Accounting for residential propagule pressure improves prediction of urban plant invasion

Abstract

Abstract. Plant invasions substantially impact the ecosystem services provided by forests in urbanizing regions. Knowing where invasion risk is greatest helps target early detection and eradication efforts, but developing an accurate predictive model of invasive species presence and spread on the basis of habitat suitability remains a challenge due to spatial variation in propagule pressure (the number of individuals released) which is likely conflated with suitability. In addition to neighborhood propagule pressure that originates with propagules dispersing from naturalized populations within invaded habitats, we expect residential propagule pressure arising from the widespread use of exotic plants in the yards of single-family residences to be an important driver of invasions, and to notably improve the predictive accuracy of species distribution models (SDMs). To this end, we collected presence/absence data for a widespread forest invader, Ligustrum sinense (Chinese privet), from 400 stratified random plots located along an urban gradient across the Charlotte, North Carolina metropolitan area. We assessed the relative contribution of residential propagule pressure and neighborhood propagule pressure to improving the predictive performance of a probit SDM for Chinese privet that only contains environmental predictors. Our results indicate that, although the environment-only model predicted the highest geographic area to be at risk of invasion by privet, it also had the highest rate of failure to accurately predict observed privet occurrences as indicated by the omission (incorrectly predicted absence) and commission (incorrectly predicted presence) error rates. Accounting for residential propagule pressure substantially improved model performance by reducing the omission error by nearly 50%, thereby improving upon the ability of the model to predict privet invasion in suboptimal habitat. Given that this increase in detection was accompanied by a decrease in the geographic area predicted at risk, we conclude that SDMs for invasive exotic shrubs and potentially for other synanthropic generalist plants may be highly inefficient when residential propagule pressure is not accounted for. Accounting for residential propagule pressure in models of invasive plants results in a more focused and accurate prediction of the area at risk, thus enabling decision makers to feasibly prioritize regional scale monitoring and control efforts.

Recreational freshwater fishing drives non‐native aquatic species richness patterns at a continental scale

“…In our analyses, the modelled pattern of freshwater fishing demand strongly predicts distribution of NAS species richness across the CONUS. The strength of this predictor is significantly greater than that of population density alone (Table ), providing further evidence that proxies of propagule pressure that more closely reflect the mechanistic relationship between human activity and NAS spread are likely to improve the accuracy of species distribution models and risk assessments (Bradie, Chivers, Leung, & Richardson, ; Davis, Singh, Thill, & Meentemeyer, ). To the best of our knowledge, this study is the first to provide empirical evidence linking recreational fishing activity with reported NAS richness patterns at the continental scale.…”

Landscape correlates of forest plant invasions: A high‐resolution analysis across the eastern United States

“…Despite the limitations of observational data, most investigations of the role of roads in invasive plant ecology have used field survey or plot data. Many of those studies have been site-specific (e.g., Barton, Brewster, Cox, & Prentiss, 2004;Parendes & Jones, 2000;Underwood, Klinger, & Moore, 2004) or species-specific (e.g., Cordero, Torchelsen, Overbeck, & Anand, 2016;Davis, Singh, Thill, & Meentemeyer, 2016;Nielsen, Hartvig, & Kollmann, 2008). Survey designs to quantify the effect of distance from a road have included transects perpendicular to a road (e.g., Flory & Clay, 2006;Honu & Gibson, 2006;Pauchard & Alaback, 2004), comparisons of "road" locations with "control" locations (e.g., Christen & Matlack, 2009;González-Moreno, Pino, Gassó, & Vilà, 2013;Hansen & Clevenger, 2005;Yates, Levia, & Williams, 2004) and comparisons of road distance to "found" locations (e.g., Vieira, Finn, & Bradley, 2014;Western & Juvik, 1983).…”

The application of selected invasion frameworks to urban ecosystems

“…Invasibility is strongly influenced by propagule pressure (Colautti et al 2006). In addition to neighbourhood propagule pressure that originates with propagules dispersing from naturalized populations within invaded habitats (spread stage) (Davis et al 2016), urban areas are exposed to large numbers of alien plant propagules through repeated local introductions and high numbers of propagules in each introduction (e.g. gardens serve as regular sources of plant propagules).…”