How propagule size and environmental suitability jointly determine establishment success: a test using dung beetle introductions

Abstract

Both the size of founding populations (propagule size) and environmental suitability are known to influence whether a species newly introduced to a location will establish a self-sustaining population. However, these two factors do not operate independently: it is the interaction between propagule size and environmental suitability that determines the probability an introduced population will establish. Here I use the example of dung beetle introductions to Australia to illustrate the importance of this interaction. I first describe equations that model establishment success jointly as a function of propagule size and environmental suitability. I then show how these equations provide insight into the different outcomes observed in two dung beetle species widely introduced to Australia. In one species, variation in propagule size had relatively little influence on establishment success due to large variation in environmental suitability, leading to an essentially bimodal outcome: sites were either very suitable for establishment and introductions succeeded, or sites were unsuitable and introductions failed regardless of propagule size. For the second species, there was much less variation among locations in environmental suitability, leading to propagule size having a strong influence on establishment success. These examples highlight how the interaction between environmental suitability and founding population size is central to determining the probability an introduced species will establish.

Benefits of increased colonist quantity and genetic diversity for colonization depend on colonist identity

“…To obtain detailed phenotypic data, we conducted 21‐day life‐history trials on each of the nine experimental genotypes. Life‐history trials were conducted from 31 May until 26 June . Twenty neonates were individually isolated from each genotype, maintained following the same trial procedures as detailed in Supplementary material Appendix 2, and checked daily for 21 days.…”

“…The field experiment was conducted at the Queen's University Biology Station, ON, Canada from 22 June until 18 August . We employed an unbalanced design in which mesocosms were inoculated by either one D. pulex from one genotype (a ‘single individual/low diversity’ treatment), nine D. pulex of the same genotype (‘many individuals/low diversity’), or a mixture comprised of one D. pulex from each of the nine genotypes (‘many individuals/high diversity’).…”

“…The 109 mesocosms (cylindrical tanks 84 cm diameter × 53 cm high) were set up on 22 June . Mesocosms were filled with 180 l of filtered water from nearby Opinicon Lake (water unfamiliar to all genotypes, Supplementary material Appendix 3 Table A1) and covered with 1 mm mesh to protect from insects and debris.…”

“…Between 25 and 28 June , 72 female neonates were collected from each experimental genotype. All neonates for each genotype were divided evenly between six 120 ml glass containers and maintained in 100 ml of filtered Elbow Lake water and fed 30 µg of carbon per container per day.…”

Drivers, impacts, mechanisms and adaptation in insect invasions

“…Hui et al (2016) adopt an ecological network approach in attempting to capture the complexity of recipient ecosystems for insect invaders. Duncan (2016) makes inferences from success rates of dung beetle introductions into Australia along climatic gradients. To highlight how model species can be used to understand invasions, Roy et al (2016) demonstrate the power of global collaboration and have compiled an impressive dataset for Harmonia axyridis that highlights the variation in traits and the success of this global invader.…”