Showing papers on "Biotic component published in 2013"
TL;DR: The drivers of endophyte community structure relating to plant growth promotion, the mechanisms of plant growth Promotion, and the current and future use of molecular techniques to study these communities are reviewed.
Abstract: Bacterial root endophytes reside in a vast number of plant species as part of their root microbiome, with some being shown to positively influence plant growth. Endophyte community structure (species diversity: richness and relative abundances) within the plant is dynamic and is influenced by abiotic and biotic factors such as soil conditions, biogeography, plant species, microbe-microbe interactions and plant-microbe interactions, both at local and larger scales. Plant-growth-promoting bacterial endophytes (PGPBEs) have been identified, but the predictive success at positively influencing plant growth in field conditions has been limited. Concurrent to the development of modern molecular techniques, the goal of predicting an organism's ability to promote plant growth can perhaps be realized by more thorough examination of endophyte community dynamics. This paper reviews the drivers of endophyte community structure relating to plant growth promotion, the mechanisms of plant growth promotion, and the current and future use of molecular techniques to study these communities.
488 citations
TL;DR: An approach to study the roles of biotic and abiotic factors in establishing elevational ranges, and to improve the ability to predict the effects of climate change on these communities is described.
Abstract: Tropical mountains contain some of the world’s richest animal communities as a result of high turnover of species along elevational gradients. We describe an approach to study the roles of biotic and abiotic factors in establishing elevational ranges, and to improve our ability to predict the effects of climate change on these communities. As a framework we use Hutchinson’s concept of the fundamental niche (determined by the match between the physical environment and the organism’s physiological and biophysical characteristics) and realized niche (the subset of the fundamental niche determined by biotic interactions). Using tropical birds as an example, we propose a method for estimating fundamental niches and discuss five biotic interactions that we expect to influence distributions of tropical montane animals: predation, competition, parasites and pathogens, mutualisms, and habitat associations. The effects of biotic factors on elevational ranges have been studied to some extent, but there is little information on physiological responses of tropical montane animals. It will be necessary to understand all of these ecological constraints in concert to predict current and future elevational ranges and potential threats to montane species. Given the importance of tropical mountains as global biodiversity hotspots, we argue that this area of research requires urgent attention.
227 citations
TL;DR: In this paper, the authors provide an overview of the potential bottlenecks for restoration of submerged macrophyte vegetation with a high biodiversity and focus on the biotic factors, including the availability of propagules, herbivory, plant competition and the role of remnant populations.
Abstract: Although many lake restoration projects have led to decreased nutrient loads and increased water transparency, the establishment or expansion of macrophytes does not immediately follow the improved abiotic conditions and it is often unclear whether vegetation with high macrophyte diversity will return. We provide an overview of the potential bottlenecks for restoration of submerged macrophyte vegetation with a high biodiversity and focus on the biotic factors, including the availability of propagules, herbivory, plant competition and the role of remnant populations. We found that the potential for restoration in many lakes is large when clear water conditions are met, even though the macrophyte community composition of the early 1900s, the start of human-induced large-scale eutrophication in Northwestern Europe, could not be restored. However, emerging charophytes and species rich vegetation are often lost due to competition with eutrophic species. Disturbances such as herbivory can limit dominance by eutrophic species and improve macrophyte diversity. We conclude that it is imperative to study the role of propagule availability more closely as well as the biotic interactions including herbivory and plant competition. After abiotic conditions are met, these will further determine macrophyte diversity and define what exactly can be restored and what not.
145 citations
TL;DR: A functional trait-based and multiscale approach was used to assess how biotic interactions and aridity determine the functional structure of semi-arid shrublands sampled along a large aridity gradient in Spain, suggesting that competition and facilitation interplayed with aridity to determine this structure.
Abstract: Summary 1. Habitat filtering (HF, trait convergence) and niche differentiation (ND, trait divergence) are known to impact upon plant community structure. Both processes integrate individual responses to the abiotic environment and biotic interactions. Thus, it is difficult to clearly identify the underlying abiotic and biotic factors that ultimately impact community structure by looking at community-level patterns of trait divergence or convergence alone. 2. We used a functional trait-based and multiscale approach to assess how biotic interactions and aridity determine the functional structure of semi-arid shrublands sampled along a large aridity gradient in Spain. At the regional scale, we investigated functional differences among species (axes of specialization) to identify important traits for community assembly. At the community scale, we evaluated the relative impact of HF and ND on community structure using a null model approach. Finally, at the plant neighbourhood scale, we evaluated the impact of biotic interactions on community structure by investigating the spatial patterns of trait aggregation. 3. The shrub species surveyed can be separated along four axes of specialization based on their above-ground architecture and leaf morphology. Our community scale analysis suggested that the functional structure of semi-arid communities was clearly non-random, HF and ND acting independently on different traits to determine community structure along the aridity gradient. At the plant neighbourhood scale, the spatial distribution of species was also clearly not random, suggesting that competition and facilitation impacted on the observed changes in the functional diversity of shrubland communities along the aridity gradient. 4. Synthesis: Our results demonstrated that HF and ND acted simultaneously on independent traits to jointly determine community structure. Most importantly, our multiscale approach suggested that competition and facilitation interplayed with aridity to determine this structure. Competition appeared to be constant along the aridity gradient and explained the high functional diversity observed in semi-arid shrublands. Facilitation affected subordinate and rare species and, thus, may act to enhance the biodiversity of these ecosystems. Finally, the framework employed in our study allows moving forward from the examination of patterns to the development of mechanistic traitbased approaches to study plant community assembly.
134 citations
TL;DR: This study demonstrates a connection between abundance, fine-scale environmental gradients, and population dynamics, providing a foundation for future research concerning movement, population connectivity, and physiology.
Abstract: Environmental gradients are instrumental in shaping the distribution and local abundance of species because at the most fundamental level, an organism’s performance is constrained by the environment it inhabits. In topographically complex landscapes, slope, aspect, and vegetative cover interact to affect solar exposure, creating temperature-moisture gradients and unique microclimates. The significance of the interaction of abiotic gradients and biotic factors such as competition, movement, or physiology has long been recognized, but the scale at which these factors vary on the landscape has generally precluded their inclusion in spatial abundance models. We used fine-scale spatial data relating to surface-soil moisture, temperature, and canopy cover to describe the spatial distribution of abundance of a terrestrial salamander, Plethodon albagula, across the landscape. Abundance was greatest in dense-canopy ravine habitats with high moisture and low solar exposure, resulting in a patchy distribution of abundance. We hypothesize that these patterns reflect the physiological constraints of Plethodontid salamanders. Furthermore, demographic cohorts were not uniformly distributed among occupied plots on the landscape. The probability of gravid female occurrence was nearly uniform among occupied plots, but juveniles were much more likely to occur on plots with lower surface temperatures. The disconnect between reproductive effort and recruitment suggests that survival differs across the landscape and that local population dynamics vary spatially. Our study demonstrates a connection between abundance, fine-scale environmental gradients, and population dynamics, providing a foundation for future research concerning movement, population connectivity, and physiology.
102 citations
01 Dec 2013
TL;DR: In this paper, the authors used Lysimeter evaporation (E) measurements and model calculations using the Penman equation to investigate the effect of the time lag between net radiation and VPD on the hysteresis in the absence of any biotic effects.
Abstract: Diurnal hysteresis between evapotranspiration (ET) and vapor pressure deficit (VPD) was reported in many ecosystems, but justification for its onset and magnitude remains incomplete with biotic and abiotic factors invoked as possible explanations. To place these explanations within a holistic framework, the occurrence of hysteresis was theoretically assessed along a hierarchy of model systems where both abiotic and biotic components are sequentially added. Lysimeter evaporation (E) measurements and model calculations using the Penman equation were used to investigate the effect of the time lag between net radiation and VPD on the hysteresis in the absence of any biotic effects. Modulations from biotic effects on the ET-VPD hysteresis were then added using soil-plant-atmosphere models of different complexities applied to a grassland ecosystem. The results suggest that the hysteresis magnitude depends on the radiation-VPD lag, while the plant and soil water potentials are both key factors modulating the hysteretic ET-VPD relation as soil moisture declines. In particular, larger hysteresis magnitude is achieved at less negative leaf water potential, root water potential, and soil water potential. While plant hydraulic capacitance affects the leaf water potential-ET relation, it has negligible effects on the ET-VPD hysteresis. Therefore, the genesis and magnitude of the ET-VPD hysteresis are controlled directly by both abiotic factors such as soil water availability, biotic factors (leaf and root water potentials, which in turn depend on soil moisture), and the time lag between radiation and VPD.
101 citations
TL;DR: This review gives an overview of the most abundant prokaryotic populations by grouping them in specific ecological guilds based on their life strategies, reflected in a distinct seasonality of the freshwater bacterioplankton.
Abstract: Lakes and ponds harbour a high number of diverse planktonic microorganisms that are centrally involved in biochemical cycles and aquatic food webs. Although the open water body (pelagial) seems to be a uniform and unstructured environment, ecological niche separation of coexisting microbial taxa might be triggered by limiting resources (bottom-up control) and mortality factors (top-down control), leading to distinct spatial and temporal distribution patterns of different microbes. This review gives an overview of the most abundant prokaryotic populations by grouping them in specific ecological guilds based on their life strategies. Defense specialists such as very small actinobacteria or big filamentous bacteria mostly occur at times of highest grazing pressure by heterotrophic nanoflagellates, the main consumers of bacteria. Oligotrophic ultramicrobacteria , on the other hand, seem to be mostly adapted to nutrient depleted water layers during summer stratification, while opportunistic bacteria profit from material released during short-living algal blooms. Seasonal changes in abiotic and biotic factors may be the main causes for periodic reoccurring density maxima of different prokaryotes populations in the pelagial of temperate lakes, reflected in a distinct seasonality of the freshwater bacterioplankton.
81 citations
16 Mar 2013
78 citations
TL;DR: It is concluded that biological predictors, in combination with environmental and spatial variables, can reveal a more complete picture of the local vs. regional control of species assemblages in lotic environments.
Abstract: Stream assemblages are structured by a combination of local (environmental filtering and biotic interactions) and regional factors (e.g., dispersal related processes). The relative importance of environmental and spatial (i.e., regional) factors structuring stream assemblages has been frequently assessed in previous large-scale studies, but biotic predictors (potentially reflecting local biotic interactions) have rarely been included. Diatoms may be useful for studying the effect of trophic interactions on community structure since: (1) a majority of experimental studies shows significant grazing effects on diatom species composition, and (2) assemblages can be divided into guilds that have different susceptibility to grazing. We used a dataset from boreal headwater streams in south-central Sweden (covering a spatial extent of ∼14000 km2), which included information about diatom taxonomic composition, abundance of invertebrate grazers (biotic factor), environmental (physicochemical) and spatial factors (obtained through spatial eigenfunction analyses). We assessed the relative importance of environmental, biotic, and spatial factors structuring diatom assemblages, and performed separate analyses on different diatom guilds. Our results showed that the diatom assemblages were mainly structured by environmental factors. However, unique spatial and biological gradients, specific to different guilds and unrelated to each other, were also evident. We conclude that biological predictors, in combination with environmental and spatial variables, can reveal a more complete picture of the local vs. regional control of species assemblages in lotic environments. Biotic factors should therefore not be overlooked in applied research since they can capture additional local control and therefore increase accuracy and performance of predictive models. The inclusion of biotic predictors did, however, not significantly influence the unique fraction explained by spatial factors, which suggests low bias in previous assessments of unique regional control of stream assemblages.
74 citations
TL;DR: It is shown that including both abiotic and biotic factors not only leads to a fuller more comprehensive understanding of the niche, but also leads to more accurate prediction models.
73 citations
TL;DR: This review focuses on how dispersal influences the ‘seedscape’, or the combination of abiotic and biotic factors that affect the probability of recruitment once a seed has reached its final location, and explores methods used to scale up from populations to communities.
Abstract: Seed dispersal sets the stage for the suite of biotic and abiotic interactions that determine the fate of individual seeds. In this review, we first focus on how dispersal influences the ‘seedscape’, or the combination of abiotic and biotic factors that affect the probability of recruitment once a seed has reached its final location. We review recent papers that examine the effect of different dispersal vectors on (1) the quality of the habitat in which a seed lands; (2) the distance seeds are dispersed from the parent tree; and (3) the density and composition of plants within the neighborhood of a seed following deposition. Next, we explore methods used to scale these processes up to the level of populations. We highlight demographic models that integrate across multiple life history stages and predict the impact of dispersal in variable environments on population growth. We also review studies that analyze existing spatial patterns of trees within large forest plots and use various strategies to infer the processes that led to those patterns. We continue to scale up from populations to communities, and discuss approaches that have been taken to understand how dispersal may affect diversity and abundance in the community. We then turn to human disturbances and discuss the implications of frugivore defaunation for plant communities. We finish by highlighting several areas of research that are particularly promising for future directions of study.
TL;DR: huge variation in biotic response in both space and time is apparent with, in some cases, totally different responses to the same climatic driver, highlighting the importance of local features such as soils, topography and also internal biotic factors in determining responses and resilience of the African biota to climate change.
Abstract: Prediction of biotic responses to future climate change in tropical Africa tends to be based on two modelling approaches: bioclimatic species envelope models and dynamic vegetation models. Another complementary but underused approach is to examine biotic responses to similar climatic changes in the past as evidenced in fossil and historical records. This paper reviews these records and highlights the information that they provide in terms of understanding the local- and regional-scale responses of African vegetation to future climate change. A key point that emerges is that a move to warmer and wetter conditions in the past resulted in a large increase in biomass and a range distribution of woody plants up to 400–500 km north of its present location, the so-called greening of the Sahara. By contrast, a transition to warmer and drier conditions resulted in a reduction in woody vegetation in many regions and an increase in grass/savanna-dominated landscapes. The rapid rate of climate warming coming into the current interglacial resulted in a dramatic increase in community turnover, but there is little evidence for widespread extinctions. However, huge variation in biotic response in both space and time is apparent with, in some cases, totally different responses to the same climatic driver. This highlights the importance of local features such as soils, topography and also internal biotic factors in determining responses and resilience of the African biota to climate change, information that is difficult to obtain from modelling but is abundant in palaeoecological records.
TL;DR: This work uses mathematical models and field data to demonstrate that divergence in population response to infection can be explained by local environmental differences between infected sites, whereas pathogen genetics, host genetics, and intrinsic epidemiological dynamics driven by fungal load are less likely to be the cause of these differing population trajectories.
Abstract: Amphibian chytridiomycosis, caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd), is an emerging infectious disease that widely threatens amphibian biodiversity. However, population-level outcomes following the introduction of the pathogen are highly context dependent and are mediated by a broad suite of biotic and abiotic variables. Here, we examine the effect of the introduction of Bd on native island populations of the IUCN red-listed amphibian species Alytes muletensis, the Mallorcan midwife toad. We show that the outcome of pathogen introduction is not only dependent on biotic factors, but is also dependent on environmental factors that vary across local scales. Our experimental infections confirm that the genotype of Bd occurring on Mallorca is hypovirulent in A. muletensis when compared against the lineage found occurring on mainland Iberia. Long-term population data show that A. muletensis populations on the island are increasing overall, but trends in highly infected populations are conflicting. We use mathematical models and field data to demonstrate that this divergence in population response to infection can be explained by local environmental differences between infected sites, whereas pathogen genetics, host genetics, and intrinsic epidemiological dynamics driven by fungal load are less likely to be the cause of these differing population trajectories. Our results illustrate the need to take into account the appropriate environmental scale and context when assessing the risk that an emerging pathogen presents to a naive population or species.
TL;DR: In this article, the authors investigated the impact of the indigenous burrowing lagomorph plateau pika (Ochotona curzoniae) on ecosystem productivity and soil properties, and especially net ecosystem carbon flux.
Abstract: Because the indigenous burrowing lagomorph plateau pika (Ochotona curzoniae) is considered to have negative ecological impacts on alpine meadow steppe grasslands of the Headwaters Region of the Yellow, Yangtze and Mekong Rivers we investigated its effects on ecosystem productivity and soil properties, and especially net ecosystem carbon flux. We measured net ecosystem CO2 exchange (NEE) and its components gross ecosystem productivity (GEP) and ecosystem respiration (ER) at peak aboveground biomass by the chamber method with reference to plant and soil characteristics of areas of alpine meadow steppe with different densities of pika burrows. Higher burrow density decreased NEE, GEP and ER. Above-ground biomass, species number, plant cover and leaf area index decreased with increasing pika density. Higher burrow density was associated with lower soil moisture and higher soil temperature. Responses of NEE were related to changes of abiotic and biotic factors affecting its two components. NEE was positively related to soil moisture, soil ammonium nitrogen, plant cover, leaf area index and above-ground biomass but was negatively correlated with higher soil nitrate nitrogen. Decrease of NEE by plateau pika may reduce the carbon sink balance of Qinghai-Tibet plateau grassland. Such effects may be influenced by grazing pressure from domestic livestock, population levels of natural predators, and climate change.
TL;DR: In this paper, the authors examined parasite pressure in sympatric morphs of threespine stickleback (Gasterosteus aculeatus) across a temperature gradient in two large Icelandic lakes, Myvatn and Thingvallavatn.
Abstract: Parasite communities of fishes are known to respond directly to the abiotic environment of the host, for example, to water quality and water temperature. Biotic factors are also important as they affect the exposure profile through heterogeneities in parasite distribution in the environment. Parasites in a particular environment may pose a strong selection on fish. For example, ecological differences in selection by parasites have been hypothesized to facilitate evolutionary differentiation of freshwater fish morphs specializing on different food types. However, as parasites may also respond directly to abiotic environment the parasite risk does not depend only on biotic features of the host environment. It is possible that different morphs experience specific selection gradients by parasites but it is not clear how consistent the selection is when abiotic factors change. We examined parasite pressure in sympatric morphs of threespine stickleback (Gasterosteus aculeatus) across a temperature gradient in two large Icelandic lakes, Myvatn and Thingvallavatn. Habitat-specific temperature gradients in these lakes are opposite. Myvatn lava rock morph lives in a warm environment, while the mud morph lives in the cold. In Thingvallavatn, the lava rock morph lives in a cold environment and the mud morph in a warm habitat. We found more parasites in fish living in higher temperature in both lakes, independent of the fish morph, and this pattern was similar for the two dominating parasite taxa, trematodes and cestodes. However, at the same time, we also found higher parasite abundance in a third morph living in deep cold–water habitat in Thingvallavatn compared to the cold-water lava morph, indicating strong effect of habitat-specific biotic factors. Our results suggest complex interactions between water temperature and biotic factors in determining the parasite community structure, a pattern that may have implications for differentiation of stickleback morphs.
TL;DR: Investigation of subalpine forests close to the Qinghai-Tibet Plateau in China concluded that frequent freeze-thaw cycles and litter chemical properties determine the winter decomposition while microbe-related factors play more important roles in determining decomposition in the subsequent growing season.
Abstract: Relationships between abiotic (soil temperature and number of freeze-thaw cycles) or biotic factors (chemical elements, microbial biomass, extracellular enzymes, and decomposer communities in litter) and litter decomposition rates were investigated over two years in subalpine forests close to the Qinghai-Tibet Plateau in China. Litterbags with senescent birch, fir, and spruce leaves were placed on the forest floor at 2,704 m, 3,023 m, 3,298 m, and 3,582 m elevation. Results showed that the decomposition rate positively correlated with soil mean temperature during the plant growing season, and with the number of soil freeze-thaw cycles during the winter. Concentrations of soluble nitrogen (N), phosphorus (P) and potassium (K) had positive effects but C:N and lignin:N ratios had negative effects on the decomposition rate (k), especially during the winter. Meanwhile, microbial biomass carbon (MBC), N (MBN), and P (MBP) were positively correlated with k values during the first growing season. These biotic factors accounted for 60.0% and 56.4% of the variation in decomposition rate during the winter and the growing season in the first year, respectively. Specifically, litter chemistry (C, N, P, K, lignin, C:N and lignin:N ratio) independently explained 29.6% and 13.3%, and the microbe-related factors (MBC, MBN, MBP, bacterial and fungal biomass, sucrase and ACP activity) explained 22.9% and 34.9% during the first winter and the first growing season, respectively. We conclude that frequent freeze-thaw cycles and litter chemical properties determine the winter decomposition while microbe-related factors play more important roles in determining decomposition in the subsequent growing season.
TL;DR: It is found that the species and functional dissimilarities between communities on infertile serpentine and fertile non-serpentine soils were higher in more productive (wetter) regions, illustrating a novel mechanism wherein climatic productivity is associated with higher species, functional, and landscape-level dissimilarity (beta diversity).
Abstract: Spatially distinct communities can arise through interactions and feedbacks between abiotic and biotic factors. We suggest that, for plants, patches of infertile soils such as serpentine may support more distinct communities from those in the surrounding non-serpentine matrix in regions where the climate is more productive (i.e., warmer and/or wetter). Where both soil fertility and climatic productivity are high, communities may be dominated by plants with fast-growing functional traits, whereas where either soils or climate impose low productivity, species with stress-tolerant functional traits may predominate. As a result, both species and functional composition may show higher dissimilarity between patch and matrix in productive climates. This pattern may be reinforced by positive feedbacks, in which higher plant growth under favorable climate and soil conditions leads to higher soil fertility, further enhancing plant growth. For 96 pairs of sites across a 200-km latitudinal gradient in California, we ...
TL;DR: It is suggested that both ‘biotic’ and abiotic factors contribute either directly or indirectly to the diversification of languages and that both models can be applied when studying language evolution.
Abstract: Quantitative phylogenetic methods have been used to study the evolutionary relationships and divergence times of biological species, and recently, these have also been applied to linguistic data to elucidate the evolutionary history of language families. In biology, the factors driving macroevolutionary processes are assumed to be either mainly biotic (the Red Queen model) or mainly abiotic (the Court Jester model) or a combination of both. The applicability of these models is assumed to depend on the temporal and spatial scale observed as biotic factors act on species divergence faster and in smaller spatial scale than the abiotic factors. Here, we used the Uralic language family to investigate whether both ‘biotic’ interactions (i.e. cultural interactions) and abiotic changes (i.e. climatic fluctuations) are also connected to language diversification. We estimated the times of divergence using Bayesian phylogenetics with a relaxed-clock method and related our results to climatic, historical and archaeological information. Our timing results paralleled the previous linguistic studies but suggested a later divergence of Finno-Ugric, Finnic and Saami languages. Some of the divergences co-occurred with climatic fluctuation and some with cultural interaction and migrations of populations. Thus, we suggest that both ‘biotic’ and abiotic factors contribute either directly or indirectly to the diversification of languages and that both models can be applied when studying language evolution.
TL;DR: In this article, a series of laboratory mesocosm experiments were conducted to investigate the role of macrofauna assemblages in leaf litter mass loss in temperate forests.
Abstract: Changing climatic conditions and habitat fragmentation are predicted to alter the soil moisture conditions of temperate forests. It is not well understood how the soil macrofauna community will respond to changes in soil moisture, and how changes to species diversity and community composition may affect ecosystem functions, such as litter decomposition and soil fluxes. Moreover, few studies have considered the interactions between the abiotic and biotic factors that regulate soil processes. Here we attempt to disentangle the interactive effects of two of the main factors that regulate soil processes at small scales - moisture and macrofauna assemblage composition. The response of assemblages of three common temperate soil invertebrates (Glomeris marginata Villers, Porcellio scaber Latreille and Philoscia muscorum Scopoli) to two contrasting soil moisture levels was examined in a series of laboratory mesocosm experiments. The contribution of the invertebrates to the leaf litter mass loss of two common temperate tree species of contrasting litter quality (easily decomposing Fraxinus excelsior L. and recalcitrant Quercus robur L.) and to soil CO2 fluxes were measured. Both moisture conditions and litter type influenced the functioning of the invertebrate assemblages, which was greater in high moisture conditions compared with low moisture conditions and on good quality vs. recalcitrant litter. In high moisture conditions, all macrofauna assemblages functioned at equal rates, whereas in low moisture conditions there were pronounced differences in litter mass loss among the assemblages. This indicates that species identity and assemblage composition are more important when moisture is limited. We suggest that complementarity between macrofauna species may mitigate the reduced functioning of some species, highlighting the importance of maintaining macrofauna species richness.
TL;DR: Patterns in biotic or abiotic pathways underpinning changes in the composition and diversity of plant communities under three components of climate change are identified and how these differ across spatial scales are explored.
Abstract: Premise of the study Processes that drive ecological dynamics differ across spatial scales. Therefore, the pathways through which plant communities and plant-insect relationships respond to changing environmental conditions are also expected to be scale-dependent. Furthermore, the processes that affect individual species or interactions at single sites may differ from those affecting communities across multiple sites. Methods We reviewed and synthesized peer-reviewed literature to identify patterns in biotic or abiotic pathways underpinning changes in the composition and diversity of plant communities under three components of climate change (increasing temperature, CO2, and changes in precipitation) and how these differ across spatial scales. We also explored how these changes to plants affect plant-insect interactions. Key results The relative frequency of biotic vs. abiotic pathways of climate effects at larger spatial scales often differ from those at smaller scales. Local-scale studies show variable responses to climate drivers, often driven by biotic factors. However, larger scale studies identify changes to species composition and/or reduced diversity as a result of abiotic factors. Differing pathways of climate effects can result from different responses of multiple species, habitat effects, and differing effects of invasions at local vs. regional to global scales. Plant community changes can affect higher trophic levels as a result of spatial or phenological mismatch, foliar quality changes, and plant abundance changes, though studies on plant-insect interactions at larger scales are rare. Conclusions Climate-induced changes to plant communities will have considerable effects on community-scale trophic exchanges, which may differ from the responses of individual species or pairwise interactions.
TL;DR: It is suggested that high elevation soil show greater variation in fungal assemblages that may in turn impact plant turnover among communities, and including the fungal richness information in the models of plant species distributions improves predictive accuracy.
Abstract: The distribution of plants along environmental gradients is constrained by abiotic and biotic factors. Cumulative evidence attests of the impact of biotic factors on plant distributions, but only few studies discuss the role of belowground communities. Soil fungi, in particular, are thought to play an important role in how plant species assemble locally into communities. We first review existing evidence, and then test the effect of the number of soil fungal operational taxonomic units (OTUs) on plant species distributions using a recently collected dataset of plant and metagenomic information on soil fungi in the Western Swiss Alps. Using species distribution models (SDMs), we investigated whether the distribution of individual plant species is correlated to the number of OTUs of two important soil fungal classes known to interact with plants: the Glomeromycetes, that are obligatory symbionts of plants, and the Agaricomycetes, that may be facultative plant symbionts, pathogens, or wood decayers. We show that including the fungal richness information in the models of plant species distributions improves predictive accuracy. Number of fungal OTUs is especially correlated to the distribution of high elevation plant species. We suggest that high elevation soil show greater variation in fungal assemblages that may in turn impact plant turnover among communities. We finally discuss how to move beyond correlative analyses, through the design of field experiments manipulating plant and fungal communities along environmental gradients.
TL;DR: The results support Darwin's hypothesis that biotic factors, associated with variation in the abiotic environment, are more important in explaining evolution than is abiotic variation per se.
Abstract: Summary 1. Body size is a defining phenotypic trait, but the ecological causes of its evolution are poorly understood. Most studies have considered only a single putative causal agent and have failed to recognise that different environmental agents are often correlated. 2. Darwin suggested that although trait variation across populations is often associated with abiotic variation, evolution is more likely to be driven by biotic factors correlated with the abiotic variation. This hypothesis has received little explicit attention. 3. We use structural equation modelling to quantify the relative importance of abiotic (pH, metal concentrations) and biotic (competition, predation) factors in the evolution of body size in three-spined sticklebacks Gasterosteus aculeatus on the island of North Uist, Scotland. We combine phenotypic data from multiple isolated populations, detailed characterisation of their environment and a common garden experiment that establishes the genetic basis of size differences. 4. Three-spined sticklebacks on North Uist show almost unprecedented intraspecific evolution of body size that has taken place rapidly (<16 000 years). The smallest fish mature at only 7% of the mass of ancestral, anadromous fish. Dwarfism is associated with reduced abundance of a smaller competitor species, the nine-spined stickleback Pungitius pungitius, and with low pH indicative of poor resource conditions. Dwarfism also tends to occur where an important predator, the brown trout Salmo trutta, is also small. The abundance of P. pungitius and the size of S. trutta are themselves related to underlying abiotic environmental variation. 5. Despite the close association between abiotic and biotic factors across populations, our results support Darwin’s hypothesis that biotic factors, associated with variation in the abiotic environment, are more important in explaining evolution than is abiotic variation per se. This study demonstrates the importance of considering the relationships between environmental variables before conclusions can be drawn about the causes of (body size) evolution on islands.
TL;DR: It is suggested that overstory and understory vegetation exhibit greater control over regeneration patterns than substrate and soil attributes, or silvicultural treatment, in partially harvested Acadian Forest mixedwood stands, and also indicated the potential for composition control through selective overstory removal.
TL;DR: The models developed depict the combinatorial and multicomponent signaling triggered in response to several abiotic and biotic factors and can be used to predict behavior of cells in event of various stresses depending on their time and exposure through activation of complex signaling cascades.
Abstract: Mitogen-Activated Protein Kinases (MAPKs) cascade plays an important role in regulating plant growth and development, generating cellular responses to the extracellular stimuli. MAPKs cascade mainly consist of three sub-families i.e. mitogen-activated protein kinase kinase kinase (MAPKKK), mitogen-activated protein kinase kinase (MAPKK) and mitogen activated protein kinase (MAPK), several cascades of which are activated by various abiotic and biotic stresses. In this work we have modeled the holistic molecular mechanisms essential to MAPKs activation in response to several abiotic and biotic stresses through a system biology approach and performed its simulation studies. As extent of abiotic and biotic stresses goes on increasing, the process of cell division, cell growth and cell differentiation slow down in time dependent manner. The models developed depict the combinatorial and multicomponent signaling triggered in response to several abiotic and biotic factors. These models can be used to predict behavior of cells in event of various stresses depending on their time and exposure through activation of complex signaling cascades.
TL;DR: The results add to the understanding of the factors that contribute to soil biodiversity, and they show that combining plant and abiotic variables into one set of environmental variables hide important information about the drivers for belowground community assembly.
Abstract: Belowground communities support a great diversity of organisms, but the factors that maintain and regulate this diversity are poorly understood Both abiotic and biotic factors affect the abundance, diversity and distribution of soil organisms, and the spatial heterogeneity in these factors is a key in explaining belowground biodiversity However, a combined approach estimating the relative importance of spatial and environmental factors in small-scale structuring of soil communities is yet missing Here, a semi-natural grassland in south-central Sweden with high diversity of plants was sampled at two spatial scales (10 and 60 cm intervals) with the aim to examine the relative roles of plant identity, abiotic environmental factors and spatial factors for the small-scale spatial patterns of nematodes The data were analysed by variance partitioning with redundancy analysis Space, vegetation and abiotics were of similar importance for variation in nematode community composition However, the contribution of the different sets of variables differed between the different nematode feeding groups: plant-feeding nematodes were influenced more by spatial variables, fungal-feeding nematodes and omnivores/predators more by plants and bacterial-feeding nematodes more by abiotic variables The ranges of spatial dependence for the different feeding groups were all of the same magnitude, around 1 m The results add to the understanding of the factors that contribute to soil biodiversity, and they show that combining plant and abiotic variables into one set of environmental variables hide important information about the drivers for belowground community assembly
TL;DR: It was found that biological disturbances were the major forces driving the spatial heterogeneity of the alpine grassland vegetation and abiotic factors were of secondary importance and it was concluded that rat control and light grazing should be applied first in implementing restoration strategies.
Abstract: Understanding the complex effects of biotic and abiotic factors on the composition of vegetation is very important for developing and implementing strategies for promoting sustainable grassland development. The vegetation-disturbance-environment relationship was examined in degraded alpine grasslands in the headwater areas of three rivers on the Qinghai-Tibet Plateau in this study. The investigated hypotheses were that (1) the heterogeneity of the vegetation of the alpine grassland is due to a combination of biotic and abiotic factors and that (2) at a small scale, biotic factors are more important for the distribution of alpine vegetation. On this basis, four transects were set along altitudinal gradients from 3,770 to 3,890 m on a sunny slope, and four parallel transects were set along altitudinal gradients on a shady slope in alpine grasslands in Guoluo Prefecture of Qinghai Province, China. It was found that biological disturbances were the major forces driving the spatial heterogeneity of the alpine grassland vegetation and abiotic factors were of secondary importance. Heavy grazing and intensive rat activity resulted in increases in unpalatable and poisonous weeds and decreased fine forages in the form of sedges, forbs, and grasses in the vegetation composition. Habitat degradation associated with biological disturbances significantly affected the spatial variation of the alpine grassland vegetation, i.e., more pioneer plants of poisonous or unpalatable weed species, such as Ligularia virgaurea and Euphorbia fischeriana, were found in bare patches. Environmental/abiotic factors were less important than biological disturbances in affecting the spatial distribution of the alpine grassland vegetation at a small scale. It was concluded that rat control and light grazing should be applied first in implementing restoration strategies. The primary vegetation in lightly grazed and less rat-damaged sites should be regarded as a reference for devising vegetation restoration measures in alpine pastoral regions.
TL;DR: The hypotheses that as succession progresses, the strength and direction of certain community interactions shift, and B. tectorum leads to reductions in biological soil crust cover regardless of successional stage are supported.
TL;DR: The results suggest the need for urgent implementation of elementary reproductive studies in all cases, and for ex situ conservation measures for the most endangered taxa, even without prior studies.
TL;DR: The results demonstrate that changes in daily temperature regimes can alter predator–prey interactions among arthropods with consequences for ecosystem processes such as primary production and the relative importance of top–down and bottom–up processes.
Abstract: Because species interactions are often context-dependent, abiotic factors such as temperature and biotic factors such as food quality may alter species interactions with potential consequences to ecosystem structure and function. For example, altered predator–prey interactions may influence the dynamics of trophic cascades, affecting net primary production. In a three-year field experiment, we manipulated a plant–grasshopper–spider food chain in mesic tallgrass prairie to investigate the effects of temperature and food quality on grasshopper performance, and to understand the direct and indirect tritrophic interactions that contribute to trophic cascades. Because spiders are active at cooler temperatures than grasshoppers in our system, we hypothesized that predator effects would be strongest in cooled treatments, and weakest in warmed treatments. Grasshopper spider interactions were highly context-dependent and varied significantly with food quality, temperature treatment and year. Spiders most often reduced grasshopper survival in the cooled and ambient temperature treatments, but had little to no effect on grasshopper survival in the warmed treatments, as hypothesized. In some years, plants compensated for grasshopper herbivory and trophic cascades were not observed despite significant effects of predators on grasshopper survival. However, in the year they were observed, trophic cascades only occurred in cooled treatments where predator effects on grasshoppers were strongest. Predicting ecosystem responses to climate change will require an understanding of how temperature influences species interactions. Our results demonstrate that changes in daily temperature regimes can alter predator–prey interactions among arthropods with consequences for ecosystem processes such as primary production and the relative importance of top–down and bottom–up processes.
TL;DR: The richness of damage types due to natural enemies increased with abundance of the host species, suggesting an important role of enemy diversity in the maintenance of tree diversity.
Abstract: Summary
1.The Janzen–Connell hypothesis (JC) is one potential mechanism to explain the maintenance of high alpha diversity of tree species in tropical forests, operating through differential pressure by natural enemies.
2.We proposed that this differing pressure could arise from the richness of damage types due to natural enemies (RDNE). Following a community compensatory trend (CCT), we hypothesized greater RDNE on common species than on rare species.
3.We evaluated this novel interpretation of the JC by assessing damage patterns on leaves, as a proxy for natural enemy species in 44 tree species. We first evaluated which abiotic and biotic factors affect RDNE. Then, we tested whether increasing RDNE leads to an increasing amount of foliar damage.
4.We found that RDNE
Was affected by biotic environments: RDNE increased with mean seedling species abundance. RDNE was higher on species occurring near more closely related neighbours.
Was not impacted by abiotic factors. Yet, seedlings of shade-tolerant species hosted a higher RDNE than seedlings of shade-intolerant species.
Was positively correlated with amount of foliar damage at the species level.
5.Finally, we tested whether RDNE increased seedling mortality risk. We found that
Foliar damage, species abundance and RDNE2 increased mortality risk.
Richness of damage types due to natural enemies linearly decreased mortality risk more strongly than RDNE2 increased it.
Seedling age decreased mortality risk.
6.Synthesis. The richness of damage types due to natural enemies increased with abundance of the host species, suggesting an important role of enemy diversity in the maintenance of tree diversity. Supporting a novel interpretation of the Janzen–Connell hypothesis, we found a greater mortality risk with increasing RDNE2, but not with increasing RDNE. There was a stronger negative linear effect of RDNE on mortality risk. Rare species with low RDNE as well as species with very high RDNE suffered greater mortality than species hosting intermediate RDNE, reinforcing the complexity of the effect of multiple enemies on prey.