The relationship between invader abundance and impact

Abstract

The impacts of invasive species generally increase with their abundance, but the form of invader abundance–impact relationships remain poorly described. We highlight the utility of abundance–impact curves for three questions. First, abundance–impact relationships can clarify whether prevention and management should focus on the species likely to become abundant or those likely to cause large impacts per individual. Second, comparing abundance–impact relationships between native and exotic species can reveal any systematic differences in their effects on ecological systems. Third, identifying any thresholds in the relationship between invader impact and abundance can be used to select management targets and design invasive species control strategies. With increasing extent and resolution of datasets of invasive organisms worldwide, we now have the opportunity to explore in detail the form and context dependence of the abundance–impact relationship. Doing so provides opportunities to improve the prediction of invader impact, to better understand the differences between exotic and resident organisms, and to scale the impacts of invasive species from localities to ranges.

To list or not to list: using time since invasion to refine impact assessment for an exotic plant proposed as noxious

“…Moreover, we found that native overstory cover varied negatively with time since invasion, consistent with an impact scenario wherein local-scale decrements in native abundance build over time as a function of invader abundance (Dost al et al 2013, Sofaer et al 2018. First, we minimized background variation in conditions by sampling plant abundance in uninvaded plots located proximal to invaded plots at each study site.…”

“…Populations of potent invaders are generally assumed to increase over time ), but population growth may eventually attenuate due to many factors (Ricciardi et al 2013, Yelenik and D'Antonio 2013. This pattern is in line with theory linking local-scale competitive effects to biomass (Parker et al 1999, Pearson et al 2016, Sofaer et al 2018. 2), with some weak evidence for an eventual slowing of population growth (Appendix S2: Table S3).…”

“…In fact, >40% of all species classified as invasive globally fall in this group (Hulme et al 2013), yet their ecological impacts are understudied relative to other lifeforms, in part due to methodological challenges (Stricker et al 2015, Mueller et al 2018. While invasion ecology is increasingly recognizing the need to consider time since invasion in studies of invader impact, research examining local-scale patterns, including linkages to invader abundance over time, will be particularly informative (Mitchell et al 2011, Sofaer et al 2018. Importantly, regardless of how these data are derived, the spatial resolution must be sufficient to allow evaluation of local-scale patterns given that invader impacts typically accrue at this scale.…”

“…The magnitude of invader impacts should generally change over time as a function of invader abundance (Dost al et al 2013, Sofaer et al 2018; but see D'Antonio and Flory 2017). The magnitude of invader impacts should generally change over time as a function of invader abundance (Dost al et al 2013, Sofaer et al 2018; but see D'Antonio and Flory 2017).…”

Impacts of dominant plant species on trait composition of communities: comparison between the native and invaded ranges

“…It is apparent that neither species richness nor traits such as height, clonality, or perennial life form show any suppression or exhibit even a positive relation to the dominants’ cover, until some threshold value of its dominance is reached, and then the relationships change to negative (see also Sofaer et al. ).…”