Extended leaf phenology may drive plant invasion through direct and apparent competition

Abstract

Invasive plants can inflict great harm, yet drivers of successful invasion remain unclear. Many invaders of North American deciduous forests exhibit extended leaf phenology (ELP), or longer growing season relative to natives. ELP may grant invaders competitive advantages, but we argue that ELP more potently drives invasion in the presence of herbivores. ELP invaders can support herbivores by lessening starvation during winter; consequently, native plants may suffer when attacked later through apparent competition. As modeled here, even short ELP can promote competitive success of invaders, and apparent competition sharply enhances ELP invader dominance. In 'partial enemy escape' scenarios, a less palatable ELP invader nearly excludes a preferred native where an invader without ELP could not. Together, ELP and apparent competition enhance invasion even when biotic resistance should suppress it, i.e. when the invader competes weakly or provides preferred forage. Thus, ELP-apparent competition interactions grant invaders considerable success while challenging core tenets of invasion ecology.

Geographic variation in apparent competition between native and invasive Phragmites australis

“…In deciduous forests, invasive plant species often have extended leaf phenologies that may confer an advantage to them over neighboring native plant species (Fridley 2012, Smith 2013. Using a mathematical model, Smith and Hall (2016) showed that the combined effect of greater preference by herbivores for native taxa and extended phenology of invasive taxa could significantly increase the performance of the invader and potentially result in the exclusion of the native apparent competitor. Using a mathematical model, Smith and Hall (2016) showed that the combined effect of greater preference by herbivores for native taxa and extended phenology of invasive taxa could significantly increase the performance of the invader and potentially result in the exclusion of the native apparent competitor.…”

“…In a common garden study (see Bhattarai et al 2016), plant genotypes from the invasive lineage sprouted earlier than genotypes of the native lineage (Bhattarai et al unpublished data; see also Park and Blossey 2008), which may result in larger populations of herbivores in early spring that are likely to spillover to plants of the more preferred native lineage. Using a mathematical model, Smith and Hall (2016) showed that the combined effect of greater preference by herbivores for native taxa and extended phenology of invasive taxa could significantly increase the performance of the invader and potentially result in the exclusion of the native apparent competitor.…”

“…Refuge-mediated apparent competition has recently been proposed as one of the mechanisms for plant invasions (Orrock et al 2010, Enge et al 2013. Finally, extended leaf phenology of invasive plants can lessen winter starvation of herbivores and has been proposed as a mechanism that could elevate herbivory on sympatric native plants (Smith and Hall 2016). Reduced fitness of native plants can, in turn, facilitate the invasion success of the invasive plants.…”

“…Reduced fitness of native plants can, in turn, facilitate the invasion success of the invasive plants. Finally, extended leaf phenology of invasive plants can lessen winter starvation of herbivores and has been proposed as a mechanism that could elevate herbivory on sympatric native plants (Smith and Hall 2016).…”

Warming delays the phenological sequences of an autumn‐flowering invader

“…The success of invasive plants can be ascribed to a suite of contributors. Mounting evidence suggests that plant phenology may play a pivotal role in driving plant invasions (Fridley, ; Godoy, Castro‐Diez, Valladares, & Costa‐Tenorio, ; Novy, Flory, & Hartman, ; Rejmánek, ; Smith & Hall, ; Smith & Reynolds, ; Wolkovich & Cleland, ). Harrington, Brown, and Reich () pioneered work in this aspect, and their research has brought renewed interest in the study of plant phenology (Cleland, Chuine, Menzel, Mooney, & Schwartz, ).…”