported by Christensen (1970), very large numbers of Chukars were released unsuccessfully in some states. Our results strongly imply that factors other than sheer numbers are more important. Site-to-site differences are the most likely explanation for the variation in success.
An important source of information concerning the fates of intentionally introduced exotic bird species has been collections of historical data that sometimes include species released, numbers released, locations of release, and establishment success. These data have been used to assess potential predictors of establishment success such as propagule pressure, site-level factors, and species characteristics. In order to better understand the limitations of such historical compilations, we compared data for the Chukar (Alectoris chukar) introductions to the USA from two often used compilations and from other sources associated with Chukar introduction programs. We found the major compilations of Long (1981) and Lever (1987) are inconsistent and likely to be incomplete, and inaccurate, in terms of the taxa introduced, the numbers introduced, and the fates of these introductions. Propagule pressure analyses have often assumed that every bird in every release must be summed to represent the propagule pressure necessary for establishment. We found, however, that large numbers of birds were released into states and counties with already established populations. Additionally, in numerous states very large numbers of Chukars were unsuccessfully released. We conclude that site-level factors were more important influences of establishment success than propagule pressure was. PeerJ PrePrints Abstract 20An important source of information concerning the fates of intentionally 21 introduced exotic bird species has been collections of historical data that sometimes 22 include species released, numbers released, locations of release, and establishment 23 success. These data have been used to assess potential predictors of establishment 24 success such as propagule pressure, site--level factors, and species characteristics. In 25 order to better understand the limitations of such historical compilations, we 26
An important source of information concerning the fates of intentionally introduced exotic bird species has been collections of historical data that sometimes include species released, numbers released, locations of release, and establishment success. These data have been used to assess potential predictors of establishment success such as propagule pressure, site-level factors, and species characteristics. In order to better understand the limitations of such historical compilations, we compared data for the Chukar (Alectoris chukar) introductions to the USA from two often used compilations and from other sources associated with Chukar introduction programs. We found the major compilations of Long (1981) and Lever (1987) are inconsistent and likely to be incomplete, and inaccurate, in terms of the taxa introduced, the numbers introduced, and the fates of these introductions. Propagule pressure analyses have often assumed that every bird in every release must be summed to represent the propagule pressure necessary for establishment. We found, however, that large numbers of birds were released into states and counties with already established populations. Additionally, in numerous states very large numbers of Chukars were unsuccessfully released. We conclude that site-level factors were more important influences of establishment success than propagule pressure was.
21Better predictions of the success of species' introductions require careful 22 evaluation of the relative importance of at least three kinds of factors: species 23 characteristics, characteristics of the site of introduction, and event--level factors 24 such as propagule pressure. Historical records of bird introductions provide a 25 unique method for addressing the relative importance of these factors. We compiled 26 a list of introductions of 17 Phasianid species released in the USA during the Foreign 27Game Investigation Program (FGIP). These records indicate that releases for some 28Phasianid species in the USA continued long after establishment. For many of the 13 29 species that always failed, even numerous releases and large numbers of individuals 30 per release were not enough for successful establishment, yet several of these 31 species were successfully introduced elsewhere. Only four species were successful 32 in at least one state. Yet, all four were unsuccessful either in other states, or in other 33 regions of states where they were not already successfully established, or both. 34These results support the notion that the number of individuals released and the 35 number of releases are less important than characteristics of the location where the 36 introductions occurred. 37 38 39PeerJ PrePrints | https://doi.org/10.7287/peerj.preprints.1765v1 | CC-BY 4.0 Open Access |
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