Beneficiary Species Research Articles

Species diversity promotes facilitation under stressful conditions

Climate change is expected to lead to a drier world, with more frequent and severe droughts, constituting a growing threat to biodiversity, especially in drylands. Positive plant−plant interactions, such as nurse plants facilitating beneficiary communities in their understorey, could mitigate such climate‐induced stress. However, testing the real‐world relevance of nurse facilitation under drought requires accounting for interactions within the diverse beneficiary communities, which may reduce, or amplify the buffering effect of a nurse. Here, we investigated when and how the interactions among nurse plants and beneficiary community members buffered drought effects in a Mediterranean semiarid abandoned cropland. We transplanted sapling beneficiary communities of either one or three species either under a nurse or in open microsites for different soil moisture levels through watering. Net facilitative effects on survival and biomass were only observed when beneficiary communities were species‐diverse and under drought (without watering), meaning that under these conditions, facilitation provided by the nurse had larger positive effects than the negative effects stemming from competition with the nurse and among beneficiary species. Nurses appear to be generating these increases in survival and biomass in drought conditions via two mechanisms commonly associated with watering in open sites: they generate complementarity among the beneficiaries and shift traits to lower stress profiles. Contrasting with watering, which was found to enhance competitive hierarchy, our study shows that nurses appear to alter species dominance, favouring the less competitive species. Our results highlight three mechanisms (complementarity, competitive dominance, and trait plasticity) by which nurse species could mitigate the loss of biodiversity and biomass production due to water stress. Maintaining and supporting nurse species is thus a potentially pivotal approach in the face of projected increase in drought conditions for many drylands across the world.Keywords: biodiversity, dryland, ecosystem functioning, facilitation, functional traits, plant–plant interactions

Ecological and Public Advantages of a Dual Flagship Strategy: Giant Panda and Snow Leopard

Flagship species’ conservation strategies hold significant prominence in biodiversity preservation. The giant panda, a globally recognized species, has drawn attention to its benefits and constraints as a flagship species. This study aimed to assess the potential benefits of a dual flagship strategy using both the giant panda and snow leopard, compared to an approach solely using the giant panda. We identified the number of potential beneficiary species based on their habitat overlap with the giant panda and snow leopard in Sichuan and Gansu, China. Subsequently, we examined public preferences for these two flagships and their influencing factors through questionnaire surveys within and outside China. The dual flagship strategy covered the habitats of more species and amplified existing protection for those species already benefiting from giant panda conservation efforts. The giant panda was commonly perceived as “Adorable”, “Innocent”, and “Rare”, while perceptions of the snow leopard leaned towards “Mighty”, “Mysterious”, and “Rare”. Though the giant panda is widely favored, the survey indicates a notable preference for snow leopards among a proportion of respondents. The dual flagship strategy offers expanded wildlife habitat coverage and benefits a broader range of species. Moreover, the combined appeal of the snow leopard and giant panda, each possessing unique charm and symbolism, holds the potential to garner broader societal interest and support. This study may serve as a reference for policy decisions in the Giant Panda National Park and other similar protected areas, optimizing conservation management and outreach initiatives for flagship species strategies. It may also benefit conservation strategies centered on other flagship species.

Homogeneous microenvironmental conditions under nurses promote facilitation

Abstract Biotic interactions are highly affected by species traits and micro‐environmental variability. Research on facilitation has primarily focused on how nurse species alleviate abiotic stress for beneficiary species, while the impact of the micro‐environmental variability generated by nurse plants in shaping facilitation outcomes is poorly understood. This study has two objectives: (i) To evaluate which traits define beneficiary species and (ii) to evaluate whether nurse and non‐nurse species differ in their ability to reduce abiotic stress and its variability under their canopy. We sampled recruits in two arid and stressful environments to assess (i) which species accumulate more juveniles beneath their canopy controlling for their coverage (nurse vs. non‐nurse species) and (ii) which species benefited from facilitation by determining whether they tend to recruit more beneath other species or on the bare ground (beneficiary/non‐beneficiary). First, we compared how nurse and non‐nurse species modify the physical and chemical microenvironments underneath their canopy, both in terms of magnitude and variation. Second, we compared root growth, water retention and nutrient accumulation in juvenile plants of beneficiary and non‐beneficiary species. We found that facilitation is enhanced by species that provide a more homogeneous microenvironment rather than an intense reduction of microenvironmental stress under their canopy. In addition, the juveniles of beneficiary species invest more in root development, accumulate Ca and S in their shoot tissues, and show a higher water content than non‐beneficiary species. Our findings indicate that the homogeneity of microenvironments plays a crucial role in facilitative interactions, and the juveniles of beneficiary species show a less conservative strategy, investing more in resource acquisition than juveniles of non‐beneficiary species. Read the free Plain Language Summary for this article on the Journal blog.

Facilitation of benthic assemblages by Bluehead Chubs: Testing the stress‐gradient hypothesis in streams

AbstractEcosystem engineers facilitate beneficiary species by ameliorating physical habitat. The stress‐gradient hypothesis (SGH) predicts the importance of facilitation in communities should increase with physical stress but has rarely been tested in freshwater. Bluehead Chubs (Nocomis leptocephalus) build gravel nests for spawning, which can reduce negative effects of sedimentation for lithophilic species including invertebrates and other taxa. Our goal was to test the SGH using chubs and benthic assemblages as a model system. We surveyed assemblages in chub nests, paired unmodified substrate and reach‐wide samples in 10 Piedmont streams in South Carolina, USA, placed across a gradient of sedimentation. Based on the SGH, we predicted benthic assemblage diversity in chub nests would show no relationship to increasing embeddedness but that diversity in unmodified substrate should decrease with embeddedness. We found that taxa counts, richness and Shannon diversity were higher in chub nests than unmodified substrate but were lower than reach‐wide samples. Canonical correspondence analyses indicated benthic assemblages differed between nests and unmodified substrate, but assemblages in both microhabitats were nested subsets of the more diverse reach‐wide assemblage. Contrary to our hypotheses, diversity in both microhabitats decreased significantly with substrate embeddedness but was consistently higher in nests. While substrate modification by chubs clearly facilitated benthic diversity at the microhabitat scale, it was not sufficient to overcome the worst effects of sedimentation. This study provides mixed evidence for SGH in streams; chub nesting appears to be facilitative at the microhabitat scale but may not have reach‐wide effects on benthic assemblages in this system.

Assessing the accuracy of paired and random sampling for quantifying plant–plant interactions in natural communities

AbstractPlant interactions in extreme environments are often inferred from spatial associations and quantified by means of paired sampling. Yet, this method might be confounded by habitat‐sharing effects. Here, we address whether paired and random sampling methods provide similar results at varying levels of environmental heterogeneity. We quantified spatial associations with the two methods at three sites that encompass different micro‐environmental heterogeneity and stress levels: Mediterranean environments in Canary Islands, Spain, and Sardinia, Italy, and a cold alpine environment in Hokkaido, Japan. Then, we simulated plant communities with different levels of species micro‐habitat preferences, environmental heterogeneity, and stress levels. We found that differences in species associations between paired and random sampling were indistinguishable from zero in a homogeneous space. When simulating codispersion over a decreasing abundance gradient, both sampling methods correctly identified facilitation and distinguished it from codispersion. Yet, the pairwise method provided higher facilitation estimates than the random one. At each site, there were strong differences between beneficiary species in their spatial association with nurse species, and associations became more positive with increasing stress in Spain. Most importantly, there were no differences in results yielded by the two methods at any of the different stress levels at the Spanish and Japanese sites. At the Italian site, although micro‐environmental heterogeneity was low, we found weakly significant differences between methods that were unlikely due to habitat‐sharing effects. Thus, the paired sampling method can provide significant insights into net and long‐term effects of plant interactions in spatially conspicuous environments.

Are nurse plants useful for facilitating the reintroduction of mid- and late successional tree species in tropical montane cloud forests?

Background: In Mexico, where 50 % of the original Tropical montane cloud forest (TMCF) has been lost due to human activities, the restoration of these forests is essential.
 Questions and/or hypotheses: (1) L. styraciflua favors the survival and growth of Q. germana and M. schiedeana species (2) Are there competitive effects between nurses and beneficiary species? and (3) Is the magnitude of these positive/negative interspecific interactions affected by the canopy cover of nurses?
 Studied species: Liquidambar styraciflua L. (pioneer tree), Magnolia schiedeana Schltdl. (mid-successional tree) and Quercus germana Schltdl. & Cham. (late-successional tree).
 Study site and dates: A fallow in Xilitla, state of San Luis Potosí, Mexico, between 2016 and 2018.
 Methods: Seedling of mid- and late-successional species were transplanted 0.3 m and 2 m away from the stems of pioneer tree (protected and unprotected saplings, respectively). Performance of the species were compared after two years and the effects of canopy cover of pioneer trees.
 Results: Pioneer trees facilitated the establishment probabilities of the mid-and late-successional ones. Increasing canopy cover of pioneer trees enhanced the establishment probabilities of both beneficiary species.
 Conclusions: Joint transplanting of pioneer trees with mid- and late-successional tree seedlings in their close vicinity is a strategy to favor the recovery of the ecosystem.

Can pikas hold the umbrella? Understanding the current and future umbrella potential of keystone species Pika (Ochotona spp.)

The umbrella species concept is a frequently used concept in conservation since the conservation of an umbrella species may benefit other species. Keystone species are often suggested as potential umbrella species, but the validity of this approach remains uncertain. Moreover, climate change can have a multidirectional effect on the distribution of species, in which the distribution of umbrella species can be affected differently than that of beneficiary species. The validity of applying the umbrella species concept in conservation may thus be jeopardised by climate change. This study assessed the potential of two keystone species, the plateau pika ( Ochotona curzoniae ) and the Daurian pika ( Ochotona dauurica ), to be umbrella species for 13 potentially beneficiary species under current and future environmental conditions. Of these 13 species, five currently only co-occur with the plateau pika, five only with the Daurian pika, and three with both pika species. Current and future distributions of the pika species and potentially beneficiary species were predicted using bioclimatic and land-use variables. Range overlaps, Pearson correlations, niche similarity tests and relative suitability tests were performed to assess the umbrella potential of both pika species. Our results show that at present, both pika species may be considered to be umbrella species, benefitting several co-occurring species. However, species that currently co-occur with both pika species will not benefit from conservation of either of the pikas in the future years under climate change scenarios. The plateau pika loses its potential to act as umbrella species for two of the four species which currently may benefit. We can conclude that keystone species like pikas can act as umbrella species for carefully selected potentially beneficiary species under current conditions. Due to climate change related shifts in species distributions, they may however lose their umbrella species status in the future, which should be considered when selecting species conservation strategies. • The umbrella potential of two keystone species was explored under multiple scenarios of climate change. • Predicted umbrella potential of one keystone species was stronger than the other. • Umbrella potential is not necessarily maintained under future scenarios of climate change • Choice of beneficiary species highly influences the umbrella potential of keystone species. • Integration of predicted distribution range shifts in action plans is essential.

Plant-plant interactions determine natural restoration of plant biodiversity over time, in a degraded mined land.

Restoration of degraded environments is essential to mitigate adverse impacts of human activities on ecosystems. Plant–plant interactions may provide effective means for restoring degraded arid lands, but little is understood about these impacts. In this regard, we analyzed the effects of two dominant nurse plants (i.e., Artemisia sieberi and Stipa arabica) on taxonomic, functional, and phylogenetic diversity across different ages of land abandonment (i.e., control, recent, and old ages) in a limestone mine site in Iran. In addition, we considered two spatial scales: i) the plot scale (i.e., under 1m2 plots) and ii) the vegetation‐patch scale (i.e., under the canopies of nurse plants), to assess nurse plant effects, land abandonment ages, and their relative importance on biodiversity facets by performing Kruskal–Wallis H test and variation partitioning analysis. Our results indicated an increase in taxonomic, functional, and phylogenetic diversity at the plot scale, when considering the presence of nurse plants under old ages of land abandonment. Such significant differences were consistent with the positive effects of Artemisia patches on taxonomic diversity and Stipa patches on functional and phylogenetic diversity. In addition, we found a larger contribution from nurse plants than land abandonment age on biodiversity variation at both spatial scales studied. Therefore, these results indicate the importance of plant–plant interactions in restoring vegetation, with their effects on the presence of beneficiary species and their functional and phylogenetic relatedness depending on the nurse life forms under the stress‐gradient hypothesis.

Metapopulation‐level associations in positively interacting stream fishes

Positive biotic interactions are recognized as important factors determining species distributions. Although effects of positive interactions have often been observed at local scales, much less is known about consequences at larger spatial scales. Here, we study nest associations of stream fishes – widespread reproductive facilitation between host (nest‐builder) and beneficiary (nest associate) species in North America – as a model system to examine the role of positive interactions in determining the metapopulation‐level relationship between host and beneficiary species. Using regional data of fish distribution in the Midwestern US, we found that watershed‐level occupancy of host species (i.e. metapopulation occupancy) remarkably increased that of nest associates. Our results illustrated that the effects of positive biotic interactions at the metapopulation level were comparable or even stronger than environmental drivers, i.e. factors that have been studied most extensively in metapopulation studies. Further, our model supported the hypothesis that the metapopulation‐level relationship between hosts and nest associates was mediated by a gradient of environmental conditions: strong associations occurred under stressful habitats. This study provides insightful evidence that positive biotic interactions have larger scale consequences for distributions of organisms than previously thought. Successful biodiversity conservation may need a broader framework that appreciates the role of positive biotic interactions at larger spatial scales.

Plant–plant interactions determine taxonomic, functional and phylogenetic diversity in severe ecosystems

AbstractAimPlant–plant interactions are an important factor in structuring plant biodiversity. However, most studies on the impacts of plant–plant interactions on biodiversity focus on species richness and to a lesser extent on other facets of diversity. When other facets of biodiversity are considered, studies often include a limited set of environmental conditions. We aimed to quantify the impacts of nurse plants on taxonomic, functional and phylogenetic facets of plant biodiversity and how these impacts change across environmental gradients.LocationWe report data on 28 alpine and 50 dryland sites, established in 11 countries.Time period1998–2019.Major taxa studiedVascular plants.MethodsWe analysed plant–plant interactions using co‐occurrence analyses and obtained information on the functional traits and phylogenetic relationships of the beneficiary species. We calculated the change in taxonomic, functional and phylogenetic diversity caused by the presence of nurse plants and environmental conditions.ResultsNurse plants enhanced taxonomic and phylogenetic diversity in alpine communities and enhanced functional and phylogenetic diversity in dryland communities. However, they had a positive effect on functional and taxonomic diversity only in moderate environments in alpine and dryland communities, respectively. The effects of nurse plants were larger in drylands for functional and phylogenetic diversity and in alpine communities for taxonomic diversity. Interestingly, nurse plants induced nonlinear changes in all facets of biodiversity across environmental gradients, whereas biodiversity tended to increase linearly toward more benign conditions in open interspaces.Main conclusionsFacilitation is important in alpine environments to maximize taxonomic diversity and has a more consistent positive effect on the functional and phylogenetic diversity of drylands. In general, effects of facilitation on biodiversity peak in moderate environmental conditions, which suggests that nurse plants can protect biodiversity from impacts of climate change mostly in those places currently under low environmental stress and that will be likely to experience moderate stress levels in the future.

Seabird population changes following mammal eradication at oceanic Saint-Paul Island, Indian Ocean

The eradication of invasive mammals on islands is important for protecting seabird populations and insular ecosystems. However, the impacts of such eradications are insufficiently known because monitoring of potentially beneficiary species is often sporadic and limited. We performed a survey of all seabird species on Saint-Paul Island, southern Indian Ocean, 20 years after successful eradication of invasive black rat (Rattus rattus) and European rabbit (Oryctolagus cuniculus). Using complementary sampling designs including adaptive cluster sampling, stratified random sampling and entire sampling, we estimated population changes and colonization by new seabird species. A total of 13 seabird species were found breeding on Saint-Paul post-eradication compared to six before the eradication. Among the seven species that colonized the island, five (MacGillivray’s prion Pachyptila macgillivrayi, fairy prion P. turtur, white-bellied storm petrel Fregetta grallaria, Antarctic tern Sterna vittata, sooty tern Onychoprion fuscatus) had relictual populations breeding on a nearby islet, and one (brown skua Catharacta antarctica) was a new breeding species. We also found breeding subantarctic little shearwaters Puffinus elegans. For species that were breeding on the Saint Paul pre-eradication, the mean annual population growth rate was 1.030 ± 0.093 (SE). Species known to be vulnerable to rat predation (prions, great-winged petrel Pterodroma macroptera, flesh-footed shearwater Puffinus carneipes, subantarctic little shearwater, white-bellied storm petrel, Antarctic tern) had the highest population growth rates. Two decades after the eradication of invasive mammals on a remote oceanic island, seabird populations were high beneficiaries. These findings further highlight the importance of invasive mammal eradication on islands as a conservation tool. Results are encouraging for the planned eradication of invasive mammals from nearby Amsterdam Island, and suggest this will mainly benefit terns and small burrowing petrels.

Co-ordination between xylem anatomy, plant architecture and leaf functional traits in response to abiotic and biotic drivers in a nurse cushion plant.

Plants in dry Mediterranean mountains experience a double climatic stress: at low elevations, high temperatures coincide with water shortage during summer, while at high elevations temperature decreases and water availability increases. Cushion plants often act as nurses by improving the microclimate underneath their canopies, hosting beneficiary species that may reciprocally modify their benefactors' microenvironment. We assess how the nurse cushion plant Arenaria tetraquetra subsp. amabilis adjusts its hydraulic system to face these complex abiotic and biotic constraints. We evaluated intra-specific variation and co-ordination of stem xylem anatomy, leaf functional traits and plant architecture in response to elevation, aspect and the presence of beneficiary species in four A. tetraquetra subsp. amabilis populations in the Sierra Nevada mountains, southern Spain. Xylem anatomical and plant architectural traits were the most responsive to environmental conditions, showing the highest mutual co-ordination. Cushions were more compact and had smaller, more isolated conductive vessels in the southern than in the northern aspect, which allow minimization of the negative impacts of more intense drought. Only vessel size, leaf mass per area and terminal branch length varied with elevation. Nurse cushions co-ordinated plant architecture and xylem traits, having higher canopy compactness, fewer leaves per branch and fewer, more isolated vessels than non-nurse cushions, which reflects the negative effects of beneficiary plants on nurse water status. In non-nurse cushions, plant architecture co-ordinated with leaf traits instead. The interacting effects of aspect and elevation on xylem traits showed that stress due to frost at high elevation constrained xylem anatomy in the north, whereas stress due to drought had a parallel effect in the south. Trait co-ordination was weaker under more demanding environmental conditions, which agrees with the hypothesis that trait independence allows plants to better optimize different functions, probably entailing higher adjustment potential against future environmental changes.

Interspecific facilitation mediates the outcome of intraspecific interactions across an elevational gradient.

Where interspecific facilitation favors the establishment of high densities of a beneficiary species, strong intraspecific competition may subsequently impede beneficiary performance. Consequently, the negative influence of intraspecific competition between beneficiary individuals could potentially outweigh the positive influence of interspecific facilitation when, for example, higher densities of a beneficiary are negated by the negative effect of crowding on beneficiary reproduction. The aim of this study was, therefore, to examine the impact of an interspecific interaction on the outcome of intraspecific interactions within the context of plant-plant facilitation. We used the cushion-forming Azorella selago and a commonly co-occurring dominant perennial grass species, Agrostis magellanica, on sub-Antarctic Marion Island as a model system. We assessed the impact of an interspecific interaction (between A. selago and A. magellanica) on the outcome of intraspecific interactions (between A. magellanica individuals), by testing if the impact of A. magellanica density on A. magellanica performance is mediated by its interaction with A. selago. We observed evidence for competition among A. magellanica conspecifics, with a decreasing proportion of A. magellanica individuals being reproductive under higher conspecific density. This negative intraspecific effect was greater on A. selago than on the adjacent substrate, suggesting that the facilitative effect of A. selago changes the intensity of intraspecific interactions between A. magellanica individuals. However, experimentally reducing A. magellanica density did not affect the species' performance. We also observed that the effect of A. selago on A. magellanica was positive, and despite the negative effect of intraspecific density on the proportion of reproductive A. magellanica individuals, the net reproductive effort of A. magellanica (i.e., the density of reproductive individuals) was significantly greater on A. selago than on the adjacent substrate. These results highlight that, in abiotically severe environments, the positive effects of interspecific facilitation by a benefactor species may outweigh the negative effects of intraspecific competition among beneficiaries. More broadly, these results suggest that both positive inter- and intraspecific biotic interactions may be key to consider when examining spatial and temporal variation in species' performance.

The effects of growth form on the impact of companion planting of nectar-producing plant species with Sedum album for extensive green roofs

Pollinators provide crucial urban ecosystem services. Introducing nectar-producing species on green roofs is one method to support pollinator populations. However, novel cultivation methods may be required to improve plant health with minimal irrigation on extensive green roofs, which are severely restricted in soil thickness. Although companion planting with CAM plants such as Sedum has been reported to improve the performance of neighboring plants, the growth form of the beneficiary species seems important in determining the effectiveness of the technique. In this study, eleven species of nectar-producing plants were classified into two growth forms: carpet species (Phyla canescens, Trifolium repens, Thymus serpyllum and Thymus longicaulis), non-carpet species (Calamintha nepeta, Lavandula officinalis, Lavandula stoechas, Melissa officinalis, Mimosa pudica, Rosmarinus officinalis ‘Erectus’, Rosmarinus officinalis ‘Prostratus’), and were planted together with Sedum album in a greenhouse or on a rooftop space. There were no net positive effects in the impacts of companion planting with S. album on plant biomass both in carpet and non-carpet species. However, companion planting with S. album had net positive effects on leaf health in L. stoechas, M. officinalis, M. pudica, and R. officinalis ‘Prostratus’, classified as non-carpet species. In contrast, there were no positive effects on carpet species, planted together with S. album. These results suggest that complementary growth forms could be one of the factors to determine effective planting combinations to improve plant health conditions on extensive green roofs. Additionally, the increase in soil water content by suppressing evapotranspiration when water is limiting can be effective in improving leaf health conditions of neighbors in companion planting with S. album. While past studies have shown positive benefits of companion planting with CAM species, this experiment suggests the possibility that not all growth forms may benefit from facilitation by Sedum.

Testing the role of functional trait expression in plant–plant facilitation

AbstractPositive biotic interactions between plant species may strongly affect species and community‐level patterns, but the processes through which benefactor species alter the performance of interacting species (via, e.g. beneficial mechanisms like resource provisioning) are still inadequately understood. One poorly explored potential explanation is that plant–plant facilitation could occur through the impact of benefactor species on the functional trait expression of beneficiary species. Indeed, plant species that affect local conditions can modify functional trait expression of interacting species, thereby improving their performance and resulting in a facilitative interaction. However, the response of intraspecific trait variation to biotically driven microhabitat modification, and its role in determining the outcome of plant–plant interactions, has rarely been explored.Here, we test whether growing with benefactor species affects the expression of functional traits of eight species, encompassing different plant growth forms, in two contrasting study systems. This is achieved using a paired sampling approach to compare values of seven functional traits of conspecific individuals growing within and adjacent to cushion plants (i.e. benefactor species which are known to strongly alter microhabitat conditions and to have positive effects on some of the focal species). In addition, we test whether the effect of biotic interactions on functional trait expression changes along elevational gradients, as the outcome of biotic interactions is expected to vary with elevation.Contrary to predictions, in both systems, intraspecific trait variation was not well explained by the biotic interaction with the cushion plant species or the variation in abiotic conditions associated with elevational gradients. Where biotic interactions did affect functional trait expression and bivariate trait relationships, traits responded variably between species, suggesting that context specificity may be a constraint to predicting how intraspecific trait variation responds to plant–plant interactions, adding to the growing body of literature that challenges the generality and predictability of the drivers of intraspecific trait variation.This research, therefore, suggests that benefactor species’ facilitative process is likely not through an impact on intraspecific trait expression, and that instead other processes may be more important for translating beneficial microhabitat modification or increased resource availability by benefactor species into positive impacts on beneficiary species.A freePlain Language Summarycan be found within the Supporting Information of this article.

Constructed pine log piles facilitate plant establishment in mining drylands

Ecological facilitation, though accepted as a main mechanism of plant community assembly, is just starting to be utilized in restoration programmes. Constructing nurse objects that mimic the effect of natural nurse species can be an option to trigger plant nucleation processes in disturbed stressful ecosystems.We hypothesized that arranged log piles might imitate plant facilitation by alleviating abiotic stress and expanding the regeneration niche of beneficiary species, eventually promoting plant establishment, fitness and diversity. With this aim, within a pilot restoration programme in abandoned mining structures in SE Spain where climatic and edaphic stresses concur, we constructed 133 pine log piles from natural wastes generated by local silvicultural activities. We monitored 51 of them plus their adjacent open areas for 15 months, measuring soil temperature, radiation and humidity. We recorded natural seedling establishment, plant nutritional status and heavy metal accumulation. We further performed a seed sowing experiment to investigate how log piles affect plant taxonomic and functional diversity based on 11 establishment and phytostabilization traits.Pine log piles significantly softened microclimatic conditions and accelerated plant establishment in unfertile and metal-polluted mining substrates, simultaneously capturing water, providing shade and pine seeds. Plant communities that naturally established beneath the piles were 15 times denser and five times taxonomically more diverse than those in open areas, despite being skewed towards pine recruitment. Experimental communities sown under log piles were also 1.4 times functionally more diverse, as theory predicts for relaxed abiotic conditions. Log piles improved seedling nutritional status, in terms of P and K content, at the cost of increased metal accumulation.At the landscape scale, nurse objects triggered plant establishment promoting taxonomic and functional diversity in extremely stressful environments. This study exemplifies how soft restoration tools can be based on mechanisms that are widely accepted in the ecological theory.

Warming enhances growth but does not affect plant interactions in an alpine cushion species

Climate change is more pronounced in high-elevation habitats than elsewhere, potentially causing disruptions in plant community structure and dynamics through changes in plant interactions. We tested the effect of warming and rainfall manipulations on growth and gas exchange of a cushion plant species, Arenaria tetraquetra, in the Sierra Nevada Mountains in SE Spain and assessed its consequences for plant interactions. Arenaria tetraquetra is a facilitator that often hosts a variety of beneficiary species within its canopy. Warming and drought could alter cushion growth patterns and canopy compaction, which in turn affect facilitation. We increased temperature using acrylic open-top chambers (OTC) and increased or decreased water availability with rainfall collectors. Our rainfall treatments did not have significant effects on cushion growth or facilitation. Three years of warming enhanced cushion photosynthesis and respiration, leading to larger cushions with thinner leaves, but did not change other cushion traits nor alter its facilitation effects. Some traits, however, readily responded to inter-annual climate variability. Global warming will change cushion plant physiology, as higher temperatures at times increase plant respiration above the level of carbon fixation. However, we did not find changes in interaction between benefactor and beneficiary species, perhaps due to the short-term nature of our experiment. Recorded physiological and morphological changes might be, however, signs of more pronounced, long-term consequences of warming on plant survival and community composition.

Developing a Modified Umbrella Index for Conservation of Macroinvertebrate Diversity in Taizi River Basin, China

Conservation strategies for a reliable set of umbrella species should benefit many co-occurring species and will improve conservation efficiency. The umbrella index (UI) is increasingly applied for umbrella species selection in different ecosystems. We developed a modified river UI to select potential macroinvertebrate umbrella species with a combination of 69 sites in the Taizi River Basin of northeast China. Calculation of UI and comparison of biotic indices between sites of presence and absence of umbrella species were performed to make the final umbrella species list. The umbrella scheme, based on the proportion and composition of sites supporting the confirmed umbrella species, was introduced to illustrate the conservation effectiveness. A total of eight umbrella species were obtained and all of them were aquatic insects, such as caddisfly and mayfly larva. Umbrella schemes supporting the top umbrella species, hosted the majority of co-occurring species and only 7% of beneficiary species were missed by the umbrella schemes of 70% effort. The positive relationship between abundance of co-occurring species and umbrella species, validated the ability of umbrella species to confer protection and co-existence of co-occurring species, and thus indicated the effectiveness of umbrella species conservation. Co-occurring species were located close to umbrella species in ordinations, suggesting they respond to similar environmental variables characterized by high flow velocity, dissolved oxygen and pebble-covered substrate. On account of good performance of umbrella schemes in our study, UI with further improving methods should be promoted for selection of umbrella species and decision for optimizing of conservation sites in the future.

Interactions between nurse plants and parasitic beneficiaries: A theoretical approach to indirect facilitation

When a nurse species facilitates the density of more than one species, strong indirect interactions can occur between the facilitated, or beneficiary, species, and these could lead to cascading interactive effects on community dynamics. In this context, negative effects of beneficiaries on the growth or reproduction of nurses are much more common than positive effects. This suggests beneficiaries frequently act as parasites of their nurses, and the consequences of this are largely unexplored. Our general aim is to analyze whether competition between parasitic beneficiaries can lead to indirect facilitation to nurse species and how this influences nurse-beneficiary systems. We explored potential outcomes of such reciprocal interactions in the general case of one facilitator and two facultative parasitic beneficiary species with different strategies for competing for space, one having a high carrying capacity but low maximum intrinsic growth rate (K-species), and the other having low carrying capacity but a higher intrinsic growth rate (r-species). These are defined in terms of the logistic equation, and reflect the abundances they can reach when growing alone. By considering a set of ordinary differential equations for the abundances of the nurse and the two parasitic beneficiaries in the mean-field approximation (where spatial correlations do not play a role), we first show analytically that coexistence of the three species is only possible when the r-species beneficiary is, at the same time, more harmful than the K-species and receives more benefit from the nurse. We then show that only the K-species can indirectly facilitate the nurse in such system. These are general, analytic results, independent of particular values of the parameters. We then explore these results using a 2-D lattice model informed by cushion plants in alpine ecosystems, and their interactions with beneficiaries with r and K strategies. Interesting spatial effects emerge in this case, such as a seeding effect: facilitation by the nurse increases beneficiary abundances also outside nurse patches. These in turn generate a negative feedback to the nurse, due to local competition for space near its edge. Spatial distribution effects are also crucial for relaxing the conditions for the survival of the r-species, allowing an r-strategist with weaker parasitic effects to indirectly facilitate the nurse through suppression of a more harmful K-species. Unexpectedly, this also has an indirect positive effect on the K species because of increased abundance of nurses. In the case of the r-species representing a ruderal invader, our lattice results would suggest that invaders have the potential to benefit both nurse and native beneficiary species via indirect facilitation. More generally, our results indicate that facilitation of more than one other species varying in competitive ability and which act as parasites on a nurse, can in turn promote indirect facilitation effects. This form of indirect facilitation has not been explicitly studied before, although it may create substantial conditionality in the outcomes of interactions among multiple species and the dynamics of nurse-beneficiary systems.

Azorella compacta: survival champions in extreme, high‐elevation environments

AbstractCushion plants are life forms with a hemispherical or mat‐like, prostrate canopy well adapted to the extreme conditions of cold regions that have appealed to scientists for their ability to cope with extreme environments in most mountains, arctic, and subantarctic regions of the world. They can buffer the effects of low temperature and drought and improve soil conditions, which makes them notable facilitator species. Living at the edge in the Atacama Desert is one such species, Azorella compacta (yareta or llareta), in the Apiaceae family that can reach much over 6 m (~20 ft) in diameter with a mat‐like shape that tends to hemispherical growth form. Azorella compacta can be found in the dry Puna system, which spreads from northern Chile and Argentina to southern Peru and western Bolivia, between 3800 and 5200 m elevation, making it one of the woody plant species occurring at highest elevations in the world. In this deserted edge of the Atacama, nutrient limitation adds to other stressors such as water scarcity and high UV radiation. A compact canopy and the fact that they are embedded in resin prevent beneficiary species from growing within the cushion and condition how senesced leaves decompose inside the canopy. They can reach 3000 yr old and have to deal with episodic disturbance and herbivory events. Plants in such environments may potentially act as microbial refuges, and it could be expected that bacterial endophytes and mycorrhizal fungi have a main role in the functioning of these survival champions.