Plant competition as a mechanism of invasion on islands: Revisiting the conclusions of Kuebbing and Nuñez (2016)

Abstract

Identifying the mechanisms underlying invasive plant establishment and native plant decline remains a central goal in ecology, particularly for biodiversity hotspots such as islands. We re-analyzed a previously published meta-dataset to test the prediction that neighbor effects are stronger on islands vs. continents because island plants are weaker competitors. Although we detected marginally stronger neighbor effects on islands than continents, this was due, at least in part, to stronger competition among native species. An absence of studies testing neighbor effects between native vs.invasive plants on islands prevents a rigorous test for competition effects on islands, highlighting an important knowledge gap. K E Y W O R D Sisland rules, meta-analysis, neighbor effects, plant invasions

Nutrient‐use strategy and not competition determines native and invasive species response to changes in soil nutrient availability

“…Mean of Slopes (SD) number of studies that directly tested competition between native and invasive plants on islands (Barton & Wong 2019). The competition index (Rii) results of this study do not support our hypothesis that lowering soil nutrient availability provides native species with a direct competitive advantage over invasive species.…”

“…Understanding how competition and varying soil nutrient availability, individually and collectively, affect species growth, photosynthesis, and resource use strategies could be beneficial in informing restoration strategies. This is one of only a limited number of studies that directly tested competition between native and invasive plants on islands (Barton & Wong 2019). The competition index ( Rii ) results of this study do not support our hypothesis that lowering soil nutrient availability provides native species with a direct competitive advantage over invasive species.…”

Island plant functional syndromes and competition with invasive species

“…Multiple approaches can be used to test the competition abilities of native and invasive island plants, ideally via demographic assessments quantifying neighbour effects on focal plant performance (survival, growth, reproduction), using experimental tests (removal/addition at the individual or community scale), and, if limited by time and resources, via functional trait comparative analyses (Figure 2a). Nuñez, 2016), few of these experiments have tested island species (Barton & Wong, 2019;D'Antonio et al, 2017;Radford et al, 2009).…”

“…Whether invasion-driven losses in island biodiversity are directly related to island plant syndromes is widely assumed (Cronk, 1997;Simberloff, 1995), but surprisingly lacking in robust confirmatory evidence. For example, recent syntheses have found island plants to have similar levels of anti-herbivore defences as continental species (Meredith et al, 2019;Moreira et al, 2021), while direct tests of competitive ability for island versus continental plants are few (Barton & Wong, 2019). Furthermore, islands are highly variable with considerable environmental heterogeneity, sometimes comparable to continents, thereby challenging the prediction that island plant syndromes have evolved convergently.…”

Influence of multiple global change drivers on plant invasion: Additive effects are uncommon

“…But the current comprehensive studies ( Jia et al., 2016 ; Liu et al., 2017 ; Stephens et al., 2019 ) mainly focus on the performance of plants growing individually (and not under competitive conditions). A focus on competition is important because a stronger competitiveness may help invasive plants occupy niches originally occupied by local indigenous communities ( Barton and Wong, 2019 ). Competitive ability against native plants may be a key factor that determines whether invasive plants can successfully invade ( Gioria and Osborne, 2014 ; Zhang and van Kleunen, 2019 ).…”