Performance of the herb Verbascum thapsus along environmental gradients in its native and non‐native ranges

Abstract

Aim We evaluated whether the performance of individuals and populations of the invasive plant Verbascum thapsus differs between its native and non-native ranges, across climate gradients, and in response to its position in a globalscaled niche model.Location India (Kashmir) and Switzerland (native range) and Australia and USA (Hawaii, Montana and Oregon) (non-native range). MethodsWe measured population characteristics (density of flowering individuals, population size), plant traits (plant height, number of flowering branches) and seed germination for 50 populations of V. thapsus growing along elevational gradients in six mountain regions around the world (two in the native range, and four in the non-native range). We fitted linear regression models to determine the relationship of plant and population level performance variables to range, region, climate and probability of occurrence from a global niche model. ResultsPlant height, number of flowering branches and population density of V. thapsus did not differ consistently between the native and non-native ranges, but the area covered by populations in the non-native range was on average two orders of magnitude larger than the area of native populations. Within and among regions, individual plant performance traits responded variably to precipitation and mean annual temperature, depending on the climatic range of the observed populations; however, performance was greater for populations that had a greater modelled probability of occurrence. Seed germination under controlled conditions was highest between 20 and 35°C and consistent across populations, although germination at low temperatures was substantially higher for native populations from Kashmir. Main conclusionsThe introduction of V. thapsus to its non-native range is not associated with consistent increases in plant performance. Instead, plant performance is more strongly influenced by position within the climate niche of the species, position along environmental gradients, and climatic or other differences among regions. We demonstrate that individual-level and population-level performance traits can yield different predictors of plant performance. Therefore, future studies comparing plant performance in native and non-native ranges should include both plant and population characteristics and should also sample the target species from multiple regions in both ranges and along environmental gradients that comprehensively represent the niche of the species. 132

Will climate change increase the risk of plant invasions into mountains?

“…Furthermore, non-native richness patterns might be shaped by the same abiotic factors (i.e., area, climate, productivity, and water availability) that explain a decline of native species richness with elevation (Rahbek 1995, McCain 2007, Romdal and Grytnes 2007, Jakobs et al 2010, Alexander et al 2011. Although many factors may affect the spread of non-native species from lowlands to high elevations in mountains, climate is clearly important (Marini et al 2009, Jakobs et al 2010, Trtikova et al 2010, Kueffer et al 2013, Seipel et al 2015.…”

Natives and non‐natives plants show different responses to elevation and disturbance on the tropical high Andes of Ecuador

“…In tropical mountains, the establishment of non‐native species along an elevational gradient depends on the degree of preadaptation and plasticity inherent in species for the abiotic conditions at a given site (Alexander et al., ; Haider et al., ; Seipel et al., , ). A match between the overall climatic conditions on the native range and the elevational location on the introduced range can be expected.…”

Mountain roads shift native and non‐native plant species' ranges

“…The function of roads as corridors for non‐native species has also been reported several times in other ecosystems (Gelbard and Belnap , Pauchard et al , Pollnac et al ). Invasion away from roadsides into the adjacent mountain vegetation has until now been limited (Leung et al , Alexander et al , Lembrechts et al , Pollnac and Rew , Seipel et al ), which suggests that disturbance might at this time be a more important explanatory variable than climate to explain the observed patterns of non‐native species distributions in mountains (Marini et al ).…”