Abstract: Both Southern Ocean and terrestrial systems contain three-dimensional biotic components that are key in shaping and defining their respective ecosystems and communities. Antarctic suspension-feeding communities, which inhabit the shelf of the Southern Ocean, resemble “Terrestrial Vegetation Forests” (TVF) or shrublands and support the concept of “Antarctic Marine Animal Forests” (AMAF). They comprise mostly sessile animals, provide microniches for an associated mobile fauna, and are fragmented and regionally mixed with other communities. On land, only high mountains and very dry regions are unsuitable for TVF, analogous to the virtual absence of AMAF from the deep sea (>1000 m). Besides fundamental differences between these systems in energy flow and other ecological drivers such as light requirements and dispersal opportunities, both “forests” experience similar disturbances, which impact ecosystem dynamics and diversity in similar ways. While land use affects and reduces terrestrial forests, climate change and fishing impacts are the most serious threats to the Southern Ocean ecosystem. Research priorities for a better understanding of “Antarctic Marine Animal Forests” demand (1) mapping biotic communities and their structural and functional diversity, especially in terms of hot and cold spots; (2) understanding ecological function, including ecosystem productivity and dynamics; (3) cross-system comparison to identify generality or uniqueness in ecosystem structure and dynamics; and (4) implication of existing and new research approaches and conservation strategies.

Abstract: Question Plant–soil feedback (PSF) has emerged as a ubiquitous phenomenon and a potentially important predictor of plant community structure and dynamics. However, the predictive power of PSF in field contexts is mixed, and ecologists do not yet understand its relative importance compared to other factors that structure communities. Further progress requires a more nuanced understanding of how PSF interacts with other biotic and abiotic factors. Environmental factors (e.g. natural enemies, moisture, light, nutrients) are known to affect plant interactions with soil and soil organisms, leading to an expectation of environmental context dependence in plant–soil feedback. Such context dependence could explain when PSF is expected to be an important driver of community dynamics, and under what conditions PSF is likely to be positive (destabilizing) vs negative (stabilizing). Methods We conducted a literature review of studies that examined PSF across biotic and abiotic gradients. Results Although few relevant studies have been conducted in this emerging research area, results to date suggest that plant–soil feedback is sensitive to biotic factors, such as above- and below-ground herbivory, and abiotic factors, such as nutrients and light. Conclusions We develop a conceptual framework to predict variation in the direction and strength of PSF depending on the biotic or abiotic drivers of feedback (e.g. pathogens, nutrients) and the environmental context (e.g. intensity of herbivory, soil fertility). We explore the utility of our predictive framework through discussion of case studies from the literature on context dependence in PSF. We also consider how different experimental approaches might yield different insights about PSF–environment interactions, and suggest key future research directions.

Abstract: There is no unified evidence base to help decision-makers understand how the multiple components of natural capital interact to deliver ecosystem services. We systematically reviewed 780 papers, recording how natural capital attributes (29 biotic attributes and 11 abiotic factors) affect the delivery of 13 ecosystem services. We develop a simple typology based on the observation that five main attribute groups influence the capacity of natural capital to provide ecosystem services, related to: A) the physical amount of vegetation cover; B) presence of suitable habitat to support species or functional groups that provide a service; C) characteristics of particular species or functional groups; D) physical and biological diversity; and E) abiotic factors that interact with the biotic factors in groups A–D. ‘Bundles’ of services can be identified that are governed by different attribute groups. Management aimed at maximising only one service often has negative impacts on other services and on biological and physical diversity. Sustainable ecosystem management should aim to maintain healthy, diverse and resilient ecosystems that can deliver a wide range of ecosystem services in the long term. This can maximise the synergies and minimise the trade-offs between ecosystem services and is also compatible with the aim of conserving biodiversity.

Abstract: Carrion is a valuable nutrient resource used by a diversity of vertebrates across the globe. However, vertebrate scavenging ecology remains an understudied area of science, especially in regards to how biotic and abiotic factors influence scavenging community composition. Here we elucidate how fundamental biotic and abiotic factors interact to modulate the efficiency and composition of vertebrate scavengers by investigating scavenging dynamics across a large gradient in carcass sizes and habitat types representative of many temperate ecosystems, as well as between two seasons reflecting differences in invertebrate activity. We found carcass size and season influenced carcass fate and persistence, as well as the richness and composition of vertebrate scavenger communities utilizing carrion resources. Species richness, which increased as carcass size increased and was higher during the cool season, had a significant effect on carcass persistence. In addition, habitat type influenced carcass detection times by vertebrates, and we observed relatively distinct scavenging communities associated with carcasses of differing sizes. This research highlights a pervasive limitation to the interpretation of results of previous studies as research failing to incorporate carcass size and habitat type could result in the over or underrepresentation of vertebrate scavengers in food web dynamics. This article is protected by copyright. All rights reserved.

Abstract: Gross ecosystem productivity (GEP) in tropical forests varies both with the environment and with biotic changes in photosynthetic infrastructure, but our understanding of the relative effects of these factors across timescales is limited. Here, we used a statistical model to partition the variability of seven years of eddy covariance-derived GEP in a central Amazon evergreen forest into two main causes: variation in environmental drivers (solar radiation, diffuse light fraction, and vapor pressure deficit) that interact with model parameters that govern photosynthesis and biotic variation in canopy photosynthetic light-use efficiency associated with changes in the parameters themselves. Our fitted model was able to explain most of the variability in GEP at hourly (R2 = 0.77) to interannual (R2 = 0.80) timescales. At hourly timescales, we found that 75% of observed GEP variability could be attributed to environmental variability. When aggregating GEP to the longer timescales (daily, monthly, and yearly), however, environmental variation explained progressively less GEP variability: At monthly timescales, it explained only 3%, much less than biotic variation in canopy photosynthetic light-use efficiency, which accounted for 63%. These results challenge modeling approaches that assume GEP is primarily controlled by the environment at both short and long timescales. Our approach distinguishing biotic from environmental variability can help to resolve debates about environmental limitations to tropical forest photosynthesis. For example, we found that biotically regulated canopy photosynthetic light-use efficiency (associated with leaf phenology) increased with sunlight during dry seasons (consistent with light but not water limitation of canopy development) but that realized GEP was nonetheless lower relative to its potential efficiency during dry than wet seasons (consistent with water limitation of photosynthesis in given assemblages of leaves). This work highlights the importance of accounting for differential regulation of GEP at different timescales and of identifying the underlying feedbacks and adaptive mechanisms.

Abstract: The only known biological sink for the greenhouse gas nitrous oxide (N2O) is its reduction to nitrogen gas (N2) by bacteria and archaea that possess the nosZ gene conferring this trait. Phylogenetic and genomic evidence indicates that N2O reducing communities can be divided into two genetically distinct groups, termed clade I and II. Differing abundance or diversity of each clade may have significant consequences for N2O emissions from soil. However, whether the two groups respond similarly to gradients of environmental or biotic factors in soils remains unclear. Here, we explore spatial patterns of nosZ clade I and II abundance, phylogenetic diversity and community structure across a 44-ha farm, and compare with edaphic factors and abundances of ammonia oxidizing and denitrifying communities, which are the main N2O producers in soil. Contrasting spatial distributions of the total abundance and phylogenetic diversity of each clade, as well as disparate associations with various edaphic and biotic factors indicated potential niche differentiation between the two clades. This is supported by the greater occurrence of significant phylogenetic clustering or overdispersion in clade I communities compared to clade II, indicating differences in the underlying mechanisms of community assembly for each group. Variance partitioning of phylogenetic community structure further showed that biotic factors, particularly the abundance of denitrifiers, played a more substantial role in explaining clade II community structure compared to that of clade I. Finally, identification of nosZ lineages driving differences in community structure and spatial distribution patterns of gene abundances suggests a shift in the genetic potential for N2O production and consumption dynamics across the farm.

Abstract: Soil is a complex ecosystem with defined microbial community signatures, modulated by the interaction between biotic and abiotic factors. Amidst biotic factors, land usage have significant impact onto the soil microbial structure and ecosystem functioning. In the current study, metagenomic approach was used to decipher effect of hospital settings on soil microbiome structure and physiological functions. Physico-chemical properties analysis revealed that key elements for maintenance of soil microflora, such as organic carbon, nitrogen, phosphorus and sulfur were relatively diminished within hospital soil, compared to garden soil. Comparative microbial diversity analysis with 97,315 SSU rRNA gene sequences generated from both the soil samples highlight relatively low microbial diversity, with an enrichment for Acidobacteria and Bacteroidetes and decreased Proteobacteria/Acidobacteria ratio. Comparative shotgun metagenome sequence analysis further revealed a shift in the physiological role of soil microbiomes with change in soil usage. Genes for carbohydrate, sulfur, potassium and nitrogen metabolism were significantly (q value <0.05) higher in the garden soil; while the genes for phage, plasmid DNA, transposon and aromatic compound metabolism were significantly enriched within hospital soil. Thus, the current study highlights a correlation between soil biochemistry and microbial ecology based on land usage.

Abstract: The 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. Climatic 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. This 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.

Abstract: In recent decades, the use of molecular techniques in rotifers has revealed the existence of many cryptic species. Although strong competition is expected among cryptic species, these species are often sympatric. Here, we present a review of sympatric cryptic rotifer species, focusing on those cases in which niche differentiation has been investigated. There are at least 42 cryptic rotifer species complexes, and species coexistence is commonly reported. Ecological differentiation among cryptic species has been detected in several complexes. However, the only available information regarding mechanisms that allow cryptic species coexistence is for several species of the Brachionus plicatilis complex: B. plicatilis, B. ibericus, B. rotundiformis and B. manjavacas. According to these studies, when species differ in body size, niche differentiation is related to abiotic and biotic factors (e.g. the differential use of resources and vulnerability to predation). In contrast, if species are almost identical in body size, their biotic niches and competitive abilities are very similar, and niche differentiation is facilitated by the differences in the species responses to fluctuating, physical environment in combination with the divergence in life-history traits related to diapause. Further studies of additional cryptic rotifer species are essential to know the generality of these conclusions.

Abstract: Flowering and fruiting are key events in the life history of plants, and both are critical to their reproductive success. Besides the role of evolutionary history, plant reproductive phenology is regulated by abiotic factors and shaped by biotic interactions with pollinators and seed dispersers. In Melastomataceae, a dominant Neotropical clade, the reproductive systems vary from allogamous with biotic pollination to apomitic, and seed dispersal varies from dry (self-dispersed) to fleshy fruits (animal-dispersed). Such variety of reproductive strategies is likely to affect flowering and fruiting phenologies. In this study, we described the reproductive phenology of 81 Melastomataceae species occurring in two biodiversity hotspots: the Atlantic rainforest and the campo rupestre. We aim to disentangle the role of abiotic and biotic factors defining flowering and fruiting times of Melastomataceae species, considering the contrasting breeding and seed dispersal systems, and their evolutionary history. In both vegetation types, pollinator-dependent species had a higher flowering seasonality than pollinator-independent ones. Flowering patterns also presented phylogenetic signal regardless of vegetation type. Fruiting of fleshy-fruited species was seasonal in campo rupestre but not in Atlantic rainforest; the fruiting of dry-fruited species was also not seasonal in both vegetation. Fruiting showed a low phylogenetic signal, probably because the influence of environment and dispersal agents on fruiting time is stronger than the phylogenetic affinity. Considering these ecophylogenetic patterns, our results indicate that flowering may be shaped by the different reproductive strategies of Melastomataceae lineages, while the fruiting patterns may be governed mainly by the seed dispersal strategy and flowering time, with smaller phylogenetic influence. This article is protected by copyright. All rights reserved.

Abstract: Plant stress is a state where the plant is growing in non-ideal growth conditions that increase the demands made upon it. The effects of stress can lead to deficiencies in growth, crop yields, permanent damage or death if the stress exceeds the plant tolerance limits. Plant stress factors are mainly categorized into two main groups; abiotic factors and biotic factors. The abiotic factors include the different environmental factors that affect plant growth (such as light, water, and temperature), while the biotic factors are the other organisms that share the environment and interact with the plants (such as pathogens and pests). Response to stress usually involves complex molecular mechanisms, including changes in gene expression and regulatory networks. In this chapter, we will provide a general overview of the different types of plant stresses, their effects and how plants respond these different types of stress.

Abstract: Despite the major role of Collembola in forest soil animal food webs, ecological and evolutionary determinants of their community composition are not well understood. We investigated abundance, community structure, life forms, and reproductive mode of Collembola in four different forest types (coniferous, young managed beech, old managed beech, and unmanaged beech forests) representing different management intensities. Forest types were replicated within three regions across Germany: the Schorfheide-Chorin, the Hainich, and the Swabian Alb, differing in geology, altitude, and climate. To account for temporal variation, samples were taken twice with an interval of 3 years. To identify driving factors of Collembola community structure, we applied structural equation modeling, including an index of forest management intensity, abiotic and biotic factors such as pH, C-to-N ratio of leaf litter, microbial biomass, and fungal-to-bacterial ratio. Collembola abundance, biomass, and community composition differed markedly between years, with most pronounced differences in the Schorfheide, the region with the harshest climatic conditions. There, temporal fluctuations of parthenogenetic Collembola were significantly higher than in the other regions. In the year with the more favorable conditions, parthenogenetic species flourished, with their abundance depending mainly on abiotic, density-independent factors. This is in line with the "Structured Resource Theory of Sexual Reproduction," stating that parthenogenetic species are favored if density-independent factors, such as desiccation, frost or flooding, prevail. In contrast, sexual species in the same year were mainly influenced by resource quality-related factors such as the fungal-to-bacterial ratio and the C-to-N ratio of leaf litter. The influence of forest management intensity on abundances was low, indicating that disturbance through forest management plays a minor role. Accordingly, differences in community composition were more pronounced between regions than between different forest types, pointing to the importance of regional factors.

Abstract: A number of abiotic and biotic factors are known to regulate arthropod attraction, colonization, and utilization of decomposing vertebrate remains. Such information is critical when assessing arthropod evidence associated with said remains in terms of forensic relevance. Interactions are not limited to just between the resource and arthropods. There is another biotic factor that has been historically overlooked; however, with the advent of high-throughput sequencing, and other molecular techniques, the curtain has been pulled back to reveal a microscopic world that is playing a major role with regards to carrion decomposition patterns in association with arthropods. The objective of this publication is to review many of these factors and draw attention to their impact on microbial, specifically bacteria, activity associated with these remains as it is our contention that microbes serve as a primary mechanism regulating associated arthropod behavior.

Abstract: Drylands account globally for 30% of terrestrial net primary production and 20% of soil organic carbon. Present ecosystem models under predict litter decay in drylands, limiting assessments of biogeochemical cycling at multiple scales. Overlooked decomposition drivers, such as soil–litter mixing (SLM), may account for part of this model-measurement disconnect. We documented SLM and decomposition in relation to the formation of soil-microbial films and microbial extracellular enzyme activity (EEA) in the North American Chihuahuan Desert by placing mesh bags containing shrub (Prosopis glandulosa) foliar litter on the soil surface within contrasting vegetation microsites. Mass loss (in terms of k, the decay constant) was best described by the degree of SLM and soil-microbial film cover. EEA was greatest during periods of rapid litter decomposition and associated SLM. Soil-microbial film cover on litter surfaces increased over time and was greater in bare ground microsites (50% litter surface area covered) compared to shrub and grass microsites (37 and 33% covered, respectively). Soil aggregates that formed in association with decomposing leaf material had organic C and N concentrations 1.5–2× that of local surface soils. Micrographs of soil aggregates revealed a strong biotic component in their structure, suggesting that microbial decomposition facilitates aggregate formation and their C and N content. Decomposition drivers in arid lands fall into two major categories, abiotic and biotic, and it is challenging to ascertain their relative importance. The temporal synchrony between surface litter mass loss, EEA, biotic film development, and aggregate formation observed in this study supports the hypothesis that SLM enhances decomposition on detached litter by promoting conditions favorable for microbial processes. Inclusion of interactions between SLM and biological drivers will improve the ability of ecosystem models to predict decomposition rates and dynamics in drylands.

Abstract: A recurring goal in ecological and paleoclimatic studies is to either forecast how ecosystems will respond to future climate or hindcast climate from past ecosystem assemblages. The Pliocene is a useful deep-time laboratory for understanding an equilibrium climate state under modern atmospheric CO2, and has been a focus for climate modelers. Accurate estimates of proxy data-model mismatch are hindered by the scarcity of well-constrained observations from well-dated sites in the High Arctic. Using a recently developed community-based approach (Climate Reconstruction Analysis using Coexistence Likelihood Estimation: CRACLE) compared with an established method (The Coexistence Approach: CA), and applied to extraordinary, permafrost-driven preservation of floras, we explore the climate and community assemblages at five Pliocene sites in the Canadian Arctic Archipelago The results suggest that climatic differences at this scale do not simply correlate to differences in community assemblage between sites. The threshold temperature for tree line is one important component, but other factors in the environment (e.g. soil characteristics) may drive dissimilarity of communities where the taxa could share the same climate space. Estimates from CRACLE agree with previous estimates where available, and generally fall within the ranges of CA. Mean annual temperatures were ~22°C hotter (ranging from 0.8 to 6.2°C by species across sites) and mean annual precipitation ~500 mm wetter (ranging from 530 to 860 mm by species across sites) during the Early to ‘mid’-Pliocene (~3.6 Ma) when compared with modern climate station data in the Canadian Arctic Archipelago. Comparison of estimates for three levels of taxonomic input suggest judicious interpretation is needed when generic level identifications are used, especially in the Polar Regions. The results herein are a reminder of the large impact of non-climatic abiotic and biotic factors to be accounted for when predicting future ranges of communities under different climate conditions from the present, and when hindcasting climate from past ecosystem assemblages.

Abstract: Abiotic conditions, biotic factors, and disturbances can act as filters that control community structure and composition. Understanding the relative importance of these drivers would allow us to understand and predict the causes and consequences of changes in community structure. We used long-term data (1989-2002) from the sagebrush steppe in the state of Washington, USA, to ask three questions: (1) What are the key drivers of community-level metrics of community structure? (2) Do community-level metrics and functional groups differ in magnitude or direction of response to drivers of community structure? (3) What is the relative importance of drivers of community structure? The vegetation in 2002 was expressed as seven response variables: three community-level metrics (species richness, total cover, compositional change from 1989 to 2002) and the relative abundances of four functional groups. We used a multi-model inference framework to identify a set of top models for each response metric beginning from a global model that included two abiotic drivers, six disturbances, a biotic driver (initial plant community), and interactions between the disturbance and biotic drivers. We also used a permutational relative variable importance metric to rank the influence of drivers. Moisture availability was the most important driver of species richness and of native forb cover. Fire was the most important driver of shrub cover and training area usage was important for compositional change, but disturbances, including grazing, were of secondary importance for most other variables. Biotic drivers, as represented by the initial plant communities, were the most important driver for total cover and for the relative covers of exotics and native grasses. Our results indicate that the relative importance of drivers is dependent on the choice of metric, and that drivers such as disturbance and initial plant community can interact.

Abstract: Mountains, due to their often steep gradients in abiotic and biotic factors, offer an ideal setting to improve our understanding of mechanisms that underlie species distribution and community assembly The current knowledge on the effects of elevation on richness and community composition is almost entirely based on vascular plants and animals, where most studied groups display a monotonal decline in richness with increasing elevation, a mid-elevation peak, or some combinations of the two Taxa with similar ecology share certain distributional patterns that often differ from patterns exhibited by other ecological groups The handful of published studies on the distribution of mycorrhizal fungi along altitudinal gradients confirm both the above general patterns and the differences among functional groups: richness of arbuscular mycorrhizal fungi negatively correlates with altitude, while ectomycorrhizal fungal richness shows either a decrease with increasing elevation or a mid-elevation peak, the latter being particularly prominent in low latitudes Although the above patterns are particularly pronounced when the gradients span different vegetation zones with correlated strong compositional shifts, some changes can still be detected in relatively short gradients within a vegetation type Therefore, both climate and the composition of biotic communities, particularly that of potential hosts, appear to shape the distribution of mycorrhizal fungi More studies are needed, particularly on understudied groups, such as orchid and ericoid mycorrhizal fungi, to attain a better understanding of factors shaping the distribution of mycorrhizal fungi along altitudinal gradients

Abstract: Aim Insect distribution patterns can result from historical contingency (biogeography and dispersal limitation), abiotic filtering and biotic factors (ecological interactions and evolutionary associations) Here, we analyse turnover of plant and insect herbivore community composition at multiple spatial scales to tease apart these influences While positive associations between plant and insect turnover across broad spatial scales could arise through any of these influences, strong association at very local scales is only likely if insect distributions are determined primarily by biotic factors (ie host specificity) Location The Cape Floristic Region (CFR), South Africa Methods To characterize the relationship between spatial turnover in plant and insect composition in the CFR, communities of Restionaceae, a dominant family in the florally diverse CFR, and their associated herbivores were sampled using a spatially nested sampling design on three spatially separated mountain blocks with similar climates, thus controlling for broad abiotic influences This allowed us to quantify insect and plant turnover, and their association, at multiple independent spatial scales Redundancy analysis was used to determine the effects of plant on insect composition, controlling for geographical distance Results Insect species turnover was significantly related to plant species and phylogenetic turnover at local, as well as broad, spatial scales, suggesting that insect distribution patterns are mainly structured by host specificity Plant communities show near complete turnover at small spatial scales (ie communities situated 01–3 km apart), with insects mirroring this pattern Further, insect turnover increased significantly with increasing geographical separation (eg between mountains), suggesting an additional influence of biogeographical factors on insect distributions in the CFR Measured environmental and plant structural components had no influence on insect composition Main conclusions High insect beta diversity positively associated with plant turnover at local scales suggests insect herbivore diversity patterns in the CFR are primarily structured by plant distribution patterns

Abstract: Many biotic and abiotic factors influence the structural and functional diversity of microbial communities in the rhizosphere. This study aimed to understand the dynamics of fungal community in the soybean rhizosphere during soybean growth and directly compare the influence of abiotic and biotic factors in shaping the fungal communities across different growth periods. High-throughput sequencing based on internal transcribed spacer (ITS) region, quantitative PCR, and statistical analysis approaches were used to measure the fungal community structure, abundance, and dynamic changes of 63 rhizosphere soil samples which were taken from different fertilization regimes and rhizobium inoculation treatments during three soybean growth stages. Among the taxa examined, more than 16 fungal classes were detected from the 21 soil samples. Sordariomycetes was the most abundant class, followed by Dothideomycetes, Agaricomycetes, and Eurotiomycetes. Soybean growth stage was the most important factor determining the diversity patterns of the fungal communities. Fungal community diversity was closely related to the base-fertilizer application, and fungal community richness was associated with rhizobium inoculation. Beta diversity of the fungal community based on the Bray-Curtis distance was significantly related to plant growth stage. Network analysis showed that mutual cooperation among fungal taxa became more intimate during the plant growth. Compared with edaphic properties, plant growth stage was the dominant factor in determining soil fungal community dynamics. Base-fertilizer and rhizobium inoculation affected the alpha diversity of the soil fungi.

Abstract: Conflicting hypotheses predict how traits mediate species establishment and community assembly. Traits of newly establishing individuals are predicted to converge, or be more similar to the resident, preexisting community, when the biotic or abiotic environment favors a single best phenotype, but are predicted to diverge when trait differences reduce competitive interactions. We tested these competing hypotheses using transplant seedlings in an old-field environment, and assessed the contribution of inter- and intra-specific transplant trait variation to community-level patterns. Using a soil moisture gradient and resident plant removals, we determined when traits of newly-establishing plants converge or diverge from the resident community by calculating community weighted mean traits for transplant and resident communities. We saw evidence of environmentally- and competitively-driven trait shifts that resulted in both trait convergence and divergence from the resident community, whose traits reflect the combined effects of both drivers. Leaf dry matter content (LDMC) of transplants diverged in the presence of competition, whereas plant height and stem-specific density (SSD) showed the opposite pattern, converging with the resident community in their presence. Specific leaf area (SLA) shifted with competition but did not reflect resident community SLA. All transplant traits were influenced by soil moisture, often in an interaction with competition, indicating that the strength of convergence or divergence is contingent on the abiotic environment. Intraspecific differences in transplant traits among treatments were evident in three of four traits; intraspecific height and SLA trends mirrored transplant community-level trends, whereas intraspecific shifts in SSD were distinct from community-level trends. Our study shows competition between plant species may cause traits of newly establishing plants to converge with the resident community, as frequently as it selects for trait divergence. These opposing effects of competition suggest that it plays a pervasive role in both intraspecific and species-level trait differences among communities.

Abstract: Summary Large-scale disturbances can be important components of the temporal landscape of natural ecosystems, but generalities regarding ecosystem impacts are difficult due to their infrequent and unpredictable nature. Volcanic eruptions figure as one of the most prominent of these natural disturbances, but the effects on microbes and ground-dwelling arthropods, which modulate carbon and nutrient turnover, are relatively unknown. We evaluated the effects of the 2011 Puyehue-Cordon Caulle eruption in Patagonia, Argentina, on the litter and soil microbial and faunal communities in natural and afforested semi-arid ecosystems located 70 km west of the epicentre of the eruption. We hypothesized that volcanic ash deposition would strongly reduce soil faunal and microbial communities due to insecticidal effects of ash on arthropods, with a concomitant reduction in ecosystem processes. Our objective was to quantify the impact of the volcanic eruption by comparing pre- and post-eruption time points in the same study site, with nearly identical field methodology. We measured environmental variables of soil and litter moisture, pH, microbial biomass, and soil and litter microbial enzymatic activity. We evaluated ground-dwelling arthropods and nematodes using pitfall traps and soil extraction, respectively. Additionally, a parallel, controlled-condition experiment of simulated ash deposition was conducted to evaluate ash effects on litter decomposition and enzymatic activity. In the field, post-eruption soils had lower soil water content, pH and soil organic matter. Additionally, nematode abundance and soil microbial enzyme activity were significantly reduced. In contrast, ground-dwelling arthropods and litter enzymatic activity increased significantly. Finally, with simulated ash deposition, litter decomposition increased fourfold for native litter decomposition. Large-scale disturbances may play a key role in biogeochemical cycling in affected natural ecosystems, but not necessarily due to their catastrophic effects. In contrast to our original predictions, we observed a marked stimulation of biotic activity and carbon turnover in the aftermath of the Puyehue volcanic eruption, which demonstrates that the biotic component of these ecosystems has a substantial capacity to respond to these disturbances in short time frames. These results can contribute to placing the role of these large-scale infrequent disturbances in a more robust ecological context. A Lay Summary is available for this article.

Abstract: Aim Species richness patterns are generally thought to be determined by abiotic variables at broad spatial scales, with biotic factors being only important at fine spatial scales. However, many organism groups depend intimately on other organisms, raising questions about this generalization. As an example, woodpeckers (Picidae) are closely associated with trees and woody habitats because of multiple morphological and ecological specializations. In this study, we test whether this strong biotic association causes woodpecker diversity to be closely linked to tree availability at a global scale. Location Global. Methods We used spatial and non-spatial regressions to test for relationships between broad-scale woodpecker species richness and predictor variables describing current and deep-time availability of trees, current climate, Quaternary climate change, human impact, topographical heterogeneity and biogeographical region. We further used structural equation models to test for direct and indirect effects of predictor variables. Results There was a strong positive relationship between woodpecker species richness and current tree cover and annual precipitation, respectively. Precipitation also showed a strong indirect effect on woodpecker richness via the effects on tree availability. Deep-time tree availability, Quaternary climate change, human influence and other abiotic factors showed weaker direct effects. Human influence had a negative effect on tree availability, and hence a negative indirect effect on woodpecker species richness. Main conclusions Global species richness of woodpeckers is primarily shaped by current tree cover and precipitation, reflecting a strong biotic association between woodpeckers and trees. Human influence can have a negative effect on woodpecker diversity when humans reduce tree availability. Hence, woodpeckers exemplify how broad-scale diversity patterns are predominantly shaped by a biotic factor, and how climate and human influence can have indirect effects on animal biodiversity via the effects on tree availability and forest cover.

Abstract: Biotic stress caused by viruses, bacteria, fungi, insect pests and nematode parasites is affecting the yield and quality of crop plants worldwide. Farmers use the agrochemicals extensively for the control of pathogens and pests, and this has led to the resistance by these biotic factors against agrochemicals. Therefore, the development of crop plants resistant to pathogens and pests with increased yields using novel alternative approaches has become the area of focus to meet the needs of growing population. In response to biotic stress, plants express the regulating genes such as miRNAs, which control the expression of defense responsive genes. The miRNAs expression is either induced or over-expressed after biotic stress, targeting the inhibitors of biotic stress responsive resistant genes and leading to their over-expression. The miRNAs, which negatively regulate the resistant genes are down-regulated upon biotic stress. The pathogens or pests also express miRNAs, which interferes with the expression of host plant’s genes that are involved in defense. Whereas, in resistant plants the miRNAs that positively regulate the resistant genes are over-expressed in response to biotic stress. Therefore, the miRNAs can be exploited for the control of pathogens and pests for crop improvement. In this review, we have updated the literature pertaining to the involvement of miRNAs in biotic stress responses and miRNA interference for crop improvement.

Abstract: Question Quantifying the duration and drivers of seedling persistence is critical for understanding seedling dynamics and species coexistence in plant communities. In this study, we incorporated data from multiple seedling censuses to characterize patterns of seedling persistence in a tropical karst forest. Specifically, we evaluated the effects of density dependence, habitat heterogeneity, and recruitment timing on seedling persistence. Location A tropical karst forest in Taiwan. Methods Using data from 144 seedling plots censused every three months from 2007 to 2012, we examined persistence times of 6399 seedlings of 36 species. Seedling survival was estimated by the Kaplan-Meier method. Mixed effects Cox models were used to identify significant biotic (i.e., initial height, conspecific and heterospecific seedling and adult densities) and abiotic (i.e., mean elevation, convexity, slope, effective soil depth, and recruitment time) drivers of seedling persistence at the community, guild and species levels. Results At the community level, newly recruited seedlings had a median survival time of 6 months. Median survival time was higher for seedlings in the shade-tolerant guild compared to seedlings in the shade-intolerant guild (9 vs. 3 months). When all species were analyzed together, seedling persistence significantly increased with increasing initial size and soil depth and significantly decreased with increasing density of conspecific and heterospecific seedling neighbors. Drivers of seedling persistence tended to be guild- and species-specific, however negative effects of conspecific seedling neighbors were consistently detected in all models, indicating strong and pervasive conspecific negative density dependence. Significant effects of recruitment time, soil depth and convexity were revealed by guild- and species-specific models, suggesting abiotic niche differences. Conclusions This study highlights the importance of multiple ecological processes for seedling persistence. Both abiotic and biotic factors may play an important role in species coexistence in this forest via niche partitioning and negative density dependence. Among these factors, negative conspecific density dependence had the strongest and most consistent effect. In addition, soil depth played a key role in shaping seedling regeneration, likely through effects of soil moisture. Overall, this study contributes to a better understanding of the ecology of karst forests. Analyzing seedling persistence in karst forest expands our general understanding of forest dynamics and species coexistence in tropical forests as a whole, especially at sites with high spatial heterogeneity. This article is protected by copyright. All rights reserved.

Abstract: Charles Elton proposed that high species diversity and low levels of disturbance provide a measure of biotic resistance against invasions by alien species. While there is some evidence for this hypothesis, there are numerous other factors associated with invasive species richness, and the strength of those relationships is often scale-dependent. Among oceanic island groups, habitat diversity, human population size and economic activity have been identified as among the significant drivers of invasive species richness. However, intra-island patterns are rarely analyzed. We investigate the relationship between the number of invasive seed plant species and human, physical and biotic factors among municipalities of the tropical island of Puerto Rico using Generalized Linear Models. While elevation amplitude and, to a lesser extent, area had significant effects on the diversity of the most abundant invasive species, we found that the best models, according to Akaike Information Criterion, consistently involve a positive relationship between the number of invasive and native species. Moreover, when we examined the relationship between forest reserves and those regions without reserves, proportionately fewer invasive species occur in forest reserves where native species richness is higher, resource competition is presumably greater, and human impacts are no longer as pervasive. Because the invasive species pool consists almost entirely of ruderal species, forest reserves, while not impenetrable, are less susceptible to invasions than the heavily human-impacted landscapes. Consequently, forest reserves may play an important role in slowing the pace of biological invasions on tropical islands.

Abstract: Abiotic global change drivers affect ecosystem structure and function, but how they interact with biotic factors such as invasive plants is understudied. Such interactions may be additive, synergistic, or offsetting, and difficult to predict. We present methods to test the individual and interactive effects of drought and plant invasion on native ecosystems. We coupled a factorial common garden experiment containing resident communities exposed to drought (imposed with rainout shelters) and invasion with a field experiment where the invader was removed from sites spanning a natural soil moisture gradient. We detail treatments and their effects on abiotic conditions, including soil moisture, light, temperature, and humidity, which shape community and ecosystem responses. Ambient precipitation during the garden experiment exceeded historic norms despite severe drought in prior years. Soil moisture was 48% lower in drought than ambient plots, but the invader largely offset drought effects. Additionally, temperature and light were lower and humidity higher in invaded plots. Field sites spanned up to a 10-fold range in soil moisture and up to a 2.5-fold range in light availability. Invaded and resident vegetation did not differentially mediate soil moisture, unlike in the garden experiment. Herbicide effectively removed invaded and resident vegetation, with removal having site-specific effects on soil moisture and light availability. However, light was generally higher in invader-removal than control plots, whereas resident removal had less effect on light, similar to the garden experiment. Invasion mitigated a constellation of abiotic conditions associated with drought stress in the garden experiment. In the field, where other factors co-varied, these patterns did not emerge. Still, neither experiment suggested that drought and invasion will have synergistic negative effects on ecosystems, although invasion can limit light availability. Coupling factorial garden experiments with field experiments across environmental gradients will be effective for predicting how multiple stressors interact in natural systems.