Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “exploitation competition”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 217 records · Page 12Linked to original sources
PubMed2006

Effect of nitrite concentration on the distribution and competition of nitrite-oxidizing bacteria in nitratation reactor systems and their kinetic characteristics.

Genus Nitrospira and Nitrobacter species are the key nitrite-oxidizing bacteria (NOB) in nitrifying wastewater treatment plants. It has been hypothesized that genus Nitrospira are K-strategists and can exploit low amounts of nitrite more efficiently than Nitrobacter. In contrast, Nitrobacter species are r-strategists that can grow faster than Nitrospira. To elucidate the K/r hypothesis and to analyze the effect of substrate (nitrite) concentration on the competition and distribution of the two NOB, two different reactor types were employed for nitrite oxidation (nitratation) and NOB growth. The continuous biofilm airlift reactor (CBAR) maintained low nitrite concentration due to the complete oxidation of nitrite in continuous operation while the sequencing batch reactor (SBR) was kept in a relatively high nitrite concentration environment due to a cyclic substrate concentration profile. Fluorescence in situ hybridization (FISH) and confocal laser scanning microscopy (CLSM) showed that both Nitrobacter species and genus Nitrospira were present in the CBAR and the SBR. Quantitative FISH analyses of the CBAR showed that Nitrospira occupied 59% of the total bacteria while Nitrobacter occupied only 5%. On the other hand, Nitrobacter, occupying 64%, was the dominant NOB in the SBR, and only 3% of total bacteria belonged to genus Nitrospira. Nitrite oxidation kinetics and quantitative FISH analyses revealed that the specific nitrite oxidation activities of Nitrobacter and Nitrospira are 93.8 and 10.5 mg/g NOB h, respectively, and the specific activity of Nitrobacter is about 9 times higher than that of Nitrospira. In conclusion, the results confirm the K/r hypothesis and the distribution of Nitrobacter and Nitrospira is likely to depend mainly on nitrite concentration. It seems that nitrite load and starvation conditions do not give a direct effect on the distribution of NOB.

Bacteria↗
PubMed2006

Evolutionary regime shifts in age and size at maturation of exploited fish stocks.

Worldwide declines of fish stocks raise concerns about deleterious consequences of harvesting for stock abundances and individual life histories, and call for appropriate recovery strategies. Fishes in exploited stocks mature earlier at either larger or smaller sizes due to both genetic and plastic responses. The latter occur commonly when reduced competition for food leads to faster growth. Using a size-structured consumer-resource model, which accounts for both genetic and plastic responses, we show that fisheries-induced evolutionary changes in individual life history and stock properties can easily become irreversible. As a result of annual spawning, early maturation at small sizes and late maturation at large sizes can become alternative, evolutionarily and ecologically stable states under otherwise identical environmental conditions. Exploitation of late-maturing populations can then induce an evolutionary regime shift to smaller maturation sizes associated with stepwise, 1-year decreases in age at first reproduction. Complete and early fishing moratoria slowly reverse this process, but belated or partial closure of fisheries may accelerate or even instigate further evolution to smaller sizes at maturation. We suggest that stepwise decreases in maturation age can be used as early warnings of upcoming evolutionary changes, and should inspire timely restrictions of fisheries.

Adaptation, Physiological↗
PubMed1999

'Un chant d'appel amoureux': acoustic communication in moths

Tympanal sound receptors in moths evolved in response to selective pressures provided by echolocating insectivorous bats. The presence of these ultrasound detectors also set the stage for the later evolution of ultrasonic courtship signals in the tympanate moth families. Male moths have repeatedly exploited the bat-detection mechanisms in females for the purpose of finding, identifying and obtaining mates. Ultrasonic courtship has been described in several members of the moth families Arctiidae, Noctuidae and Pyralidae, and ultrasound is predicted to play a significant role in the courtship of other tympanate moths including the Sphingidae, Lymantriidae, Notodontidae and Geometridae. Ultrasonic signals are involved in species recognition, in male-male competition for mates and in female mate-choice systems. Pre-existing motor systems, including those involved in bat defence, have also been exploited for the purpose of generating high-frequency courtship signals. Sound production mechanisms in moths include thoracic tymbals, tegular tymbals, alar castanets and genital stridulatory organs. Thus, in both their sensory and motor aspects, the weapons of bat/moth warfare have frequently evolved into components of courtship systems.

Journal Article↗
PubMed2006

Character displacement promotes cooperation in bacterial biofilms.

Resource competition within a group of cooperators is expected to decrease selection for cooperative behavior but can also result in diversifying selection for the use of different resources, which in turn could retard the breakdown of cooperation. Diverse groups are likely to be less susceptible to invasion by noncooperating social cheats: First, competition repression resulting from character displacement may provide less of a selective advantage to cheating; second, cheats may trade off the ability to exploit cooperators that specialize in one type of resource against cooperators that specialize in another ; third, diverse communities of any kind may have higher invasion resistance because there are fewer resources available for an invader to use . Furthermore, diverse groups are likely to be more productive than clonal groups if a wider range of total resources are being used . We addressed these issues by using the cooperative trait of biofilm formation in Pseudomonas fluorescens. Character displacement through resource competition evolved within biofilms; productivity increased with increasing character displacement, and diverse biofilms were less susceptible to invasion by cheats. These results demonstrate that diversification into different ecological niches can minimize selection against cooperation in the face of local resource competition.

Biofilms↗
PubMed1990

Insulinlike growth factor I: a potent mitogen for human osteogenic sarcoma.

Insulinlike growth factor I (IGF-I) is among the peptide mitogens that play key roles in the regulation of normal skeletal growth. To investigate the possibility that certain skeletal neoplasms retain a sensitivity to mitogenic stimulation by IGF-I, we studied the effects of this growth factor on human osteosarcoma. Competitive-binding assays and affinity-labeling experiments on membranes prepared from MG-63 immortalized human osteosarcoma cells and primary human osteogenic sarcoma cells demonstrate the presence of specific IGF-I receptors. Furthermore, we show that IGF-I is a potent stimulator of proliferation of MG-63 cells in vitro and is active at concentrations as low as 10(-10) M. A blocking antibody against the IGF-I receptor (alpha-IR3) significantly reduces IGF-I-stimulated proliferation in a dose-dependent manner. These results are consistent with the hypothesis that at least a subset of human osteogenic sarcomas are responsive to IGF-I and indicate that it may be possible to exploit this responsiveness therapeutically.

Affinity Labels↗
PubMed2004

Design of a high-affinity competitive antagonist of the vanilloid receptor selective for the calcium entry-linked receptor population.

We describe the synthesis and characterization of N-(4-chlorobenzyl) -N'-(4-hydroxy-3-iodo-5-methoxybenzyl)thiourea (IBTU), a novel antagonist of the vanilloid receptor 1 (TRPV1 or VR1). IBTU competitively inhibited 45Ca2+ uptake into CHO cells heterologously expressing rat TRPV1, whether induced by capsaicin or resiniferatoxin (Ki = 99 +/- 23 and 93 +/- 34 nM, respectively). IBTU was thus somewhat more potent (5-fold) than capsazepine. In contrast to its antagonism of vanilloid-induced calcium uptake, IBTU (30 microM) inhibited [3H]resiniferatoxin binding to TRPV1 by less than 10%. We hypothesize that these dramatically distinct potencies reflect different fractions of TRPV1 in this system: namely, a minor plasma membrane fraction controlling 45Ca2+ uptake, and the predominant intracellular fraction that dominates the [3H]resiniferatoxin binding measurements. Intracellular Ca2+ imaging supports this explanation. IBTU antagonized the elevation in intracellular Ca2+ in response to 50 nM capsaicin with an IC50 of 106 +/- 35 nM. Likewise, 600 nM IBTU was able to antagonize the elevation in intracellular Ca2+ in response to 100 pM resiniferatoxin in the presence of normal (1.8 mM) extracellular Ca2+, where the increase in intracellular calcium reflects calcium influx. In contrast, in the absence of extracellular Ca2+, where in this system resiniferatoxin induces a modest increase in calcium from intracellular stores, IBTU was unable to block the response to resiniferatoxin, although the TRPV1 antagonist 5-iodoresiniferatoxin was able to do so. In summary, IBTU is a novel, potent TRPV1 antagonist with marked selectivity between subpopulations of TRPV1 and may permit the function of these distinct pools to be explored and potentially exploited.

Animals↗
PubMed1993

On the replacement of the red squirrel in Britain: a phytotoxic explanation.

Diffusion modelling has shown that conservative demographic traits combined with feeding competition could explain red squirrel replacement by grey squirrels. We used field data from seven separate red and grey squirrel populations, in oak-hazel woods and Scots pines, to reject the hypothesis that red squirrel density and breeding is intrinsically poorer than that of grey squirrels. In oak-hazel woods, grey squirrel foraging, density and productivity were related to oak and acorn abundance. In contrast, red squirrels foraged where hazels were abundant; their relatively low density and breeding success were related to the abundance of hazel nuts. Red squirrels failed to exploit good acorn crops, although acorns were more abundant than hazels, but in Scots pines had densities and breeding success as high as grey squirrels in deciduous woods. Captive grey squirrels thrived on a diet of acorns, but red squirrels had a comparative digestive efficiency of only 59%, apparently because they were much less able than grey squirrels to neutralize acorn polyphenols. A model with simple competition for the autumn hazel crop, which was eaten by grey squirrels before the acorn crop, shows that red squirrels are unlikely to persist with grey squirrels in woods with more than 14% oak canopy. With oaks in most British deciduous woods giving grey squirrels a food refuge which red squirrels fail to exploit, replacement of red squirrels can be explained by feeding competition alone, exacerbated by the post-war decline in coppiced hazel.

Animal Feed↗
PubMed1987

Cellular competition in the development of ocular tissues in allophenic mice.

C57BL/6 mice exhibit impaired lens development as evidenced by competition studies with allophenic (chimeric) mice. Strain-specific differences in electrophoretic forms of glucose phosphate isomerase were exploited to determine the strain composition of various ocular and nonocular tissues in allophenic mice constructed from C57BL/6 and DBA/2 strains. As expected, there was variation from one animal to the next in overall mosaic composition, as well as variation among most ocular and nonocular tissues within individual animals. In contrast, when individual lenses from the same animals were assayed there was a marked and consistent deficiency of the C57BL/6 component. Control experiments indicated that these results are not the consequence of peculiarities of marker enzyme expression in the lens. Since lens formation occurs early in embryogenesis any anomaly at this stage could influence the normal induction of later ocular structures. We believe that the impaired lens-forming capacity of C57BL/6 mice may be the underlying cause of the 5-10% frequency of overt ocular defects in this strain.

Animals↗
PubMed2001

A strategy for the assembly of multiple porphyrin arrays based on the coordination chemistry of Ru-centered porphyrin pentamers.

An approach which employs pentameric porphyrin arrays as building blocks toward larger porphyrin arrays is described. Two flexible, and one relatively rigid, Ru-centered porphyrin pentamers (1-3) were synthesized and fully characterized. Their potential as building blocks toward larger porphyrin arrays has been studied via their coordination chemistry using bidentate and tetradentate ligands. DABCO (diazabicyclo[2.2.2]octane) can bind two monomeric porphyrins but was found to be too small to allow the complete formation of a 10-porphyrin array. On the other hand, titration of a larger bridging dipyridyl porphyrin ligand 17 (0.5 equiv) with 1 or 2 and tetrapyridyl ligand 18 (0.25 equiv) with 3 results in the formation of the 11-porphyrin and 21-porphyrin arrays, respectively, with the 21-porphyrin array containing porphyrins in three different metalation states. Changes in the chemical shift of the inner NH protons as well as the ortho- and meso-protons of the pyridyl groups of the porphyrin ligand clearly indicate the formation of large multiple porphyrin complexes. These studies demonstrate that by use of carefully designed building blocks and suitable bridging ligands, porphyrin arrays can be constructed with a dramatic increase in size in relatively few steps. Exploiting the fact that the strength of binding of pyridyl ligands is Ru > Zn > Ni, intra- vs intermolecular competition has been used to investigate aspects of the folding of the array. The photophysical properties of 3 are also described.

Magnetic Resonance Spectroscopy↗
PubMed2003

Building the bridge between molecular diagnostics and therapeutics.

Molecular diagnostics will ultimately have a broad and significant impact on patient treatment. An array of emerging diagnostic tests answer specific and important clinical questions which could offer opportunities for existing and new therapeutics. The development of new diagnostic tests will take time and will require investment in new strategies to find the optimum set of markers, as well as education programs to persuade clinicians, payers and patients to use the new tests and take advantage of the improved therapeutics. Competition among the molecular technologies will be intense; however, it is expected that the most successful companies will exploit synergies between the technologies to develop the most effective molecular diagnostics and, in turn, will improve efficacy of therapeutic practice.

Diagnosis, Differential↗
PubMed2002

The role of parasites in sympatric and allopatric host diversification.

Exploiters (parasites and predators) are thought to play a significant role in diversification, and ultimately speciation, of their hosts or prey. Exploiters may drive sympatric (within-population) diversification if there are a variety of exploiter-resistance strategies or fitness costs associated with exploiter resistance. Exploiters may also drive allopatric (between-population) diversification by creating different selection pressures and increasing the rate of random divergence. We examined the effect of a virulent viral parasite (phage) on the diversification of the bacterium Pseudomonas fluorescens in spatially structured microcosms. Here we show that in the absence of phages, bacteria rapidly diversified into spatial niche specialists with similar patterns of diversity across replicate populations. In the presence of phages, sympatric diversity was greatly reduced, as a result of phage-imposed reductions in host density decreasing competition for resources. In contrast, allopatric diversity was greatly increased as a result of phage-imposed selection for resistance, which caused populations to follow divergent evolutionary trajectories. These results show that exploiters can drive diversification between populations, but may inhibit diversification within populations by opposing diversifying selection that arises from resource competition.

Animals↗
PubMed2004

A nicotine delivery device without the nicotine? Tobacco industry development of low nicotine cigarettes.

BACKGROUND: Defining harm reduction and regulating potentially reduced exposure products (PREPs), including low nicotine products, are key issues in tobacco control policy. The US Congress has been considering legislation authorising the Food and Drug Administration (FDA) to regulate tobacco products. OBJECTIVE: To investigate tobacco industry perceptions, interests, motivations, and knowledge regarding the marketability of low nicotine tobacco products. METHODS: Qualitative analysis of internal tobacco industry documents identified in the Legacy Tobacco Documents Library between February 2002 and June 2004. Search terms included low-, no-, reduced-nicotine; denicotinization; low-, reduced- alkaloids; Next; de-nic; and key names of people, organisations, projects, and their common abbreviations and acronyms. RESULTS: The tobacco industry has made repeated efforts to develop low nicotine cigarettes. Reasons for doing so include consumer appeal and economic importance in a highly competitive cigarette market for "healthier" products. The industry considered the development of a new "denic" market segment a critical challenge. CONCLUSIONS: The tobacco industry exploits consumer misunderstanding of the health effects of nicotine in development and marketing efforts. The industry has risked the development of a less addictive product to expand the market reach of tobacco products based on perceived health benefits and appeal to quitters.

Alkaloids↗
PubMed2001

Strategy as simple rules.

The success of Yahoo!, eBay, Enron, and other companies that have become adept at morphing to meet the demands of changing markets can't be explained using traditional thinking about competitive strategy. These companies have succeeded by pursuing constantly evolving strategies in market spaces that were considered unattractive according to traditional measures. In this article--the third in an HBR series by Kathleen Eisenhardt and Donald Sull on strategy in the new economy--the authors ask, what are the sources of competitive advantage in high-velocity markets? The secret, they say, is strategy as simple rules. The companies know that the greatest opportunities for competitive advantage lie in market confusion, but they recognize the need for a few crucial strategic processes and a few simple rules. In traditional strategy, advantage comes from exploiting resources or stable market positions. In strategy as simple rules, advantage comes from successfully seizing fleeting opportunities. Key strategic processes, such as product innovation, partnering, or spinout creation, place the company where the flow of opportunities is greatest. Simple rules then provide the guidelines within which managers can pursue such opportunities. Simple rules, which grow out of experience, fall into five broad categories: how- to rules, boundary conditions, priority rules, timing rules, and exit rules. Companies with simple-rules strategies must follow the rules religiously and avoid the temptation to change them too frequently. A consistent strategy helps managers sort through opportunities and gain short-term advantage by exploiting the attractive ones. In stable markets, managers rely on complicated strategies built on detailed predictions of the future. But when business is complicated, strategy should be simple.

Commerce↗
PubMed1998

Competitive behaviour in an island population of house mice, Mus domesticus.

Because of the cryptic nature of small mammals inhabiting vegetation with widely scattered food resources, little is known about the behavioural mechanisms underlying their spatial dispersion. While house mice exploiting human-built environments attempt to exclude intruders aggressively from small territories that contain concentrated food resources, comparative tests show that the grassland mouse, M. spretus, establishes dominance relationships and then avoids sites used by dominant competitors, probably to avoid displacement from sites that provide safety from predators. We carried out further comparative tests to examine competitive behaviour and response to odours from same-sex conspecifics among house mice living ferally on the Isle of May, U.K., using recently captured adult males (N=62) and females (N=23). In contrast both to house mice caught from buildings and to the grassland M. spretus, feral house mice from the Isle of May showed no aggressive, defensive or cautious behaviour on meeting a same-sex conspecific, with the exception of one aggressive male. Scent marks had no effect on their response to a competitor, although intruders in a scent-marked arena showed a significant sex difference in choice between a clean nest site versus one soiled by a same-sex resident: males spent more time in the soiled nest while females spent more time in the clean one. We propose that the lack of aggression among feral May mice may be due to the infeasibility of defending large territories, containing scattered resources, on an island where there is no real predation risk. We suggest that this hypothesis may explain the lower aggression and higher densities that are characteristic of populations of small mammals, reptiles and birds living on small islands. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed2003

The costs of New Zealand pathology.

This paper focuses on methods for costing and funding hospital pathology services, and their relevance for government cost-control goals. Cost is an elusive, socially constructed phenomenon. As such it is context dependent and can be defined in different ways for different purposes. Misunderstanding of the contexts and purposes creates confusion and leads to contradictions and 'costly' mistakes for the New Zealand taxpayer. The cost to the taxpayer is not synonymous with the costs incurred in laboratories. The calculations of the latter, in a hospital setting, are so complex that often those responsible for running the cost systems do not understand the inscriptions produced by computer translations. In this paper, two costing initiatives potentially useful for non-competitive cost containment are outlined. The paper argues that the multiple funding methods resulting from New Zealand's public/private health care mix perpetuate perverse incentives that drive laboratory test volume escalation and discourage the full exploitation of potential economies-of-scale. The long-held objective of successive New Zealand governments to divert health funding away from hospitals and into preventive health care, is being subverted by the retention, at laboratory service level, of a competitive contracting system that was initially set up to contain test prices. The result for the New Zealand taxpayer is that costs are excessive, with millions of dollars passing to foreign-owned laboratories, which have incentives to take the tests, as well as the profits, offshore.

Benchmarking↗
PubMed2003

Invasion, competitive dominance, and resource use by exotic and native California grassland species.

The dynamics of invasive species may depend on their abilities to compete for resources and exploit disturbances relative to the abilities of native species. We test this hypothesis and explore its implications for the restoration of native ecosystems in one of the most dramatic ecological invasions worldwide, the replacement of native perennial grasses by exotic annual grasses and forbs in 9.2 million hectares of California grasslands. The long-term persistence of these exotic annuals has been thought to imply that the exotics are superior competitors. However, seed-addition experiments in a southern California grassland revealed that native perennial species, which had lower requirements for deep soil water, soil nitrate, and light, were strong competitors, and they markedly depressed the abundance and fecundity of exotic annuals after overcoming recruitment limitations. Native species reinvaded exotic grasslands across experimentally imposed nitrogen, water, and disturbance gradients. Thus, exotic annuals are not superior competitors but rather may dominate because of prior disturbance and the low dispersal abilities and extreme current rarity of native perennials. If our results prove to be general, it may be feasible to restore native California grassland flora to at least parts of its former range.

California↗
PubMed1996

Binocular rivalry with isoluminant stimuli visible only via short-wavelength-sensitive cones.

To test whether the binocular contour rivalry mechanism is tritanopic, we presented isoluminant, rival stimuli visible only via the short-wavelength-sensitive (S) cones. We stimulated only the S cones with violet gratings superimposed on a bright yellow field that adapted the responses of the middle- and long-wavelength-sensitive (M and L) cones. We found that an S-cone grating presented to one eye rivalled with an orthogonal grating presented to the other. Rivalry persisted over a range of luminances and contrasts of the S-cone stimuli, and was greater than could be accounted for by nonrival fading. The spatial spread of rivalry from S-cone stimuli is similar to that for the same stimuli when visible also to the M and L cones (luminance stimuli). We found that an S-cone stimulus would rival with a luminance stimulus, and exploited this to determine the equivalent luminance contrast of S-cone stimuli by putting them in a rivalry competition with luminance stimuli. For rivalry, the equivalent luminance contrast of isoluminant, S-cone stimuli is much less than their S-cone contrast. The existence of rivalry with isoluminant stimuli, along with earlier evidence that such stimuli can support stereopsis, challenges the view that an achromatic channel alone drives certain higher level functions such as depth perception.

Contrast Sensitivity↗
PubMed2005

Face adaptation depends on seeing the face.

Retinal input that is suppressed from visual awareness can nevertheless produce measurable aftereffects, revealing neural processes that do not directly result in a conscious percept. We here report that the face identity-specific aftereffect requires a visible face; it is effectively cancelled by binocular suppression or by inattentional blindness of the inducing face. Conversely, the same suppression does not interfere with the orientation-specific aftereffect. Thus, the competition between incompatible or interfering visual inputs to reach awareness is resolved before those aspects of information that are exploited in face identification are processed. We also found that the face aftereffect remained intact when the visual distracters in the inattention experiment were replaced with auditory distracters. Thus, cross-modal or cognitive interference that does not affect the visibility of the face does not interfere with the face aftereffect. We conclude that adaptation to face identity depends on seeing the face.

Adaptation, Physiological↗