Contrasting distribution patterns of invasive and naturalized non‐native species along environmental gradients in a semi‐arid montane ecosystem

Abstract

Questions Mountain systems have high abiotic heterogeneity over local spatial scales, offering natural experiments for examining plant species invasions. We ask whether functional groupings explain non‐native species spread into native vegetation and up elevation gradients. We examine whether non‐native species distribution patterns are related to environmental variables after controlling for elevation and, thus, driven by niche processes. Location The Wallowa Mountains, northeast Oregon, USA. Methods We surveyed non‐native plant species along three mountain roads and into the native habitat matrix to assess the extent of invasion success along distance from roadside and elevation gradients. We used GLM to predict single species occurrence probabilities, LMM to examine differences in distribution patterns among functional types, and pCCA to examine multivariate responses of the non‐native community to ecological variables. Results Probability of occurrence of the eight focal invasive species was not significantly related to distance from the road, but declined with elevation. Non‐native species with annual life history strategies were more restricted to lower elevations than perennial species. Non‐native species considered invasive occurred at lower minimum elevations than naturalized species. Shifts in the species composition of the non‐native plant community were related to changes in soil and climate variables. Conclusions Our results suggest that invasive species have similar patterns of habitat associations and spread from roadsides to interior vegetation zones, whereas naturalized species partition environmental gradients in this semi‐arid montane ecosystem. Furthermore, annual and invasive species groups occupy lower elevations and perennial and naturalized species groups have invaded further up the mountain roads and into the native vegetation. Thus, functional groupings may explain contrasting distribution patterns of non‐native species and could be used to inform management strategies for non‐native species.

Alien plant species that invade high elevations are generalists: support for the directional ecological filtering hypothesis

“…There is growing evidence in favour of the DEFH, but no study has yet concurrently explicitly tested both the DEFH and the ALH, nor have analyses of functional traits been used to complement nestedness analyses when assessing these hypotheses (but see Andersen et al. ). Therefore, the aim of this study was to investigate support for the DEFH and for the ALH along an elevational gradient using two complementary approaches.…”

“…As a result, high-elevation sites with low species richness would comprise only widespread species, while lowland sites with high species richness would contain more range-restricted species (Wright & Reeves 1992). Several studies that looked at species richness and community structure of alien species along elevation gradients have, without implicitly testing for it, found that the DEFH plays a role in their studies (Py sek et al 2011;Pollnac et al 2012;Seipel et al 2012;Andersen et al 2015;Zhang et al 2015). The DEFH has also been identified as relevant at both small and large spatial scales (Seipel 2011;Dainese et al 2014;Pollnac & Rew 2014).…”

“…Due to low elevations generally being more heavily invaded than higher elevations (Kueffer et al 2014), there are comparatively few studies of invasions in mountainous regions (although see Dietz et al 2006;Kueffer et al 2008Kueffer et al , 2014, potentially limiting our understanding of how biological invasions function across the full range of elevations (MacDougall et al 2006;Van Kleunen & Johnson 2007). There is growing evidence in favour of the DEFH, but no study has yet concurrently explicitly tested both the DEFH and the ALH, nor have analyses of functional traits been used to complement nestedness analyses when assessing these hypotheses (but see Andersen et al 2015). Therefore, the aim of this study was to investigate support for the DEFH and for the ALH along an elevational gradient using two complementary approaches.…”

Phytochemical screening, GC-MS profiling of invasive cocklebur (Xanthium strumarium)-insect-pathogen interaction and simulated volatile chemical signaling at Northeast China

“…X. strumarium was attacked naturally by Rust ( P. xanthii ) and E. struneuna infestations were identified from the leaves. The transect line was sixty meters long parallel to the road or riverside, this line was divided into three similar portions each of twenty meter long collected randomly and data were recorded using quadratic ring [96-98] ring (100×100 cm) according to standardized protocol [99]. Three whole cocklebur plants in each quadratic ring were selected randomly for measuring their growth parameters and other characteristics.…”

“…The accuracy of natural enemy pressure was estimated with latitude. One-way analysis of variance conducted to test the effect of latitude on different growth parameters, natural enemy’s abundance and phyto-chemical yield extractions [99]. Principal component and redundant analysis were conducted to explore the multivariate relationship between natural enemy’s abundance and different abiotic trends.…”