Spatial patterns of discovery points and invasion hotspots of non‐native forest pests

Abstract

Aim Establishments of non‐native forest pests (insects and pathogens) continue to increase worldwide with growing numbers of introductions and changes in invasion pathways. Quantifying spatio‐temporal patterns in establishment locations and subsequent invasion dynamics can provide insight into the underlying mechanisms driving invasions and assist biosecurity agencies with prioritizing areas for proactive surveillance and management. Location United States of America. Time period 1794–2018. Major taxa studied Insecta, plant pathogens. Methods Using locations of first discovery and county‐level occurrence data for 101 non‐native pests across the contiguous USA, we (a) quantified spatial patterns in discovery points and county‐level species richness with spatial point process models and spatial hotspot analyses, respectively, and (b) identified potential proxies for propagule pressure (e.g., human population density) associated with these observed patterns. Results Discovery points were highly aggregated in space and located in areas with high densities of ports and roads. Although concentrated in the north‐eastern USA, discovery points also occurred farther west and became less aggregated as time progressed. Invasion hotspots were more common in the north‐east. Geographic patterns of discovery points and hotspots varied substantially among pest origins (i.e., global region of pests’ native ranges) and pest feeding guilds. Significant variation in invasion richness was attributed to the patterns of first discovery locations. Data and shapefiles comprising analyses are provided. Main conclusions Use of spatial point pattern analyses provided a quantitative characterization of the central role of human activities in establishment of non‐native pests. Moreover, the decreased aggregation of discovery points through time suggests that invasion pathways to certain areas in the USA have either been created or intensified by human activities. Overall, our results suggest that spatio‐temporal variability in the intensity of invasion pathways has resulted in marked geographic patterns of establishment and contributed to current macroscale patterns of pest invasion in the USA.

Impact of introduction pathways on the spread and geographical distribution of alien species: Implications for preventive management in mediterranean ecosystems

“…Following Ward et al. (2019), we performed a Bonferroni correction, due to the calculation of a large number of Z‐scores (one for each of the 327 10‐km UTM cells). Thus, we identified hotspots as those 10‐km UTM cells with Z‐score ≥ 3.610 ( p <.05/327 = p < .0001).…”

“…The G i * statistic can be standardized to produce a Z-score, that can be compared to a standard normal distribution to check for significance (Ord & Getis, 1995). Following Ward et al (2019), we performed a Bonferroni correction, due to the calculation of a large number of Z-scores (one for each of the 327 10-km UTM cells). Thus, we identified hotspots as those 10-km UTM cells with Z-score ≥ 3.610 (p <.05/327 = p < .0001).…”

Global drivers of historical true fruit fly (Diptera: Tephritidae) invasions

“…However, all of these variables were positively associated with invasion incidence when fit individually (Figure S5.2B). Invasions of many types of organisms are often related to human population size (Cadotte et al 2017;Ward et al 2019). Urbanization may be closely related to propagule pressure associated with general movement of humans and their goods but also with invasibility related to disturbance and habitat modification.…”

Comparing generalized and customized spread models for nonnative forest pests

“…Second, we simulated the best‐known starting location of each pest species (Ward et al. ) and the host centroid as a starting point for each pest's dispersal. While the use of best‐known starting points did not improve the overall fit of the GDK (Hudgins et al.…”