Propagule pressure as a driver of establishment success in deliberately introduced exotic species: fact or artefact?

Context According to the tens rule, 10% of introduced species establish themselves. Aims We tested this component of the tens rule for amphibians and reptiles globally, in Europe and North America, where data are presumably of good quality, and on islands versus continents. We also tested whether there was a taxonomic difference in establishment success between amphibians and reptiles. Methods We examined data comprising 206 successful and 165 failed introduction records for 161 species of amphibians to 55 locations, and 560 successful and 641 failed introduction records for 469 species of reptiles to 116 locations around the world. Key results Globally, establishment success was not different between amphibians (67%) and reptiles (62%). Both means were well above the 10% value predicted by the tens rule. In Europe and North America, establishment success was lower, although still higher than 10%. For reptiles, establishment success was higher on islands than on continents. Our results question the tens rule and do not show taxonomic differences in establishment success. Implications Similar to studies on other taxa (birds and mammals), we found that establishment success was generally above 40%. This suggests that we should focus management on reducing the number of herptile species introduced because both reptiles and amphibians have a high likelihood of establishing. As data collection on invasions continue, testing establishment success in light of other factors, including propagule pressure, climate matching and taxonomic classifications, may provide additional insight into which species are most likely to establish in particular areas.

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

10.7287/peerj.preprints.1362v1 ◽

2015 ◽

Author(s):

Michael P Moulton ◽

Wendell P Cropper, Jr ◽

Andrew J Broz

Keyword(s):

Propagule Pressure ◽

Bird Species ◽

The United States ◽

Establishment Success ◽

Secondary Sources ◽

Alectoris Chukar ◽

Large Numbers ◽

The Usa ◽

Species Characteristics ◽

Chukar Partridge

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.

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Timing between successive introduction events determines establishment success in bacteria with an Allee effect

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2019.0598 ◽

2019 ◽

Vol 286 (1902) ◽

pp. 20190598 ◽

Cited By ~ 2

Author(s):

Michael D. Dressler ◽

Josue Conde ◽

Omar Tonsi Eldakar ◽

Robert P. Smith

Keyword(s):

Infectious Disease ◽

Allee Effect ◽

Propagule Pressure ◽

Temporal Distribution ◽

Invasion Biology ◽

Theoretical Studies ◽

Establishment Success ◽

Propagule Size ◽

Population Establishment ◽

Principal Parts

Propagule pressure is a leading determinant of population establishment. Yet, an experimental understanding of how propagule size and number (two principal parts of propagule pressure) determine establishment success remains incomplete. Theoretical studies suggest that the timing between introduction events, a component of propagule number, can influence establishment success. However, this dynamic has rarely been explored experimentally. Using Escherichia coli engineered with an Allee effect, we investigated how the timing of two introduction events influences establishment. For populations introduced below the Allee threshold, establishment occurred if the time between two introduction events was sufficiently short, with the length of time between events further reduced by reducing growth rate. Interestingly, we observed that as the density of bacteria introduced in one introduction event increased, the time between introduction events that allowed for establishment increased. Using a mathematical model, we provide support that the mechanism behind these trends is the ability of the first population to modify the environment, which can pave the way for establishment of the second population. Our results provide experimental evidence that the temporal distribution of introduction events regulates establishment, furthering our understanding of propagule pressure and may have implications in invasion biology and infectious disease.

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How to incorporate information on propagule pressure in the analysis of alien establishment success

Methods in Ecology and Evolution ◽

10.1111/2041-210x.12930 ◽

2017 ◽

Vol 9 (4) ◽

pp. 1097-1108 ◽

Cited By ~ 3

Author(s):

Alex L. Pigot ◽

Phillip Cassey ◽

Tim M. Blackburn

Keyword(s):

Propagule Pressure ◽

Establishment Success

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Passerine introductions to New Zealand support a positive effect of propagule pressure on establishment success

Biodiversity and Conservation ◽

10.1007/s10531-011-0081-5 ◽

2011 ◽

Vol 20 (10) ◽

pp. 2189-2199 ◽

Cited By ~ 24

Author(s):

Tim M. Blackburn ◽

Thomas A. A. Prowse ◽

Julie L. Lockwood ◽

Phillip Cassey

Keyword(s):

New Zealand ◽

Propagule Pressure ◽

Establishment Success ◽

Positive Effect

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

10.7287/peerj.preprints.1362 ◽

2015 ◽

Author(s):

Michael P Moulton ◽

Wendell P Cropper, Jr ◽

Andrew J Broz

Keyword(s):

Propagule Pressure ◽

Bird Species ◽

The United States ◽

Establishment Success ◽

Secondary Sources ◽

Alectoris Chukar ◽

Large Numbers ◽

The Usa ◽

Species Characteristics ◽

Chukar Partridge

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.

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Human-related processes drive the richness of exotic birds in Europe

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2008.0994 ◽

2008 ◽

Vol 276 (1654) ◽

pp. 47-53 ◽

Cited By ~ 49

Author(s):

François Chiron ◽

Susan Shirley ◽

Salit Kark

Keyword(s):

Exotic Species ◽

Propagule Pressure ◽

Abiotic Factors ◽

Bird Species ◽

Community Level ◽

Minor Importance ◽

Relative Role ◽

Natural Factors ◽

Bird Richness ◽

Exotic Birds

Both human-related and natural factors can affect the establishment and distribution of exotic species. Understanding the relative role of the different factors has important scientific and applied implications. Here, we examined the relative effect of human-related and natural factors in determining the richness of exotic bird species established across Europe. Using hierarchical partitioning, which controls for covariation among factors, we show that the most important factor is the human-related community-level propagule pressure (the number of exotic species introduced), which is often not included in invasion studies due to the lack of information for this early stage in the invasion process. Another, though less important, factor was the human footprint (an index that includes human population size, land use and infrastructure). Biotic and abiotic factors of the environment were of minor importance in shaping the number of established birds when tested at a European extent using 50×50 km 2 grid squares. We provide, to our knowledge, the first map of the distribution of exotic bird richness in Europe. The richest hotspot of established exotic birds is located in southeastern England, followed by areas in Belgium and The Netherlands. Community-level propagule pressure remains the major factor shaping the distribution of exotic birds also when tested for the UK separately. Thus, studies examining the patterns of establishment should aim at collecting the crucial and hard-to-find information on community-level propagule pressure or develop reliable surrogates for estimating this factor. Allowing future introductions of exotic birds into Europe should be reconsidered carefully, as the number of introduced species is basically the main factor that determines the number established.

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Causes of exotic bird establishment across oceanic islands

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2005.3193 ◽

2005 ◽

Vol 272 (1576) ◽

pp. 2059-2063 ◽

Cited By ~ 24

Author(s):

Phillip Cassey ◽

Tim M Blackburn ◽

Richard P Duncan ◽

Kevin J Gaston

Keyword(s):

Exotic Species ◽

Human Disturbance ◽

Island Biogeography ◽

Habitat Diversity ◽

Oceanic Islands ◽

Negative Interaction ◽

Establishment Success ◽

Exotic Birds ◽

Mammalian Predator

The probability that exotic species will successfully establish viable populations varies between regions, for reasons that are currently unknown. Here, we use data for exotic bird introductions to 41 oceanic islands and archipelagos around the globe to test five hypotheses for this variation: the effects of introduction effort, competition, predation, human disturbance and habitat diversity (island biogeography). Our analyses demonstrate the primary importance of introduction effort for avian establishment success across regions, in concordance with previous analyses within regions. However, they also reveal a strong negative interaction across regions between establishment success and predation; exotic birds are more likely to fail on islands with species-rich mammalian predator assemblages.

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