Canadian Forest Service Publications

Unwanted spatial bias in predicting establishment of an invasive insect based on simulated demographics. 2014. Gray, D.R. International Journal of Biometeorology 58: 949–961. doi: 10.1007/s00484-013-0678-3

Year: 2014

Issued by: Atlantic Forestry Centre

Catalog ID: 35602

Language: English

Availability: Order paper copy (free)

Available from the Journal's Web site.
DOI: 10.1007/s00484-013-0678-3

† This site may require a fee

Mark record


A strategy to estimate the probability of successful establishment of the invasive gypsy moth (given an introduction) is growing in popularity. The strategy calls for an examination of the demographic output of a phenology model of the complete life-cycle to estimate the generational success under the climate of the location under consideration. The probability is maximal where the climate satisfies the life-cycle requirements of all life-stages of 100% of the population every year. The probability decreases where a smaller proportion of the population has its requirements satisfied every year, or where the frequency of unsatisfactory years increases. The strategy can give an unbiased and objective estimate of the probability. However, implementation of the strategy has most often forced unnatural and overly simplistic modifications onto the demographic structure that is simulated by the phenology model, and used an inappropriate and arbitrary calendar date to estimate demographic changes from winter mortality. This produces pronounced spatial bias in the estimates of generational success, and therefore in the estimates of climate-mediated establishment probability. In an examination of the strategy, as implemented in New Zealand, one demographic simplification caused an overestimation of 21% in a southern location; a second simplification caused an overestimate of 17% in a northern location. One hundred percent of the generations were incorrectly considered to have failed in a northern location because of the arbitrary calendar date that was used; and 78% of the generations were incorrectly considered successful in a southern location because of the arbitrary date.

Plain Language Summary

A phenology model predicts the timing of life-cycle events based on the daily fluctuations of temperature. A phenology model can, therefore, estimate the probability that an invasive insect can become established in a given location by simulating how the temperature regime of the location influences the timing of life-cycle events. A widely accepted phenology model has been used for this purpose (estimation of the probability of establishment of an invasive insect). But the author shows how bias has been included in the estimations because the model has been used with arbitrary, and biologically unwarranted requirements that certain life-cycle events occur by a calendar deadline. The author provides a solution without bias.