Assessing the Potential Distribution of Asian Gypsy Moth in Canada: A Comparison of Two Methodological Approaches

Abstract

Gypsy moth (Lymantria dispar L.) is one of the world's worst hardwood defoliating invasive alien species. It is currently spreading across North America, damaging forest ecosystems and posing a significant economic threat. Two subspecies L. d. asiatica and L. d. japonica, collectively referred to as Asian gypsy moth (AGM) are of special concern as they have traits that make them better invaders than their European counterpart (e.g. flight capability of females). We assessed the potential distribution of AGM in Canada using two presence-only species distribution models, Maximum Entropy (MaxEnt) and Genetic Algorithm for Rule-set Prediction (GARP). In addition, we mapped AGM potential future distribution under two climate change scenarios (A1B and A2) while implementing dispersal constraints using the cellular automation model MigClim. MaxEnt had higher AUC, pAUC and sensitivity scores (0.82/1.40/1.00) when compared to GARP (0.70/1.26/0.9), indicating better discrimination of suitable versus unsuitable areas for AGM. The models indicated that suitable conditions for AGM were present in the provinces of British Columbia, Ontario, Quebec, Nova Scotia and New Brunswick. The human influence index was the variable found to contribute the most in predicting the distribution of AGM. These model results can be used to identify areas at risk for this pest, to inform strategic and tactical pest management decisions.

Figure 1

Predicted potential distribution of AGM in Asia and Canada, using GARP and MaxEnt. For Asia, higher probability (red colors) represent areas suitable for AGM. Zero probability or lower probability (dark green) indicates areas less suitable. Whereas, for Canada the continuous suitability values (0–1) from GARP and MaxEnt outputs were classified as: very low (0–0.25), low (0.25–0.50), medium (0.50–0.75) and high (0.75–1.00) for easy interpretation and comparison purposes.

Figure 2

Potential distribution (enlarged view) of AGM using GARP and MaxEnt in Canada at 20 km² spatial resolution.

Figure 3

Relationships between environmental predictors and the probability of the presence of AGM: Red curves show the mean response and blue bands around them are ±1 standard deviation calculated using 10 independent data subsets.

Figure 4

Jackknife test for AUC of environmental variable importance for the MaxEnt model.

Figure 5

Dispersal restricted future distribution of AGM under A1B and A2 climate change scenarios. Color gradient from rose to dark red represents first 10 years of the simulation timeframe when colonization first occurred, the light sand to cherry red color gradient represents the next 10 years followed by green and sky blue color gradients (years 2031–2050). Red pixel indicates the hypothesized point of AGM introduction while the dark grey pixels represent suitable areas that were not colonized due to dispersal limitations.

Figure 6

Flowchart representing the modelling flow used to model Asian gypsy moth distribution in this study.

Figure 7

Occurrences of Asian gypsy moth. The shaded region represents the background used for creating the SDM based on a buffered minimum convex polygon. The Köppen-Geiger climate classification (vegetation-based) system was used as a background. This is done to allow assessing risk based preliminary on whether a species is found in the same climate zone as the pest risk assessment area.