Summary
It has been suggested that establishment of one alien invader might promote further invasions. Such a so‐called invasional meltdown could be mediated by differences in soil‐legacy effects ...between alien and native plants. Whether such legacy effects might depend on the diversity of the invaded community has not been explored to date.
Here, we conducted a two‐phase plant–soil feedback experiment. In a soil‐conditioning phase, we grew five alien and five native species as invaders in 21 communities of one, two or four species. In the subsequent test phase, we grew five alien and five native species on the conditioned soils.
We found that growth of these test species was negatively affected by soils conditioned by both a community and an invader, and particularly if the previous invader was a conspecific (i.e. negative plant–soil feedback). Alien test species suffered less from soil‐legacy effects of previous allospecific alien invaders than from the legacy effects of previous native invaders. However, this effect decreased when the soil had been co‐conditioned by a multispecies community.
Our findings suggest that plant–soil feedback‐mediated invasional meltdown may depend on community diversity and therefore provide some evidence that diverse communities could increase resistance against subsequent alien invasions.
Biological invasions have steadily increased over recent centuries. However, we still lack a clear expectation about future trends in alien species numbers. In particular, we do not know whether ...alien species will continue to accumulate in regional floras and faunas, or whether the pace of accumulation will decrease due to the depletion of native source pools. Here, we apply a new model to simulate future numbers of alien species based on estimated sizes of source pools and dynamics of historical invasions, assuming a continuation of processes in the future as observed in the past (a business‐as‐usual scenario). We first validated performance of different model versions by conducting a back‐casting approach, therefore fitting the model to alien species numbers until 1950 and validating predictions on trends from 1950 to 2005. In a second step, we selected the best performing model that provided the most robust predictions to project trajectories of alien species numbers until 2050. Altogether, this resulted in 3,790 stochastic simulation runs for 38 taxon–continent combinations. We provide the first quantitative projections of future trajectories of alien species numbers for seven major taxonomic groups in eight continents, accounting for variation in sampling intensity and uncertainty in projections. Overall, established alien species numbers per continent were predicted to increase from 2005 to 2050 by 36%. Particularly, strong increases were projected for Europe in absolute (+2,543 ± 237 alien species) and relative terms, followed by Temperate Asia (+1,597 ± 197), Northern America (1,484 ± 74) and Southern America (1,391 ± 258). Among individual taxonomic groups, especially strong increases were projected for invertebrates globally. Declining (but still positive) rates were projected only for Australasia. Our projections provide a first baseline for the assessment of future developments of biological invasions, which will help to inform policies to contain the spread of alien species.
The number of alien species has been increasing worldwide, but we still lack clear expectations about future developments of biological invasions. Using a model predicting alien species numbers based on observed developments and species pools, we here provide the first quantitative projections of alien species numbers until 2050 worldwide for a range of taxonomic groups and regions. Our projections show that the rise in alien species numbers will persist to grow with little signs of slowdowns. Overall, the number of alien species is predicted to increase by 36% with particularly steep increases expected for Europe and invertebrates.
1. Global environmental change not only includes changes in mean environmental conditions but also in temporal environmental fluctuations. Because it is frequently suggested that common species, and ...particularly invasive alien species, are phenotypically highly plastic, they might benefit more from these fluctuations than rare native and rare alien species. Experimental tests, however, are still lacking. 2. Here, we tested whether alien plant species take more advantage of increases in resource levels and fluctuations therein than native species, and whether common species do so more than rare species. Therefore, we grew seven common alien, seven rare alien, nine common native and six rare native herbaceous plants, in one treatment with constantly low nutrient availability and five treatments with high nutrient availability that differed in temporal availability of nutrients (constant, increasing, decreasing, single large pulse, multiple smaller pulses). 3. We found that all species produced more biomass and longer roots, and had a lower root mass fraction under high nutrient conditions than under low nutrient conditions, irrespective of their origin and commonness. Among the high nutrient treatments, the temporal pattern of nutrient supply also influenced biomass production, root allocation and root thickness, but the magnitude and/or directions of these responses varied among the groups of species. Particularly, we found that alien plant species, irrespective of whether they are common or rare, produced more biomass, and had a higher root mass fraction when nutrients were supplied as a single pulse in the middle of the growth period instead of supplied at a constant rate, whereas the reverse was true for the native species. 4. Synthesis. Our study suggests that species origin does not drive differences in plant biomass production, root morphology and allocation in response to changes in mean environmental nutrient availability. However in our study, alien plant species, in contrast to native plant species, benefited from a large nutrient pulse. This suggests that increased fluctuations in nutrient availability might promote alien plant invasions.
The ecological consequences of microplastic pollution for plants remain largely unknown, and the few studies that tested the effects usually focused on a single type of microplastic and a single ...plant species. However, most plants will be exposed to multiple microplastic types simultaneously, and the effects may vary among species.
To test the effects of microplastic diversity on plants, we grew single plants of eight invasive and eight native species in pots with substrate polluted with 0, 1, 3 and 6 types of microplastics.
We found that the growth suppression by microplastic pollution became stronger with the number of microplastic types the plants were exposed to. This tended to be particularly the case for invasive species, as their biomass advantage over natives diminished with the number of microplastic types. The biomass responses coincided with a positive effect of the number of microplastic types on root allocation and thickness, which was also stronger for invasive than for native species. In addition, the results of hierarchical diversity–interaction models suggest that the negative impact of microplastic diversity on the total biomass of invasive plant species was influenced by both the identities of the microplastic and certain types of microplastic with strong pairwise interactions. In contrast, the effect on native species was determined solely by the microplastic identities.
Synthesis. Our multispecies study thus shows for the first time that the negative effects of microplastic pollution on plant growth increase with the number of microplastic types. We also found tentative evidence that the negative impacts of microplastic diversity were more pronounced for invasive plants compared to native plants, and that this might be due to differences in the responses of root allocation and thickness.
Our multispecies study thus shows for the first time that the negative effects of microplastic pollution on plant growth increase with the number of microplastic types. We also found tentative evidence that the negative impacts of microplastic diversity were more pronounced for invasive plants compared to native plants, and that this might be due to differences in the responses of root allocation and thickness.
Editor's Choice
Numerous studies have highlighted the roles of nutrient availability and fluctuations therein for invasion success of alien plants. Many others also highlighted the role of herbivores in invasion ...success. However, how herbivory and the level and fluctuations in nutrient availability interact in driving alien plant invasion into native communities remains largely unexplored.
We grew eight invasive alien species as target species in pot‐mesocosms with five different synthetic native communities in a three‐factorial design with two levels of nutrient availability (low vs. high), two levels of nutrient fluctuation (constant vs. pulsed) and two levels of above‐ground insect herbivory (with vs. without herbivores). As natural communities have both specialist and generalist herbivores, we simulated this using both a generalist and a specialist herbivorous grasshopper.
The relative biomass production of the alien target plants to the total biomass production (i.e. alien biomass/total biomass) decreased in response to an increase in nutrient availability, but increased in response to the presence of herbivores. Furthermore, we found indications that the dominance of the alien target species may depend on interactions of herbivory with changes in nutrient availability and nutrient fluctuations, although these interactions were only marginally significant.
Our multi‐trophic multi‐species experiment suggests that herbivory could mediate the interactive effect of nutrient enrichment and variability in nutrient supply on invasion of alien plants into native communities. Therefore, we recommend that studies testing the effects of resources on plant invasion should also consider interactive effects of other trophic levels.
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.
Scientists' warning on invasive alien species Pyšek, Petr; Hulme, Philip E.; Simberloff, Dan ...
Biological reviews of the Cambridge Philosophical Society,
December 2020, Letnik:
95, Številka:
6
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
Biological invasions are a global consequence of an increasingly connected world and the rise in human population size. The numbers of invasive alien species – the subset of alien species ...that spread widely in areas where they are not native, affecting the environment or human livelihoods – are increasing. Synergies with other global changes are exacerbating current invasions and facilitating new ones, thereby escalating the extent and impacts of invaders. Invasions have complex and often immense long‐term direct and indirect impacts. In many cases, such impacts become apparent or problematic only when invaders are well established and have large ranges. Invasive alien species break down biogeographic realms, affect native species richness and abundance, increase the risk of native species extinction, affect the genetic composition of native populations, change native animal behaviour, alter phylogenetic diversity across communities, and modify trophic networks. Many invasive alien species also change ecosystem functioning and the delivery of ecosystem services by altering nutrient and contaminant cycling, hydrology, habitat structure, and disturbance regimes. These biodiversity and ecosystem impacts are accelerating and will increase further in the future. Scientific evidence has identified policy strategies to reduce future invasions, but these strategies are often insufficiently implemented. For some nations, notably Australia and New Zealand, biosecurity has become a national priority. There have been long‐term successes, such as eradication of rats and cats on increasingly large islands and biological control of weeds across continental areas. However, in many countries, invasions receive little attention. Improved international cooperation is crucial to reduce the impacts of invasive alien species on biodiversity, ecosystem services, and human livelihoods. Countries can strengthen their biosecurity regulations to implement and enforce more effective management strategies that should also address other global changes that interact with invasions.
Although many studies have tested the direct effects of drought on alien plant invasion, less is known about whether drought affects alien plant invasion indirectly via interactions of plants with ...other groups of organisms such as soil mesofauna.
To test for such indirect effects, we grew single plants of nine naturalized alien target species in pot mesocosms with a community of five native grassland species under four combinations of two drought (well‐watered vs. drought) and two soil‐mesofauna inoculation (with vs. without) treatments.
We found that drought decreased the absolute and the relative biomass production of the alien plants, and thus reduced their competitive strength in the native community. Drought also decreased the abundance of soil mesofauna, particularly soil mites, but did not affect the abundance and richness of soil herbivores. Soil‐fauna inoculation did not affect the biomass of the alien plants but increased the biomass of the native plant community, and thereby decreased the relative biomass production of the alien plants. This increased invasion resistance due to soil fauna, however, tended (p = 0.09) to be stronger for plants growing under well‐watered conditions than under drought.
Synthesis. Our multispecies experiment thus shows that soil fauna might help native communities to resist alien plant invasions, but that this effect might be weakened under drought. In other words, soil mesofauna may buffer the negative effects of drought on alien plant invasions.
Our multispecies experiment shows that soil fauna might help native communities to resist alien plant invasions, but that this effect might be weakened under drought. In other words, soil mesofauna may buffer the negative effects of drought on alien plant invasions.
Invasive alien plants are likely to be released from specialist herbivores and at the same time encounter biotic resistance from resident generalist herbivores in their new ranges. The Shifting ...Defense hypothesis predicts that this will result in evolution of decreased defense against specialist herbivores and increased defense against generalist herbivores. To test this, we performed a comprehensive meta-analysis of 61 common garden studies that provide data on resistance and/or tolerance for both introduced and native populations of 32 invasive plant species. We demonstrate that introduced populations, relative to native populations, decreased their resistance against specialists, and increased their resistance against generalists. These differences were significant when resistance was measured in terms of damage caused by the herbivore, but not in terms of performance of the herbivore. Furthermore, we found the first evidence that the magnitude of resistance differences between introduced and native populations depended significantly on herbivore origin (i.e., whether the test herbivore was collected from the native or non-native range of the invasive plant). Finally, tolerance to generalists was found to be higher in introduced populations, while neither tolerance to specialists nor that to simulated herbivory differed between introduced and native plant populations. We conclude that enemy release from specialist herbivores and biotic resistance from generalist herbivores have contrasting effects on resistance evolution in invasive plants. Our results thus provide strong support for the Shifting Defense hypothesis.
Cascading effects are ubiquitous in nature and can modify ecological processes. Most plants have mutualistic associations with mycorrhizal fungi, and can be connected to neighboring plants through ...common mycorrhizal networks (CMNs). However, little is known about how the distribution of nutrients by CMNs to the interconnected plants is affected by higher trophic levels, such as parasitic plants. We hypothesized that parasitism would indirectly drive CMNs to allocate more nutrients to the nonparasitized neighboring plants rather than to the parasitized host plants, and that this would result in a negative-feedback effect on the growth of the parasitic plant. To test this, we conducted a container experiment, where each container housed two in-growth cores that isolated the root system of a single Trifolium pratense seedling. The formation of CMNs was either prevented or permitted using nylon fabric with a mesh width of 0.5 or 25 μm, respectively. In each container, either both T. pratense plants were not parasitized or only one was parasitized by the holoparasite Cuscuta australis. To quantify the nutrient distribution by CMNs to the host and neighboring plants, we used 15N labeling. Growth and 15N concentrations of C. australis and T. pratense were measured, as well the arbuscular mycorrhizal fungi–colonization rates of T. pratense. We found that parasitism by C. australis reduced the biomass of T. pratense. In the absence of the parasite, CMNs increased the 15N concentration of both T. pratense plants, but did not affect their biomass. However, with the parasite, the difference between host and neighboring T. pratense plants in 15N concentration and biomass were amplified by CMNs. Furthermore, CMNs decreased the negative effect of C. australis on growth of the host T. pratense plants. Finally, although CMNs did not influence the 15N concentration of C. australis, they reduced its biomass. Our results indicate that when T. pratense was parasitized by C. australis, CMNs preferentially distributed more mineral nutrients to the nonparasitized neighboring T. pratense plant, and that this had a negative feedback on the growth of the parasite.
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.
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