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Reduced Densities (reduced + density)
Selected AbstractsSoybean meal alters autochthonous microbial populations, microvilli morphology and compromises intestinal enterocyte integrity of rainbow trout, Oncorhynchus mykiss (Walbaum)JOURNAL OF FISH DISEASES, Issue 9 2009D L Merrifield Abstract Rainbow trout were fed either a diet containing fishmeal (FM) as the crude protein source or a diet containing 50% replacement with soybean meal (SBM) for 16 weeks. An enteritis-like effect was observed in the SBM group; villi, enterocytes and microvilli were noticeably damaged compared with the FM group. The posterior intestine microvilli of SBM-fed fish were significantly shorter and the anterior intestine microvilli significantly less dense than the FM-fed fish. Electron microscopy confirmed the presence of autochthonous bacterial populations associated with microvilli of both fish groups. Reduced density of microvilli consequently led to increased exposure of enterocyte tight junctions, which combined with necrotic enterocytes is likely to diminish the protective barrier of the intestinal epithelium. No significant differences in total viable counts of culturable microbial populations were found between the groups in any of the intestinal regions. A total of 1500 isolates were tentatively placed into groups or genera, according to standard methods. Subsequent partial 16S rRNA sequencing revealed species that have not been identified from the rainbow trout intestine previously. Compared with the FM group levels of Psychrobacter spp. and yeast were considerably higher in the SBM group; a reduction of Aeromonas spp. was also observed. [source] Effects of a toxicant on population growth rates: sublethal and delayed responses in blowfly populationsFUNCTIONAL ECOLOGY, Issue 6 2001S. J. MOE Summary 1,Previous studies have shown that cadmium exposure of blowfly populations (Lucilia sericata[Meigen 1826]) results in reduced population growth rate, but also in higher individual mass, because of reduced competition for food. In this study, the discrepancy between the positive effect on individual growth and the negative effect on population growth is investigated, by measuring direct and delayed effects of cadmium in the adult stage. 2,Blowfly populations were exposed to cadmium through the diet in four treatment combinations: larval stage, adult stage, both stages or neither stage. The effects on accumulation of cadmium, survival, development time, mass and reproductive rate were measured. 3,Cadmium was accumulated from both stages. 4,Individuals exposed to cadmium in the larval stage had higher mean pupal and adult mass (because of reduced densities), but also reduced adult longevity and fecundity. 5,Adult longevity and fecundity were also reduced by cadmium exposure in the adult stage. 6,In stage-structured populations, the link between individual-level and population-level responses to a toxicant may be complicated by stage-specific sensitivities to the toxicant, by delayed responses in the adult stage to sublethal effects in the juvenile stage, and by density-dependent compensatory responses to toxicant-induced mortality. [source] Habitat influences on urban avian assemblagesIBIS, Issue 1 2009KARL L. EVANS Urbanization is increasing across the globe and there is growing interest in urban ecology and a recognition that developed areas may be important for conservation. We review the factors influencing urban avian assemblages, focusing on habitat type and anthropogenic resource provision, and analyse data from a common bird monitoring scheme to assess some of these issues. The review suggests that (1) local factors are more important than regional ones in determining the species richness of urban avian assemblages, raising the potential for the management of urban sites to deliver conservation; (2) habitat fragmentation frequently influences urban avian assemblages, with the effects of patch size being greater than those of isolation, and (3) urban bird assemblages appear to respond positively to increasing the structural complexity, species richness of woody vegetation and supplementary feeding, and negatively to human disturbance. Data from Britain's Breeding Bird Survey, combined with habitat data obtained from aerial photographs, were used to assess a number of these issues at the resolution of 1-km squares. Green-space constituted 45% of these squares, and domestic gardens contributed 50% of this green-space, though their contribution to large continuous patches of green-space was negligible. There was no significant positive correlation between the densities of individual species in urban areas and surrounding rural areas. Rural species richness declined with increasing latitude, but urban species richness was not correlated with latitude. This contrast contributes to slightly higher avian species richness in rural squares in Southern England than urban ones. Occupancy and abundance were strongly positively correlated in urban avian assemblages, and some indicator species of conservation concern occurred in few urban areas and at low densities. Such species will require conservation action to be precisely targeted within urban areas. Of the urban indicators of conservation concern, only the House Sparrow Passer domesticus and Common Starling Sturnus vulgaris were more abundant in urban than rural areas. Moreover, the densities of these two species were strongly and positively correlated, indicating that they may be limited by shared resources, such as nest-sites or supplementary food. There was little evidence that high densities of nest-predating corvids were associated with reduced densities of their prey species. Species richness and the densities of individual species frequently declined with an increasing number of buildings. Current trends for the densification of many British urban areas are thus likely to be detrimental for many bird species. [source] Dynamics of regional coexistence for more or less equal competitorsJOURNAL OF ANIMAL ECOLOGY, Issue 1 2003C. Patrick Doncaster Summary 1Competition between two species in a metapopulation involves each inhibiting the other's ability firstly to colonize an already occupied area and then to persist in it. Models for regional competition of this kind have 3-D dynamics, from which it has proved difficult to extract useful predictions except for special conditions. We introduce a 2-D general model for species that are equally vigorous at inhibiting the ability of others to remain in an occupied patch as to arrive there. The model covers the full spectrum of competitive interactions, from weak to strong and symmetrical to asymmetrical. Its Lotka,Volterra dynamics extend the general theory of competitive coexistence by generating clear predictions for community structure, amenable to cross-system comparisons and experimental manipulations. 2Previous 2-D models of interactions between dominant and fugitive species are special cases of the 2-D general model. Moderately asymmetrical competition has two outcomes distinctly different from dominant,fugitive interactions, at both the scale of metapopulation and population: (i) slow growing and weak competitors coexist with faster growing superior competitors, albeit at reduced densities; and (b) habitat removal always yields relative gains in abundance for species with higher growth capacity, but the gains are absolute only for species subjected to competitive impacts that exceed within-species impacts. Extinctions of slow growing and weak competitors provide the most sensitive indication of habitat degradation, and their losses also have the least effect on community structure. 3The 2-D general model further predicts that highly productive communities will tolerate differences between species in their capacity for population growth, whereas less productive communities will tolerate stronger competitive interactions between species. This prediction applies equally to a population of resource consumers as to a metapopulation of colonists. The model explicitly links local and regional population dynamics to r,K selection in community structure by predicting a prevalence of growth-orientated species in resource-poor habitats and competition-orientated species in resource-rich habitats. [source] Predator, prey and pathogen interactions in introduced snail populationsANIMAL CONSERVATION, Issue 3 2001J. Gerlach The introduction of the carnivorous snail Euglandina rosea to Pacific islands by biological control programmes has had a devastating effect on native snail populations. In most areas the target species, Achatina fulica, has not been affected, although some unsubstantiated reports have led to E. rosea being viewed as an effective control agent. Data from recent laboratory and field studies of E. rosea were combined into a simple model of the interactions between populations of E. rosea and A. fulica and a disease agent. Predictions from the model correspond closely with field data from a number of sites. The model suggests that apparent reductions in A. fulica numbers following E. rosea introduction are the result of a combination of predation and disease effects, and that although the maximum population levels are reduced the population is stabilized at a relatively high level. The model predicts that both A. fulica and E. rosea populations will persist. Partulidae will decline following E. rosea invasion although Samoana spp. may persist at reduced densities. More effective control of A. fulica can be achieved through manual collecting. Control of E. rosea requires the imposition of a significant novel mortality factor. [source] Generalist predators in organically and conventionally managed grass-clover fields: implications for conservation biological controlANNALS OF APPLIED BIOLOGY, Issue 2 2008K Birkhofer Abstract Organically managed agroecosystems rely in part on biological control to prevent pest outbreaks. Generalist predators (Araneae, Carabidae and Staphylinidae) are a major component of the natural enemy community in agroecosystems. We assessed the seasonal dynamics of major generalist predator groups in conventionally and organically managed grass,clover fields that primarily differed by fertilisation strategy. We further established an experiment, manipulating the abundant wolf spider genus Pardosa, to identify the importance of these predators for herbivore suppression in the same system and growth period. Organic management significantly enhanced ground-active spider numbers early and late in the growing season, with potentially positive effects of plant cover and non-pest decomposer prey. However, enhancing spider numbers in the field experiment did not improve biological control in organically managed grass,clover fields. Similar to the survey results, reduced densities of Pardosa had no short-term effect on any prey taxa; however, spider guild structure changed in response to Pardosa manipulation. In the presence of fewer Pardosa, other ground-running spiders were more abundant; therefore, their impact on herbivore numbers may have been elevated, possibly cancelling increases in herbivore numbers because of reduced predation by Pardosa. Our results indicate positive effects of organic farming on spider activity density; however, our survey data and the predator manipulation experiment failed to find evidence that ground-running spiders reduced herbivore numbers. We therefore suggest that a positive impact of organic fertilisers on wolf spiders in grass,clover agroecosystems may not necessarily improve biological control when compared with conventional farming. [source] Is the pollen-limited mistletoe Peraxilla tetrapetala (Loranthaceae) also seed limited?AUSTRAL ECOLOGY, Issue 8 2007DAVE KELLY Abstract Seed production in the endemic New Zealand mistletoe Peraxilla tetrapetala (Loranthaceae) has been shown to be consistently pollen limited, but to date there has been no test of whether the species is also seed limited. If it is not seed limited, then pollen limitation may have no effect on population size. We tested for seed limitation by sowing seeds onto host trees at high and low densities at two sites, and following survival for up to 69 months. Our rationale was that unless there is strong density-dependent seedling mortality sufficient to negate increases in seed supply, the species would be seed limited. We simultaneously measured pollen limitation at both sites using pollen augmentation. Peraxilla tetrapetala was strongly pollen limited at both sites over 7 years at Ohau (mean Pollen Limitation Index 0.62), and 12 years at Craigieburn (mean PLI 0.44), before and during the seed-limitation study. There was no significant overall negative effect of density on survival in sown P. tetrapetala seeds over 42,69 months. There was a significant positive effect: seeds were more likely to adhere to branches when sown at high densities. This initial advantage to high-density seeds was gradually eroded by slightly (but non-significantly) lower survival rates of adhered seeds at high density. By the end of the study there was no significant difference in overall survival in high and low density plantings. This means that P. tetrapetala was apparently both pollen limited and seed limited at both our sites. Hence, reduced densities of native bird pollinators caused by introduced mammalian carnivores are likely to reduce the density of adult mistletoes in the next generation. However, the generality of this result may be affected by the fact that mistletoes do not have a dense ,seedling shadow' under the parent mistletoe. [source] GluR5,6,7 subunit immunoreactivity on apical pyramidal cell dendrites in hippocampus of schizophrenics and manic depressivesHIPPOCAMPUS, Issue 5 2001Francine M. Benes Abstract Recent postmortem studies have suggested that changes in the regulation of kainate-sensitive glutamate receptors (kainate receptors) in the hippocampus may play a role in schizophrenia. To explore this possibility further, the distribution of immunoreactivity (IR) for the GluR5,6,7 subunits of the KR was assessed in a cohort consisting of 15 normal controls, 15 schizophrenics, and 9 manic depressives matched for age and postmortem interval (PMI). Cross sections of hippocampus showed abundant GluR5,6,7 -IR on apical dendrites of pyramidal neurons in the stratum radiatum and stratum moleculare. In normal controls, both the numerical and length density of IR dendrites were much higher in sector CA2 than in sectors CA3 or CA1. When data for the individual groups were separately examined, the schizophrenics showed a 30,35% reduction in the density of GluR5,6,7 -IR dendrites found in both stratum radiatum and stratum moleculare of sectors CA3 and CA2, as well as proximal and middle portions of CA1. In CA2, the magnitude of this decrease in schizophrenia was 2.5 times larger than that seen in any of the other sectors. For the manic depressive group, no significant differences were observed in any sectors or laminae examined. The potential confounding effects of either age, PMI, or neuroleptic exposure do not explain the reduced density of IR dendrites detected in the schizophrenic group. Taken together, the preferential reduction of GluR5,6,7 -IR observed on apical dendrites of pyramidal neurons is consistent with a functional downregulation of the kainate receptor in the hippocampus of schizophrenic brain. Hippocampus 2001;11:482,491. © 2001 Wiley-Liss, Inc. [source] Density-dependent growth rate in an age-structured population: a field study on stream-dwelling brown trout Salmo truttaJOURNAL OF FISH BIOLOGY, Issue 10 2009R. Kaspersson A field experiment during autumn, winter and spring was performed in a small stream on the west coast of Sweden, aiming to examine the direct and indirect consequences of density-dependent intercohort competition in brown trout Salmo trutta. Individual growth rate, recapture rate and site fidelity were used as response variables in the young-of-the-year (YOY) age class, experiencing two different treatments: presence or absence of yearlings and over-yearlings (age , 1+ year individuals). YOY individuals in stream sections with reduced density of age , 1+ year individuals grew significantly faster than individuals experiencing natural cohort structure. In the latter, growth rate was negatively correlated with density and biomass of age , 1+ year individuals, which may induce indirect effects on year-class strength through, for example, reduced fecundity and survival. Movement of YOY individuals and turnover rate (i.e. proportion of untagged individuals) were used to demonstrate potential effects of intercohort competition on site fidelity. While YOY movement was remarkably restricted (83% recaptured within 50 m from the release points), turnover rate was higher in sections with reduced density of age ,1+ year individuals, suggesting that reduced density of age ,1+ year individuals may have released favourable microhabitats. [source] Serotonin transporter, 5-HT1A receptor, and behavior in DBA/2J mice in comparison with four inbred mouse strainsJOURNAL OF NEUROSCIENCE RESEARCH, Issue 16 2009Nina K. Popova Abstract Prepulse inhibition (PPI), the reduction in acoustic startle produced when it is preceded by a weak prepulse stimulus, is impaired in schizophrenic patients. The DBA/2J mouse strain displayed deficient PPI and is therefore suggested as an experimental animal model for the loss of sensorimotor gating in schizophrenia. Brain serotonin (5-HT) has been implicated in the pathophysiology of several psychiatric disorders, including major depressive disorder and schizophrenia. In the present study, behavior, 5-HT transporter (5-HTT) mRNA level, 5-HT1A receptor mRNA level, and 5-HT1A receptor density in the brain regions were studied in DBA/2J mice in comparison with four inbred mouse strains (CBA/Lac, C57BL/6, BALB/c, and ICR). A decrease in 5-HTT mRNA level in the midbrain and a reduced density of 5-HT1A receptors in the frontal cortex without significant changes in 5-HT1A receptor mRNA level in DBA/2J mice were found. It was shown that, along with decreased PPI, DBA/2J mice demonstrated considerably reduced immobility in the tail suspension test and in the forced swim test. No significant interstrain differences in intermale aggression, or in light-dark box and elevated plus-maze tests, were found. The results suggested the involvement of decreased 5-HTT gene expression and 5-HT1A receptor density in genetically defined PPI deficiency and showed a lack of any association between PPI deficiency and predisposition to aggressive, anxiety, and depressive-like behaviors. © 2009 Wiley-Liss, Inc. [source] Radiofrequency ablation of colorectal liver metastases induces an inflammatory response in distant hepatic metastases but not in local accelerated outgrowthJOURNAL OF SURGICAL ONCOLOGY, Issue 7 2010Maarten W. Nijkamp MD Abstract Background Recently, we have shown in a murine model that radiofrequency ablation (RFA) induces accelerated outgrowth of colorectal micrometastases in the transition zone (TZ) surrounding the ablated lesion. Conversely, RFA also induces an anti-tumor T-cell response that may limit tumor growth at distant sites. Here we have evaluated whether an altered density of inflammatory cells could be observed in the perinecrotic (TZ) metastases compared to hepatic metastases in the distant reference zone (RZ). Methods RFA-treated tumor-bearing mice (n,=,10) were sacrificed. The inflammatory cell density (neutrophils, macrophages, CD4+ T-cells, and CD8+ T-cells) of tumors in the TZ (TZ tumors) was compared to that in tumors in the RZ (RZ tumors). Sham-operated, tumor-bearing mice (n,=,10) were analyzed simultaneously as controls (sham-treated tumors). Results In RFA-treated, tumor-bearing mice RZ tumors contained a significantly higher density of neutrophils and CD4+ T-cells, but not macrophages and CD8+ T-cells compared to sham-treated tumors. Notably, TZ tumors had a significantly lower density of neutrophils, CD4+ T-cells, and CD8+ T-cells, but not macrophages, when compared to RZ tumors. Conclusions The accelerated perinecrotic tumor outgrowth following RFA is associated with a reduced density of neutrophils and T-cells compared to distant hepatic metastases. This may have implications for local tumor recurrence following RFA. J. Surg. Oncol. 2010; 101:551,556. © 2010 Wiley-Liss, Inc. [source] Quasilocal vibrations and the Boson peak in glassesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2004D. A. ParshinArticle first published online: 16 NOV 200 Abstract The problem of the low-frequency harmonic excitations and of the Boson peak in glasses is reviewed in the scope of recent theoretical developments. It is shown that the Boson peak inevitably appears in the reduced density of states g(,)/,2 of quasilocal vibrations in glasses which are additional to phonons harmonic excitations. We show that the same physical mechanism is fundamental for such seemingly different phenomenon as formation of the two-level systems in glasses. The fundamental reason for the Boson peak and two-level system formation is an instability of the spectrum of quasilocal harmonic modes weakly interacting with the high frequency surrounding and with each other. The instability controlled by the anharmonicity creates a new stable universal spectrum of harmonic vibrations with a Boson peak feature. We show that under pressure the Boson peak in glasses is always shifted to higher frequencies. For high enough pressures P the Boson peak frequency ,b , P1/3. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Performance evaluation of concurrent rice,fish,prawn culture with and without cull harvestingAQUACULTURE RESEARCH, Issue 9 2010Rajeeb K Mohanty Abstract This study was carried out in farmers' fields for three experimental culture cycles to evaluate the performance of rice,fish,prawn culture. The treatments carried out were deepwater rice mono-cropping (R), and rice,fish,prawn culture with cull harvesting (R,FC) and without cull harvesting (R,F). Water pH and total alkalinity were significantly higher (P<0.05) in R,FC than in R,F, while the concentrations of total suspended solids, plankton and chlorophyll a were higher in R,F. Cull harvesting in R,FC had no marked influence on the concentrations of dissolved oxygen, NH4+, nitrite, nitrate and phosphate compared with the R,F treatment. The significantly higher fish and prawn yields (P<0.05) and species-wise faster individual growth performance in R,FC than in R,F were probably due to periodic cull harvesting, which minimized the competition for food and space as well as physiological stress at reduced density. The paddy yield and percentage increase in paddy yield over rice mono-crop was significantly higher (P<0.05) in R,FC (25%), followed by R,F (16.9%), probably due to lower chlorophyll a (36.7 mg m,3) and plankton density (1.4 × 104 L,1), which minimized the competition for nutrients with rice plants. The highest rice equivalent yield (38.5), output value,cultivation cost ratio (1.56) and enhanced net return (28%) in deepwater rice,fish culture were recorded when cull harvesting was practiced. [source] | ||||||||||||||||||||||