Finding optimal control strategies for invasive species: a density‐structured model forSpartina alterniflora

Abstract

Summary 1.There are very few general guidelines available to improve the process of eradicating invasive species. We addressed the basic question of whether it is more efficient to prioritize the removal of outliers or core populations of an invasive grass, Spartina alterniflora . 2. We used a structured model in which the population of the invasive species is partitioned into different classes based on local conspecific density in order to investigate density-based eradication strategies. 3. The Spartina population at a Pacific coast estuary in Washington state, USA, is subject to an Allee effect: at low density plants produce fewer propagules than in high-density coalesced meadows. Plants at low density, however, are able to spread faster vegetatively. We used a genetic algorithm to find the optimal division of resources between removal of high-density and low-density plants. We explored the consequences of the Allee effect, contrasting financial budgets available for control operations and the inclusion of seedling control in addition to the control of mature plants. 4. We found that the optimal strategy was dependent on the annual budget available for control. At low and medium budgets, it was necessary to remove the low-density plants first to achieve eradication, but if more money was available then the optimal strategy was to prioritize high-density areas. 5. Without an Allee effect the optimal strategy would always be to prioritize the removal of fast-growing, low-density sub-populations. Seedling control did not change the optimal strategy but did, in some cases, reduce the cost of eradication. 6. Synthesis and applications . Given the uncertainty in future budgets allocated for control of invasive Spartina , we recommend a strategy that prioritizes the removal of lowdensity subpopulations of S. alterniflora over high-density subpopulations. The Allee effect in this system is not sufficiently strong to outweigh the importance of the rapid vegetative spread of the plants at low density.

Management of invasive Phragmites australis in the Adirondacks: a cautionary tale about prospects of eradication

“…Rapidly responding to new, small populations not only increases the likelihood of eradicating P. australis, it also reduces resource requirements and potential future detrimental non-target impacts. This approach is supported by early theoretical models (Moody and Mack 1988), empirical evidence from our study, and other investigations (Taylor and Hastings 2004;Delanoy and Archibold 2007;Simberloff 2009;Buhle et al 2012).…”

Estimation of the Probability of Long-Distance Dispersal: Stratified Diffusion of <i>Spartina alterniflora</i> in the Yangtze River Estuary

“…For example, the effectiveness of control measures can be greatly increased by preventing the establishment of new foci or by eliminating new foci rather than focusing efforts on established invasion fronts [22] [23] [28] [32]. As demonstrated in this study, the establishment of new foci through long-distance dispersal is of paramount importance in the spread of S. alterniflora and control efforts should be placed on the transition zone, and focus on preventing the dispersal processes and slowing the advancing wave fronts.…”

“…Invasion of the intertidal mudflats of estuaries by S. alterniflora is a primary example of a stratified diffusion in a relatively simple habitat [22] [23]. Its long distance dispersal along a tidal elevation gradient was driven primarily by seedling recruitment [1] [24] [25].…”

Assessing the flexibility of the Analytic Hierarchy Process for prioritization of invasive plant management

“…Moreover, existing applications of decision tools in invasion management were built to address a specific stage of the invasion process. For instance, certain models focus on preventing the introduction of high impact invaders (Cunningham et al 2004) while others prioritize management areas based on detection, spread, or impacts of the invaders (Taylor and Hastings 2004, Mehta et al 2007, Cook et al 2007). Individually, these static models are not suitable to address the complex range of invasion scenarios that managers often encounter.…”