Are exotic plants more abundant in the introduced versus native range?

Abstract

1. Many invasion hypotheses postulate that introducing species to novel environments allows some organisms to escape population controls within the native range to attain higher abundance in the introduced range. However, introductions may also allow inherently successful species access to new regions where they may flourish without increasing in abundance.2. To examine these hypotheses, we randomly surveyed semi-arid grasslands in the native and two introduced ranges (12,000-21,000 km 2 per range) to quantify local abundance (mean cover per occupied plot) and occurrence (percentage of 1-m 2 plots occupied) for 20 plant introductions that included pest and non-pest species.For each of these metrics, we evaluated relationships between abundance in the introduced vs. native range (1) across all species and (2) according to designated pest status in the introduced range. We predicted that if escape from population controls primarily explained invader success, then these species would be more abundant in the introduced range; while if invader success was driven primarily by intrinsic species attributes, then their abundance would be correlated between ranges.3. Across all 20 invaders, we found that neither cover nor occurrence metrics were correlated between ranges. While cover was significantly higher in the introduced range, this result was driven by pest species. When the four pest species were excluded, cover but not occurrence was correlated between ranges. Interestingly, whereas cover of pest and non-pest species was comparably low in the native range, pest species cover increased sevenfold in the introduced range. Synthesis.Our results confirm previous findings that local abundance in the native range predicts local abundance in the introduced range for many introduced plants, suggesting that intrinsic species' attributes may determine most invasion outcomes.However, we also found that some species increased in local abundance in the 728 |

The Neolithic Plant Invasion Hypothesis: the role of preadaptation and disturbance in grassland invasion

“…Other studies have observed outcomes that do conform to the NPIH prediction. A more recent study confirmed the findings of Firn et al ., that plant species local abundance at native sites measured both as cover and occurrence can predict plant species abundance at introduced sites, and attributed these results to intrinsic species attributes (Pearson et al ., ), but with the caveat that the four species considered to be invasive were more abundant at introduced sites. Beckmann et al .…”

Plant Community Assembly in Invaded Recipient Californian Grasslands and Putative Donor Grasslands in Spain

“…As a result, many exotic species co-occur in habitats outside their native regions [5,6]. However, to date only a few studies have assessed whether exotic species are equally abundant, and if pools of exotic species assemble similarly, in their recipient communities as in putative donor communities of their native range (see [7,8]). Because patterns may arise from local differences in species richness and diversity, these comparisons need to consider the entire plant community, not just one focal species [9].…”

“…Biogeographical comparisons of exotic plant species in their native and recipient communities are important and gaining interest [8][9][10][11]. A general assumption is that exotic species are more abundant 2 of 13 in the introduced region than in the native range [9,12].…”

Enemy release from the effects of generalist granivores can facilitate Bromus tectorum invasion in the Great Basin Desert

“…Interestingly, our main finding corresponded with a region‐specific foraging pattern: rodents selected against cheatgrass seeds relative to seeds from native competitors in the Great Basin but not in western Asia (with the exception of one species in Iran; Figure ). Our results suggest that enemy release from the effects of rodent foraging—possibly due to region‐specific seed preferences—might help explain why cheatgrass is much more abundant in North America than in western Asia (Pearson et al, ).…”

“…Since then, cheatgrass has expanded to dominate at least 650,000 km 2 of perennial grassland and shrubland in the central Great Basin (Balch, Bradley, D'Antonio, & Gomez‐Dans, ). Importantly, cheatgrass is much more abundant in North America than in Eurasia (Pearson et al, ). This biogeographic difference in abundance might be at least partially due to enemy release from generalists.…”