21 resultados para shortage of prey

em CentAUR: Central Archive University of Reading - UK


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The interactions among the multiple factors regulating predator-prey relationships make predation a more complex process than previously thought. The degree to which substandard individuals are captured disproportionately seems to be better a function of the difficulty of prey capture than of the hunting techniques (coursing vs. ambushing predators). That is, when the capture and killing of a prey species is easy, substandard individuals will be predated in proportion to their occurrence in the prey population. In the present study, we made use of eagle owls Bubo bubo and their main prey, the rabbit Oryctolagus cuniculus: (a) the brightness of the white tails of rabbits seems to be correlated with the physical condition of individuals, (b) by using the tails of predated rabbits as an index of individual condition, we found that eagle owls seem to prefer substandard individuals (characterized by duller tails), and (c) by using information from continuous radiotracking of 14 individuals, we suggest that the difficulty of rabbit capture could be low. Although the relative benefits of preying on substandard individuals should considerably decrease when a predator is attacking an easy prey, we hypothesise that the eagle owl preference for substandard individuals could be due to the easy detection of poor individuals by a visual cue, the brightness of the rabbit tail. Several elements allow us to believe that this form of visual communication between a prey and one of its main predators could be more widespread than previously thought. In fact: (a) visual signalling plays a relevant role in intraspecific communication in eagle owls and, consequently, visual signals could also play a role in interspecific interactions, and (b) empirical studies showed that signals may inform the predator that it has been perceived, or that the prey is in a sufficiently healthy state to elude the predator.

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In this study, we assessed the influence of prey quality and prey biomass during a standardized 3-week test on adult survival and reproductive output of the predatory mite Hypoaspis aculeifer when fed one of six different diets: springtails (Folsomia candida and Folsomia fimetaria), a storage mite (Caloglyphus cf. michaeli), an oligochaete (Enchytraeus crypticus), a nematode (Turbatrix silusiae), and a 1:1:1 mix of F. candida:F.fimetaria:E. crypticus. Our results revealed that a single prey species may be nutritionally sufficient for a 3-week period, as H. aculeifer performed equally well, or better, on a diet based on a 1:1:1 mix of F. candida:F. fimetaria:E. crypticus. However, when fed C. cf. michaeli, H. aculeifer had a poor reproductive output (< 200 juveniles) and a reduced survival (60-70%). Thus, investigators should validate their choice of prey prior to testing H. aculeifer performance during toxicant exposure. (c) 2007 Elsevier B.V. All rights reserved.

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Determining the degree of nitrate pollution in Chalk groundwater is difficult without a clear understanding of concentrations naturally present. In the UK, a general shortage of long-term records of nitrate concentrations in Chalk groundwater prevents a full quantification of baseline concentrations. This paper presents late nineteenth and early twentieth century data on nitrate concentrations in Chalk groundwater in south Dorset, UK and compares them with corresponding data for the last 25 years. The nitrate record is instructive in (1) providing an insight into the baseline nitrate concentration of groundwater; (2) defining the level of nitrate pollution in potable supplies from the Chalk aquifer; and (3) identifying the long-term variations in local nitrate concentrations. Over a period exceeding 100 years mean nitrate concentrations increased from 1.04 mg NO3-N l(-1) to 6.37 mg NO3-N l(-1). Anthropogenic modification of the local groundwater composition is not evident in the early nitrate record. Nitrate data throughout this early period reflect natural background concentrations of approximately I mg NO3-N l(-1) Intensified fertilser use and increased livestock numbers are suggested as the fundamental cause of the rise in nitrate concentrations. The implications of the nitrate record for regional hydrogeological processes are discussed. (C) 2003 Elsevier Science B.V. All rights reserved.

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A model of sugarcane digestion was applied to indicate the suitability of various locally available supplements for enhancing milk production of Indian crossbred dairy cattle. Milk production was calculated according to simulated energy, lipogenic, glucogenic and aminogenic substrate availability. The model identified the most limiting substrate for milk production from different sugarcane-based diets. For sugarcane tops/urea fed alone, milk production was most limited by amino acid followed by long chain fatty acid availability. Among the protein-rich oil cake supplements at 100, 200 and 300 g supplement/kg total DM, cottonseed oil cake proved superior with a milk yield of 5.5, 7.3 and 8.3 kg/day, respectively. This was followed by mustard oil cake with 5.1, 6.5 and 7.6 kg/day, respectively. In the case of a protein-rich supplement (fish meal), milk yield was limited to 6.6 kg/day due to a shortage of long chain fatty acids. However, at 300 g of supplementation, energy became limiting, with a milk yield of 6.7 kg/day. Supplementation with rice bran and rice polishings at 100, 200 and 300 g restricted milk yield to 4.3, 4.9 and 5.5 and 4.5, 5.3 and 6.1 kg/day, respectively, and amino acids became the factor limiting milk production. The diet comprising basal sugarcane tops supplemented by leguminous fodder, dry fodder (e.g. rice or wheat straw) and concentrates at levels of 100, 200 and 300 g supplements/kg total diet DM proved to be the most balanced with a milk yield of 5.1, 6.7 and 9.0 kg/day, respectively.

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Biodiversity-ecosystem functioning theory would predict that increasing natural enemy richness should enhance prey consumption rate due to functional complementarity of enemy species. However, several studies show that ecological interactions among natural enemies may result in complex effects of enemy diversity on prey consumption. Therefore, the challenge in understanding natural enemy diversity effects is to predict consumption rates of multiple enemies taking into account effects arising from patterns of prey use together with species interactions. Here, we show how complementary and redundant prey use patterns result in additive and saturating effects, respectively, and how ecological interactions such as phenotypic niche shifts, synergy and intraguild predation enlarge the range of outcomes to include null, synergistic and antagonistic effects. This study provides a simple theoretical framework that can be applied to experimental studies to infer the biological mechanisms underlying natural enemy diversity effects on prey.

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The major threat to Short-toed Eagles (Circaetus gallicus) is the reduction of suitable foraging habitats, but no quantitative studies have been conducted to understand this process. Here, the spatial distribution of foraging Short-toed Eagles was studied in relation to nine habitat types in Dadia-Lefkimi-Soufli National Park, Greece, during 1996-1998. Compared to the observed occurrence of foraging individuals over a particular habitat type with the expected utilization of that same habitat type, Short-toed Eagles concentrated their foraging efforts on three types of open habitat: intensive and non-intensive cultivation, and grasslands. Forested areas (pine forests, oak forests and mixed oak-pine forests) were largely avoided by foraging individuals. The density of prey items on the ground may not necessarily be a good indicator as to where an eagle individual will forage, as vegetation structure is also highly influential. The results highlight the importance of open habitat types which provide foraging opportunities for the Short-toed Eagle population. Management guidelines that maintain the region as a patchy network of open and wooded habitats are discussed in order to conserve a viable population of Short-toed Eagles, and possibly certain other raptor species that forage over open areas.

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Question: What are the life-history costs for a predatory insect of surviving parasitoid attack, and can parasitoid attack alter predator-prey interactions? Hypotheses: Survivorship is influenced by host age. Hosts that suffer parasitoid attack grow more slowly and consume fewer prey. Those that survive attack are smaller as adults and show reduced survivorship. Organisms: The aphidophagous hoverfly Episyrphus balteatus, its endoparasitoid wasp Diplazon laetatorius and its prey, the pea aphid, Acyrthosiphon pisum. Site of experiments: All experiments were conducted in controlled temperature rooms and chambers in the laboratory. Methods: Episyrphus balteatus larvae of each instar were exposed to attack by Diplazon laetatorius, then dissected to measure the encapsulation response (a measure of immunity). Second instar larvae were either attacked or not attacked by D. laetatorius. Their development rates and numbers of prey consumed were noted. The size and survivorship of surviving (immune) and control hoverflies were compared following eclosion. Conclusions: Successful immune response increased with larval age (first instar 0%, second instar 40%, third instar 100% survival). Second instar larvae that successfully resisted parasitoid attack were larger as pupae (but not as adults) and showed reduced adult survivorship. Female adult survivors were more likely than male survivors to have died within 16 days of eclosion, but there was no difference between unattacked male and female control hoverflies. Attacked larvae, irrespective of immune status, consumed fewer aphids than unattacked individuals. Episyrphus balteatus suffers significant costs of resisting parasitoid attack, and parasitoid attack can reduce the top-down effects of an insect predator, irrespective of whether the host mounts an immune response or not.

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This thesis is aimed to initiate implementing sustainable building construction in the kingdom of Bahrain, i.e. Building-Integration PhotoVoltaic (BIPV) or Wind Energy (BIWE). It highlights the main constrains that discourage such modern concept in building and construction. Three groups have been questioned using a questionnaire. These are the policy and decision makers, the leading consultants and the contractors. The main constrains of the dissemination of BIVP and BIWE, according to the policy and decision makers, are: lack of knowledge and awareness of the public in sustainable technology, low cost of electricity, low cost of gas and oil and difficulty in applying local environmental taxes. The consultants had attributed the constrains to ignorance of life cycle cost of PV and Wind turbines systems, lack of education and knowledge in sustainable design, political system, shortage of markets importing sustainable technologies and client worries in profitability and pay-back period. The contractors are found to be very enthusiastic and ready to take over any sustainable building project and prefer to have a construction manger to coordinate between the design and contracting team. Design and Build is found the favorable procurement method in Bahrain for conducting BIPV or BIWE projects.

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Background:  Poor diet quality is a major public health concern that has prompted governments to introduce a range of measures to promote healthy eating. For these measures to be effective, they should target segments of the population with messages relevant to their needs, aspirations and circumstances. The present study investigates the extent to which attitudes and constraints influence healthy eating, as well as how these vary by demographic characteristics of the UK population. It further considers how such information may be used in segmented diet and health policy messages. Methods:  A survey of 250 UK adults elicited information on conformity to dietary guidelines, attitudes towards healthy eating, constraints to healthy eating and demographic characteristics. Ordered logit regressions were estimated to determine the importance of attitudes and constraints in determining how closely respondents follow healthy eating guidelines. Further regressions explored the demographic characteristics associated with the attitudinal and constraint variables. Results:  People who attach high importance to their own health and appearance eat more healthily than those who do not. Risk-averse people and those able to resist temptation also eat more healthily. Shortage of time is considered an important barrier to healthy eating, although the cost of a healthy diet is not. These variables are associated with a number of demographic characteristics of the population; for example, young adults are more motivated to eat healthily by concerns over their appearance than their health. Conclusions:  The approach employed in the present study could be used to inform future healthy eating campaigns. For example, messages to encourage the young to eat more healthily could focus on the impact of diets on their appearance rather than health.

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Snakebites are a major neglected tropical disease responsible for as many as 95000 deaths every year worldwide. Viper venom serine proteases disrupt haemostasis of prey and victims by affecting various stages of the blood coagulation system. A better understanding of their sequence, structure, function and phylogenetic relationships will improve the knowledge on the pathological conditions and aid in the development of novel therapeutics for treating snakebites. A large dataset for all available viper venom serine proteases was developed and analysed to study various features of these enzymes. Despite the large number of venom serine protease sequences available, only a small proportion of these have been functionally characterised. Although, they share some of the common features such as a C-terminal extension, GWG motif and disulphide linkages, they vary widely between each other in features such as isoelectric points, potential N-glycosylation sites and functional characteristics. Some of the serine proteases contain substitutions for one or more of the critical residues in catalytic triad or primary specificity pockets. Phylogenetic analysis clustered all the sequences in three major groups. The sequences with substitutions in catalytic triad or specificity pocket clustered together in separate groups. Our study provides the most complete information on viper venom serine proteases to date and improves the current knowledge on the sequence, structure, function and phylogenetic relationships of these enzymes. This collective analysis of venom serine proteases will help in understanding the complexity of envenomation and potential therapeutic avenues.

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Diffuse pollution, and the contribution from agriculture in particular, has become increasingly important as pollution from point sources has been addressed by wastewater treatment. Land management approaches, such as construction of field wetlands, provide one group of mitigation options available to farmers. Although field wetlands are widely used for diffuse pollution control in temperate environments worldwide, there is a shortage of evidence for the effectiveness and viability of these mitigation options in the UK. The Mitigation Options for Phosphorus and Sediment Project aims to make recommendations regarding the design and effectiveness of field wetlands for diffuse pollution control in UK landscapes. Ten wetlands have been built on four farms in Cumbria and Leicestershire. This paper focuses on sediment retention within the wetlands, estimated from annual sediment surveys in the first two years, and discusses establishment costs. It is clear that the wetlands are effective in trapping a substantial amount of sediment. Estimates of annual sediment retention suggest higher trapping rates at sandy sites (0.5–6 t ha�1 yr�1), compared to silty sites (0.02–0.4 t ha�1 yr�1) and clay sites (0.01–0.07 t ha�1 yr�1). Establishment costs for the wetlands ranged from £280 to £3100 and depended more on site specific factors, such as fencing and gateways on livestock farms, rather than on wetland size or design. Wetlands with lower trapping rates would also have lower maintenance costs, as dredging would be required less frequently. The results indicate that field wetlands show promise for inclusion in agri-environment schemes, particularly if capital payments can be provided for establishment, to encourage uptake of these multi-functional features.

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In today's global economic conditions, improving the productivity of the construction industry is becoming more pressing than ever. Several factors impact the efficiency of construction operatives, but motivation is among the most important. Since low productivity is one of the significant challenges facing the construction industry in the State of Kuwait, the objective of this case study is to identify, explore, and rank the relative importance of the factors perceived to impact the motivational level of master craftsmen involved in primary construction trades. To achieve this objective, a structured questionnaire survey comprising 23 factors, which were shortlisted based on relevant previous research on motivation, the input of local industry experts, and numerous interviews with skilled operatives, was distributed to a large number of master craftsmen. Using the “Relative Importance Index” technique, the following prominent factors are identified: (1) payment delay; (2) rework; (3) lack of a financial incentive scheme; (4) the extent of change orders during execution; (5) incompetent supervisors; (6) delays in responding to Requests For Information (RFI); (7) overcrowding and operatives interface; (8) unrealistic scheduling and performance expectation; (9) shortage of materials on site; and (10) drawings quality level. The findings can be used to provide industry practitioners with guidance for focusing, acting upon, and controlling the critical factors influencing the performance of master craftsmen, hence, assist in achieving an efficient utilization of the workforce, and a reasonable level of competitiveness and cost effective operation.

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Simple predator–prey models with a prey-dependent functional response predict that enrichment (increased carrying capacity) destabilizes community dynamics: this is the ‘paradox of enrichment’. However, the energy value of prey is very important in this context. The intraspecific chemical composition of prey species determines its energy value as a food for the potential predator. Theoretical and experimental studies establish that variable chemical composition of prey affects the predator–prey dynamics. Recently, experimental and theoretical approaches have been made to incorporate explicitly the stoichiometric heterogeneity of simple predator–prey systems. Following the results of the previous experimental and theoretical advances, in this article we propose a simple phenomenological formulation of the variation of energy value at increased level of carrying capacity. Results of our study demonstrate that coupling the parameters representing the phenomenological energy value and carrying capacity in a realistic way, may avoid destabilization of community dynamics following enrichment. Additionally, under such coupling the producer–grazer system persists for only an intermediate zone of production—a result consistent with recent studies. We suggest that, while addressing the issue of enrichment in a general predator–prey model, the phenomenological relationship that we propose here might be applicable to avoid Rosenzweig’s paradox.

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In theory, enrichment of resource in a predator-prey model leads to destabilization of the system, thereby collapsing the trophic interaction, a phenomenon referred to as "the paradox of enrichment". After it was first proposed by Rosenzweig (1971), a number of subsequent studies were carried out on this dilemma over many decades. In this article, we review these theoretical and experimental works and give a brief overview of the proposed solutions to the paradox. The mechanisms that have been discussed are modifications of simple predator-prey models in the presence of prey that is inedible, invulnerable, unpalatable and toxic. Another class of mechanisms includes an incorporation of a ratio-dependent functional form, inducible defence of prey and density-dependent mortality of the predator. Moreover, we find a third set of explanations based on complex population dynamics including chaos in space and time. We conclude that, although any one of the various mechanisms proposed so far might potentially prevent destabilization of the predator-prey dynamics following enrichment, in nature different mechanisms may combine to cause stability, even when a system is enriched. The exact mechanisms, which may differ among systems, need to be disentangled through extensive field studies and laboratory experiments coupled with realistic theoretical models.

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1.Habitat conversion for agriculture is a major driver of biodiversity loss, but our understanding of the demographic processes involved remains poor. We typically investigate the impacts of agriculture in isolation even though populations are likely to experience multiple, concurrent changes in the environment (e.g. land and climate change). Drivers of environmental change may interact to affect demography but the mechanisms have yet to be explored fully in wild populations. 2.Here, we investigate the mechanisms linking agricultural land-use with breeding success using long-term data for the formerly Critically Endangered Mauritius kestrel Falco punctatus; a tropical forest specialist that also occupies agricultural habitats. We specifically focused on the relationship between breeding success, agriculture and the timing of breeding because the latter is sensitive to changes in climatic conditions (spring rainfall), and enables us to explore the interactive effects of different (land and climate) drivers of environmental change. 3.Breeding success, measured as egg survival to fledging, declines seasonally in this population, but we found that the rate of this decline became increasingly rapid as the area of agriculture around a nest site increased. If the relationship between breeding success and agriculture was used in isolation to estimate the demographic impact of agriculture it would significantly under-estimate breeding success in dry (early) springs, and over-estimate breeding success in wet (late) springs. 4.Analysis of prey delivered to nests suggests that the relationship between breeding success and agriculture might be due, in part, to spatial variation in the availability of native, arboreal geckos. 5.Synthesis and applications. Agriculture modifies the seasonal decline in breeding success in this population. As springs are becoming wetter in our study area and since the kestrels breed later in wetter springs, the impact of agriculture on breeding success will become worse over time. Our results suggest that forest restoration designed to reduce the detrimental impacts of agriculture on breeding may also help reduce the detrimental effects of breeding late due to wetter springs. Our results therefore highlight the importance of considering the interactive effects of environmental change when managing wild populations.