Human activities have increasingly introduced plant species far outside their native ranges under environmental conditions that can strongly differ from those originally met. Therefore, before spreading, and potentially causing ecological and economical damage, non-native species may rapidly evolve. Evidence of genetically based adaptation during the process of becoming invasive is very scant, however, which is due to the lack of knowledge regarding the historical genetic makeup of the introduced populations and the lack of genomic resources. Capitalizing on the availability of old non-native herbarium specimens, we examined frequency shifts in genic SNPs of the Pyrenean Rocket (Sisymbrium austriacum subsp. chrysanthum), comparing the (i) native, (ii) currently spreading non-native and (iii) historically introduced gene pool. Results show strong divergence in flowering time genes during the establishment phase, indicating that rapid genetic adaptation preceded the spread of this species and possibly assisted in overcoming environmental constraints.

Community assembly or succession was traditionally thought of as being deterministic and directional, leading to a clearly defined climax state. The alternative view, however, keeps gaining attention. This view states that community assembly is influenced by historical processes, where differences in the sequence and timing of species arrival result in distinct communities. Here we tested the hypothesis that both views are valid, but at a different level, with increasing dissimilarity in species composition among sites with increasing age (divergence), caused by historical processes (priority effects), and with increasing similarity in mean trait composition (convergence) among sites, indicating a directional development at the niche level. We surveyed a chronosequence of restored semi‐natural grassland patches on former pine plantations over seven restoration age classes, covering 22 grasslands. Pairwise multivariate distances were calculated between the different grassland patches based on species abundance on the one hand, and on mean community trait values for 28 plant life history traits on the other. Trait composition showed a clear decrease in multivariate distance with increasing restoration age, indicating trait convergence through time. At the species level, we found no evidence of convergence through time, with even a trend towards divergence. Furthermore, spatial variation and environmental heterogeneity were found to remain constant through time. These results confirm our hypothesis. At the trait level, limited niches occur, only filled by species having the appropriate traits, resulting in a clear deterministic model of assembly. Species identity, on the contrary, has no role in this niche filling. The first appropriate species to reach a restoration site will be most likely the ones that get established, resulting in divergence of the species composition among restored grasslands.

Summary1. Ecological restoration schemes often assume that after reinstating appropriate abiotic conditions, plant communities will assemble following a single predictable pathway towards a fixed target state. This idea has recently been challenged, with increasing evidence that plant community assembly can only be considered deterministic at the plant trait level, rather than at the species level, and that the assembly outcome is largely influenced by the spatial context of the restoration site. 2. We surveyed 147 vegetation plots across a chronosequence of 22 restored semi-natural grassland patches to quantify the effects of spatial isolation on both plant species and plant trait assembly. Trait level assembly was analysed using an emergent group approach, based on 28 functional plant traits. Additionally, we examined the effects of several dispersal-related plant traits on species recolonization capacities. 3. Whereas total plant species richness of the restoration patches did not change through space or through time, progressing assembly was found to consist of a sequential replacement of generalist species with specialist species, which was reflected by a directional assembly at the plant trait level. Grassland isolation was found to slow down community assembly at both the species and the trait level without changing the general direction of assembly. This slowdown became less pronounced with increasing time since restoration. 4. Spatial isolation of the restoration patches was found to act as a trait filter, independent of assembly age. We found a proportionally higher occurrence of species with light seeds and a high seed attachment potential in more isolated restoration patches, suggesting that colonization is more limited in isolated grasslands. 5. Synthesis and applications. We demonstrate that the assembly process, at both the species and the trait level, is influenced by the position of the restoration patch in the landscape. Monitoring schemes following ecological restoration should therefore include the spatial context of the system while using both a trait-based and a species-based plant community analysis. Successful restoration requires physically interconnecting grassland fragments and probably the introduction of seeds or seedlings of species with low dispersability.

1. Linear landscape elements such as hedgerows and road verges have the potential to mitigate the adverse effects of habitat fragmentation and climate change on species, for instance, by serving as a refuge habitat or by improving functional connectivity across the landscape. However, so far this hypothesis has not been evaluated at large spatial scales, preventing us from making generalized conclusions about their efficacy and implementation in conservation policies.2. Here, we assessed plant diversity patterns in 336 vegetation plots distributed along hedgerows and road verges, spanning a macro-environmental gradient across temperate Europe. We compared herb-layer species richness and composition in these linear elements with the respective seed-source (core) habitats, that is, semi-natural forests and grasslands. Next, we assessed how these differences related to several environmental drivers acting either locally, at the landscape level or along the studied macro-ecological gradient.3. Across all regions, about 55% of the plant species were shared between forests and hedgerows, and 52% between grasslands and road verges. Habitat-specialist richness was 11% lower in the linear habitats than in the core habitats, while generalist richness was 14% higher. The difference in floristic composition between both habitat types was mainly due to species turnover, and not nestedness. Most notably, forest-specialist richness in hedgerows responded positively to tree cover, tree height and the proportion of forests in the surrounding landscape, while generalist richness was negatively affected by tree height and buffering effect of trees on subcanopy temperatures. Grassland and road verge diversity was

Observed and projected changes in temperature and precipitation are destabilizing existing relationships between natural communities and their abiotic context across the globe (

BackgroundThe importance of intraspecific trait variation (ITV) is increasingly acknowledged among plant ecologists. However, our understanding of what drives ITV between individual plants (ITVBI) at the population level is still limited. Contrasting theoretical hypotheses state that ITVBI can be either suppressed (stress-reduced plasticity hypothesis) or enhanced (stress-induced variability hypothesis) under high abiotic stress. Similarly, other hypotheses predict either suppressed (niche packing hypothesis) or enhanced ITVBI (individual variation hypothesis) under high niche packing in species rich communities. In this study we assess the relative effects of both abiotic and biotic niche effects on ITVBI of four functional traits (leaf area, specific leaf area, plant height and seed mass), for three herbaceous plant species across a 2300 km long gradient in Europe. The study species were the slow colonizing Anemone nemorosa, a species with intermediate colonization rates, Milium effusum, and the fast colonizing, non-native Impatiens glandulifera.ResultsClimatic stress consistently increased ITVBI across species and traits. Soil nutrient stress, on the other hand, reduced ITVBI for A. nemorosa and I. glandulifera, but had a reversed effect for M. effusum. We furthermore observed a reversed effect of high niche packing on ITVBI for the fast colonizing non-native I. glandulifera (increased ITVBI), as compared to the slow colonizing native A. nemorosa and M. effusum (reduced ITVBI). Additionally, ITVBI in the fast colonizing species tended to be highest for the vegetative traits plant height and leaf area, but lowest for the measured generative trait seed mass.ConclusionsThis study shows that stress can both reduce and increase ITVBI, seemingly supporting both the stress-reduced plasticity and stress-induced variability hypotheses. Similarly, niche packing effects on ITVBI supported both the niche packing hypothesis and the individual variation hypothesis. These results clearly illustrates the importance of simultaneously evaluating both abiotic and biotic factors on ITVBI. This study adds to the growing realization that within-population trait variation should not be ignored and can provide valuable ecological insights.Electronic supplementary materialThe online version of this article (10.1186/s12898-017-0151-y) contains supplementary material, which is available to authorized users.

In most landscapes the success of habitat restoration is largely dependent on spontaneous colonization of plant species. This colonization process, and the outcome of restoration practices, can only be considered successful if the genetic makeup of founding populations is not eroded through founder effects and subsequent genetic drift. Here we used 10 microsatellite markers to investigate the genetic effects of recent colonization of the long-lived gynodioecious species Origanum vulgare in restored semi-natural grassland patches. We compared the genetic diversity and differentiation of fourteen recent populations with that of thirteen old, putative source populations, and we evaluated the effects of spatial configuration of the populations on colonization patterns. We did not observe decreased genetic diversity in recent populations, or inflated genetic differentiation among them. Nevertheless, a significantly higher inbreeding coefficient was observed in recent populations, although this was not associated with negative fitness effects. Overall population genetic differentiation was low (FST = 0.040). Individuals of restored populations were assigned to on average 6.1 different source populations (likely following the ‘migrant pool’ model). Gene flow was, however, affected by the spatial configuration of the grasslands, with gene flow into the recent populations mainly originating from nearby source populations. This study demonstrates how spontaneous colonization after habitat restoration can lead to viable populations in a relatively short time, overcoming pronounced founder effects, when several source populations are nearby. Restored populations can therefore rapidly act as stepping stones and sources of genetic diversity, likely increasing overall metapopulation viability of the study species.

Abstract. Invasive alien plant effects on ecosystem functions are often difficult to predict across environmental gradients due to the context-dependent interactions between the invader and the recipient communities. Adopting a functional trait-based framework could provide more mechanistic predictions for invasive species' impacts. In this study, we contrast litter decomposition rates among communities with and without the invasive plant Impatiens glandulifera in five regions along a 1600 km long latitudinal gradient in Europe. Across this gradient, four functional traits, namely leaf dry matter content (LDMC), specific leaf area (SLA), stem-specific density (SSD), and plant height, are correlated to rates of litter decomposition of standardized rooibos (labile), green tea (recalcitrant), and I. glandulifera litter. Our results show that both invaded and non-invaded plant communities had a higher expression of acquisitive traits (low LDMC and SSD, high SLA) with increasing temperature along the latitudinal gradient, partly explaining the variation in decomposition rates along the gradient. At the same time, invasion shifted community trait composition toward more acquisitive traits across the latitudinal gradient. These trait changes partly explained the increased litter decomposition rates of the labile litter fraction of rooibos and I. glandulifera litter in invaded communities, a shift that was most evident in the warmer study regions. Plant available nitrogen was lower in invaded communities, likely due to high nutrient uptake by I. glandulifera. Meanwhile, the coldest study region was characterized by a reversed effect of invasion on decomposition rates. Here, community traits related to low litter quality and potential allelopathic effects of the invader resulted in reduced litter decomposition rates, suggesting a threshold temperature at which invader effects on litter decomposition turn positive. This study therefore illustrates how functional trait changes toward acquisitive traits can help explain invader-induced changes in ecosystem functions such as increased litter decomposition.