Raw data - Ch2 - Probing role of Allee etc.csv (0.94 kB)

Raw data - Ch2 - Probing role of Allee etc.csv

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posted on 02.11.2020, 17:50 by Hester Williams, Eckehard Brockerhoff, Andrew Liebhold, Darren Ward

Title: Probing the role of propagule pressure, stochasticity and Allee effects on invasion success using experimental introductions of a biological control agent

Experimental design:

The initial population sizes of Neolema ogloblini adults were manipulated over replicated releases at 30 isolated sites in the Selwyn district of Canterbury, New Zealand. All sites were located in an area classified as the Canterbury-Otago tussock grasslands ecoregion (Department of Conservation, 1987).

At each site, potted plants of Tradescantia mundula were arranged to form a patch size with a leaf-cover of ca. 1 m2. The potted plants were placed on weed-mat to prevent rooting and minimize the likelihood of becoming established. Plants were watered on a regular basis to ensure plants stayed in a healthy growing condition.

Six population sizes were used for releases and consisted of either 2, 4, 8, 16, 32, and 64 unmated adults released onto patches. These population size treatments were assigned randomly to the 30 sites, resulting in five replicates for each of the six population sizes. Releases were made between 16 and 29 November 2017, and populations were left in the field through mid-April 2018.

Visits to sites depended on weather and the watering needs of the potted plants, which ranged from once a week during hot, dry weather (November to February), to every 2nd week during cooler, rainy weather (March to April). During selected visits, each plant patch was inspected for ten minutes by carefully lifting stems and turning leaves, and the presence of adults (or signs indicating the presence of adults – fresh feeding marks, newly-laid eggs, and newly-emerged larvae) was noted.

After 10 weeks following release (mid-summer census), plants at all sites were carefully searched for pupal cases. Pupal cases with exit holes were counted, recorded, and then removed, while those without exit holes were counted and recorded, but left in the patch.

At the completion of the field trials (19 weeks following release), all plants were transferred to sealed plastic bags and brought to the laboratory, where all plants were carefully searched for all life stages of N. ogloblini and the number of each stage was recorded. Observations suggested that populations were able to produce at least one generation during this time period. To prevent double counting of pupae recorded at week 10, the number of pupal cases left in patches at that time was subtracted from the final count.

In the context of this study, population establishment was thus defined as successful development to the pupal stage of any offspring produced within the first growing season after introduction.

Dataset Headings

Population.released – Number of adults released

Larv.produced.binary – Larvae produced at this site – yes(1), no(0)

Pup.produced.binary – Pupae produced at this site – yes(1), no(0)

Number.Mid.summer.pupae – Number of pupae produced as counted during mid-summer census (10 weeks following release)

Number.Conclusion.pupae – Number of pupae produced as counted at conclusion of experiment (19 weeks following release)

No.Weeks.adults noted – Number of weeks adults were noted at sites

ln.growthrate – per capita growth rate (r) was calculated as r=ln(N1/N0), with (N1) the number of pupae produced during the season and (N0) the population size released. A small non-zero number (0.001) was added to each growth rate data point prior to calculation to enable inclusion of extinct populations (r=ln((N1/N0)+ 0.001)).


EVA4.0, No. CZ.02.1.01/0.0/0.0/16_019/0000803 financed by OP RDE

MBIE (contract C04X1501)



University of Auckland


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