Evidence of an active role of resveratrol derivatives in the tolerance of wild grapevines (Vitis vinifera ssp. sylvestris) to salinity.

Resveratrol and its derivatives are the most important phytoalexins with a crucial role in plant defense mechanisms. These compounds can occur either naturally or in response to abiotic stresses. Among them, salinity is one of the major threats to the sustainability and productivity of agro-economically important species, particularly those involved in the vini-viticulture sector. Understating salinity tolerance mechanisms in plants is required for the development of novel engineering tools. This study aimed to investigate the potential role of resveratrol derivatives in salinity tolerance of wild grapevines. Our data revealed that the tolerant Tunisian wild grapevine genotype "Ouchtata" exhibited an increased accumulation of resveratrol derivatives (glycosylated and non-glycosylated resveratrol and t-ɛ-viniferin and hydroxylated t-piceatannol) in both stems and roots, along with an increased total antioxidant activity (TAA) compared to the sensitive genotype "Djebba" under stress conditions, suggesting an involvement of these stilbenes in redox homeostasis, thereby, protecting cells from salt-induced oxidative damage. Overall, our study revealed, for the first time, an active role for resveratrol derivatives in salt stress tolerance in wild grapevine, highlighting their potential use as metabolic markers in future grapevine breeding programs for a sustainable vini-viticulture in salt-affected regions.

A successful defence strategy in grapevine cultivar 'Tocai friulano' provides compartmentation of grapevine Flavescence dorée phytoplasma.

BACKGROUND: Flavescence dorée (FD) is a grapevine disease caused by phytoplasma and it is one of the most destructive pathologies in Europe. Nowadays, the only strategies used to control the epidemics are insecticides against vector, but more sustainable techniques are required. Completely resistant Vitis vinifera varieties have not been uncovered yet, but differences in susceptibility among cultivars and spontaneous recovery from FD symptoms have been observed. The grapevine cultivar 'Tocai friulano' shows very low susceptibility to FD but its defence strategy to counteract the phytoplasma spread has not been deciphered yet. In this work, the mechanisms occurring within 'Tocai friulano' FD-infected plants were examined in depth to identify the phytoplasma distribution and the defence pathways involved. RESULTS: In 'Tocai friulano' symptoms of FD-infection remained confined near the area where they appeared during all the vegetative season. Analyses of secondary phloem showed a total absence of FD phytoplasma (FDp) in the trunk and its disappearance in 2-year-old arms from July to November, which was different from 'Pinot gris', a highly susceptible variety. Diverse modulations of defence genes and accumulation of metabolites were revealed in 1-year-old canes of 'Tocai friulano' FD-infected plants, depending on the sanitary status. Symptomatic portions showed high activation of both jasmonate- and salicylate-mediated responses, together with a great accumulation of resveratrol. Whereas activation of jasmonate-mediated response and high content of ε-viniferin were identified in asymptomatic 1-year-old cane portions close to the symptomatic ones. CONCLUSION: Successful defence mechanisms activated near the symptomatic areas allowed the compartmentation of FD symptoms and phytoplasmas within the infected 'Tocai friulano' plants. These results could suggest specific agronomical practices to be adopted during FD management of this variety, and drive research of resistance genes against FD.

Caftaric Acid Isolation from Unripe Grape: A "Green" Alternative for Hydroxycinnamic Acids Recovery.

Phenolic acids represent about one-third of the dietary phenols and are widespread in vegetable and fruits. Several plants belonging to both vegetables and medical herbs have been studied for their hydroxycinnamic acid content. Among them, Echinacea purpurea is preferentially used for caffeic acid-derivatives extraction. The wine industry is a source of by-products that are rich in phenolic compounds. This work demonstrates that unripe grape juice (verjuice) presents a simple high-pressure liquid chromatography (HPLC) profile for hydroxycinnamic acids (HCAs), with a great separation of the caffeic-derived acids and a low content of other phenolic compounds when compared to E. purpurea and other grape by-products. Here it is shown how this allows the recovery of pure hydroxycinnamic acids by a simple and fast method, fast protein liquid chromatography (FPLC). In addition, verjuice can be easily obtained by pressing grape berries and filtering, thus avoiding any extraction step as required for other vegetable sources. Overall, the proposed protocol could strongly reduce the engagement of solvent in industrial phenolic extraction.

Within-individual trophic variability drives short-term intraspecific trait variation in natural populations.

Intraspecific trait variability (ITV) maintains functional diversity in populations and communities, and plays a crucial role in ecological and evolutionary processes such as trophic cascades or speciation. Furthermore, functional variation within a species and its populations can help buffer against harmful environmental changes. Trait variability within species can be observed from differences among populations, and between- and within individuals. In animals, ITV can be driven by ontogeny, the environment in which populations live and by within-individual specialization or variation unrelated to growth. However, we still know little about the relative strength of these drivers in determining ITV variation in natural populations. Here, we aimed to (a) measure the relative strength of between- and within-individual effects of body size on ITV over time, and (b) disentangle the trophic changes due to ontogeny from other sources of variability, such as the environment experienced by populations and individual preferences at varying temporal and spatial scales. We used as a model system the endangered marble trout Salmo marmoratus, a freshwater fish living in a restricted geographical area (<900 km2 ) that shows marked changes in diet through ontogeny. We investigated two trophic traits, trophic position and resource use, with stable isotopes (δ15 N and δ13 C), and followed over time 238 individually tagged marble trout from six populations to estimate the trophic changes between and within individuals through ontogeny at three different time-scales (short term: 3 months, medium term: 1 year and long term: 2 years). We found that the relative strength of between- and within-individual effects of body size on trophic position and resource use change strongly over time. Both effects played a similar role in ITV over medium- and long-term time-scales, but within-individual effects were significantly driving trophic variability over short-term scales. Apart from ontogenetic shifts, individuals showed variability in trophic traits as big as the variability estimated between populations. Overall, our results show how the relative strengths of ITV drivers change over time. This study evidences the crucial importance of considering effects of time-scales on functional variability at individual, population and species levels.

The Secondary Structure of a Major Wine Protein is Modified upon Interaction with Polyphenols.

Polyphenols are an important constituent of wines and they are largely studied due to their antioxidant properties and for their effects on wine quality and stability, which is also related to their capacity to bind to proteins. The effects of some selected polyphenols, including procyanidins B1 and B2, tannic acid, quercetin, and rutin, as well as those of a total white wine procyanidin extract on the conformational properties of the major wine protein VVTL1 (Vitis vinifera Thaumatin-Like-1) were investigated by Synchrotron Radiation Circular Dichroism (SRCD). Results showed that VVTL1 interacts with polyphenols as demonstrated by the changes in the secondary (far-UV) and tertiary (near-UV) structures, which were differently affected by different polyphenols. Additionally, polyphenols modified the two melting temperatures (TM) that were found for VVTL1 (32.2 °C and 53.9 °C for the protein alone). The circular dichroism (CD) spectra in the near-UV region revealed an involvement of the aromatic side-chains of the protein in the interaction with phenolics. The data demonstrate the existence of an interaction between polyphenols and VVTL1, which results in modification of its thermal and UV denaturation pattern. This information can be useful in understanding the behavior of wine proteins in presence of polyphenols, thus giving new insights on the phenomena that are involved in wine stability.

Influence of pruning time and viral infection on stilbenoid levels in Pinot noir grape canes.

BACKGROUND: Grapevine canes represent a large source of waste derived from grape cultivation. In the present study, the effect of different processes of storage and different pruning times on the stilbene accumulation on Pinot noir canes was analyzed. Whether the alteration of the secondary metabolism accompanying leafroll symptom expressions could affect the stilbenoid accumulation in canes harvested at pruning time was also investigated. RESULTS: The maximum accumulation of trans-resveratrol and trans-piceatannol was obtained in canes harvested in October and dried at 40 °C. Even in grape canes harvested in October, November, and December and stored for different times at room temperature (20 ± 2 °C) a marked increase in trans-resveratrol and trans-piceatannol was evident, which reached a maximum at around 8 weeks of storage. A significant higher accumulation of trans-resveratrol and trans-piceatannol was also found in canes harvested from symptomatic plants compared to those harvested from asymptomatic plants for all the pruning times. CONCLUSION: This study confirms that the biosynthetic enzyme activities and, particularly, those involved in the stilbene pathway, persist during Pinot noir cane storage at different harvest times, with different storage times and conditions, and different sanitary status. © 2019 Society of Chemical Industry.

Evaluation of the phenolic profile and immunoreactivity of Mal d 3 allergen in ancient apple cultivars from Italy.

BACKGROUND: Since the second half of the 20th century, the cultivation of ancient and local apple cultivars has almost disappeared from orchards in Italy. Some of these ancient apple cultivars often possess high nutraceutical values and display lower allergenicity than the modern ones, supporting the so-called 'green revolution' theory. RESULTS: In this study, the phenolic composition and the antioxidant activity of five ancient apple cultivars ('Belfiore', 'Pomella Genovese', 'Gravenstein', 'Bella del Bosco', and 'Piatlin') were compared with a 'Golden Delicious' commercial cultivar. Additionally, apples were tested for their potential allergenicity by detecting the presence of Mal d 3, a non-specific lipid transfer protein that represents the main apples' allergen. All apples came from northern Italy (Trentino Region) and were organically produced. Results showed that, for all cultivars, the skins contained more polyphenols than the pulps. 'Bella del Bosco' had the highest amount of polyphenols and antioxidant activity, whereas 'Piatlin' had the lowest phenolic content. All ancient cultivars presented a higher amount of pulp phenolic compounds than 'Golden Delicious'. Immunoblotting techniques showed that 'Bella del Bosco' and 'Piatlin' had very low quantities of Mal d 3 allergen; hence, they can be considered hypoallergenic cultivars. CONCLUSIONS: The preservation of ancient apple cultivars would be of great importance, not only to maintain the biodiversity but also for their nutritional properties. The hypoallergenic activity of some of these cultivars could be of interest also for the preparation of different apple-based products. © 2020 Society of Chemical Industry.

Wine Fining with Plant Proteins.

Fining treatments involve the addition of a substance or a mixture to wine, and are generally carried out in order to clarify, stabilize or modify the wine's organoleptic characteristics. Usually these fining agents will bind the target compound(s) to form insoluble aggregates that are subsequently removed from the wine. The main reasons to perform wine fining treatments are to carry out wine clarification, stabilization and to remove phenolic compounds imparting unwanted sensory characteristics on the wine, which is an operation that often relies on the use of animal proteins, such as casein, gelatin, egg and fish proteins. However, due to the allergenic potential of these animal proteins, there is an increasing interest in developing alternative solutions including the use of fining proteins extracted from plants (e.g., proteins from cereals, grape seeds, potatoes, legumes, etc.), and non-proteinaceous plant-based substances (e.g., cell wall polysaccharides and pomace materials). In this article, the state of the art alternative fining agents of plant origins are reviewed for the first time, including considerations of their organoleptic and technological effects on wine, and of the allergenic risks that they can pose for consumers.

Characterization and emulsifying properties of extracts obtained by physical and enzymatic methods from an oenological yeast strain.

BACKGROUND: Glycosylated compounds are one of the main fractions of the yeast cell wall. Thanks to their amphiphilic structure, they have been studied as stabilizers in food emulsions over a broad range of pH conditions with encouraging results. Nevertheless, extraction costs still represent an important limit for their application in the food industry. RESULTS: In this research, four extraction methods were applied to yeast cells exploiting both physical (heating and sonication) and enzymatic approaches (use of three industrial enzyme preparations, namely Glucanex®, Sur Lies and Elevage). A fifth method involving a pure ß-glucanase enzyme (Zymolyase) was taken as reference. These extraction methods were applied to the oenological strain Saccharomyces cerevisiae EC1118, and their extraction yields and chemical properties (quantitative and qualitative determination of sugars and proteins) were studied. Emulsifying activities were determined at three different pH values (3, 5 and 7). Extractions with Physical, Glucanex and Sur Lies methods were the most successful approaches to obtain relevant amounts of yeast compounds with good emulsifying activities for 2:1 oil-in-water emulsions at pH 3 and 7 over 48 h. CONCLUSIONS: These results indicate that there is the potential for the extraction approaches here proposed to become viable tools for the recovery of yeast compounds to be used as emulsifiers in foods. This approach can be considered as the starting point to explore the possibility to exploit yeast by-products from the fermentation processes (e.g. fermentation lees from wine and beer making) as valuable compounds for food applications. © 2019 Society of Chemical Industry.

Stronger effects of heterozygosity on survival in harsher environments.

The hypothesis that the effects of heterozygosity vary with environmental conditions was tested using six populations of marble trout Salmo marmoratus from western Slovenia as a model system. The hypotheses tested were: stronger effects of heterozygosity on survival in populations characterized by low average survival; no effects of heterozygosity on probability of surviving flash floods owing to their largely non-selective effects across traits; stronger effects of heterozygosity on survival for fish born after floods than fish born before. A significant effect of heterozygosity on survival was found in populations characterized by low average survival. There were no effects of heterozygosity on probability of surviving flash floods, but in one population a positive correlation between heterozygosity and survival for fish born after the extreme events was found, probably because crowding in a small section of the stream caused more intense competition for resources.

A Novel Method for the Quantification of White Wine Mannoproteins by a Competitive Indirect Enzyme-Linked Lectin Sorbent Assay (CI-ELLSA).

Mannoproteins (MPs) are cell wall proteoglycans released in wine by yeast during fermentation and ageing on lees, a procedure used for the production of several wines to enrich them in these components with consequences from both a technological and sensory point of view. Given the significance that wine MPs have for wine quality, winemakers would welcome a simple and accurate method for their quantification, as this would allow them to have a better control of this aspect at different winemaking stages. This study develops and validates a novel, simple and accurate method for MPs quantification in white wines based on a competitive indirect enzyme-linked lectin sorbent assay (CI-ELLSA), using the highly mannosylated yeast invertase as the standard. The method utilizes the lectin concanavalin A (ConA) as the immobilized ligand for MPs, and peroxidase, an enzyme rich in mannose, as the competitor for ConA. After addition of the peroxidase substrate, the intensity of the signal produced by the activity of this enzyme (absorbance at 450 nm) is inversely proportional to the amount of mannosylated proteins in the sample. Results have been validated on several wine styles including still, sparkling and sweet wines.

Genetic and life-history consequences of extreme climate events.

Climate change is predicted to increase the frequency and intensity of extreme climate events. Tests on empirical data of theory-based predictions on the consequences of extreme climate events are thus necessary to understand the adaptive potential of species and the overarching risks associated with all aspects of climate change. We tested predictions on the genetic and life-history consequences of extreme climate events in two populations of marble trout Salmo marmoratus that have experienced severe demographic bottlenecks due to flash floods. We combined long-term field and genotyping data with pedigree reconstruction in a theory-based framework. Our results show that after flash floods, reproduction occurred at a younger age in one population. In both populations, we found the highest reproductive variance in the first cohort born after the floods due to a combination of fewer parents and higher early survival of offspring. A small number of parents allowed for demographic recovery after the floods, but the genetic bottleneck further reduced genetic diversity in both populations. Our results also elucidate some of the mechanisms responsible for a greater prevalence of faster life histories after the extreme event.

[Multicenter validation of an evaluation tool for clinical training activities (SVAT) of the nursing students]. / Validazione multicentrica di uno strumento di valutazione delle attivita' di tirocinio (SVAT) degli studenti infermieri.

OBJECTIVE: To evaluate the psychometric characteristics of the Scheda di Valutazione delle Attività di Tirocinio (SVAT). METHOD: The degree courses in Nursing of the University of Modena and Reggio Emilia, site of Reggio Emilia, the University of Bologna Formative Section BO1, Imola and training center of Cesena, the University of Ferrara training centers of Ferrara and Codigoro were all enrolled in the research. For the content validation the reactive Delphi method was chosen. The panel of experts expressed a qualitative-intuitive judgment on the adequacy of language and on the stimulus material (SVAT). For internal consistency Cronbach's alpha was calculated the. The test-retest method was used for the reliability of stability. RESULTS: all indicators of the SVAT have achieved a degree of consensus not less than 80% demonstrating its content validity. The face validity is demonstrated by an average score equal to or greater than 7 obtained by all indicators. The reliability of internal consistency of the SVAT was appraised by Cronbach's alpha that was 0.987 for the entire instrument. The reliability of the stability has been calculated through the correlation's coefficient expressed by Pearson's r that was 0.983 (p = 1.3E-198). DISCUSSION: in Italy there is no a "gold standard" tool to evaluate the clinical performance of nursing students during and at the end of their clinical training. The SVAT proves to be a valuable and reliable tool it furthermore could stimulate the discussion and the debate among educators and nurses, so that also in our country, it may be possible develop and refine tools that support the evaluation of clinical skills of nursing students.

Trade-offs between accuracy and interpretability in von Bertalanffy random-effects models of growth.

Better understanding of variation in growth will always be an important problem in ecology. Individual variation in growth can arise from a variety of processes; for example, individuals within a population vary in their intrinsic metabolic rates and behavioral traits, which may influence their foraging dynamics and access to resources. However, when adopting a growth model, we face trade-offs between model complexity, biological interpretability of parameters, and goodness of fit. We explore how different formulations of the von Bertalanffy growth function (vBGF) with individual random effects and environmental predictors affect these trade-offs. In the vBGF, the growth of an organism results from a dynamic balance between anabolic and catabolic processes. We start from a formulation of the vBGF that models the anabolic coefficient (q) as a function of the catabolic coefficient (k), a coefficient related to the properties of the environment (γ) and a parameter that determines the relative importance of behavior and environment in determining growth (ψ). We treat the vBGF parameters as a function of individual random effects and environmental variables. We use simulations to show how different functional forms and individual or group variability in the growth function's parameters provide a very flexible description of growth trajectories. We then consider a case study of two fish populations of Salmo marmoratus and Salmo trutta to test the goodness of fit and predictive power of the models, along with the biological interpretability of vBGF's parameters when using different model formulations. The best models, according to AIC, included individual variability in both k and γ and cohort as predictor of growth trajectories, and are consistent with the hypothesis that habitat selection is more important than behavioral and metabolic traits in determining lifetime growth trajectories of the two fish species. Model predictions of individual growth trajectories were largely more accurate than predictions based on mean size-at-age of fish. Our method shares information across individuals, and thus, for both fish populations investigated, allows using a single measurement early in the life of individual fish or cohort to obtain accurate predictions of lifetime individual or cohort size-at-age.

Within- and among-population variation in vital rates and population dynamics in a variable environment.

Understanding the causes of within- and among-population differences in vital rates, life histories, and population dynamics is a central topic in ecology. To understand how within- and among-population variation emerges, we need long-term studies that include episodic events and contrasting environmental conditions, data to characterize individual and shared variation, and statistical models that can tease apart shared and individual contribution to the observed variation. We used long-term tag-recapture data to investigate and estimate within- and among-population differences in vital rates, life histories, and population dynamics of marble trout Salmo marmoratus, an endemic freshwater salmonid with a narrow range. Only ten populations of pure marble trout persist in headwaters of Alpine rivers in western Slovenia. Marble trout populations are also threatened by floods and landslides, which have already caused the extinction of two populations in recent years. We estimated and determined causes of variation in growth, survival, and recruitment both within and among populations, and evaluated trade-offs between them. Specifically, we estimated the responses of these traits to variation in water temperature, density, sex, early life conditions, and extreme events. We found that the effects of population density on traits were mostly limited to the early stages of life and that growth trajectories were established early in life. We found no clear effects of water temperature on vital rates. Population density varied over time, with flash floods and debris flows causing massive mortalities (>55% decrease in survival with respect to years with no floods) and threatening population persistence. Apart from flood events, variation in population density within streams was largely determined by variation in recruitment, with survival of older fish being relatively constant over time within populations, but substantially different among populations. Marble trout show a fast to slow continuum of life histories, with slow growth associated with higher survival at the population level, possibly determined by food conditions and age at maturity. Our work provides unprecedented insight into the causes of variation in vital rates, life histories, and population dynamics in an endemic species that is teetering on the edge of extinction.

Carry-over effects of food supplementation on recruitment and breeding performance of long-lived seabirds.

Supplementation of food to wild animals is extensively applied as a conservation tool to increase local production of young. However, in long-lived migratory animals, the carry-over effects of food supplementation early in life on the subsequent recruitment of individuals into natal populations and their lifetime reproductive success are largely unknown. We examine how experimental food supplementation early in life affects: (i) recruitment as breeders of kittiwakes Rissa tridactyla born in a colony on Middleton Island (Alaska) between 1996 and 2006 (n = 1629) that bred in the same colony through 2013 (n = 235); and (ii) breeding success of individuals that have completed their life cycle at the colony (n = 56). Birds were raised in nests that were either supplemented with food (Fed) or unsupplemented (Unfed). Fledging success was higher in Fed compared with Unfed nests. After accounting for hatching rank, growth and oceanic conditions at fledging, Fed fledglings had a lower probability of recruiting as breeders in the Middleton colony than Unfed birds. The per-nest contribution of breeders was still significantly higher for Fed nests because of their higher productivity. Lifetime reproductive success of a subset of kittiwakes that thus far had completed their life cycle was not affected by the food supplementation during development. Our results cast light on the carry-over effects of early food conditions on the vital rates of long-lived animals and support food supplementation as an effective conservation strategy for long-lived seabirds.

Determining individual variation in growth and its implication for life-history and population processes using the empirical Bayes method.

The differences in demographic and life-history processes between organisms living in the same population have important consequences for ecological and evolutionary dynamics. Modern statistical and computational methods allow the investigation of individual and shared (among homogeneous groups) determinants of the observed variation in growth. We use an Empirical Bayes approach to estimate individual and shared variation in somatic growth using a von Bertalanffy growth model with random effects. To illustrate the power and generality of the method, we consider two populations of marble trout Salmo marmoratus living in Slovenian streams, where individually tagged fish have been sampled for more than 15 years. We use year-of-birth cohort, population density during the first year of life, and individual random effects as potential predictors of the von Bertalanffy growth function's parameters k (rate of growth) and L∞ (asymptotic size). Our results showed that size ranks were largely maintained throughout marble trout lifetime in both populations. According to the Akaike Information Criterion (AIC), the best models showed different growth patterns for year-of-birth cohorts as well as the existence of substantial individual variation in growth trajectories after accounting for the cohort effect. For both populations, models including density during the first year of life showed that growth tended to decrease with increasing population density early in life. Model validation showed that predictions of individual growth trajectories using the random-effects model were more accurate than predictions based on mean size-at-age of fish.

Seasonal Dynamics and Damage of Halyomorpha halys in Italian Vineyards.

The brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), is an invasive polyphagous pest often observed in vineyards. In Europe, a gap needs to be filled in the knowledge on H. halys seasonal dynamics and damage on grapes. With this study, we described the seasonal dynamics of H. halys and its distribution in multi-cultivar vineyards, and we evaluated the damage on grape clusters induced by different pest densities. In vineyards, the seasonal occurrence of H. halys varied across time and grape cultivars, and the pest was more abundant on Cabernet Franc, Merlot and, to a lesser extent, Pinot gris. Moreover, higher densities of H. halys were found on red berry cultivars than on white ones, and on cultivars ripening late in the season. An edge effect was also detected in pest distribution within vineyards, with more stink bugs observed in the borders. In the study on pest infestation density, H. halys caused damage on berries, showing differences in susceptibility among different cultivars and with regard to the time of infestation (i.e., plant phenological stages). Halyomorpha halys infestation induced an increase in Botrytis cinerea and sour rot incidence, which probably represents the main issue related to the impact of brown marmorated stink bug on grapevine.

Food availability affects onset of reproduction in a long-lived seabird.

Life-history theory predicts that suboptimal developmental conditions may lead to faster life histories (younger age at recruitment and higher reproductive investment), but experimental testing of this prediction is still scarce in long-lived species. We report the effects of an experimental manipulation of food availability during early development and at recruitment on the onset of reproduction and reproductive performance (productivity at first breeding) in a long-lived seabird, the black-legged kittiwake Rissa tridactyla, breeding on Middleton Island, Alaska. Birds were born and raised in nests with supplemented food ('fed') or unsupplemented control nests ('unfed'), and later recruited into either fed or unfed nests. Fed chicks grew faster than unfed chicks, and males grew faster than females. Birds were more likely to reproduce at younger ages when recruiting into fed nests. Faster growth during development tended to increase age at recruitment in all individuals. Social rank of individuals also affected age at recruitment: B-chicks recruited earlier than A-chicks and singletons recruited later than A- and B-chicks. Productivity increased with the age at recruitment and growth rate as chick, but much of the variability remained unexplained. We conclude that results of this study at least partially support predictions of life-history theory: younger age at first breeding for kittiwakes that experienced suboptimal natal conditions, as well as greater productivity of early recruiting kittiwakes that grew in control nests compared with those that grew in food-supplemented nests.

Robustness of empirical food webs with varying consumer's sensitivities to loss of resources.

Food web responses to species loss have been mostly studied in binary food webs, thus without accounting for the amount of energy transferred in consumer-resource interactions. We introduce an energetic criterion, called extinction threshold, for which a species goes secondarily extinct when a certain fraction of its incoming energy is lost. We study the robustness to random node loss of 10 food webs based on empirically-derived weightings. We use different extinction scenarios (random removal and from most- to least-connected species), and we simulate 10(5) replicates for each extinction threshold to account for stochasticity of extinction dynamics. We quantified robustness on the basis of how many additional species (i.e. secondary extinctions) were lost after the direct removal of species (i.e. primary extinctions). For all food webs, the expected robustness linearly decreases with extinction threshold, although a large variance in robustness is observed. The sensitivity of robustness to variations in extinction threshold increases with food web species richness and quantitative unweighted link density, while we observed a nonlinear relationship when the predictor is food web connectance and no relationship with the proportion of autotrophs.