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At least 163 records · Page 9Linked to original sources
PubMed2006

The evolutionary consequences of ecological interactions mediated through phenotypic plasticity.

Phenotypic plasticity describes the capacity of a genotype to exhibit a range of phenotypes in response to variation in the environment. Environmental variation encompasses both abiotic and biotic components of the environment, including interactions among organisms. The strength and outcome of many ecological interactions, ranging from antagonism to mutualism, are mediated through the phenotypically plastic responses of one or more players in the interaction. Herein, three broadly defined, non-mutually exclusive, evolutionary consequences of ecological interactions mediated through phenotypic plasticity are discussed. (1) The predictable plastic response of one partner can favor behaviors, physiological responses, and life history traits of an interacting partner that manipulate, circumvent, or ameliorate the response of that partner. (2) Phenotypic plasticity can generate substantial spatial and temporal variation within and among populations. Such phenotypic variation can depend on the density and identity of interacting players in an ecological community, and can ultimately affect the evolutionary outcome of ecological interactions. (3) Phenotypic plasticity affects the strength and direction of natural selection. Ecological interactions mediated through phenotypic plasticity are ubiquitous in nature, and the potential evolutionary consequences of these interactions illustrate the complexity inherent in understanding evolution in a community context.

Adaptation, Physiological↗
PubMed1997

Abiotic and biotic determinants of the seasonal dynamics of the tick Rhipicephalus appendiculatus in South Africa.

The creation of a generic population model for the tick Rhipicephalus appendiculatus requires a detailed, quantified understanding of the interactions of these ticks with their biotic and abiotic environment in the different parts of their range, from the tropical regions of East Africa to the temperate regions of South Africa. The much greater seasonal variation in climatic conditions, particularly temperature, further from the equator introduces variable development rates and diapause into the life cycle. Estimates of natural temperature-dependent interstadial development periods, derived from a combination of published laboratory and field data, were applied to published data on the seasonal abundance of R.appendiculatus on three farms in the Eastern Cape Province of South Africa. This enabled an assessment of which ticks of one stage give rise to which ticks of the next stage, from which (a) the onset and duration of diapause in unfed adults, and (b) seasonal interstadial mortality indices in the form of k-values, could be estimated. The contribution of biotic (tick density) and abiotic (climatic) factors as predictors of mortality at each life stage was investigated by step-wise multiple regression. Density-independent mortality at the female-to-larval stage is correlated with geographically variable climatic factors, minimum temperature at two farms and minimum relative humidity at the third. The other two stages are governed by density-dependent mortality, which, it is argued, may be caused largely by the hosts' acquired resistance to ticks. As expected on theoretical grounds, this density dependence is weaker nearer to the edge of the tick's range and for the more vulnerable immature stages.

Animals↗
PubMedDate not supplied

[Enzyme-substrate mode of action for bacteria survival in water biotic community].

The role of enzyme--substrate interactions for the survival of bacteria in natural biocenoses has been analyzed with the systems "lysozyme-antilysozyme", "histon-antihiston" used as models. The conception of a possible universal mechanism for supporting the circulation of pathogenic and opportunistic microorganisms among eukaryotes, irrespective of their evolutionary status and environment, has been formulated. This mechanism is ensured by the natural resistance of the eukaryotic cells and by persistence factors on the part of the pathogen; as a result, the dynamic system of interactions is formed which facilitates the survival of microorganisms due to their persistence potential. New knowledge thus obtained opens prospects in the study of sanitary and ecological aspects of water biocenoses.

Animals↗
PubMed2007

Zea mays: benzoxazolinone detoxification under sulfur deficiency conditions--a complex allelopathic alliance including endophytic Fusarium verticillioides.

Benzoxazolinone detoxification is similar in plants grown under sulfur deficiency conditions and in control plants grown with an optimal S supply. However, when S-deficient plants were treated with metolachlor before benzoxazolin-2(3H)-one (BOA) incubation, detoxification was reduced, as indicated by a lower accumulation of the detoxification products BOA-6-O-glucoside and glucoside carbamate and by a loss of BOA-6-OH glucosyltransfease activity. Root colonizing microorganisms and the endophytic fungus Fusarium verticillioides participated in benzoxazolinone detoxification by converting the compound to 2-acetamidophenol (AAP) or O-hydroxyphenyl malonamic acid (OHPMA), a process accompanied by the appearance of phenoxazinone. Maize roots, however, absorbed AAP and OHPMA only in traces. Absorbed traces of OHPMA stimulated maize radicle growth, and traces of AAP stimulated cress. Phenoxazinone inhibited the growth of cress radicles at concentrations higher than 500 microM, whereas maize radicles were hardly affected. F. verticillioides did not convert benzoxazolinone to any known microbial degradation product when the medium of maize seedlings was inoculated with the fungus under sterile condition. Plant-fungus interactions seem to be important in plant survival of allelopathic attacks. This study points to a complicated network of allelopathic interactions that are influenced by biotic and abiotic factors, including herbicides.

Acetamides↗
PubMed1999

Climate change and trophic interactions.

With confirmation of anthropogenically induced climate change, the spotlight is on biologists to predict and detect effects on populations. The complexity of interactions within and between the biotic and abiotic components involved makes this a tough challenge, and most studies have consequently considered effects of only single climate variables on single species. However, some have gone further, and recently published long-term datasets now offer opportunities that complement new experimental approaches that span trophic levels. With these datasets, predicting relative shifts in temporal and spatial associations could be among the most tractable problems.

Journal Article↗
PubMed2001

Molecular basis of plant growth promotion and biocontrol by rhizobacteria.

Plant-growth-promoting rhizobacteria (PGPRs) are used as inoculants for biofertilization, phytostimulation and biocontrol. The interactions of PGPRs with their biotic environment, for example with plants and microorganisms, are often complex. Substantial advances in elucidating the genetic basis of the beneficial effects of PGPRs on plants have been made, some from whole-genome sequencing projects. This progress will lead to a more efficient use of these strains and possibly to their improvement by genetic modification.

Fertilizers↗
PubMed2002

Metal sulfides in oxygenated aquatic systems: implications for the biotic ligand model.

The Biotic Ligand Model (BLM) attempts to predict metal toxicity to aquatic organisms on the basis of metal speciation and effects at the cell surface. Current versions of the BLM for silver and copper consider metal binding by inorganic ligands, dissolved organic matter (DOM) and also competition at the cell surface from calcium and protons (pH). Recent studies reported in the geochemical and ecotoxicological literature have indicated the importance of sulfide as a ligand, even in fully oxygenated aquatic systems. Speciation calculations for oxygenated waters do not currently include reduced sulfur as a ligand and as a consequence, no version of the BLM model has been published including reduced sulfur. This reflects the limitations on our knowledge regarding reduced sulfur in aquatic systems. In this paper we highlight the need to include reduced sulfur in the Biotic Ligand Model, with the interaction between silver and inorganic metal sulfides as a specific example. The geochemical importance of metal sulfides as ligands for silver and the effect of 'dissolved' metal sulfide and other ligands on metal toxicity and accumulation are described and reviewed. Recommendations are made for future work needed to incorporate sulfide ligands into the BLM's modeling framework.

Animals↗
PubMed2006

Community maturity, species saturation and the variant diversity-productivity relationships in grasslands.

Detailed knowledge of the relationship between plant diversity and productivity is critical for advancing our understanding of ecosystem functioning and for achieving success in habitat restoration efforts. However, effects and interactions of diversity, succession and biotic invasions on productivity remain elusive. We studied newly established communities in relation to preexisting homogeneous vegetation invaded by exotic plants in the northern Great Plains, USA, at four study sites for 3 years. We observed variant diversity-productivity relationships for the seeded communities (generally positive monotonic at three sites and non-monotonic at the other site) but no relationships for the resident community or the seeded and resident communities combined at all sites and all years. Community richness was enhanced by seeding additional species but productivity was not. The optimal diversity (as indicated by maximum productivity) changed among sites and as the community developed. The findings shed new light on ecosystem functioning of biodiversity under different conditions and have important implications for restoration.

Biodiversity↗
PubMed2004

Spatial and temporal changes in microbial community structure associated with recharge-influenced chemical gradients in a contaminated aquifer.

In a contaminated water-table aquifer, we related microbial community structure on aquifer sediments to gradients in 24 geochemical and contaminant variables at five depths, under three recharge conditions. Community amplified ribsosomal DNA restriction analysis (ARDRA) using universal 16S rDNA primers and denaturing gradient gel electrophoresis (DGGE) using bacterial 16S rDNA primers indicated: (i). communities in the anoxic, contaminated central zone were similar regardless of recharge; (ii). after recharge, communities at greatest depth were similar to those in uncontaminated zones; and (iii). after extended lack of recharge, communities at upper and lower aquifer margins differed from communities at the same depths on other dates. General aquifer geochemistry was as important as contaminant or terminal electron accepting process (TEAP) chemistry in discriminant analysis of community groups. The Shannon index of diversity (H) and the evenness index (E), based on DGGE operational taxonomic units (OTUs), were statistically different across community groups and aquifer depths. Archaea or sulphate-reducing bacteria 16S rRNA abundance was not clearly correlated with TEAP chemistry indicative of methanogenesis or sulphate reduction. Eukarya rRNA abundance varied by depth and date from 0 to 13% of the microbial community. This contaminated aquifer is a dynamic ecosystem, with complex interactions between physical, chemical and biotic components, which should be considered in the interpretation of aquifer geochemistry and in the development of conceptual or predictive models for natural attenuation or remediation.

Archaea↗
PubMedDate not supplied

Calcium-dependent signal transduction pathways in plants--phytochrome mechanism of action as an example.

Higher plants appear to have some signalling molecules that are similar to those in animals. Early events in the response of plant cell to many physiological stimuli share common features, such as membrane depolarization and elevation in cytosolic free calcium level. Ca2+ has a vital role in mediating plant responses to external stimuli of both abiotic origin (e.g. light, cold, heat, movement, hypoxia and drought) and biotic origin (e.g. phytohormones, pathogens, interaction with symbionts). Recently, tremendous progress has been made in understanding the role of Ca2+ as a second messenger in plants. It has been shown that plasma membrane Ca2+ channels and vacuolar Ca2+ release channels may participate in multiple signalling pathways in higher plants. Ca(2+)-dependent modulation of cellular processes occurs via intracellular calcium-binding proteins, of which calmodulin is one of the best characterized. It is well documented that calcium is involved in light-induced, phytochrome-controlled signal transduction pathways in higher plants.

Calcium↗
PubMed2000

The effects of hybridization in plants on secondary chemistry: implications for the ecology and evolution of plant-herbivore interactions.

Natural hybridization is a frequent phenomenon in plants. It can lead to the formation of new species, facilitate introgression of plant traits, and affect the interactions between plants and their biotic and abiotic environments. An important consequence of hybridization is the generation of qualitative and quantitative variation in secondary chemistry. Using the literature and my own results, I review the effects of hybridization on plant secondary chemistry, the mechanisms that generate patterns of chemical variation, and the possible consequences of this variation for plants and herbivores. Hybrids are immensely variable. Qualitatively, hybrids may express all of the secondary chemicals of the parental taxa, may fail to express certain parental chemicals, or may express novel chemicals that are absent in each parent. Quantitatively, concentrations of parental chemicals may vary markedly among hybrids. There are five primary factors that contribute to variation: parental taxa, hybrid class (F(1), F(2), etc.), ploidy level, chemical class, and the genetics of expression (dominance, recessive vs. additive inheritance). This variation is likely to affect the process of chemical diversification, the potential for introgression, the likelihood that hybrids will facilitate host shifts by herbivores, and the conditions that might lead to enhanced hybrid susceptibility and lower fitness.

Journal Article↗
PubMed2003

A complete classification of Darwinian extinction in ecological interactions.

The evolution of a population by individual-level natural selection can result in the population's extinction. Selection causes the spread of phenotypes with higher relative fitness, but at the same time, selection can also indirectly produce changes in the physical, biotic, or genotypical environment through population interactions (e.g., environment modification, interspecific interactions, and genomic conflict). Because fitness is environment dependent, this can cause mean fitness to decrease, resulting in extinction. I call this process "Darwinian extinction." Examples of Darwinian extinction include a variety of dynamics and modes of extinction, but the variation is constrained. I determine the complete classification of possible dynamics and modes of Darwinian extinction due to ecological interactions, using bifurcation theory and models with ecological and evolutionary changes occurring on different timescales. This classification is also extended to extinctions due to interactions within the population. The mode of extinction may be either sudden or gradual (requiring additional stochastic processes), and each mode has specific types of dynamics associated with it. Darwinian extinction is a robust and normal phenomenon, and this reasonably complete classification can help us understand more thoroughly its role in nature.

Animals↗
PubMed2005

Evidence of species interactions within an ectomycorrhizal fungal community.

Ectomycorrhizal fungal communities can be structured by abiotic and biotic factors. Here, we present evidence for community structuring by species interactions. We sampled ectomycorrhizas and forest floor seven times during a 13-month period. The presence of various ectomycorrhizal fungal species was determined for each sample, and species co-occurrence analyses were performed. For both ectomycorrhizas and forest floor samples there was significantly less co-occurrence among species within the community than expected by chance, mostly because of negative associations involving Cenococcum geophilum or Clavulina cinerea. For some species pairs, there was significantly more co-occurrence than expected by chance. Both nitrogen and tannin additions to the forest floor altered some interactions among species. The causes of these nonrandom distributions are currently unknown. Future investigations on competition, antibiosis, parasitism and facilitation among ectomycorrhizal fungal species appear to be warranted.

Hyphae↗
PubMed2002

Species positions and extinction dynamics in simple food webs.

Recent investigations on the structure of complex networks have provided interesting results for ecologists. Being inspired by these studies, we analyse a well-defined set of small model food webs. The extinction probability caused by internal Lotka-Volterra dynamics is compared to the position of species. Simulations have revealed that some global properties of these food webs (e.g. the homogeneity of connectedness) and the positions of species therein (e.g. interaction pattern) make them prone to modelled biotic extinction caused by population dynamical effects. We found that: (a) homogeneity in the connectedness structure increases the probability of extinction events; (b) in addition to the number of interactions, their orientations also influence the future of species in a web. Since species in characteristic network positions are prone to extinction, results could also be interpreted as describing the properties of preferred states of food webs during community assembly. Our results may contribute to understanding the intimate relationship between pattern and process in ecology.

Animals↗
PubMedDate not supplied

[Originality and biogeographical specificities if intertropical zones].

The author gives a synthesis of original and specific characteristics of inter-tropical zones, abiotic (climate, soils) and especially biotic data: biodiversity originality, adaptations, ecosystems. He concludes his review by considering the richness of biological interactions (with two or three partners) as well as the biotic systems with parasites and hosts and the struggle against parasites of ecological (via bioindication) or biological nature.

Adaptation, Biological↗
PubMed2004

Parasitoids and competitors influence colony-level responses in the red imported fire ant, Solenopsis invicta.

Social insect colonies respond to challenges set by a variable environment by re-allocating work among colony members. In many social insects, such colony-level task allocation strategies are achieved through individual decisions that produce a self-organized adapting group. We investigated colony responses to parasitoid and native ant competitors in the red imported fire ant ( Solenopsis invicta). Parasitoid flies affected fire ants by decreasing the proportion of workers engaged in foraging. Competitors also altered colony-level behaviours by reducing the proportion of foraging ants and by increasing the proportion of roaming majors, whose role is colony defence. Interestingly, the presence of both parasitism and competition almost always had similar effects on task allocation in comparison to each of the biotic factors on its own. Thus, our study uniquely demonstrates that the interactive effect of both parasitism and competition is not necessarily additive, implying that these biotic factors alter colony behaviour in distinct ways. More generally, our work demonstrates the importance of studying the dynamics of species interactions in a broader context.

Animals↗
PubMed2002

Biological and chemical factors influencing shallow lake eutrophication: a long-term study.

The focus of eutrophication research has tended to be upon short-term and experimental studies. However, given the range of factors that can influence eutrophication dynamics, and that these matter over a range of time scales, some discrete, some continuous, eutrophication dynamics may only be fully investigated when long-term, time-series data are available. The present study aims to evaluate the interacting effects of abiotic processes and biotic dynamics in explaining variations of phytoplankton biomass in a eutrophic shallow lake, Barton Broad (Norfolk, UK) using a long-term data set. Multivariate statistical analysis shows that the inter-relationships between phytoplankton variability, nutrient and grazing factors were highly sensitive to seasonal periodicity. In spring phytoplankton biomass was related to phosphorus, nitrogen and silicon. In summer phytoplankton biomass was associated with phosphorus, nitrogen and zooplankton. In autumn phytoplankton was related to phosphorus, nitrogen, silicon and zooplankton. In winter, no significant relationship could be established between phytoplankton and environmental variables. This paper improves our understanding of the governing role of nitrogen, phosphorus, silicon and zooplankton upon phytoplankton variability, and hence, improves management methods for eutrophic lakes.

Animals↗
PubMed2002

Ecological risk assessment (ERA) and hormesis.

Based on our current state of knowledge, the significance and importance of hormesis is likely to be greater for ecotoxicology, a component of ecological risk assessment (ERA), than for the overall process of ERA. Appropriately determining the role of hormesis in ERA will require extension of hormesis beyond chemical stressors to abiotic (e.g. habitat) and biotic stressors (e.g. species introductions, organism interactions). It will also require determining for all stressors whether at both individual and higher levels of organization, hormesis has positive, neutral or adverse effects. This determination must be made for model organisms, populations and communities. Adverse effects are the least likely, however, neutral effects cannot be ruled out. Presently, consideration of hormetic effects in ERA is most appropriate in a detailed level ecological risk assessment (DLERA), the most complex form of ERA. It is not appropriate in either problem formulation or a screening level ERA (SLERA). Further, for hormetic effects to be recognized and accepted fully into ERA may require a paradigm shift. Three on-going paradigm shifts to which hormesis could be linked are: recognition of the low utility of no-observed effects concentrations (NOECs); recognition of the need for special treatment of essential element dose/concentration-responses, which are similar to hormetic responses; and, the replacement of environmental toxicology with ecological toxicology (ecotoxicology).

Adaptation, Physiological↗