Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Carrying Capacity”

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 109 records · Page 6Linked to original sources
PubMed2005

Sustainability in single-species population models.

In this paper, we review the concept of sustainability with regard to a single-species, age-structured fish population with density dependence at some stage of its life history. We trace the development of the view of sustainability through four periods. The classical view of sustainability, prevalent in the 1970s and earlier, developed from deterministic production models, in which equilibrium abundance or biomass is derived as a function of fishing mortality. When there is no fishing mortality, the population equilibrates about its carrying capacity. We show that carrying capacity is the result of reproductive and mortality processes and is not a fixed constant unless these processes are constant. There is usually a fishing mortality, F(MSY), which results in MSY, and a higher value, F(ext), for which the population is eventually driven to extinction. For each F between 0 and F(ext), there is a corresponding sustainable population. From this viewpoint, the primary tool for achieving sustainability is the control of fishing mortality. The neoclassical view of sustainability, developed in the 1980s, involved population models with depensation and stochasticity. This view point is in accord with the perception that a population at a low level is susceptible to collapse or to a lack of rebuilding regardless of fishing. Sustainability occurs in a more restricted range from that in the classical view and includes an abundance threshold. A variety of studies has suggested that fishing mortality should not let a population drop below a threshold at 10-20% of carrying capacity. The modern view of sustainability in the 1990s moves further in the direction of precaution. The fishing mortality limit is the former target of F(MSY) (or some proxy), and the target fishing mortality is set lower. This viewpoint further reduces the range of permissible fishing mortalities and resultant desired population sizes. The objective has shifted from optimizing long-term catch to preserving spawning biomass and egg production for the future. The use of discount rates in objective functions involving catch is not a suitable alternative to protecting reproductive value. As we move into the post-modern time period, new definitions of sustainability will attempt to incorporate he economic and social aspects of fisheries and/or ecosystem and habitat requirements. These definitions now involve "warm and fuzzy" notions (healthy ecosystems and fishing communities, the needs of future generations, diverse fish communities) and value judgements of desired outcomes. Additional work is needed to make these definitions operational and to specify quantitative objectives to be achieved. In addition, multiple objectives may be incompatible, so trade-offs in what constitutes sustainability must be made. The advances made under the single-species approach should not be abandoned in the post-modern era, but rather enhanced and combined with new approaches in the multi-species and economic realms.

Animals↗
PubMed2006

Modeling the effect of population dynamics on the impact of rabbit hemorrhagic disease.

The European wild rabbit (Oryctolagus cuniculus) is a staple prey species in Mediterranean ecosystems. The arrival and subsequent spread of rabbit hemorrhagic disease throughout southwestern Europe, however has caused a decline in rabbit numbers, leading to considerable efforts to enhance wild rabbit populations, especially through habitat management. Because rabbit population dynamics depend on habitat suitability and changes in habitat structure and composition subsequent to habitat management, I evaluated the effects of population dynamics on the long-term impact of rabbit hemorrhagic disease on rabbit populations. I used an age-structured model with varying degrees of population productivity and turnover and different habitat carrying capacities, and I assumed the existence of a unique, highly pathogenic virus. My results suggest that disease impact may be highly dependent on habitat carrying capacity and rabbit population dynamics, and the model provided some insight into the current abundance of wild rabbits in different locations in southwestern Europe. The highest disease impact was estimated for populations located in habitats with low to medium carrying capacity In contrast, disease impact was lower in high-density populations in habitats with high carrying capacity, corresponding to a lower mean age of rabbit infection and a resulting lower mortality from rabbit hemorrhagic disease. The outcomes of the model suggest that management strategies to help rabbit populations recover should be based on improving habitats to their maximum carrying capacity and increasing rabbit population productivity. In contrast, the use of strategies based on temporary increases in rabbit density, including vaccination campaigns, translocations, and temporal habitat improvements at medium carrying capacities, may increase disease impact, resulting in short-term decreases in rabbit population density.

Animals↗
PubMed1976

Predator prey interactions with time delays.

A general (Volterra-Lotka type) integrodifferential system which describes a predator-prey interaction subject to delay effects is considered. A rather complete picture is drawn of certain qualitative aspects of the solutions as they are functions of the parameters in the system. Namely, it is argued that such systems have, roughly speaking, the following features. If the carrying capacity of the prey is smaller than a critical value then the predator goes extinct while the prey tends to this carrying capacity; and if the carrying capacity is greater than, but close to this critical value then there is a (globally) asymptotically stable positive equilibrium. However, unlike the classical, non-delay Volterra-Lotka model, if the carrying capacity of the prey is too large then this equilibrium becomes unstable. In this event there are critical values of the birth and death rates of the prey and predator respectively (which hitherto have been fixed) at which "stable" periodic solutions bifurcate from the equilibrium and hence at which the system is stabilized. These features are illustrated by means of a numerically solved example.

Animals↗
PubMed2004

Effects of insect population size on evolution of resistance to transgenic crops.

Models of the evolution of insect resistance to transgenic crops have often assumed that population size is infinite or that carrying capacity is fixed. To evaluate potential effects of population size on resistance evolution, we conducted sensitivity analyses by using a stochastic, spatially explicit model based partly on the interaction between pink bollworm and Bacillus thuringiensis (Bt) cotton. We examined interactions of carrying capacity, region size, dispersal, and percentage of fields planted with Bt cotton. The median and variance in the time to resistance decreased as region size increased, regardless of carrying capacity. This occurred because larger regions were more likely to have at least one field in which resistance evolved rapidly and served as a source from which resistance spread throughout the region. Carrying capacity significantly affected the median time to resistance with 75% of fields planted with Bt cotton, but not with 50% Bt cotton. In contrast, carrying capacity significantly influenced the variance in the time to resistance with 50% Bt cotton, but not with 75% Bt cotton. We also found resistance evolution was affected by interactions between carrying capacity, dispersal, and the percentage of fields planted with Bt cotton. The high variability observed in our simulations indicates that factors affecting stochastic events can play an important role in the evolution of resistance. Because population size determines the extent to which stochastic events are important, reasonable estimates of population size are essential for devising robust models of resistance evolution.

Animals↗
PubMed1997

Antisense inhibition and adeno-associated viral vector delivery for reducing hypertension.

Antisense oligodeoxynucleotides have been designed to inhibit the production of specific proteins. In models of hypertension, we have targeted the renin-angiotensin system at the level of synthesis (angiotensinogen) and the receptor (AT1 receptor). The design of antisense oligonucleotides requires choosing a site to inhibit mRNA processig or translation. The strategy we use is to make three oligonucleotides of antisense sequences, upstream and downstream from the AUG site and over the AUG site. The oligonucleotides are tested in a screening test. Antisense oligonucleotides to AT1-receptor mRNA and to angiotensinogen mRNA reduce blood pressure in spontaneously hypertensive rats when injected into the brain. They significantly reduce the concentration of the appropriate protein. The oligonucleotides are also effective when administered systemically. The decrease in blood pressure with antisense oligonucleotides delivered in blood or brain lasts 3 to 7 days. To prolong the action, direct injection of naked DNA and injection of DNA in liposome carriers have been tested. Viral vectors have been developed to deliver antisense DNA. The viral vectors available include retroviruses and adenovirus, but the adeno-associated virus (AAV) vector is the vector of choice for ultimate use in gene therapy. It offers safety because it is nonpathogenic, has longevity because it integrates into the genome, and has sufficient carrying capacity to carry up to 4.5 kb antisense or gene in a recombinant AAV. Using rAAV-antisense to AT1 mRNA, there is efficient transfection into cells and an inhibition of AT1 receptor number. In in vivo tests, rAAV-AS AT1-receptor when injected into the brains of SHR reduces blood pressure for more than 2 months. In young rats (3 weeks old), rAAV-AS AT1-receptor decreases blood pressure and slows the development of hypertension. While further experiments need to be done on dose-response relationships and on the cellular mechanisms of these effects, the results show the feasibility of AAV as a vector for antisense inhibition, which may ultimately be used in gene therapy for hypertension.

Adenoviridae↗
PubMed2004

The evolution of phenotypic plasticity in spatially structured environments: implications of intraspecific competition, plasticity costs and environmental characteristics.

We model the evolution of reaction norms focusing on three aspects: frequency-dependent selection arising from resource competition, maintenance and production costs of phenotypic plasticity, and three characteristics of environmental heterogeneity (frequency of environments, their intrinsic carrying capacity and the sensitivity to phenotypic maladaptation in these environments). We show that (i) reaction norms evolve so as to trade adaptation for acquiring resources against cost avoidance; (ii) maintenance costs cause reaction norms to better adapt to frequent rather than to infrequent environments, whereas production costs do not; and (iii) evolved reaction norms confer better adaptation to environments with low rather than with high intrinsic carrying capacity. The two previous findings contradict earlier theoretical results and originate from two previously unexplored features that are included in our model. First, production costs of phenotypic plasticity are only incurred when a given phenotype is actually produced. Therefore, they are proportional to the frequency of environments, and these frequencies thus affect the selection pressure to avoid costs just as much as the selection pressure to improve adaptation. This prevents the frequency of environments from affecting the evolving reaction norm. Secondly, our model describes the evolution of plasticity for a phenotype determining an individual's capability to acquire resources, and thus its realized carrying capacity. When individuals are distributed randomly across environments, they cannot avoid experiencing environments with intrinsically low carrying capacity. As selection pressures arising from the need to improve adaptation are stronger under such extreme conditions than under mild ones, better adaptation to environments with low rather than with high intrinsic carrying capacity results.

Adaptation, Physiological↗
PubMed1998

Effects of Optimal Antipredator Behavior of Prey on Predator-Prey Dynamics: The Role of Refuges.

The influence of optimal antipredator behavior of prey on predator-prey dynamics in a two-patch environment is studied. One patch represents an open habitat while the other is a refuge for prey. It is assumed that prey maximize their fitness measured by the instantaneous per capita growth rate. In each patch population dynamics is described by the Lotka-Volterra time continuous model. The refuge is characterized by its protectiveness which is inversely related to the predation risk for prey, and the dependence of population dynamics on protectiveness is studied. It is shown that adaptive behavior of prey changes qualitative properties of the underlying Lotka-Volterra model due to the appearance of a bounded attractor. Adaptive prey behavior does not lead to a stable equilibrium but to the reduction of population fluctuations. Dynamic consequences of a limited carrying capacity of the refuge are also considered. Low refuge carrying capacity leads to stability of predator-prey dynamics while stability is lost when the carrying capacity of the refuge is high. Lastly, it is shown that optimal antipredator behavior of prey leads to persistence and reduction of oscillations in population densities. Copyright 1998 Academic Press.

Journal Article↗
PubMed2006

A mathematical analysis on public goods games in the continuous space.

We consider the population dynamics of two competing species sharing the same resource, which is modeled by the carrying capacity term of logistic equation. One species (farmer) increases the carrying capacity in exchange for a decreased survival rate, while the other species (exploiter) does not. As the carrying capacity is shared by both species, farmer is altruistic. The effect of continuous spatial structure on the performance of such strategies is studied using the reaction diffusion equations. Mathematical analysis on the traveling wave solution of the system revealed; (1) Farmers can never expel exploiters in any traveling wave solution. (2) The expanding velocity of the exploiter population invading the farmer population can be analytically determined and it depends only on a cost of altruism and the diffusion coefficients while it is independent of the benefit of altruism. (3) When the effect of altruism is small, the dynamics of the invasion of exploiters obeys the Fisher-KPP equation. Numerical calculations confirm these results.

Altruism↗
PubMed2006

Environmentally induced dispersal under heterogeneous logistic growth.

We consider a single-species model which is composed of several habitats connected by linear migration rates and having logistic growth. A spatially varying, temporally constant environment is introduced by the non-homogeneity of its carrying capacity. Under this condition any type of purely diffusive behavior, characterized in our model by symmetric migration rates, produces an unbalanced population distribution, i.e. some locations receive more individuals than can be supported by the environmental carrying capacity, while others receive less. Using an evolutionarily stable strategy (ESS) approach we show that an asymmetric migration mechanism, induced by the heterogeneous carrying capacity of the environment, will be selected. This strategy balances the inflow and outflow of individuals in each habitat (balanced dispersal), as well as 'balancing' the spatial distribution relative to variation in carrying capacity (the Ideal Free Distribution from habitat selection theory). We show that several quantities are maximized or minimized by the evolutionarily stable dispersal strategy.

Animal Migration↗
PubMed1992

Mechanical properties of biodegradable ligament augmentation device of poly(L-lactide) in vitro and in vivo.

To evaluate the mechanical properties of absorbable braided poly(L-lactide) (PLLA) fibre implants, 2.0 and 3.2 mm in diameter, maximum load defined as tensile load carrying capacity, elongation and axial rigidity were investigated after immersion in phosphate-buffered distilled water at 37 degrees C and pH 6.1 and after subcutaneous implantation in rabbit. The results confirm earlier indications that PLLA degrades faster in vivo than in vitro. The non-sterilized 2.0 mm implants lost 69% of initial tensile load carrying capacity in 46 wk in vitro. In vivo the loss of tensile load carrying capacity of the 2.0 and 3.2 mm implants was most marked between 6 to 12 wk. After 48 wk in vivo 2.0 and 3.2 mm implants retained 3 and 4% of initial tensile load carrying capacity respectively. Both in vitro and in vivo, elongation diminished in the same way as the maximum load. In vitro, mean axial rigidity of unsterilized 2.0 mm implants was 64 N during the first 34 wk but fell to 31 N at 46 wk. In vivo the initial mean axial rigidity of the 2.0 and 3.2 mm implants was 29 and 95 N respectively. At 24 wk the mean axial rigidity was 2 N in both implants.

Animals↗
PubMed1983

Density dependent selection incorporating intraspecific competition 1. A haploid model.

A haploid model is introduced and analyzed in which intraspecific competition is incorporated within a density dependent framework. It is assumed that each genotype has a unique carrying capacity corresponding to the equilibrium population size when fixed for that type. Each genotypic fitness at a single multi-allelic locus is a function of a distinctive effective population size formed by adding the numbers of each genotype present, weighted by an intraspecific competition coefficient. As a result, the fitnesses depend upon the relative frequencies of the various genotypes as well as the total population size. Intergenotypic interactions can have a profound effect upon the outcome of the population. In particular, when the density effect of one individual upon another depends upon their respective genotypes, a unique stable interior equilibrium is possible in which all alleles are present. This stands in contrast to the purely density dependent haploid system in which the only possible stable state corresponds to fixation for the type with the highest carrying capacity. In the present model selective advantage is determined by a balance between carrying capacity and sensitivity to density pressures from other genotypes. Fixation for the genotype with the highest carrying capacity, for instance, will not be stable if it exerts a sufficiently weak competitive effect upon the other genotypes. In the diallelic case, maintenance of both alleles at a stable equilibrium requires that the net intragenotypic competition between individuals of like genotype be stronger than that between unlike types. As for purely density regulated systems, there may be no stable equilibria and/or regular and chaotic cycling may occur. The results may also be interpreted in terms of a discrete time model of interspecific competition with each haplotype representing a different species.

Animals↗
PubMed1994

Inoculum Density-Dependent Mortality and Colonization of the Phyllosphere by Pseudomonas syringae.

Pseudomonas syringae inocula containing cell concentrations ranging from 10 to 10 cells per ml were applied to the primary leaves of bean plants. The plants were incubated under conditions of high temperature and illumination and low relative humidity. Bacterial mortality rates and the proportional population decline of the inoculum were lowest at the highest inoculum concentrations. Addition of a high concentration of heat-killed cells to the inoculum containing a low concentration of viable cells significantly reduced both the mortality rate and the proportional population decline of the viable cells. The mechanisms underlying this density-dependent mortality may include cooperative protective effects of extracellular factors, such as bacterial extracellular polysaccharides, and physical protection by neighboring cells. Although epiphytic populations derived from inoculum concentrations of 10 or 10 cells per ml tended toward 10 CFU/g, the presumed carrying capacity of the leaf, populations derived from lower inoculum concentrations never achieved this carrying capacity. Assuming that epiphytic populations of P. syringae reside in discrete protected sites, our results suggest that at low inoculum concentrations, following a period of environmental stress, the number of viable cells may have dropped to zero in some sites; hence, the carrying capacity of the leaf could not be achieved.

Journal Article↗
PubMed2003

Cerebrovascular response to decreased hematocrit: effect of cell-free hemoglobin, plasma viscosity, and CO2.

The effect of transfusing a nonextravasating, zero-link polymer of cell-free hemoglobin on pial arteriolar diameter, cerebral blood flow (CBF), and O2 transport (CBF x arterial O2 content) was compared with that of transfusing an albumin solution at equivalent reductions in hematocrit (approximately 19%) in anesthetized cats. The influence of viscosity was assessed by coinfusion of a high-viscosity solution of polyvinylpyrrolidone (PVP), which increased plasma viscosity two- to threefold. Exchange transfusion of a 5% albumin solution resulted in pial arteriolar dilation, increased CBF, and unchanged O2 transport, whereas there were no significant changes over time in a control group. Exchange transfusion of a 12% polymeric hemoglobin solution resulted in pial arteriolar constriction and unchanged CBF and O2 transport. Coinfusion of PVP with albumin produced pial arteriolar dilation that was similar to that obtained with transfusion of albumin alone. In contrast, coinfusion of PVP with hemoglobin converted the constrictor response to a dilator response that prevented a decrease in CBF. Pial arteriolar dilation to hypercapnia was unimpaired in groups transfused with albumin or hemoglobin alone but was attenuated in the largest vessels in albumin and hemoglobin groups coinfused with PVP. Unexpectedly, hypocapnic vasoconstriction was blunted in all groups after transfusion of albumin or hemoglobin alone or with PVP. We conclude that 1) the increase in arteriolar diameter after albumin transfusion represents a compensatory response that prevents decreased O2 transport at reduced O2-carrying capacity, 2) the decrease in diameter associated with near-normal O2-carrying capacity after cell-free polymeric hemoglobin transfusion represents a compensatory mechanism that prevents increased O2 transport at reduced blood viscosity, 3) pial arterioles are capable of dilating to an increase in plasma viscosity when hemoglobin is present in the plasma, 4) decreasing hematocrit does not impair pial arteriolar dilation to hypercapnia unless plasma viscosity is increased, and 5) pial arteriolar constriction to hypocapnia is impaired at reduced hematocrit independently of O2-carrying capacity.

Albumins↗
PubMedDate not supplied

Modern oxygen carriers: state of art 1990.

Three major components of blood with clearly defined functions are: 1) red cells 2) plasma volume 3) coagulation factors At the present time artificial or synthetic coagulation factors are not available. Plasma volume expanders are well known in clinical practice. The main subject of this paper is the complex area of red cell substitutes with particular reference to the oxygen carrying capacity. The history of blood oxygen carrying capacity is briefly presented with particular reference to contributions by G. S. Adair, C. Bohr, M. Perutz and R. R. Benesch. 3 oxygen carrying developments are discussed in detail: 1) perfluorocarbons 2) artificial red cells 3) stroma-free haemoglobin solution Perfluorocarbons were used as carriers of oxygen in experiments and clinical practice. Before their wide clinical application a number of potential problems must be solved. In selected patients (coronary angioplasty, cerebral thrombosis, cardiopulmonary by-pass) perfluorocarbons (Fluosol D-A) could be considered as beneficial. Artificial red cells (neohaemocytes) are available in some centres in which progress of micro-technology appears to lead to encapsulation of purified human haemoglobin. These preparations should receive more attention. Finally stroma-free haemoglobin solution was the subject of our own research for several years. Our preparation met the requirements of the blood substitute, but had the short half-life in the circulation. Recent advances in chemistry in some centres resulted in the modification of hb molecule and linking with P-5-P. The modified poly hb solution is an ideal oxygen delivering fluid.

Blood Substitutes↗
PubMed2003

[Preliminary study on ecological footprint in Bashang region of Zhangjiakou city].

The ecological footprint and ecological carrying capacity in Bashang region of Zhangjiakou city were calculated with the statistical data of the region in 1999. Based on calculation, the balance between ecological footprint and ecological carrying capacity was analyzed, and the threshold values of the ecological carrying capacity and population capacity of the region at the current production level were determined. Strategies on reducing ecological deficit in this region were also brought forward.

China↗
PubMed2005

[Allogenic blood transfusion for surgery].

Blood transfusion against surgical patients is mainly as a replacement therapy for intra-operative bleeding. Transfusion trigger depends on to maintain 12 ml/kg/min oxygen carrying capacity. Oxygen consumption depends on oxygen carrying capacity which multiplicity hemoglobin concentration and cardiac output. The government of United States decided the transfusion trigger of surgical patients at hemoglobin 7.0 g/dl except patients who have cardiac problem at 1988. The indication of plasma and platelet transfusion is limited in surgical field. Because bleeding tendency is usually a contra-indication of surgery itself. Dilution coagulopathy due to massive bleeding exceed one blood volume is the main indication of plasma and platelet transfusion. It is necessary to administrate fresh frozen plasma for replenishing coagulation function with 30% of one body plasma volume when prothrombin time prolong more than 16 seconds. Platelet transfusion is effective for hemostasis in case of massive bleeding which exceed 1.5 blood volume and also peripheral blood platelet count indicate lower than 50,000/mm3.

Blood Loss, Surgical↗
PubMed2003

Environmental management of marine fish culture in Hong Kong.

Marine fish farming is an important commercial practice in Hong Kong. Marine fish farms located in eutrophic coastal waters often face the threat of severe dissolved oxygen depletion associated with algal blooms and red tides. On the other hand, mariculture activities also contribute to pollution. The sustainable management of mariculture requires proper siting of the fish farms and stocking density control. Both of these are related to the carrying capacity of the water body concerned, which is mainly governed by its flushing characteristics. A simple method to determine the carrying capacity of a fish farm has been developed by using three-dimensional (3D) hydrodynamic modelling and its effective coupling with a diagenetic water quality model. A systematic methodology using numerical tracer experiments has been developed to compute the tidal flushing in a fish farm. The flushing time is determined from the results of a numerical tracer experiment using robust 3D hydrodynamic and mass transport models. A unit tracer concentration is initially prescribed inside the region of interest and zero elsewhere; the subsequent mass transport and the mass removal process are then tracked. The fish farms are usually situated in well-sheltered shallow embayments and may not connect directly to the open water. It is found that it is necessary to define both "local" and "system-wide" flushing times to represent the effectiveness of the mass exchange with the surrounding water body and the open sea respectively. A diagenetic water quality model simulating the sediment-water-pollutant interaction is employed to address the response of the water column and the benthic layer to pollution discharges. With the flushing rate reliably computed, the carrying capacity of the fish farm can be determined in terms of key water quality parameters: chlorophyll-a, dissolved oxygen, organic nitrogen and potential lowest dissolved oxygen level on a day of negligible photosynthetic production. The predictions are well-supported by field data.

Aquaculture↗
PubMed2000

Nutrient flows for poultry production in The Netherlands.

Government targets for ammonia emission and for N and P loss per hectare (ha) of agricultural land were used to assess carrying capacity for poultry production in The Netherlands with data from 1990. In addition, the effect of alternative management strategies on carrying capacity was determined. Ammonia emission from poultry production in 1990 [20.5 gigagrams (Gg) N] exceeded the target for 2000 (i.e., 6.9 Gg N). Targets defined for 2000 and 2010 (i.e., 4.6 Gg N) can be achieved, however, without reducing poultry numbers, assuming national introduction of measurements studied. Measures that reduced ammonia emission directly, i.e., introduction of low-emission housing or manure application techniques, were most effective. In 1990, N and P losses equalled 215 kg/ha for N and 31 kg/ha for P. The N loss was slightly lower than the target for 2000 (219 kg N/ha) but exceeded the target for 2010 (144 kg N/ha). Reduction of application of artificial N fertilizer, however, reduced N loss effectively from 215 to 22 kg/ha. National P loss in 1990 exceeded the target for 2000 (15.3 kg P/ha). Reduction of application of artificial P fertilizer reduced P loss most effectively from 31 to 14 kg/ha. To achieve the target for 2010 (8.7 kg P/ha), additional reduction in P excretion by poultry is required. This reduction can be achieved by use of phytase in layer and broiler feed and by use of a coarse Ca source in layer feed. Unlike pig production, carrying capacity for poultry production in The Netherlands is not limited by governmental targets for acidification, eutrophication, or drinking water contamination.

Ammonia↗