Several prominent hypotheses have been posed to explain the immense variability among plant species in defense against herbivores. A major concept in the evolutionary ecology of plant defenses is that tradeoffs of defense strategies are likely to generate and maintain species diversity. In particular, tradeoffs between constitutive and induced resistance and tradeoffs relating these strategies to growth and competitive ability have been predicted. We performed three independent experiments on 58 plant species from 15 different plant families to address these hypotheses in a phylogenetic framework. Because evolutionary tradeoffs may be altered by human-imposed artificial selection, we used 18 wild plant species and 40 cultivated garden-plant species. Across all 58 plant species, we demonstrate a tradeoff between constitutive and induced resistance, which was robust to accounting for phylogenetic history of the species. Moreover, the tradeoff was driven by wild species and was not evident for cultivated species. In addition, we demonstrate that more competitive species-but not fast growing ones-had lower constitutive but higher induced resistance. Thus, our multispecies experiments indicate that the competition-defense tradeoff holds for constitutive resistance and is complemented by a positive relationship of competitive ability with induced resistance. We conclude that the studied genetically determined tradeoffs are indeed likely to play an important role in shaping the high diversity observed among plant species in resistance against herbivores and in life history traits.comparative experimental study | phylogenetic corrections | plant defense theory | plant-insect interaction | Spodoptera littoralis G iven that green plants are the ultimate source of energy for most other organisms, it is not surprising that plants evolved a variety of resistance strategies, which can be constitutively expressed or induced after damage (1). Although herbivory selects for enhanced plant resistance, plants vary greatly in their resistance, both among species (2) and among genotypes within species (3). This indicates that being well defended may not always be the best strategy-most likely because allocation to resistance may physiologically constrain other investments (reviewed in refs. 4 and 5) and because constraints on resource allocation may produce negative genetic correlations between resistance mechanisms and other life-history traits (6-8). The current assumption in evolutionary ecology is that such tradeoffs contribute to the generation and maintenance of species diversity (8).Several hypotheses on tradeoffs associated with constitutive and induced resistance have been formulated. Among the most fundamental ones is the long-predicted tradeoff between constitutive and induced resistance itself (6, 9). This hypothesis is derived from the idea that resistance is costly and that a species already well defended by high constitutive resistance will benefit only negligibly by further induced resistance (1, 10). However, genera...

Determinants of plant establishment and invasion are a key issue in ecology and evolution. Although establishment success varies substantially among species, the importance of species traits and extrinsic factors as determinants of establishment in existing communities has remained difficult to prove in observational studies because they can be confounded and mask each other. Therefore, we conducted a large multispecies field experiment to disentangle the relative importance of extrinsic factors vs. species characteristics for the establishment success of plants in grasslands. We introduced 48 alien and 45 native plant species at different seed numbers into multiple grassland sites with or without experimental soil disturbance and related their establishment success to species traits assessed in five independent multispecies greenhouse experiments. High propagule pressure and high seed mass were the most important factors increasing establishment success in the very beginning of the experiment. However, after 3 y, propagule pressure became less important, and species traits related to biotic interactions (including herbivore resistance and responses to shading and competition) became the most important drivers of success or failure. The relative importance of different traits was environment-dependent and changed over time. Our approach of combining a multispecies introduction experiment in the field with trait data from independent multispecies experiments in the greenhouse allowed us to detect the relative importance of species traits for early establishment and provided evidence that species traits-fine-tuned by environmental factors-determine success or failure of alien and native plants in temperate grasslands.community assembly | functional traits | biotic filter

Invasive alien plant species are frequently characterized by a high fecundity. However, because suitable pollinators and/or mates may be absent in the new range, it is not clear how they achieve high seed production. According to Baker's Law, species capable of uniparental reproduction are more likely to establish after long-distance dispersal than species that rely on suitable mates and pollinators. To test whether selfcompatible species, and particularly species capable of autonomous seed set, are more likely to establish and spread, we experimentally assessed the breeding systems of 12 species of Asteraceae that are invasive in China. Among these 12 species of Asteraceae, the percentages of self-compatible species (66.7%) and species capable of autonomous seed set (83.3%), which included self-fertilizing and apomictic species, were significantly larger than expected from the percentages of such species in global data sets of Asteraceae (36.8% and 46.0%, respectively). Furthermore, the number of Chinese provinces in which the invasive alien species occur was significantly positively correlated with the proportion seed set on bagged capitula (i.e. with the degree of autonomous seed set). Among 36 species of Asteraceae that are invasive in China and for which we found breeding-system data in the literature, we also found a higher than expected percentage of selfcompatible species (65.7%), and that these self-compatible species are more widespread in China than self-incompatible species. These results support the predictions of Baker's Law that self-compatible species, and particularly those capable of autonomous seed production, are more likely to establish and spread in a new range. Therefore, breeding systems of plants should be included as one of the key elements in risk assessment protocols for plant invasiveness.

Traits that differ between invasive alien and native plant species are frequently interpreted as traits conferring invasiveness. However. such dilferences could reHect an introduction bias of alien species, particularly clllLivated ones, 01' hllman-medialed selection of cultivars of these species with certain traits. We tested whether this is the case for germination characteristics that are frequently reported to be associated with invasiveness. In a glasshouse experiment, we compared germination characteristics of 42 plant species native to Switzerland and 47 cultivated alien species incJuding 26 cultivars. To test whether differences in germination between these groups of species depend on an important environmental factor, we used two light levels. Cultivated alien plant species germinated earlier and more successfully than related native plant species under both light conditions. Similarly, among cultivated alien species, cultivars germinated earlier and with higher proportions than non-cultivars. Our results indicate that previously reported differences in germination characteristics between invasive alien and native species might rellect introduclion bias and human-mediatcd selection for these characteristics. Nevertheless, because fast and abundant germination is also frequently associated with naturalization and invasiveness among alien introduced species, our results suggest that biased introduction and human-mediated selection of ornamental plants with these characteristics might increase the risk that these species ultimately become invasive. Therefore, it is important that studies testing for determinants of invasiveness incJude non-invasive alien species in addition to invasive alien species. Zusammenfassung Merkmalsunterschiede zwischen invasivcn gebietsfremden und heimischen PHanzenarten werden oft dahingehend interpretiert, dass sie Invasionen ermöglichen. Allerdings könnten diese Unterschiede auch auf selektiver Einführung und Selektion von gebietsfremden Arten, insbesondere Zierpllanzenarten oder Kulturvarietäten mit di esen Eigenschaften beruhen. Wir untersuchten , ob dies für Keimungseigenschaften, die oft mit Invasivität verbunden werden, der Fall ist. In einem Gewächshaus-experiment verglichen wir die Keimungseigenschaften von 42 in der Schweiz heimischen Arten und 47 gebietsfremden Zierpflanzenarten, darunter 26 Kulturvarietäten. Um zu testen, ob Keimungsunterschiede zwischen Zierpflanzenarten und heimischen Arten von einem wichtigen Umweltfaktor abhängig sind, nutzten wir zwei unterschiedliche Lichtintensitäten. Gebietsfremde Zierpllanzenarten keimten im Vergleich zu heimischen Arten früher und mit höheren Keimungsraten unter beiden Lichtintensitätcn. Von elen ZierpflanzenarteIl keimten die Kulturvarietäten frUher und mit höheren Keimungsraten. Unsere

The majority of plant species rely, at least partly, on animals for pollination. Our knowledge on whether pollinator visitation differs between native and alien plant species, and between invasive and noninvasive alien species is still limited. Additionally, because numerous invasive plant species are escapees from horticulture, the transition from human-assisted occurrence in urbanized habitats to unassisted persistence and spread in (semi-)natural habitats requires study. To address whether pollinator visitation differs between native, invasive alien and non-invasive alien species, we did pollinator observations for a total of 17 plant species representing five plant families. To test whether pollinator visitation to the three groups of species during the initial stage of invasion depends on habitat type, we did the study in three urbanized habitats and three semi-natural grasslands, using single potted plants. Native plants had more but smaller flower units than alien plants, and invasive alien plants had more but smaller flowers than noninvasive alien plants. After accounting for these differences in floral display, pollinator visitation was higher for native than for alien plant species, but did not differ between invasive and non-invasive alien plant species. Pollinator visitation was on average higher in semi-natural than in urbanized habitats, irrespective of origin or status of the plant species. This might suggest that once an alien species has managed to escape from urbanized into more natural habitats, pollinator limitation will not be a major barrier to establishment and invasion.

Summary1. When entomophilous plants are introduced to a new region, they may leave behind their usual pollinators. In particular, plant species with specialized pollination may then be less likely to establish and spread (i.e. become invasive). Moreover, other reproductive characteristics such as selfcompatibility and flowering duration may also affect invasion success. 2. Here, we specifically asked whether plant species' specialization towards pollinator species and families, respectively, as measured in the native range, self-compatibility, flowering duration and their interactions are related to the degree of invasion (i.e. a measure of regional abundance) in nonnative regions. 3. We used plant-pollinator interaction data from 119 German grassland sites to calculate unbiased indices of plant specialization towards pollinator species and families for 118 European plant species. We related these specialization indices, flowering duration, self-compatibility and their interactions to the degree of invasion of each species in seven large countries on four non-Eurasian continents. 4. In all models, plant species with long flowering durations had the highest degree of invasion. The best model included the specialization index based on pollinator species instead of the one based on pollinator families. Specialization towards pollinator species had a marginally significant positive effect on the degree of invasion in non-native regions for self-compatible, but not for selfincompatible species. 5. Synthesis. We showed that long flowering duration is related to the degree of invasion in other parts of the world, and a trend that pollinator generalization in the native range may interact with self-compatibility in determining the degree of invasion. Therefore, we conclude that such reproductive characteristics should be considered in risk assessment and management of introduced plant species.

Within the EU LIFE-Nature project 'River and floodplain revitalisation Emmericher Ward', three small temporary waters and a former gravel pit were connected by a side channel running parallel to the river Rhine through former groyne fields. The initial status of macrozoobenthos, fish, avifauna, flora, vegetation, and habitats before and their development after implementation of the project's measures were recorded and compared. The monitoring years 2018 and 2019 were exceptionally dry and accompanied by an extremely low runoff in the Rhine and the side channel.These conditions likely affected the development of habitats and species populations in the new side channel. The new side channel showed intensive morphodynamic development and differentiation of its structures. While the more complex vegetation and habitat types appeared as mostly species-poor initial stages, shortlived species-rich pioneer habitats such as annual mud banks in the water exchange area were already established. Two years after the implementation, the benthic invertebrate fauna was still predominantly species-poor and dominated by neozoans.Occasionally, representatives of the more sensitive EPT fauna (Ephemeroptera, Plecoptera, Trichoptera) were already detected but were, in general, strongly underrepresented in the main stream. Low colonisation potential, nonpermanent flow, and lack of river wood limit the development of the macrozoobenthos community.The relative abundance of rheophilic fish species increased in the project area and high juvenile fish densities proved the function as a nursery habitat. As pioneer species of riverine landscapes, sand martins and little ringed plovers colonised the new structures already in the first year. The initial state of the side channel represented a typical dynamic pioneer habitat pattern of a sandy lowland river, which was almost absent in the Lower Rhine area. The new habitats were quickly colonised by pioneer flora and fauna, but the potential for more demanding and complex communities was restricted by the poor structural and biological states of the Lower Rhine.