Relative importance of nutrients and mortality factors on prokaryotic community composition in two lakes of different trophic status: microcosm experiments

The effect of nutrient resources (N and P enrichment) and of different grazing communities on the prokaryotic community composition (PCC) was investigated in two freshwater ecosystems: Sep reservoir (oligomesotrophic) and lake Aydat (eutrophic). An experimental approach using microcosms was chosen, that allowed control of both predation levels, by size fractionation of predators, and resources, by nutrient amendments. Changes in PCC were monitored by fluorescent in situ hybridization (FISH) and terminal-restriction fragment length polymorphism (T-RFLP). The main mortality agents were (i) heterotrophic nanoflagellates and virus-like particles in Aydat and (ii) cladocerans in Sep. All the nutritional elements assayed (N-NO3, P-PO4 and N-NH4) together with prokaryotic production (PP) always accounted for a significant part of the variations in PCC. Overall, prokaryotic diversity was mainly explained by resources in Sep, by a comparable contribution of resources and mortality factors in lake Aydat and, to a lesser extent, by the combined action of both.     

Size‐based interactions across trophic levels in food webs of shallow Mediterranean lakes

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Host‐microbiota interactions shed light on mortality events in the striped venus clam Chamelea gallina

Mass mortalities due to disease outbreaks have recently affected a number of major taxa in marine ecosystems. Climate‐ and pollution‐induced stress may compromise host immune defenses, increasing the risk of opportunistic diseases. Despite growing evidence that mass mortality events affecting marine species worldwide are strongly influenced by the interplay of numerous environmental factors, the reductionist approaches most frequently used to investigate these factors hindered the interpretation of these multifactorial pathologies. In this study, we propose a broader approach based on the combination of RNA‐sequencing and 16S microbiota analyses to decipher the factors underlying mass mortality in the striped venus clam, Chamelea gallina, along the Adriatic coast. On one hand, gene expression profiling and functional analyses of microbial communities showed the over‐expression of several genes and molecular pathways involved in xenobiotic metabolism, suggesting potential chemical contamination in mortality sites. On the other hand, the down‐regulation of several genes involved in immune and stress response, and the over‐representation of opportunistic pathogens such as Vibrio and Photobacterium spp. indicates that these microbial species may take advantage of compromised host immune pathways and defense mechanisms that are potentially affected by chemical exposure, resulting in periodic mortality events. We propose the application of our approach to interpret and anticipate the risks inherent in the combined effects of pollutants and microbes on marine animals in today's rapidly changing environment.     

Measurement, analysis, and interpretation of mortality factors in insect survivorship studies, with reference to the spruce budworm, Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae)

A theory and practical method are developed to evaluate insect survivorship as a continuous process in time and the effects of major factors that determine it, with a view to providing solutions to certain problems in survivorship studies. There are two ways of assessing mortality rates: nominal and marginal. A nominal rate is based on the number tallied in terms of the immediate cause of death; it depends on the method of observation employed and can be inconsistent between studies. A marginal rate is free of such inconsistency. The marginal rate attributable to the union of parasitism and disease is evaluated by frequent sampling in the field and rearing of each batch of samples in the laboratory for a short period of time. Comparing this rate with the field mortality rate, directly evaluated by sampling, determines marginal predation rate. The marginal parasitism and disease rates cannot be determined by observation. A computational method is developed to evaluate their approximate values. A step-by-step procedure of numerical calculations with data is provided in an appendix. The accuracy of estimating mortality depends on the frequency of sampling in the field and that of inspecting dead individuals in rearing. How frequently sampling and inspection should be conducted is discussed. The method of assessing parasitism developed here has a great advantage over the conventional method based on dissecting the samples, or rearing them through, that often results in a serious underestimation. Also discussed is the relative importance of mortality factors from the pest control point of view, and the concept of “joint contribution” is introduced. Other practical considerations include transportation of samples; rearing conditions; and how to deal with the “dead-in-the-field” in the samples, the “rearing-death syndrome,” and the “virtually dead” individuals. Received: August 25, 2000 / Accepted: May 17, 2001     

Progressive sensitivity of trophic levels to warming underlies an elevational gradient in ant–aphid mutualism strength

Although species interactions are often proposed to be stronger at lower latitudes and elevations, few studies have evaluated the mechanisms driving such patterns. In this study, we assessed whether, and by which mechanisms, abiotic changes associated with elevation altered the outcome of an ant–aphid protection mutualism. To do so, we characterized the multi‐trophic interactions among the ant Formica podzolica, the aphid Aphis varians, and aphid natural enemies occurring on the plant Chamerion angustifolium within replicate high and low elevation valleys. Low (versus high) elevation sites had longer summers (snowmelt 13 days earlier) and were on average 1.1°C warmer and 41% drier throughout the year. At low elevations, individual ant colonies consumed approximately double the volume of carbohydrate baits, likely due to a higher foraging tempo, and possibly due to a greater demand for sugar‐ versus protein‐rich resources (as indicated by stable isotope analysis). Wild aphid colonies at low elevations were visited by 1.4‐fold more natural enemies (controlling for variation in aphid abundance), while experimental aphid colonies on potted plants were tended 52% more frequently by ants. As a result, ants increased aphid colony survival by 66% at low elevations but had no detectable effect at high elevations; at low (versus high) elevations aphid colonies without ants had lower survival, demonstrating stronger predator effects, while aphid colonies with ants had higher survival, demonstrating even stronger ant benefits. Analyses for the effects of mean summer temperature yielded qualitatively identical results to those based on elevation. Collectively, these findings support predictions for a greater sensitivity of higher trophic levels to warming and demonstrate how species interactions can vary across environmental gradients due to simultaneous changes in species traits and abundances across multiple trophic levels.     

Lack of evidence for the match-mismatch hypothesis across terrestrial trophic interactions

Climate change has led to widespread shifts in the timing of key life history events between interacting species (phenological asynchrony) with hypothesized cascading negative fitness impacts on one or more of the interacting species—often termed ‘mismatch’. Yet, predicting the types of systems prone to mismatch remains a major hurdle. Recent reviews have argued that many studies do not provide strong evidence of the underlying match-mismatch hypothesis, but none have quantitatively analysed support for it. Here, we test the hypothesis by estimating the prevalence of mismatch across antagonistic trophic interactions in terrestrial systems and then examine whether studies that meet the assumptions of the hypothesis are more likely to find a mismatch. Despite a large range of synchrony to asynchrony, we did not find general support for the hypothesis. Our results thus question the general applicability of this hypothesis in terrestrial systems, but they also suggest specific types of data missing to robustly refute it. We highlight the critical need to define resource seasonality and the window of ‘match’ for the most rigorous tests of the hypothesis. Such efforts are necessary if we want to predict systems where mismatches are likely to occur.     

Development of trophic interactions in the vertebrate peripheral nervous system

During embryogenesis, the neurons of vertebrate sympathetic and sensory ganglia become dependent on neurotrophic factors, derived from their targets, for survival and maintenance of differentiated functions. Many of these interactions are mediated by the neurotrophins NGF, BDNF, and NT3 and the receptor tyrosine kinases encoded by genes of thetrk family. Both sympathetic and sensory neurons undergo developmental changes in their responsiveness to NGF, the first neurotrophin to be identified and characterized. Subpopulations of sensory neurons do not require NGF for survival, but respond instead to BDNF or NT3 with enhanced survival. In addition to their classic effects on neuron survival, neurotrophins influence the differentiation and proliferation of neural crest-derived neuronal precursors. In both sympathetic and sensory systems, production of neurotrophins by target cells and expression of neurotrophin receptors by neurons are correlated temporally and spatially with innervation patterns. In vitro, embryonic sympathetic neurons require exposure to environmental cues, such as basic FGF and retinoic acid to acquire neurotrophin-responsiveness; in contrast, embryonic sensory neurons acquire neurotrophin-responsiveness on schedule in the absence of these molecules.     

The role of interactions between trophic levels in determining the effects of UV-B on terrestrial ecosystems

Understanding the potential impact of ozone depletion on terrestrial ecosystems is constrained by lack of information on the effects of environmentally realistic UV-B doses on terrestrial organisms other than higher plants. Increasing UV-B may alter interactions between plants and consumers through direct effects on consumer organisms (herbivores, phytopathogens, decomposers, etc.). The effects of increasing UV-B on arthropods are not known. Significant UV-B effects on fungi have been reported, and may be either negative (inhibition of spore germination and mycelial growth) or positive (increased growth, induction of reproductive development and sporulation). However, in many cases consumers are unlikely to be directly exposed to UV-B in the field. In addition, UV action spectra for fungi suggest that this major group may be less sensitive to the effects of ozone depletion than higher plants. Host mediated effects of UV-B on consumers may include alterations in plant chemistry. While secondary metabolites such as phenolics may increase under increased UV-B, this is not invariably the case and evidence that such changes have significant effects on consumers is limited. In particular, there is no evidence that increased UV-B increases resistance of higher plants to fungal pathogens. Indeed, increased UV-B prior to inoculation results in no significant effect or increased disease. Such responses may be attributable to UV-B effects on host surface properties or on compounds other than phenolics. However, such changes are poorly known, and their potential effects on phytopathogens, herbivores or decomposers cannot be assessed. Understanding the effects of UV-B on terrestrial ecosystems is further limited since virtually nothing is known of possible impacts on higher trophic levels, i.e. predators, parasites or pathogens.     

Density-dependent egg mortality in early stages of gall induction by the fruit gall midge <Emphasis Type="Italic">Asphondylia aucubae</Emphasis> Yukawa and Ohsaki

Density-dependent mortality has been considered a symptom of intraspecific competition. We examined the occurrence of such mortality in the early stages of gall induction by the gall midge Asphondylia aucubae Yukawa et Ohsaki (Diptera: Cecidomyiidae). Female midges deposit eggs into young fruit of the dioecious shrub Aucuba japonica Thunberg to induce gall formation. Each host fruit received 0–67 eggs (mean 18.5 eggs) from multiple females, whereas established galls each contained one to ten larvae. Midges suffered intense mortality (65–90%) at the egg stage. Egg mortality occurred even in fruit in which no larvae had hatched, suggesting that this mortality cannot be wholly attributed to larval interference. Egg mortality was affected by fruit size, i.e., resource capacity. Midges distributed more eggs in larger fruit. Egg mortality increased as the per-fruit density increased relative to fruit size. In contrast, the mortality of hatchlings was density-independent. Our results suggest that A. aucubae intensely compete for gall-induction substrates, which are spatiotemporally rare resources.     

Environmental gradients and the evolution of tri‐trophic interactions

Long‐standing theory predicts herbivores and predators should drive selection for increased plant defences, such as the specific production of volatile organic compounds for attracting predators near the site of damage. Along elevation gradients, a general pattern is that herbivores and predators are abundant at low elevation and progressively diminish at higher elevations. To determine whether plant adaptation along such a gradient influences top‐down control of herbivores, we manipulated soil predatory nematodes, root herbivore pressure and plant ecotypes in a reciprocal transplant experiment. Plant survival was significantly higher for low‐elevation plants, but only when in the presence of predatory nematodes. Using olfactometer bioassays, we showed correlated differential nematode attraction and plant ecotype‐specific variation in volatile production. This study not only provides an assessment of how elevation gradients modulate the strength of trophic cascades, but also demonstrates how habitat specialisation drives variation in the expression of indirect plant defences.     

Alteration of trophic interactions between periphyton and invertebrates in an acidified stream: a stable carbon isotope study

The hypothesis according to which proliferation of periphytic algae under acid conditions results from a release of grazing pressure is tested. Stable carbon isotope analysis is used to investigate the autochthonous/allochthonous balance of invertebrate feeding in streamside artificial channels that were experimentally acidified. We find that the relative contribution of autochthonous food sources (epilithon) to total invertebrate biomass was slightly lower (after 1 mo of acidification) or not altered (after 2 mo) under acidified conditions when compared with a control. Feeding shifts were exhibited by some invertebrate taxa and provided evidence that acidification modifies trophic interactions between attached algae and primary consumers. Cross-treatment calculations showed that reduction of grazing pressure after the first month of acidification was an effect rather than the cause of periphyton proliferation. Our approach using stable carbon isotope analysis and biomass measurements of macroinvertebrates allows the quantification of the trophic base of lotic secondary producer communities under both experimental and natural conditions.     

Changes in woody vegetation abundance and diversity after natural disturbances causing different levels of mortality

Questions: How does woody vegetation abundance and diversity differ after natural disturbances causing different levels of mortality? Location: Abies balsamea–Betula papyrifera boreal mixed‐wood stands of southeast Quebec, Canada. Methods: Woody vegetation abundance and diversity were quantified and compared among three disturbance‐caused mortality classes, canopy gap, moderate‐severity disturbances, and catastrophic fire, using redundancy analysis, a constrained linear ordination technique, and diversity indices. Results: Substantial changes in canopy tree species abundance and diversity only occurred after catastrophic fire. Shade‐tolerant, late‐successional conifer species remained dominant after canopy gap and moderate‐severity disturbances, whereas shade‐intolerant, early‐successional colonizers dominated canopy tree regeneration after catastrophic fire. Density and diversity of mid‐tolerant and shade‐intolerant understory tree and shrub species increased as the impact of disturbance increased. Highest species richness estimates were observed after catastrophic fire, with several species establishing exclusively under these conditions. Relative abundance of canopy tree regeneration was most similar after canopy gap and moderate‐severity disturbances. For the sub‐canopy tree and shrub community, relative species abundances were most similar after moderate‐severity disturbances and catastrophic fire. Vegetation responses to moderate‐severity disturbances thus had commonalities with both extremes of the disturbance‐caused mortality gradient, but for different regeneration layers. Conclusions: Current spatio‐temporal parameters of natural disturbances causing varying degrees of mortality promote the development of a complex, multi‐cohort forest condition throughout the landscape. The projected increase in time intervals between catastrophic fires may lead to reduced diversity within the system.     

Inclusion of trophic interactions increases the vulnerability of an alpine butterfly species to climate change

Climate change is expected to have significant and complex impacts on ecological communities. In addition to direct effects of climate on species, there can also be indirect effects through an intermediary species, such as in host–plant interactions. Indirect effects are expected to be more pronounced in alpine environments because these ecosystems are sensitive to temperature changes and there are limited areas for migration of both species (i.e. closed systems), and because of simpler trophic interactions. We tested the hypothesis that climate change will reduce the range of an alpine butterfly (Parnassius smintheus) because of indirect effects through its host plant (Sedum sp.). To test for direct and indirect effects, we used the simulations of climate change to assess the distribution of P. smintheus with and without Sedum sp. We also compared the projected ranges of P. smintheus to four other butterfly species that are found in the alpine, but that are generalists feeding on many plant genera. We found that P. smintheus gained distributional area in climate‐only models, but these gains were significantly reduced with the inclusion of Sedum sp. and in dry‐climate scenarios which resulted in a reduction in net area. When compared to the more generalist butterfly species, P. smintheus exhibited the largest loss in suitable habitat. Our findings support the importance of including indirect effects in modelling species distributions in response to climate change. We highlight the potentially large and still neglected impacts climate change can have on the trophic structure of communities, which can lead to significant losses of biodiversity. In the future, communities will continue to favour species that are generalists as climate change induces asynchronies in the migration of species.     

营养相互作用对传统发酵食品微生物群落构建的推动作用研究进展

传统发酵食品是由自然接种的多微生物组成的混菌体系,了解微生物群落自发式构建的机制是认识发酵机理和调控发酵的关键。尽管大量的测序数据已经对传统发酵食品中微生物群落的结构和功能有了较为清晰的认识,但是仍然不清楚微生物群落自发式构建的机制。本文提出微生物群落是分布式的代谢系统,微生物之间的营养相互作用推动了传统发酵食品微生物群落的自发式构建。本文主要阐述了营养相互作用的概念、发生的机理以及研究方法体系,整理了传统发酵食品中微生物之间营养相互作用的研究进展,并提出了未来的研究方向。通过营养相互作用推动的传统发酵食品微生物群落的自发式构建有助于定向控制发酵过程中的微生物种类、提高生产效率和改善发酵质量。     

Antagonistic pleiotropy,mortality source interactions,and the evolutionary theory of senescence

Abstract.— Most theoretical work on the evolution of senescence has assumed that all individuals within a population are equally susceptible to extrinsic sources of mortality. An influential qualitative prediction based on this assumption is Williams's hypothesis, which states that more rapid senescence is expected to evolve when the magnitude of such extrinsic mortality sources is increased. Much evidence suggests, however, that for many groups of organisms externally imposed mortality risk is a function of an organism's internal condition and hence susceptibility to such hazards. Here we use a model of antagonistic pleiotropy to investigate the consequences that such interactions (between environmental hazard and internal condition) can have for Williams's hypothesis. As with some previous theory examining nonin-teractive extrinsic mortality sources, we find that an increase in interactive extrinsic sources of mortality makes it less likely that an individual will survive from birth to any given age, weakening selection against physiological deterioration at all ages and thus favoring more rapid senescence. However, an increase in interactive mortality sources also typically strengthens selection against physiological deterioration at any age, given an individual has survived to that age, because it reduces the fitness of poor-condition individuals more than good-condition individuals. These opposing effects are not felt equally at all ages, with the latter predominating at early ages. The combined effects can therefore result in the novel prediction that an increase in interactive extrinsic mortality sources can select for slower senescent deterioration early in life but more rapid deterioration late in life.     

The bias associated with the dispersion of length at age in the estimation of growth and mortality parameters from uni-modal length-frequency data

Values of M and M/K extracted from simulated uni-modal length-frequency data representing 28 fish stocks were biased. The bias exceeded 20% when the life span of the stock was <5 or >15 years.     

Interspecific interactions between wild felids vary across scales and levels of urbanization

Ongoing global landscape change resulting from urbanization is increasingly linked to changes in species distributions and community interactions. However, relatively little is known about how urbanization influences competitive interactions among mammalian carnivores, particularly related to wild felids. We evaluated interspecific interactions between medium‐ and large‐sized carnivores across a gradient of urbanization and multiple scales. Specifically, we investigated spatial and temporal interactions of bobcats and pumas by evaluating circadian activity patterns, broad‐scale seasonal interactions, and fine‐scale daily interactions in wildland–urban interface (WUI), exurban residential development, and wildland habitats. Across levels of urbanization, interspecific interactions were evaluated using two‐species and single‐species occupancy models with data from motion‐activated cameras. As predicted, urbanization increased the opportunity for interspecific interactions between wild felids. Although pumas did not exclude bobcats from areas at broad spatial or temporal scales, bobcats responded behaviorally to the presence of pumas at finer scales, but patterns varied across levels of urbanization. In wildland habitat, bobcats avoided using areas for short temporal periods after a puma visited an area. In contrast, bobcats did not appear to avoid areas that pumas recently visited in landscapes influenced by urbanization (exurban development and WUI habitat). In addition, overlap in circadian activity patterns between bobcats and pumas increased in exurban development compared to wildland habitat. Across study areas, bobcats used sites less frequently as the number of puma photographs increased at a site. Overall, bobcats appear to shape their behavior at fine spatial and temporal scales to reduce encounters with pumas, but residential development can potentially alter these strategies and increase interaction opportunities. We explore three hypotheses to explain our results of how urbanization affected interspecific interactions that consider activity patterns, landscape configuration, and animal scent marking. Altered competitive interactions between animals in urbanized landscapes could potentially increase aggressive encounters and the frequency of disease transmission.     

Exploring the association between extra-cardiac troponin elevations and risk of future mortality

Although the measurement of cardiac troponin I (cTnI) and T (cTnT) has now become the cornerstone for diagnosing cardiac injury, both ischemic and non-ischemic, recent evidence has become available that many patients display extra-cardiac causes of cTn elevations and carry a considerably enhanced risk of future mortality. The current literature data suggests that cTn elevations may be equally common in patients with cardiac and extra-cardiac diseases. Among the latter cohort of patients, the leading extra-cardiac diseases which may be responsible for either cTnI or cTnT elevations include infectious diseases/sepsis, pulmonary disorders, renal failure, malignancy, as well as gastrointestinal, neurological and musculoskeletal diseases. What also emerges rather clearly from the current literature data, is that the risk of dying for extra-cardiac diseases is higher (i.e., between two to three-fold) in patients with extra-cardiac cTn elevations than in those with cardiac pathologies, and that the most frequent cause of death would then be infections/sepsis, followed by malignancy, respiratory disorders, myocardial infarction, gastrointestinal and neurological diseases, heart failure, stroke, cardiac arrhythmias, renal failure, psychiatric, metabolic, urogenital and musculoskeletal disorders. These figures would lead to conclude that there is a considerable risk that the underlying pathology causing cardiac injury and cTn elevation would then become the cause of death in these patients. This important evidence shall lead the way to defining appropriate and effective strategies for managing patients with extra-cardiac cTn elevations, so that their risk of future death could be prevented or limited.     

A novel framework for linking functional diversity of plants with other trophic levels for the quantification of ecosystem services

A novel conceptual framework is presented that proposes to apply trait‐based approaches to predicting the impact of environmental change on ecosystem service delivery by multi‐trophic systems. Development of the framework was based on an extension of the response–effect trait approach to capture functional relationships that drive trophic interactions. The framework was populated with worked examples to demonstrate its flexibility and value for linking disparate data sources, identifying knowledge gaps and generating hypotheses for quantitative models.     

Mortality factors affecting the leaf-mining stages of Phyllonorycter (Lepidoptera: Gracillariidae) on oak and birch 1. Analysis of the mortality factors

Mortality of life stages of Phyllonoycter species in mined leaves of oak and birch was investigated in a Cheshire locality during 1974. Phyllonotycter species are mostly bivoltine, but P. cavella is univoltine. Parasitism and host-feeding (predation) by Hymenoptera caused most mortality. Parasitism was heaviest in the first generations, with ectoparasitism predominating, although endoparasitism caused inore mortality in the second generations. The incidence of host-feeding increased to leaf-fall when more mines contained host-fed remains than either parasites or healthy Phyllonoycter . Host-feeding occurred particularly in the first three (sap-feeding) larval instars; ectoparasitism affected mainly the two subsequent (tissue-feeding) larval stages and pupae; and endoparasitism occurred in all stages although affected hosts are killed only from the fourth larval instar onwards. Highest mortality was suffered by tissue feeders in the first generation but by sap feeders in the second. Total mortality was greatest in second generation mines and, in a given generation, survival curves for Phyllonotycter were similar on both tree species. The observed density of second generation mines relative to first in the sample was higher than predicted from first generation mortality levels, and this is discussed.