Managing propagule pressure to prevent invasive species establishments: propagule size, number, and risk–release curve

Abstract

There is considerable evidence that keeping propagule pressure low can drastically reduce establishment probability of potential invasive species. Yet, most management plans and research efforts fail to explicitly acknowledge all three of the components of propagule pressure: size, number, and the risk-release relationship. It is unclear how failing to specify one or more of these components can influence the efficacy of management plans in preventing invasive species establishment. Furthermore, even if all components are acknowledged and quantified, there currently is no mathematical tool available to calculate the levels of propagule pressure that ensure attainment of a predetermined, and system-specific, target establishment probability. Here, we quantify the resulting uncertainty in establishment probability when one or more components of propagule pressure is unknown by using parameter uncertainty analysis on realistic values of propagule pressure. In addition, to aid in the development of management plans that explicitly set propagule pressure limits, we develop a propagule-pressure sensitivity analysis that we use to determine the required reduction in levels for propagule size and number (representative of management actions) to maintain a target establishment probability. We show that the precision of establishment estimates is highly dependent on knowledge of all three propagule pressure components, where the possible range of values for establishment probability can vary by over 50% without full specification. In addition, our sensitivity analysis showed that propagule size and number can be altered independently or in conjunction to lower establishment probability below a target level. Importantly, our sensitivity analysis was able to specifically quantify how much reduction in a propagule pressure component(s) is needed to reach a given target establishment probability. Our findings suggest that quantifying the three components of propagule pressure should be a priority for invasive species prevention moving forward. Furthermore, our sensitivity analysis tool can serve to guide the development of new invasive species management plans in a transparent and quantitative manner. Together with information on the costs associated with approaches to reducing propagule pressure, our tool can be used to identify the most cost-effective approach to prevent invasive species establishments.

Tipping the balance: The role of seed density, abiotic filters, and priority effects in seed‐based wetland restoration

“…This variation does not always correlate to standing P. australis vegetation (Wilson et al, 1993), but can be partially attributed to propagule movement across the landscape (e.g., via tidal action or wind; Baldwin et al, 2010; Galatowitsch & Biederman, 1998). Given the importance of propagule pressure in driving community assembly, propagule pressure mitigation techniques and strategies need to be widely adopted in management and restoration plans (Stringham & Lockwood, 2021). More research is warranted to identify factors that predict P. australis seed bank abundance and on functional traits that shed light on P. australis seed behavior in the seed bank (e.g., longevity/persistence traits; Larson & Funk, 2016).…”

Synergies between Heat Disturbance and Inoculum Size Promote the Invasion Potential of a Bacterial Pathogen in Soil

“…Inoculum size thus interacts with other factors, such as the amount of available resources and the community composition of the invaded habitat [ 34 ]. Reducing the inoculum size is thus an effective approach to lowering the invasiveness of alien species [ 4 ], yet the development of effective management to stop new invasions by R. solanacearum seldom considers inoculum size [ 9 ]. Hence, our study provides a unique dataset that is both essential and practical.…”

“…However, the role of heat wave-induced disturbance in the invasiveness of soil-borne pathogens to healthy soils remains poorly understood. In addition, increasing empirical evidence has suggested that the size of the introduced inocula is vital in determining the invasion success of alien species [ 3 , 4 ]. Alien pathogens with larger inoculum sizes are more likely to invade successfully than species with smaller inoculum sizes, as the population growth of many introduced species with small inoculum sizes tends to be negative, making these species vulnerable to extirpation; this is summarized by the Allee effect [ 5 ].…”

Retention of viability by fragmented invasive Crassula helmsii, Elodea canadensis and Lagarosiphon major

“…Successful dispersal and establishment of invasive macrophytes are largely dependent on fragmentary propagule survival and viability in relation to root and shoot production (Coughlan, Cuthbert, Kelly, & Jansen, 2018; Heidbüchel, Sachs, Hamzehian, & Hussner, 2020). Generally, the abundance and reproductive quality of propagules that are introduced increase the likelihood of viable propagules colonising suitable environments (see Stringham & Lockwood, 2021 for discussion). While zoochorous and anthropogenic vectors can facilitate overland transport between habitats (Coughlan et al, 2018; Rothlisberger, Chadderton, McNulty, & Lodge, 2010), fragmentary propagules can also be spread through directional water currents within river systems, that is, hydrochory (Sarneel, 2013).…”