It is frequently thought that global environmental changes, and especially the concomitant changes in environmental variability, could further increase the success of invasive species in native ...resident communities. However, very few studies explicitly tested this, and it remains unknown whether invasive and noninvasive alien species respond differently to resource fluctuations in resident communities.
We grew 10 invasive and 10 noninvasive species as target species in pot‐mesocosms with four different synthetic native resident communities under six nutrient treatments differing in overall nutrient availability and temporal fluctuations in nutrient supply (constant low, constant high, gradual increasing, gradual decreasing, single large pulse, multiple smaller pulses). With the exception of plants in the constant low treatment, the plants were supplied the same total amount of nutrients during the experiment. We tested whether high‐nutrient availability and fluctuations in nutrient supply increased performance of both invasive and noninvasive alien plants within native resident communities, and whether invasive ones benefited more than noninvasive ones.
We found that the increase in biomass in response to nutrient addition was stronger for invasive than for noninvasive alien species. However, as the native competitors benefited even more from nutrient addition, the relative biomass of the alien target‐plant species, particularly the noninvasive ones, decreased. When the nutrient supply gradually increased, biomass of alien targets as well as native competitors decreased compared to the plants in the constant nutrient‐supply treatment. Surprisingly, when nutrients were supplied as a single large pulse, the absolute and relative biomass of the alien target plants decreased. The reduction in relative biomass was even stronger for invasive than for noninvasive alien species, and a similar pattern was found when nutrients were supplied as multiple smaller pulses.
Our results confirm previous findings that invasive alien species benefit more from nutrient addition than noninvasive alien species. However, in contrast to previous findings, our results suggest that nutrient fluctuations can suppress biomass of alien plants relative to that of natives, at least when the natives are themselves very successful, common species.
A plain language summary is available for this article.
Plain Language Summary
Species are the unit of analysis in many global change and conservation biology studies; however, species are not uniform entities but are composed of different, sometimes locally adapted, ...populations differing in plasticity. We examined how intraspecific variation in thermal niches and phenotypic plasticity will affect species distributions in a warming climate. We first developed a conceptual model linking plasticity and niche breadth, providing five alternative intraspecific scenarios that are consistent with existing literature. Secondly, we used ecological niche‐modeling techniques to quantify the impact of each intraspecific scenario on the distribution of a virtual species across a geographically realistic setting. Finally, we performed an analogous modeling exercise using real data on the climatic niches of different tree provenances. We show that when population differentiation is accounted for and dispersal is restricted, forecasts of species range shifts under climate change are even more pessimistic than those using the conventional assumption of homogeneously high plasticity across a species' range. Suitable population‐level data are not available for most species so identifying general patterns of population differentiation could fill this gap. However, the literature review revealed contrasting patterns among species, urging greater levels of integration among empirical, modeling and theoretical research on intraspecific phenotypic variation.
Concerns over the ecological impacts of invasive alien plant species have generated great research interest in understanding the mechanisms that underlie the capacity of such plants to occupy a broad ...range of habitats. It has been repeatedly suggested that rapid evolution of local adaptation to novel environments may enable invasive plants to occupy a broad range of habitats. However, the classical Darwinian view on evolution by natural selection is that the process is slow and gradual, occurring over thousands of years. Invasive plants typically have a relatively short residence time in their introduced ranges (decades or just a few centuries). Besides the time constraint, founder effects (reduction in population size and genetic diversity) may also limit the capacity of invasive plants to rapidly evolve local adaption. Thus, invasive plants may be less likely than native plants to evolve local adaptation. Interestingly, however, an expanding body of literature documents the existence of local adaptation in invasive plant species within their exotic ranges. Here, we did a phylogenetically controlled metaâanalysis to compare invasive and native plant species for differences in the frequency and magnitude of local adaptation. The metaâanalysis was based on different experiments performed in various habitats including grasslands, steppes, deserts, forests, mountains, wetlands and dunes, and used a total of 134 plant species in 52 families. Forty seven of these species (in 24 families) are alien invaders in the region where the studies were undertaken, while the other 91 species (in 38 families) are native. On average, local plants performed better than foreign plants, and invasive plant species expressed local adaptation just as frequently, and at least as strongly as that exhibited by native plant species. An analysis performed while taking into account different plant lifeâhistory traits showed that selfâincompatible invasive plants exhibited significantly higher frequencies of local adaptation than native plants characterized by the same breeding system. Synthesis. The present results support the suggestion that rapid evolution of local adaptation may enable invasive plant species to occupy a broad range of novel habitats.
Success of alien plants is often attributed to high competitive ability. However, not all aliens become dominant, and not all natives are vulnerable to competitive exclusion. Here, we quantified ...competitive outcomes and their determinants, using response‐surface experiments, in 48 pairs of native and naturalised alien annuals that are common or rare in Germany. Overall, aliens were not more competitive than natives. However, common aliens (invasive) were, despite strong limitation by intraspecific competition, more competitive than rare natives. This is because alien species had higher intrinsic growth rates than natives, and common species had higher intrinsic growth rates than rare ones. Strength of interspecific competition was not related to status or commonness. Our work highlights the importance of including commonness in understanding invasion success. It suggests that variation among species in intrinsic growth rates is more important in competitive outcomes than inter‐ or intraspecific competition, and thus contributes to invasion success and rarity.
Trade plays a key role in the spread of alien species and has arguably contributed to the recent enormous acceleration of biological invasions, thus homogenizing biotas worldwide. Combining data on ...60‐year trends of bilateral trade, as well as on biodiversity and climate, we modeled the global spread of plant species among 147 countries. The model results were compared with a recently compiled unique global data set on numbers of naturalized alien vascular plant species representing the most comprehensive collection of naturalized plant distributions currently available. The model identifies major source regions, introduction routes, and hot spots of plant invasions that agree well with observed naturalized plant numbers. In contrast to common knowledge, we show that the ‘imperialist dogma,’ stating that Europe has been a net exporter of naturalized plants since colonial times, does not hold for the past 60 years, when more naturalized plants were being imported to than exported from Europe. Our results highlight that the current distribution of naturalized plants is best predicted by socioeconomic activities 20 years ago. We took advantage of the observed time lag and used trade developments until recent times to predict naturalized plant trajectories for the next two decades. This shows that particularly strong increases in naturalized plant numbers are expected in the next 20 years for emerging economies in megadiverse regions. The interaction with predicted future climate change will increase invasions in northern temperate countries and reduce them in tropical and (sub)tropical regions, yet not by enough to cancel out the trade‐related increase.
Parasitic plants have been shown to affect soil‐organic‐matter (SOM) decomposition, but the mechanism is unknown. As arbuscular mycorrhizal fungi (AMF) can affect decomposition and compete with ...parasitic plants for carbon, we hypothesized that parasitic plants can indirectly regulate SOM decomposition by suppressing the effects of AMF on decomposition.
To test this hypothesis, we conducted two container experiments in which the herbaceous plant Bidens pilosa was inoculated with the AMF Rhizophagus intraradices or not, and Cuscuta australis or not. In one experiment, we provided SOM within hyphae‐in‐growth bags as 13C‐/15 N‐labelled maize leaves and in the other experiment as phytate‐P. We assessed growth and nutrient uptake of B. pilosa, growth of C. australis, the SOM remaining in the hyphae‐in‐growth bags, and the bacterial communities.
Parasitization increased the 13C and decreased the organic P remaining in the bags, but only in the presence of the extraradical AMF hyphae. AMF decreased the 13C and increased the organic P remaining in the absence of the parasite, but not in the presence of the parasite.
Our results demonstrate that parasitic plants can regulate the decomposition of organic materials indirectly by suppressing the effect of the extraradical AMF hyphae on decomposition. In other words, parasitic plants can regulate SOM decomposition indirectly via a multitrophic cascading effect. Our study helps to unravel the mechanisms of a sophisticated hidden ecological process, and is an important step forward in elucidating the roles of parasitic plants in soil nutrient cycling.
Read the free Plain Language Summary for this article on the Journal blog.
Read the free Plain Language Summary for this article on the Journal blog.
All around the globe, humans have greatly altered the abiotic and biotic environment with ever-increasing speed. One defining feature of the Anthropocene epoch is the erosion of biogeographical ...barriers by human-mediated dispersal of species into new regions, where they can naturalize and cause ecological, economic and social damage. So far, no comprehensive analysis of the global accumulation and exchange of alien plant species between continents has been performed, primarily because of a lack of data. Here we bridge this knowledge gap by using a unique global database on the occurrences of naturalized alien plant species in 481 mainland and 362 island regions. In total, 13,168 plant species, corresponding to 3.9% of the extant global vascular flora, or approximately the size of the native European flora, have become naturalized somewhere on the globe as a result of human activity. North America has accumulated the largest number of naturalized species, whereas the Pacific Islands show the fastest increase in species numbers with respect to their land area. Continents in the Northern Hemisphere have been the major donors of naturalized alien species to all other continents. Our results quantify for the first time the extent of plant naturalizations worldwide, and illustrate the urgent need for globally integrated efforts to control, manage and understand the spread of alien species.
1. Through its potential to enhance progeny performance, admixture (between-population crossing) may promote invasiveness of alien plants. The few studies that tested this idea found evidence for ...heterosis (positive effects of admixture) in the first generation (F₁), but have not considered further generations. In this paper, we test whether admixture benefits can be maintained in subsequent generations of an invasive plant. 2. We follow up on a previous study, in which we made crosses between plants of Mimulus guttatus from native- (western North America) and invaded-range populations (New Zealand and Scotland), and showed that admixture increases F₁ performance. Here, we performed further crosses to create non-admixed progeny, F₁ progeny resulting from within- and between-range admixture, and subsequent F₂ progeny both through outcrossing and through self-fertilization. As heterosis, outand inbreeding depression may depend on the environment, we assessed progeny performance under benign (well-watered) and drought-stress conditions in a greenhouse experiment. 3. We found that non-admixed progeny of M. guttatus were outperformed by admixed progeny (averaged across F₁ and F₂), particularly by progeny from betweenrange admixture. However, the benefit of admixture was stronger in F₁ than in F₂ progeny, especially when the F₂ was produced by self-fertilization. The benefit of admixture also depended on the range of origin and the test environment. 4. Synthesis. Our findings indicate that increased performance of admixed F₁ progeny is partly maintained in the F₂ progeny. Admixture might thus significantly boost performance of an invasive plant across multiple generations.
With globalisation facilitating the movement of plants and seeds beyond the native range, preventing potentially harmful introductions requires knowledge of what drives the successful establishment ...and spread of alien plants. Here, we examined global‐scale relationships between naturalisation success (incidence and extent) and invasiveness, soil seed bank properties (type and densities) and key species traits (seed mass, seed dormancy and life form) for 2350 species of angiosperms. Naturalisation and invasiveness were strongly associated with the ability to form persistent (vs. transient) seed banks but relatively weakly with seed bank densities and other traits. Our findings suggest that seed bank persistence is a trait that better captures the ability to become naturalised and invasive compared to seed traits more widely available in trait databases. Knowledge of seed persistence can contribute to our ability to predict global naturalisation and invasiveness and to identify potentially invasive flowering plants before they are introduced.
We examine global‐scale relationships between naturalization success and invasiveness, soil seed bank properties (type and density), and key species traits (seed mass, seed dormancy, and life form) for 2350 angiosperm taxa. We found that the ability to form persistent reserves of viable seeds in the soil is a consistent indicator of the incidence and extent of naturalization and of the likelihood of them becoming invasive. We also showed that seed bank persistence is a trait that better captures the ability of angiosperms to become naturalized and invasive compared to seed traits more widely available in trait databases.
Darwin’s naturalisation hypothesis posing that phylogenetic distance of alien species to native residents predicts invasion success, and Elton’s diversity–invasibility hypothesis posing that ...diversity of native communities confers resistance to invasion, are both rooted in ideas of species coexistence. Because the two hypotheses are inherently linked, the mechanisms underlying them may interact in driving the invasion success. Even so, these links and interactions have not been explicitly disentangled in one experimental study before.
To disentangle the links between the two hypotheses, we used 36 native grassland herbs to create greenhouse mesocosms with 90 grassland communities of different diversities, and introduced each of five herbaceous alien species as seeds and seedlings. We used phylogeny and four functional traits (plant height, specific leaf area, leaf size, and seed mass) to calculate different measures of phylogenetic and functional distance and diversity. Specifically, we tested how the alien–native distance (phylogenetic or functional) and the native diversity (phylogenetic or functional) affected each other in their effects on germination, seedling survival, growth, and reproduction of the aliens.
Overall, our results supported both hypotheses. Multivariate functional distance based on four traits jointly had stronger positive effects than phylogenetic distance and the univariate ones based on each trait separately. Moreover, the aliens were more successful if they were more competitive by being taller and having larger leaves with a lower SLA than the native residents. Univariate functional diversity based on each trait separately had stronger negative effects than phylogenetic and multivariate functional diversity. Most importantly, we found that the effects of alien–native phylogenetic and multivariate functional distance became stronger as diversity increased. Our analyses with single traits also showed that the strength of the effects of both alien–native hierarchical functional distances (indicative of competitive inequalities) and absolute functional distances (indicative of niche differences) increased at higher diversities, where competition is more severe.
Synthesis. Our study explicitly demonstrates for the first time how the mechanisms underlying the two classical invasion hypotheses interact in driving invasion success in grassland communities. This may help to explain some of the puzzling results of studies testing either of the two hypotheses.
This study explicitly demonstrates how the mechanisms underlying the two classical invasion hypotheses, Darwin's naturalisation hypothesis and Elton's diversity–invasibility hypothesis, interact in driving the success of alien species in experimental grassland communities. Our findings could help explain some of the puzzling results of studies testing either of the two hypotheses.
PDF
