The risk of establishment of aquatic invasive species: joining invasibility and propagule pressure

Abstract

Invasive species are increasingly becoming a policy priority. This has spurred researchers and managers to try to estimate the risk of invasion. Conceptually, invasions are dependent both on the receiving environment (invasibility) and on the ability to reach these new areas (propagule pressure). However, analyses of risk typically examine only one or the other. Here, we develop and apply a joint model of invasion risk that simultaneously incorporates invasibility and propagule pressure. We present arguments that the behaviour of these two elements of risk differs substantially-propagule pressure is a function of time, whereas invasibility is not-and therefore have different management implications. Further, we use the well-studied zebra mussel (Dreissena polymorpha) to contrast predictions made using the joint model to those made by separate invasibility and propagule pressure models. We show that predictions of invasion progress as well as of the long-term invasion pattern are strongly affected by using a joint model.

Reproductive seasonality of the invasive ascidian Didemnum vexillum in New Zealand and implications for shellfish aquaculture

“…Considerably lower recruitment at NN is consistent with the fact that source population biomass at that location was considerably less than at RK, and was spread over a wider geographic area. Such findings are in line with expectations regarding the role of propagule pressure in invasion success (Leung & Mandrak 2007, Lockwood et al 2009, with sites containing source populations of a greater biomass likely to have proportionately greater recruitment success. Additionally, the NN site is in a predominantly estuarine environment with localised salinity variations potentially influencing recruitment success at this site.…”

How propagule size and environmental suitability jointly determine establishment success: a test using dung beetle introductions

“…Second, at a given location environmental conditions, and thus p, can vary through time, such that populations could fail to establish at otherwise suitable locations due to unfavourable conditions at the time of introduction. Spatial and temporal variation in environmental conditions thought to affect establishment probability can be included in equation 1 by modelling p as a function of environmental covariates (Leung and Mandrak 2007;Leung et al 2012). While modelling spatial variation in environmental suitability is often straightforward, modelling temporal variation is harder because we often lack data on how the environment has varied over time at a given location, and thus the conditions that an introduced population encountered at the time of introduction (but see Norris et al 2002).…”

“…Importantly, it is the interaction between these two factors that is central to understanding how and why introduced species establish (D'Antonio et al 2001;Rouget and Richardson 2003;Leung and Mandrak 2007;Miller et al 2014). This is because the relationship between founding population size and establishment probability can vary as a function of environmental suitability: at locations where suitability is high few founding individuals may be required for a population to establish, while more individuals are required for success at sites of low suitability.…”

“…This will cause the shape of the relationship between establishment success and founding population size to vary as a function of environmental conditions, and it is the resulting interaction between these factors that determines the probability of population establishment (D'Antonio et al 2001). Although this interaction has been identified and modelled using species occurrence data (Rouget and Richardson 2003;Leung and Mandrak 2007;Eschtruth and Battles 2011) no studies have clearly demonstrated its importance for population establishment in the field. Studies of plant populations have shown that the form of the relationship between the number of seeds added to plots (initial population size) and the number of seedlings that recruit varies depending on environmental conditions (Thomsen et al 2006;Miller et al 2014) but these studies have not assessed population establishment.…”

Localized invasion of the North American Harris mud crab, Rhithropanopeus harrisii, in the Panama Canal: implications for eradication and spread

“…Given the previous and current connection between these lagoons and the Canal proper, it is puzzling that R. harrisii only occurs at these sites and no where else in the Canal. It is possible that the combination of sufficient propagule pressure and suitable habitat (Leung and Mandrak 2007) may have allowed nascent foci to form in the Miraflores Third Lock Lagoons, whereas other isolated and low density introductions may have failed elsewhere in the Canal, perhaps even repeatedly. For instance, R. harrisii was first reported in the Pedro Miguel Locks in 1969 (Abele and Kim 1989) but subsequent surveys suggest that it did not establish (Cohen 2006; this study).…”