A comment on the role of propagule pressure in the establishment success of introduced birds

Moulton, Michael P.; Cropper, Wendell P.

doi:10.1007/s00442-014-3184-3

Cited by 4 publications

(3 citation statements)

References 22 publications

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“…However, we disagree with those who have focused on propagule pressure, meaning the total number of individuals released, as the strongest predictor of introduction outcomes. Moreover, simply emphasizing the importance of population size to introduction outcomes can mistakenly overshadow the importance of species-level (Blackburn, Cassey & Lockwood, 2009b; Cassey, Prowse & Blackburn, 2014) and location-level factors (Moulton, Cropper & Avery, 2011, 2012b, 2013; Moulton et al, 2012a; Moulton & Cropper, 2014a, 2014b, 2015), as well as other human related, event-level factors.…”

Section: Introductionmentioning

confidence: 99%

“…It is also clear that the data involved are too limited and contain too many inaccuracies and inconsistencies for such a conclusion (Moulton et al, 2010, 2012a, 2014, 2018; Moulton, Cropper & Avery, 2011, 2012b, 2013; Moulton & Cropper, 2014a, 2015, 2016). Simple modeling of numerical responses thus assumes that the habitat in the new location was suitable, that impacts of predators or competitors are inconsequential, that the demographic factors of the individuals released did not predispose them to have abnormally reduced population growth rates (e.g., too many males not enough females, the individuals were not too old or too inbred) and that a host of potentially negative human-related factors (e.g., time in captivity or in transit, etc.)…”

Section: Introductionmentioning

confidence: 99%

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Propagule pressure does not consistently predict the outcomes of exotic bird introductions

Moulton

Cropper

2019

PeerJ

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Some have argued that the role of propagule pressure in explaining the outcomes of bird introductions is well-supported by the historical record. Here, we show that the data from a large published database (including 832 records with propagule information) do not support the conclusion that propagule pressure is the primary determinant of introduction success in birds. A few compendia of historical reports have been widely used to evaluate introduction success, typically by combining data from numerous species and introduction locations. Very few taxa, other than birds, have usable spatially explicit records of introductions over time. This availability of data inflates the perceived importance of bird analyses for addressing factors related to invasion success. The available data allow limited testing of taxonomic and site-level factors of introduction outcomes. We did find significant differences in effort and success probabilities among avian orders and across highly aggregated spatial regions. As a test of a standard and logical expectation of the propagule pressure hypothesis, we concentrated on introductions with the smallest propagules, because it is for these the hypothesis is most likely to be correct. We analyzed the effect of numbers released in small propagules (two through 10) for 227 releases. Weighted linear regression indicated no significant effect of propagule size for this range of release size. In fact, the mean success rate of 28% for propagules of 2–10 isn’t significantly different than that of 34% for propagules of 11–100. Following the example of previous analyses, we expanded the statistical test of propagule pressure to include the full range of release numbers. No significant support for the propagule pressure hypothesis was found using logistic regression with either logit or complementary log-log link functions.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Propagule pressure does not consistently predict the outcomes of exotic bird introductions

Moulton

Cropper

2019

PeerJ

Self Cite

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“…In attempting to identify the processes that deter or promote establishment of introduced bird populations, several empirical studies have concluded that propagule pressure, meaning the total number of individuals of a species released in some place, is the principal determining factor (e.g., Newsome & Noble, 1986 ; Veltman, Nee & Crawley, 1996 ; Duncan, 1997 ; Green, 1997 ; Cassey et al, 2004 ; Lockwood, Cassey & Blackburn, 2005 ; Sol et al, 2012 ). Although this conclusion has been repeatedly criticized ( Moulton et al, 2010 ; Moulton, Cropper & Avery, 2011 ; Moulton et al, 2012 ; Moulton, Cropper & Avery, 2012 ; Moulton, Cropper & Avery, 2013 ; Moulton & Cropper, 2014a ; Moulton & Cropper, 2014b ; Moulton & Cropper, 2015 ), and recent studies have emphasized the importance of species-level characteristics over propagule pressure (e.g., Sol et al, 2012 ; Cassey, Prowse & Blackburn, 2014 ), some have persisted in touting its primary importance (e.g., Blackburn, Lockwood & Cassey, 2015 ; Blackburn et al, 2015 ).…”

Section: Introductionmentioning

confidence: 99%

Inconsistencies among secondary sources of Chukar Partridge (Alectoris chukar) introductions to the United States

Moulton

Cropper

Broz

2015

PeerJ

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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.

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Patterns of success in game bird introductions in the United States

et al. 2017

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A comment on the role of propagule pressure in the establishment success of introduced birds

Cited by 4 publications

References 22 publications

Propagule pressure does not consistently predict the outcomes of exotic bird introductions

Propagule pressure does not consistently predict the outcomes of exotic bird introductions

Inconsistencies among secondary sources of Chukar Partridge (Alectoris chukar) introductions to the United States

Patterns of success in game bird introductions in the United States

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