Going beyond taxonomic diversity: deconstructing biodiversity patterns reveals the true cost of iceplant invasion

Effects of TiO2 ultraviolet filter and sunscreens on coastal dune plant performance and competitive interactions

Ultraviolet filters (UVFs) added to sunscreens (SS) are emerging contaminants in marine environments due to their adverse effects on organisms and ecosystems. UVFs have also been detected in beach-dune systems, but their influence on resident organisms has not been explored yet. Native plants are fundamental components of coastal dunes, and these ecologically/economically important systems are currently among the most threatened globally. Thus, understanding whether UVFs may act as threats to dune plants is crucial. This field study evaluated and compared the effects of titanium dioxide nanoparticles (nTiO2), one of the inorganic UVFs most commonly added to sunscreens, and those of a commercial sunscreen product containing it (SS-nTiO2) on the performance of adult dune plants of a native (Thinopyrum junceum) and a non-native invasive species (Carpobrotus sp. pl.) and their competitive interactions at environmentally realistic concentrations. The effects of nTiO2, SS-nTiO2 and of a sunscreen product containing just organic UVFs (SS-OF) on early life stages of T. junceum were also examined. Ti bulk content in sand and plants at the study site ranged from 970 to 1069 mg kg-1 and from 2 to 7.9 mg kg-1, respectively. Thinopyrum junceum adult plants periodically exposed during the summer season to seawater contaminated by SS-nTiO2 produced less biomass than un-exposed plants and nTiO2 exposed plants. nTiO2 and SS-nTiO2 reduced the capacity of T. junceum to control the spread of Carpobrotus. Both SS-nTiO2 and SS-OF reduced seedling emergence in T. junceum whereas nTiO2 did not. These results demonstrated that the periodical exposures of native dune plants to sunscreens could reduce their establishment success and growth and favor invasive plant spread potentially resulting in community structure changes. They also emphasize the need to assess the phytotoxicity not only of single UVFs but especially that of complete sunscreen products to design more eco-friendly formulations in the future.

Plastic litter in coastal sand dunes: Degradation behavior and impact on native and non-native invasive plants

Pollution associated to marine plastic litter is raising increasing concerns due to its potential harmful effects on human health, biota, and coastal ecosystems. However, limited information is available on the degradation behavior of plastics, especially biodegradable ones, in dune habitats. Moreover, the effects of plastics on dune plant growth and ability to withstand environmental stresses and invasion by non-native plants have been largely neglected. This is a particularly relevant issue since biological invasions are major threats to dune ecosystems. In this 18-month study, we examined the degradation behavior of two plastic bags, non-biodegradable (NBP) or biodegradable/compostable (BP), in the dune environment by visual observations and analytical techniques. Concomitantly, we investigated the individual and combined effects of bag type and sand burial (no burial vs. partial burial) on the performance of a native dune plant (Thinopyrum junceum) and an invasive plant (Carpobrotus sp.) and on their interaction. NBP did not show relevant degradation signs over the experimental period as expected. BP exhibited gradual surface modifications and changes in chemical functionality and were almost disintegrated after 18 months. Bags and burial reduced independently T. junceum survival and growth, and most plants died within 8 months of plastic exposure. Bags and burial did not affect Carpobrotus survival. However, burial decreased Carpobrotus growth while NBP increased it. Both plastics increased Carpobrotus competitive ability, and no T. junceum plants survived to co-occurrent Carpobrotus, BP, and burial. These findings indicate that removing all littered plastics from beach-dune systems not only is critical to reduce plastic pollution but also to prevent further spread of invasive species in coastal dunes.

Impacts of the Invasive Alien Carpobrotus spp. on Coastal Habitats on a Mediterranean Island (Giglio Island, Central Italy)

Carpobrotus acinaciformis and C. edulis are well-known invasive alien plants native to South Africa, whose detrimental effects on native communities are widely documented in the Mediterranean basin and thus largely managed in coastal ecosystems. Most of the literature on these species focuses on their impacts on habitats of sandy coastal dunes, while the effects of Carpobrotus spp. invasion on other habitats such as rocky cliffs and coastal scrubs and garrigues are almost neglected. We present a study case conducted on a small Mediterranean island where Carpobrotus spp. invaded three different natural habitats listed within the Habitat Directive 92/43/CEE (Natura 2000 codes 1240, 1430, and 5320). We surveyed the presence and abundance of native species and Carpobrotus spp. on 44 permanent square plots of 4 m² in invaded and uninvaded areas in each of the three habitats. We found impacts on plant alpha diversity (intended as the species diversity within each sampled plot) in all the habitats investigated in terms of a decrease in species richness, Shannon index, and abundance. Invaded communities also showed a severe change in species composition with a strong homogenization of the floras of the three habitats. Finally, the negative effect of invasion emerged even through the analyses of beta diversity (expressing the species diversity among sampled plots of the same habitat type), with Carpobrotus spp. replacing a large set of native species.

Advancing biological invasion hypothesis testing using functional diversity indices

Pioneering investigations on the effects of introduced populations on community structure, ecosystem functioning and services have focused on the effects of invaders on taxonomic diversity. However, taxonomic-based diversity metrics overlook the heterogeneity of species roles within and among communities. As the homogenizing effects of biological invasions on community and ecosystem processes can be subtle, they may require the use of functional diversity indices to be properly evidenced. Starting from the listing of major functional diversity indices, alongside the presentation of their strengths and limitations, we focus on studies pertaining to the effects of invasive species on native communities and recipient ecosystems using functional diversity indices. By doing so, we reveal that functional diversity of the recipient community may strongly vary at the onset of the invasion process, while it stabilizes at intermediate and high levels of invasion. As functional changes occurring during the lag phase of an invasion have been poorly investigated, we show that it is still unknown whether there are consistent changes in functional diversity metrics that could indicate the end of the lag phase. Thus, we recommend providing information on the invasion stage under consideration when computing functional diversity metrics. For the existing literature, it is also surprising that very few studies explored the functional difference between organisms from the recipient communities and invaders of the same trophic levels, or assessed the effects of non-native organism establishment into a non-analogue versus an analogue community. By providing valuable tools for obtaining in-depth diagnostics of community structure and functioning, functional diversity indices can be applied for timely implementation of restoration plans and improved conservation strategies. To conclude, our work provides a first synthetic guide for their use in hypothesis testing in invasion biology.

Nature-based coagulants for drinking water treatment: An ecotoxicological overview

The intensive human activities extensively contaminated water sources making its treatment a problem of paramount importance, especially with the increasing of global population and water scarcity. The application of natural coagulants has become a promising and environmentally friendly alternative to conventional ones. This study was aimed at evaluating the efficiency of four plant extracts namely Agave americana, Carpobrotus acinaciformis, Austrocylindropuntia subulate, and Senicio anteuphorbium as natural coagulants to remove Microcystis aeruginosa cyanobacterium from water. The effects of pH (4, 5, 6, 7, 8 9, and 10) and coagulant dose (5, 10, 15, 20, 25, and 30 mg/L) on the coagulation efficiency were investigated. Results showed that plant-based extracts exhibited high coagulant abilities significantly contributing to the removal of M. aeruginosa cells up to 80% on a case-by-case basis. The ecotoxicity (Daphnia magna, Aliivibrio fischeri, Raphidocelis subcapitata, and Sorghum saccharatum) was absent or presented very slight acute toxicity up to 12.5 mg/L being S. anteuphorbium the least toxic. PRACTITIONER POINTS: Nature-based plant extracts showed removal rates up to 80%. Lower pH and A. subulate and S. anteuphorbium were the most efficient coagulants Toxicity effects were plant extracts-based and dose function. A. subulate and S. anteuphorbium were the least toxic extracts.

Antigonon leptopus invasion is associated with plant community disassembly in a Caribbean island ecosystem

Invasions by non-native plant species are widely recognized as a major driver of biodiversity loss. Globally, (sub-)tropical islands form important components of biodiversity hotspots, while being particularly susceptible to invasions by plants in general and vines in particular. We studied the impact of the invasive vine A. leptopus on the diversity and structure of recipient plant communities on the northern Caribbean island St. Eustatius. We used a paired-plot design to study differences in species richness, evenness and community structure under A. leptopus-invaded and uninvaded conditions. Community structure was studied through species co-occurrence patterns. We found that in plots invaded by A. leptopus, species richness was 40–50% lower, and these plots also exhibited lower evenness. The magnitude of these negative impacts increased with increasing cover of A. leptopus. Invaded plots also showed higher degrees of homogeneity in species composition. Species co-occurrence patterns indicated that plant communities in uninvaded plots were characterized by segregation, whereas recipient plant communities in invaded plots exhibited random co-occurrence patterns. These observations suggest that invasion of A. leptopus is not only associated with reduced species richness and evenness of recipient communities in invaded sites, but also with a community disassembly process that may reduce diversity between sites. Given that A. leptopus is a successful invader of (sub-)tropical islands around the globe, these impacts on plant community structure highlight that this invasive species could be a particular conservation concern for these systems.

Effects of a Dominant Species on the Functional Diversity of Coexisting Species in Temperate Deciduous Understorey

The herb layer plays a significant role in maintaining forest functions, and its community composition is determined by various abiotic factors and biotic interactions. This study attempted to investigate the interspecific plant–plant biotic interactions using a functional traits approach. Specifically, the effects of a dominant species coverage on the functional diversity of coexisting species in the temperate forest understory were studied. Species coverage and soil moisture data were collected using a 1 m² quadrat couplet (2 × 1 m²) from six sites alongside a 20 m linear transect encompassing a cover gradient of Allium ursinum in southwest Hungary. Major plant functional dimensions i.e., aboveground, and clonal functional traits were considered. Linear and nonlinear mixed models to quantify the effects of biotic interaction on the functional diversity of every single trait and multiple traits were employed. Both aboveground traits and clonal traits of persistent clonal growth organs responded positively to the A. ursinum L., cover gradient. The coexistence of understory species in the presence of a monodominant species seems to be mainly influenced by aboveground traits as compared to the clonal traits suggesting, a role of niche differentiation. The consistent impact of A. ursinum coverage on coexisting species dynamics highlights a need for similar in-depth studies in various forest settings.

Unmanned Aerial Vehicle (UAV)-Based Mapping of Acacia saligna Invasion in the Mediterranean Coast

Remote Sensing (RS) is a useful tool for detecting and mapping Invasive Alien Plants (IAPs). IAPs mapping on dynamic and heterogeneous landscapes, using satellite RS data, is not always feasible. Unmanned aerial vehicles (UAV) with ultra-high spatial resolution data represent a promising tool for IAPs detection and mapping. This work develops an operational workflow for detecting and mapping Acacia saligna invasion along Mediterranean coastal dunes. In particular, it explores and tests the potential of RGB (Red, Green, Blue) and multispectral (Green, Red, Red Edge, Near Infra—Red) UAV images collected in pre-flowering and flowering phenological stages for detecting and mapping A. saligna. After ortho—mosaics generation, we derived from RGB images the DSM (Digital Surface Model) and HIS (Hue, Intensity, Saturation) variables, and we calculated the NDVI (Normalized Difference Vegetation Index). For classifying images of the two phenological stages we built a set of raster stacks which include different combination of variables. For image classification, we used the Geographic Object-Based Image Analysis techniques (GEOBIA) in combination with Random Forest (RF) classifier. All classifications derived from RS information (collected on pre-flowering and flowering stages and using different combinations of variables) produced A. saligna maps with acceptable accuracy values, with higher performances on classification derived from flowering period images, especially using DSM + HIS combination. The adopted approach resulted an efficient method for mapping and early detection of IAPs, also in complex environments offering a sound support to the prioritization of conservation and management actions claimed by the EU IAS Regulation 1143/2014.

Geographic patterns of seed trait variation in an invasive species: how much can close populations differ?

Seeds play a major role in plant species persistence and expansion, and therefore they are essential when modeling species dynamics. However, homogeneity in seed traits is generally assumed, underestimating intraspecific trait variability across the geographic space, which might bias species success models. The aim of this study was to evaluate the existence and consequences of interpopulation variability in seed traits of the invasive species Carpobrotus edulis at different geographical scales. We measured seed production, morphology, vigour and longevity of nine populations of C. edulis along the Catalan coast (NE Spain) from three differentiated zones with a human presence gradient. Geographic distances between populations were contrasted against individual and multivariate trait distances to explore trait variation along the territory, evaluating the role of bioclimatic variables and human density of the different zones. The analysis revealed high interpopulation variability that was not explained by geographic distance, as regardless of the little distance between some populations (< 0.5 km), significant differences were found in several seed traits. Seed production, germination, and persistence traits showed the strongest spatial variability up to 6000% of percent trait variability between populations, leading to differentiated C. edulis soil seed bank dynamics at small distances, which may demand differentiated strategies for a cost-effective species management. Seed trait variability was influenced by human density but also bioclimatic conditions, suggesting a potential impact of increased anthropogenic pressure and climate shifts. Geographic interpopulation trait variation should be included in ecological models and will be important for assessing species responses to environmental heterogeneity and change.

Contrasting alien effects on native diversity along biotic and abiotic gradients in an arid protected area

Alien impact on native diversity could be a function of both the relatedness of alien species to native community and resources availability. Here, we investigated whether alien plants expand or decrease the functional and phylogenetic space of native plant communities, and how this is affected by alien relatedness to natives and by resources availability. We used a trait-environment dataset of 33 alien and 130 native plants in 83 pairs of invaded and non-invaded plots, covering a gradient of soil resources (organic matter-nitrogen) in Saint-Katherine-Protectorate, Egypt. First, we compared the changes in native composition and calculated alien relatedness to natives within each pair of plots. Second, we tested the effects of resources availability and relatedness on the magnitude of alien impact (defined as a change in native diversity). We found that native composition was phylogenetically less but functionally more diverse in invaded plots compared to non-invaded ones. Moreover, in resources-rich plots, dissimilar aliens to natives significantly increased native diversity, while in resource-limited ones, similar aliens to natives declined native diversity. These results suggest that the assessment of alien impacts in arid-regions is significantly linked to resources-availability and relatedness to natives. Hence, future studies should test the generality of our findings in different environments.

Demographic analysis of an Israeli Carpobrotus population

Carpobrotus species are harmful invaders to coastal areas throughout the world, particularly in Mediterranean habitats. Demographic models are ideally suited to identify and understand population processes and stages in the life cycle of the species that could be most effectively targeted with management. However, parameterizing these models has been limited by the difficulty in accessing the cliff-side locations where its populations are typically found, as well as accurately measuring the growth and spread of individuals, which form large, dense mats. This study uses small unmanned aerial vehicles (drones) to collect demographic data and parameterize an Integral Projection Model of an Israeli Carpobrotus population. We validated our data set with ground targets of known size. Through the analysis of asymptotic growth rates and population sensitivities and elasticities, we demonstrate that the population at the study site is demographically stable, and that reducing the survival and growth of the largest individuals would have the greatest effect on reducing overall population growth rate. Our results provide a first evaluation of the demography of Carpobrotus, a species of conservation and economic concern, and provide the first structured population model of a representative of the Aizoaceae family, thus contributing to our global knowledge on plant population dynamics. In addition, we demonstrate the advantages of using drones for collecting demographic data in understudied habitats such as coastal ecosystems.

A test of native plant adaptation more than one century after introduction of the invasive Carpobrotus edulis to the NW Iberian Peninsula

Background

Although the immediate consequences of biological invasions on ecosystems and conservation have been widely studied, the long-term effects remain unclear. Invaders can either cause the extinction of native species or become integrated in the new ecosystems, thus increasing the diversity of these ecosystems and the services that they provide. The final balance of invasions will depend on how the invaders and native plants co-evolve. For a better understanding of such co-evolution, case studies that consider the changes that occur in both invasive and native species long after the introduction of the invader are especially valuable. In this work, we studied the ecological consequences of the more than one century old invasion of NW Iberia by the African plant Carpobrotus edulis. We conducted a common garden experiment to compare the reciprocal effects of competition between Carpobrotus plants from the invaded area or from the native African range and two native Iberian plant species (Artemisia crithmifolia and Helichrysum picardii) from populations exposed or unexposed to the invader.

Results

Exposure of H. picardii populations to C. edulis increased their capacity to repress the growth of Carpobrotus. The repression specifically affected the Carpobrotus from the invader populations, not those from the African native area. No effects of exposition were detected in the case of A. crithmifolia. C. edulis plants from the invader populations had higher growth than plants from the species' African area of origin.

Conclusions

We found that adaptive responses of natives to invaders can occur in the long term, but we only found evidence for adaptive responses in one of the two species studied. This might be explained by known differences between the two species in the structure of genetic variance and gene flow between subpopulations. The overall changes observed in the invader Carpobrotus are consistent with adaptation after invasion.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12862-021-01785-x.

Impact of invasive alien plants on native plant communities and Natura 2000 habitats: State of the art, gap analysis and perspectives in Italy

Invasive alien plants are a major threat to biodiversity and they contribute to the unfavourable conservation status of habitats of interest to the European Community. In order to favour implementation of European Union Regulation no. 1143/2014 on invasive alien species, the Italian Society of Vegetation Science carried out a large survey led by a task force of 49 contributors with expertise in vegetation across all the Italian administrative regions. The survey summed up the knowledge on impact mechanisms of invasive alien plants in Italy and their outcomes on plant communities and the EU habitats of Community Interest, in accordance with Directive no. 92/43/EEC. The survey covered 241 alien plant species reported as having deleterious ecological impacts. The data collected illustrate the current state of the art, highlight the main gaps in knowledge, and suggest topics to be further investigated. In particular, the survey underlined competition as being the main mechanism of ecological impact on plant communities and Natura 2000 habitats. Of the 241 species, only Ailanthus altissima was found to exert an ecological impact on plant communities and Natura 2000 habitats in all Italian regions; while a further 20 species impact up to ten out of the 20 Italian administrative regions. Our data indicate that 84 out of 132 Natura 2000 Habitats (64%) are subjected to some degree of impact by invasive alien plants. Freshwater habitats and natural and semi-natural grassland formations were impacted by the highest number of alien species, followed by coastal sand dunes and inland dunes, and forests. Although not exhaustive, this research is the first example of nationwide evaluation of the ecological impacts of invasive alien plants on plant communities and Natura 2000 Habitats.

Effect of Invasive Alien Species on the Co-Occurrence Patterns of Bryophytes and Vascular Plant Species—The Case of a Mediterranean Disturbed Sandy Coast

Cross-taxon analyses can explain patterns of interaction between taxa and their application in conservation studies can drive management actions. In a coastal sand dune system characterized by a high human pressure, we explored the co-occurrence patterns between vascular plants and bryophytes, with a focus on how the occurrence of invasive alien species (IAS) can affect those taxa and their relationships. Species congruences were evaluated at the community level considering taxonomic and functional diversities. Predictive co-correspondence analysis (Co-CA) was applied to quantify the strength of vascular plant communities in predicting bryophytes species composition. The relationship between the composition of vascular plants and bryophytes was significant, even if weak. Altitude and percentage of bare soil cover are the environmental variables exerting greater influence on the two taxa. The presence of IAS affects communities in an opposite way: for vascular plants, species richness increases with the presence of invasive alien species; for bryophytes, IAS’s presence has a low but significant negative influence, both on species richness and in terms of functional diversity. Results give elements for future studies on the effect of IAS on the bryophytes colonizing coastal sand dunes.

Drifting away. Seawater survival and stochastic transport of the invasive Carpobrotus edulis

Coastal areas are vulnerable and fluctuating habitats that include highly valuable spaces for habitat and species conservation and, at the same time, they are among the most invaded ecosystems worldwide. Occupying large areas within Mediterranean-climate coastlines, the "ecosystem engineer" Carpobrotus edulis appears as a menace for coastal biodiversity and ecosystem services. By combining the observation, current distribution, glasshouse experiment, and dispersion modeling, we aim to achieve a better understanding of the successful invasion process and potential dispersion patterns of C. edulis. We analyzed the response of plant propagules (seeds and plant fragments) to seawater immersion during increasing periods of time (up to 144 h). After 2 months of growth, plant fragments showed a total survival rate (100%) indicating high tolerance to salinity. During this time, fragment length was increased (up to 60%) and root length was higher than control in all cases. Also, immersed fragments consistently accumulated more biomass than control fragments. After two months of growth, photosynthetic parameters (F_v'/F_m', Φ_NO, and Φ_II) remained stable compared to control fragments. Physiologically, osmolyte and pigment content did not evidence significant changes regardless of immersion time. Based on the capacity of propagules to survive seawater immersion, we modeled the potential transport of C. edulis by combining an oceanic model (ROMS-AGRIF) with a particle-tracking model. Results indicated that propagules may travel variable distances maintaining physiological viability. Our model suggested that short-scale circulation would be the dominant process, however, long-scale circulation of propagules may be successfully accomplished in <6 days. Furthermore, under optimal conditions (southerly winds dominance), propagules may even travel large distances (250 km alongshore). Modeling transport processes, in combination with the dynamics of introduction and expansion, will contribute to a better understanding of the invasive mechanisms of C. edulis and, consequently, to design preventive strategies to reduce the impact of plant invasion.

Combined effects of land-use intensification and plant invasion on native communities

Land-use intensification (LUI) and biological invasions are two of the most important global change pressures driving biodiversity loss. However, their combined impacts on biological communities have been seldom explored, which may result in misleading ecological assessments or mitigation actions. Based on an extensive field survey of 445 paired invaded and control plots of coastal vegetation in SW Spain, we explored the joint effects of LUI (agricultural and urban intensification) and invasion on the taxonomic and functional richness, mean plant height and leaf area of native plants. Our survey covered five invasive species with contrasting functional similarity and competitive ability in relation to the native community. We modeled the response of native communities for the overall and invader-specific datasets, and determined if invader-native functional differences could influence the combined impacts of LUI and invasion. Overall, we found that urban intensification reduced taxonomic richness more strongly at invaded plots (synergistic interactive effects). In contrast, functional richness loss caused by urban intensification was less pronounced at invaded plots (antagonistic interactive effects). Overall models showed also that urban intensification led to reduced mean leaf area, while agriculture was linked to higher mean plant height. When exploring invader-specific models, we observed that the combined effects of agricultural and urban intensification with invasion were heterogeneous. At invaded plots, invader-native functional differences accounted for part of this variability. Our findings demonstrate the importance of considering the interactive effects of global change pressures for a better assessment and management of ecosystems.

Ecophysiological differentiation between two invasive species of Carpobrotus competing under different nutrient conditions

PREMISE

Hybridization between the South African invasive species Carpobrotus edulis and C. acinaciformis in Europe has led to the formation of highly aggressive morphotypes referred to in the scientific literature as the new large "hybrid swarm" C. aff. acinaciformis. In the present study, we aimed to determine whether the taxonomic differentiation between taxa coincides with ecophysiological differentiation. With this aim, we tested for differences between both morphotypes in functional traits related to competitive ability and resource-use efficiency. Assuming that the complex hybrid C. aff. acinaciformis is more vigorous, depends more strongly on vegetative reproduction, and invests less in sexual reproduction than C. edulis, we predicted that the hybrid would show higher competitive ability and better physiological performance compared with the species.

METHODS

We used a comparative ecophysiological approach to assess the extent to which two Carpobrotus morphotypes coexisting in northwestern Spain differ in physiological, reproductive, and growth traits when competing under different soil nutrients in controlled greenhouse conditions.

RESULTS

C. aff. acinaciformis had a greater relative growth rate and water-use and photochemical efficiencies compared to C. edulis. However, C. edulis appeared to be more responsive to incremental change in soil nutrients than C. aff. acinaciformis. They also differed in the amount of resources invested in reproduction.

CONCLUSIONS

The study findings demonstrate that the taxonomic differentiation between taxa corresponds to ecophysiological differentiation, warranting a detailed examination of all existing trades-offs to predict the long-term outcomes of the interaction between these taxa.