A seasonal, density‐dependent model for the management of an invasive weed

Abstract

Abstract. The population effects of harvest depend on complex interactions between density dependence, seasonality, stage structure, and management timing. Here we present a periodic nonlinear matrix population model that incorporates seasonal density dependence with stage-selective and seasonally selective harvest. To this model, we apply newly developed perturbation analyses to determine how population densities respond to changes in harvest and demographic parameters. We use the model to examine the effects of popular control strategies and demographic perturbations on the invasive weed garlic mustard (Alliaria petiolata). We find that seasonality is a major factor in harvest outcomes, because population dynamics may depend significantly on both the season of management and the season of observation. Strategies that reduce densities in one season can drive increases in another, with strategies giving positive sensitivities of density in the target seasons leading to compensatory effects that invasive species managers should avoid. Conversely, demographic parameters to which density is very elastic (e.g., seeding survival, second-year rosette spring survival, and the flowering to fruiting adult transition for maximum summer densities) may indicate promising management targets.

Positive frequency dependence undermines the success of restoration using historical disturbance regimes

“…2b-k). One way to maximise fitness differences between exotic and native species is to target exotic species during a sensitive life stage (Rees & Paynter 1997;Shea & Kelly 1998;McEvoy & Coombs 1999;Shyu et al 2013). For instance, prescribed fires have been successfully used to control the exotic Centaurea solstitialis when fires occur during its reproductive period, but after seed dispersal and senescence of native species (DiTomaso et al 2014).…”

Climate and rapid local adaptation as drivers of germination and seed bank dynamics of Alliaria petiolata (garlic mustard) in North America

“…; Shyu et al . ). Major differences in germination occurred in early years and our climate modelling revealed that populations could be placed into four groups with distinct germination patterns but they did not align along latitudinal clines (Colautti & Barrett ; Wilczek et al .…”

Native insect herbivory overwhelms context dependence to limit complex invasion dynamics of exotic weeds

“…; Shyu et al . ). The prediction of unbounded growth suggests that negative density‐dependence in population growth is weak at many sites.…”

“…We estimate that, in the absence of native insect herbivores, the majority of sites in our study region would be prone to aperiodic fluctuations or unbounded growth in C. vulgare density. The fluctuations are likely the result of high low-density growth rates combined with strong negative density-dependence, a combination known to give rise to complex dynamics (Costantino et al 1997), including in invasive plants (Buckley et al 2001;Pardini et al 2011;Shyu et al 2013). The prediction of unbounded growth suggests that negative densitydependence in population growth is weak at many sites.…”