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Density Dependent (density + dependent)
Selected AbstractsConsequences for a host,parasitoid interaction of host-plant aggregation, isolation, and phenologyECOLOGICAL ENTOMOLOGY, Issue 4 2007ADAM J. VANBERGEN Abstract 1.,Spatial habitat structure can influence the likelihood of patch colonisation by dispersing individuals, and this likelihood may differ according to trophic position, potentially leading to a refuge from parasitism for hosts. 2.,Whether habitat patch size, isolation, and host-plant heterogeneity differentially affected host and parasitoid abundance, and parasitism rates was tested using a tri-trophic thistle,herbivore,parasitoid system. 3.,Cirsium palustre thistles (n= 240) were transplanted in 24 blocks replicated in two sites, creating a range of habitat patch sizes at increasing distance from a pre-existing source population. Plant architecture and phenological stage were measured for each plant and the numbers of the herbivore Tephritis conura and parasitoid Pteromalus elevatus recorded. 4.,Mean herbivore numbers per plant increased with host-plant density per patch, but parasitoid numbers and parasitism rates were unaffected. Patch distance from the source population did not influence insect abundance or parasitism rates. Parasitoid abundance was positively correlated with host insect number, and parasitism rates were negatively density dependent. Host-plant phenological stage was positively correlated with herbivore and parasitoid abundance, and parasitism rates at both patch and host-plant scales. 5.,The differential response between herbivore and parasitoid to host-plant density did not lead to a spatial refuge but may have contributed to the observed parasitism rates being negatively density dependent. Heterogeneity in patch quality, mediated by variation in host-plant phenology, was more important than spatial habitat structure for both the herbivore and parasitoid populations, and for parasitism rates. [source] Costs of cannibalism in the presence of an iridovirus pathogen of Spodoptera frugiperdaECOLOGICAL ENTOMOLOGY, Issue 2 2006Trevor Williams Abstract., 1.,The costs of cannibalism were examined in larvae of Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) in the presence of conspecifics infected by a lethal invertebrate iridescent virus (IIV). The hypothesis of a positive correlation between insect density and the likelihood of disease transmission by cannibalism was examined in laboratory microcosms and a field experiment. 2.,Transmission was negligible following peroral infection of early instars with purified virus suspensions or following coprophagy of virus-contaminated faeces excreted by infected insects. In contrast, 92% of the insects that predated infected conspecifics acquired the infection and died prior to adult emergence in the laboratory. Diseased larvae were more likely to be victims of cannibalism than healthy larvae. 3.,The prevalence of cannibalism was density dependent in laboratory microcosms with a low density (10 healthy insects + one infected insect) or high density (30 healthy insects + one infected insect) of insects, and field experiments performed on maize plants infested with one or four healthy insects + one infected insect. 4.,Cannibalism in the presence of virus-infected conspecifics was highly costly to S. frugiperda; in all cases, insect survival was reduced by between ,,50% (laboratory) and ,,30% (field) in the presence of the pathogen. Contrary to expectations, the prevalence of disease was not sensitive to density because cannibalism resulted in self-thinning. As infected individuals are consumed and disappear from the population, the prevalence of disease will be determined by the timescale over which transmission can be achieved, and the rate at which individuals that have acquired an infection become themselves infectious to conspecific predators. [source] The ecology of virulenceECOLOGY LETTERS, Issue 10 2006Curtis M. Lively Abstract Theoretical work has shown that parasites should evolve intermediate levels of virulence. Less attention has been given to the ecology of virulence. Here I explore population-dynamic models of infection in an annual host. The infection does not kill the host; but it can decrease the number of offspring produced by the host, and the magnitude of this effect depends on host population size. Hence, ,virulence' is density dependent, and is defined here as the difference in birth rates between uninfected and infected hosts, divided by the birth rate of uninfected hosts. The results suggest that infection can be highly virulent at the host's equilibrium density, even though the parasite has no effect on the host's intrinsic birth rate. The results also suggest that parasites may help to stabilize host population dynamics. In general, the impact of infection may be underestimated in natural populations. [source] Host,parasite interactions and competition between tubificid species in a benthic communityFRESHWATER BIOLOGY, Issue 8 2009L. C. STEINBACH ELWELL Summary 1. Parasites can be important determinants of host community structure while host community structure can influence the success of parasites, although both are often overlooked. In two laboratory experiments, we examined interactions among Myxobolus cerebralis syn Myxosoma cerebralis Höfer, the myxozoan parasite that causes salmonid whirling disease, and two coexisting tubificid species: Tubifex tubifex (Müller), which is the alternate host of the parasite, and Limnodrilus hoffmeisteri Claparède, which is not susceptible. In the first experiment, we examined T. tubifex infection prevalence when exposed to nine doses of spores. In the second experiment, we examined tubificid and parasite success under three spore doses when tubificids were combined in a response surface experimental design used to detect interactions among species. 2. The outcomes of interactions between tubificid species were complex. The number and biomass of offspring of both tubificid species were density dependent when in monoculture or in combination with the other species. Adult growth of T. tubifex was also density dependent in monoculture, but when L. hoffmeisteri replaced one-half of the T. tubifex in the high-density treatment, adult growth of T. tubifex was higher than in monoculture. Adult growth of L. hoffmeisteri was always density independent. Whether T. tubifex was exposed to the parasite or not did not change the outcome of these interactions. However, adult growth of T. tubifex, but not L. hoffmeisteri, was highest when M. cerebralis was present. 3. Infection prevalence of T. tubifex increased with increasing spore dose. Infection prevalence was lowest in the high-density T. tubifex monoculture and highest in the low-density T. tubifex monoculture and when T. tubifex was in combination with L. hoffmeisteri. 4. Both intraspecific and interspecific competition influenced tubificid success, but T. tubifex gained some competitive advantage through increased adult growth when in combination with L. hoffmeisteri. Whether T. tubifex was exposed to the parasite or not did not change the outcome of the interactions between the tubificid species. 5. The presence of L. hoffmeisteri did not decrease the prevalence of infection in T. tubifex, suggesting that parasite success was unaltered by the presence of this non-susceptible species. [source] [CO2]- and density-dependent competition between grassland speciesGLOBAL CHANGE BIOLOGY, Issue 11 2006MARK Van KLEUNEN Abstract The predicted ongoing increase of atmospheric carbon dioxide levels is considered to be one of the main threats to biodiversity due to potential changes in biotic interactions. We tested whether effects of intra- and interspecific planting density of the calcareous grassland perennials Bromus erectus and Carex flacca change in response to elevated [CO2] (600 ppm) by using factorial combinations of seven densities (0, 1, 2, 4, 8, 16, 24 tillers per 8 × 8 cm2 cell) of both species in plots with and without CO2 enrichment. Although aboveground biomass of C. flacca was increased by 54% under elevated [CO2], the combined aboveground biomass of the whole stand was not significantly increased. C. flacca tended to produce more tillers under elevated [CO2] while B. erectus produced less tillers. The positive effect of [CO2] on the number of tillers of C. flacca was strongest at high intraspecific densities. On the other hand, the negative effect of [CO2] on the number of tillers of B. erectus was not present at intermediate intraspecific planting densities. Seed production of C. flacca was more than doubled under elevated [CO2], while seed production of B. erectus was not affected. Moreover, the mass per seed of C. flacca was increased by elevated [CO2] at intermediate interspecific planting densities while the mass per seed of B. erectus was decreased by elevated [CO2] at high interspecific planting densities. Our results show that the responses of C. flacca and B. erectus to elevated [CO2] depend in a complex way on initial planting densities of both species. In other words, competition between these two model species is both [CO2]- and density dependent. On average, however, the effects of [CO2] on the individual species indicate that the composition of calcareous grasslands is likely to change under elevated [CO2] in favor of C. flacca. [source] Movement characteristics of the Scarce Blue-tailed Damselfly, Ischnura pumilioINSECT CONSERVATION AND DIVERSITY, Issue 1 2010KATHERINE A. ALLEN Abstract., 1. The Scarce Blue-tailed Damselfly, Ischnura pumilio, is threatened in the UK and exists in small, transient colonies. Consequently, little is known about its dispersal characteristics. This study investigates movement in two contrasting habitats with the aim of informing conservation management on a landscape scale. 2. Mark-release-recapture studies were performed at an established colony in the New Forest and a smaller population in the Red River valley in southern England. A total of 2304 individuals was marked. 3. Ischnura pumilio was found to be exceptionally sedentary. Mean gross lifetime movement was 56 m and 43% of individuals moved <50 m in their lifetime. Movements over 150 m were very rare. Maximum lifetime movement was 1165 m. As such, I. pumilio is the most sedentary odonate studied in the UK to date. 4. Movement was inversely density dependent, which has important conservation implications if individuals attempt to emigrate from small populations because of low density. The presence of parasitic mites (Hydryphantes sp.) significantly increased movement distance. 5. Ischnura pumilio had a low dispersal probability compared to other damselflies. As the smallest British odonate, this is in keeping with the relationship between size and dispersal found across taxa. 6. Ischnura pumilio has been regarded as a ,wandering opportunist' due to its tendency to appear in locations far from known sites. However, this study suggests that long range movement rarely occurs from prime habitat that is maintained in an early successional stage. This has implications for the conservation of the species in the UK. [source] Within-sex density dependence and population dynamics of red squirrels Sciurus vulgarisJOURNAL OF ANIMAL ECOLOGY, Issue 1 2004Luc A. Wauters Summary 1Social organization and dispersal of red squirrels (Sciurus vulgaris L.) differ between sexes, and intrasexual competition is intense. Therefore, we predicted that demographic parameters should be gender-specific: that is density-dependent factors will be more strongly related to density of the same sex than to density of the opposite sex. We studied the relative importance of within- and between-sex density-dependent factors and of density-independent factors (habitat type, food abundance, winter temperature) on different demographic parameters, in two populations in northern Belgium. 2Spring density of males was positively correlated with tree-seed abundance in the previous year, but this was not the case for females. None of the population parameters we measured differed between habitats, indicating that the same density-dependent and density-independent mechanisms prevailed in coniferous and deciduous habitat. 3Within each sex, we found several demographic parameters that were dependent on the densities of the same sex; however, none of these parameters was found to be dependent on the density of the opposite sex. 4Reproductive rate increased with food abundance and decreased with female density. Adult survival of females decreased with female density in autumn,winter, while survival of adult males in spring,summer increased with the size of the previous year's seed crop. 5Immigration rate of males was higher in spring than in autumn, and spring immigration increased with food abundance. Male recruitment rate, in both seasons, increased with food abundance, but was male density dependent. However, spring,summer loss rates also increased when food supplies were good, suggesting that despite high food availability, emigration of juvenile and subadult males increased when intrasexual competition was intense. Recruitment rate of females decreased with increasing female density. After a good seed crop, more subadult females dispersed, but their settlement success (recruitment) was lower at high female density. 6Seed crop size positively affected red squirrel densities through increased reproduction, immigration and adult survival of males, but density-dependent reproduction and within-sex density-dependent recruitment of locally born juveniles and dispersing subadults limit the fluctuations in numbers and regulate densities in winter,early spring, as well as in summer. [source] Spatial dynamics of predation by carabid beetles on slugsJOURNAL OF ANIMAL ECOLOGY, Issue 3 2000David A. Bohan Summary 1.,An explicitly spatial sampling approach was employed to test the null hypothesis that the predation on slugs by the carabid beetle Pterostichus melanarius (Illiger) was opportunistic. 2.,The beetles and slugs were sampled across a nested series of grids of sampling points, in a field of winter wheat during June and July 1997. 3.,The spatial distribution of all slugs in June was found to change with the scale of the sampling grid, from random on the 0.25 m scale, through aggregation at 1 m, to random at 4 m. At the highest scale of 16 m, the slugs were significantly spatially aggregated. 4.,The distribution of beetles in June was also spatially dynamic, with randomness observed at the 4 m and 8 m scales. At 16 m, significant aggregation was observed. 5.,The dynamic distributions of slugs and beetles, at 16 m, were found not to be associated with, and thus were not determined by, soil or crop factors. 6.,Comparison of slug and beetle populations showed, however, that the distributions at 16 m were dynamically associated with each other. In June where there were many slugs there were also many carabids, whilst in July where there were many carabids there were few slugs. 7.,Approximately 11% of the beetles sampled across the 16 m grid in June and July were found to have ingested slug protein, following intensive enzyme-linked immunosorbent assay (ELISA) testing. 8.,The spatial distribution of these slug-positive beetles was significantly associated with the distribution of the larger slug classes, over 25 mg. Where there were many large slugs in June there were many slug-positive beetles. Conversely, in July few large slugs were found where there were many slug-positive beetles. 9.,Parametric analysis revealed that these changes in the large slug class, at each sampling point between June and July (growth), were negatively related to the local numbers of slug-positive beetles, and that growth declined as the local numbers of beetles increased. 10.,These findings suggest that predation was not opportunistic, but direct and dynamic, falsifying the null hypothesis. Moreover, this predation elicited significant changes in the spatial distribution and local density of the slugs, in a manner that may be termed spatially density dependent. [source] Effects of air pollution on natural enemies of the leaf beetle Melasoma lapponicaJOURNAL OF APPLIED ECOLOGY, Issue 2 2000Elena L. Zvereva Summary 1. ,Air pollution might have differential effects on herbivores and their natural enemies, thus changing population dynamics. Therefore, from 1993 to 1998 we studied mortality caused by parasitoids and predators to the willow-feeding leaf beetle Melasoma lapponica in the impact zone of the Severonikel nickel,copper smelter (Kola Peninsula, north-western Russia). 2. ,Densities of M. lapponica were very low at clean forest sites (below five beetles per 10-min count) but higher in polluted areas (10,340 beetles per count). There were, however, variations between study years. 3. ,Egg predation, mainly by syrphid larvae and zoophagous bugs, was higher at relatively clean sites (55·3%) than at polluted sites (22·2%). Similarly, predation on larvae by zoophagous bugs and wood ants was higher at clean sites (68·4%) than at polluted sites (32·9%). 4. ,In contrast to predation, mortality caused by the parasitoid flies Megaselia opacicornis (Phoridae) and Cleonice nitidiuscula (Tachinidae) was lower at clean sites (12·3%) than at polluted sites (35·3%). Total parasitism levels increased significantly with pollution load. 5. ,Total mortality caused by natural enemies was higher at clean sites (93·7%) than at polluted sites (79·4%) due to higher predation rates, which may partly explain increased leaf beetle density within the smelter's impact zone. The effects of predators in clean forests were confirmed by the extinction of adults of M. lapponica introduced to one of the forest sites. 6. ,Although some individual sources of mortality appeared to be density dependent (direct or inverse), the joint effect of all natural enemies was not. 7. ,Our data show that a decrease in predation can contribute to increased leaf beetle density at polluted sites. However, the overall effects of natural enemies in this case were not sufficient to account for all density variations between sites. To our knowledge this is the first study to assess how pollution affects the partitioning of mortality in herbivorous insects between predators and parasitoids. [source] The effect of initial seed density on the structure of a desert annual plant communityJOURNAL OF ECOLOGY, Issue 3 2002Christopher J. Lortie Summary 1,Few experiments directly test the role of density dependence in natural plant communities. 2,We tested (i) whether different initial seed densities of the entire seed bank of an annual plant community affected performance (emergence, mean plant biomass and survival) and (ii) whether density-dependent processes were operating within the communities. We also tested whether life-stage, year and soil moisture (both on a topographic gradient and in an experimental manipulation) influenced the effects of seed density. 3,We considered two distinct phases: seed to emergent seedlings, and emergent seedlings to established plants. 4,The seed bank was collected from a semistabilized sand dune in the Negev Desert, Israel. This was added to sieved sand in plots at the same site at four different initial seed densities: 1/16×, 1/4×, 1× (natural seed density) and 2×. The experiment was repeated for three consecutive growing seasons. 5,Emergence of seedlings was significantly influenced by initial seed density in all 3 years, with higher initial seed densities having lower rates of emergence. 6,Mean final plant size was negatively density dependent and consistently unaffected by the initial seed density sown. 7,In general, there were no strong interactions of topographic position with initial seed density, processes within the vegetation were not density dependent and the experimental addition of water did not influence any of the performance measures tested. Density-dependent processes vary from year to year, while moisture effects do not. 8,We conclude that seedling emergence and some processes in the established plant community are density dependent, but the established plant community is also affected by other processes, such as resource limitation. [source] Reproductive performance of clonal and sexual bark beetles (Coleoptera: Scolytidae) in the fieldJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 5 2000Løyning In Ips acuminatus (Gyll.) parthenogenetic females occur together with sexual females and with sexual males upon which they depend for sperm. In a reciprocal-transplant experiment, I studied fecundity differences among parthenogenetic and sexual females from two populations that differ dramatically in the proportion of clonal females. In a second experiment, I studied competition between larvae from different mothers and between females from the two source populations. Fecundity measured by the number of eggs per egg tunnel was influenced by the ambient environment at the sites of the experiment as well as the origin of the female, and was generally higher for clonal than for sexual females at both sites. In experimental groups where larvae competed with larvae from their own population (pure treatments), the number of surviving pupae was significantly lower than in groups where females from the two source populations were mixed. The high fecundity of clonal females makes coexistence of the two types of females difficult to explain. It makes the reproductive advantage associated with clonality in I. acuminatus even higher than the two-fold difference due to asexuality per sé. The significant differences in the number of pupae in mixed vs. pure groups suggest ecological divergence between sexual and clonal females. This would make the mortality of larvae not only density dependent, but also frequency dependent, which could explain the coexistence of sexual and clonal females. [source] Feeding resumption, morphological changes and mortality during starvation in Japanese flounder larvaeJOURNAL OF FISH BIOLOGY, Issue 6 2002S. Dou Japanese flounder Paralichthys olivaceus larvae established first feeding 3 days after hatching (DAH) at c. 17° C. Non-fed fish reached irreversible starvation at age 5 DAH. Non-fed fish showed similar feeding rate and feeding intensity as the fed fish when they were provided with prey before 5 DAH, after which the starved larvae did not feed even when prey became available. None of the six morphological measurements examined (total length, body height, eye height, head height, gut height and myotome height) showed significant differences between the non-fed and fed larvae until 5 DAH. Normal development continued only in the fed group, and the non-fed larvae showed reverse growth or body collapse after 5 DAH. Owing to the shrinkage and collapse at the top of head due to starvation, head height could be a sensitive indicator of starvation in Japanese flounder larvae. In the fed treatments, high mortality occurred from first feeding (3 DAH) to irreversible starvation (5 DAH), accounting for about two-thirds to three-quarters of the overall mortality (46,52%) throughout the experiments. This mortality was not prey density or larval density dependent. Mortality during the same period in the non-fed larvae accounted for about a third of the overall mortality (100%). [source] Intrinsic and extrinsic determinants of mountain pine beetle population growthAGRICULTURAL AND FOREST ENTOMOLOGY, Issue 2 2009M. Kurtis Trzcinski Abstract 1,Mountain pine beetle Dendroctonus ponderosae populations have large, economically significant outbreaks. Density dependence and environmental variability are expected to have important effects on their dynamics. We analysed time series data from an outbreak in the 1930s to determine the relative importance of population density and environmental variability on local population growth rates. 2,Resource depletion occurred rapidly at the scale of 0.4 ha and population growth rates were strongly density dependent. Annual environmental changes did not have detectable effects on population growth rates, leading to the conclusion that intrinsic processes influenced local population density more than extrinsic factors during this outbreak. 3,Our calculated value of rmax (1.16) does not suggest intrinsically cyclic population dynamics. Our estimate of rmax and density dependence will be useful in developing applied models of mountain pine beetle outbreaks, and the subsequent evaluation of management strategies. [source] Growth and Wood/Bark Properties of Abies faxoniana Seedlings as Affected by Elevated CO2JOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 3 2008Yun-Zhou Qiao Abstract Growth and wood and bark properties of Abies faxoniana seedlings after one year's exposure to elevated CO2 concentration (ambient + 350 (± 25) ,mol/mol) under two planting densities (28 or 84 plants/m2) were investigated in closed-top chambers. Tree height, stem diameter and cross-sectional area, and total biomass were enhanced under elevated CO2 concentration, and reduced under high planting density. Most traits of stem bark were improved under elevated CO2 concentration and reduced under high planting density. Stem wood production was significantly increased in volume under elevated CO2 concentration under both densities, and the stem wood density decreased under elevated CO2 concentration and increased under high planting density. These results suggest that the response of stem wood and bark to elevated CO2 concentration is density dependent. This may be of great importance in a future CO2 enriched world in natural forests where plant density varies considerably. The results also show that the bark/wood ratio in diameter, stem cross-sectional area and dry weight are not proportionally affected by elevated CO2 concentration under the two contrasting planting densities. This indicates that the response magnitude of stem bark and stem wood to elevated CO2 concentration are different but their response directions are the same. [source] Effects of Macrocheles mites on longevity of males of the dimorphic dung beetle Onthophagus binodisJOURNAL OF ZOOLOGY, Issue 4 2001Janne S. Kotiaho Abstract In this study we tested the nature of the phoretic relationship between the cosmopolitan mite Macrocheles merdarius and the dimorphic dung beetle Onthophagus binodis. We observed and experimentally manipulated the number of mites on individual beetles and tested how mite infestation affects male longevity. There was a significant effect of mites on male longevity: males in our mites-added treatment died on average 15 days earlier than males in our mites-removed treatment. Interestingly, the number of mites on males was significantly repeatable suggesting that individuals may differ in their susceptibility to infestation. Major males had more mites on them than minor males, and the proportion of mites on minor males was negatively density dependent. [source] On the asymptotic positivity of solutions for the extended Fisher,Kolmogorov equation with nonlinear diffusionMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 8 2002M. V. Bartuccelli Abstract The objective of this paper aims to prove positivity of solutions for a semilinear dissipative partial differential equation with non-linear diffusion. The equation is a generalized model of the well-known Fisher,Kolmogorov equation and represents a class of dissipative partial differential equations containing differential operators of higher order than the Laplacian. It arises in a variety of meaningful physical situations including gas flows, diffusion of an electron,ion plasma and the dynamics of biological populations whose mobility is density dependent. In all these situations, the solutions of the equation must be positive functions. Copyright © 2002 John Wiley & Sons, Ltd. [source] The influence of sediment type on the aggregative response of oystercatchers, Haematopus ostralegus, searching for cockles, Cerastoderma eduleOIKOS, Issue 1 2000Ian Johnstone Models that describe the dispersion patterns of predators between a series of patches that vary in prey density frequently assume that predators, in the absence of interference, will aggregate in patches with the highest prey density, at any point in time. This assumption has important implications for patterns of prey mortality, and the extent to which prey mortality is density dependent. In natural predator-prey systems, it is likely that environmental factors interact with spatial variation in prey density to influence the aggregative response of predators. We show data consistent with this idea on a population of overwintering oystercatchers foraging on cockles. There was no evidence that birds aggregated in patches with the highest biomass density of cockles. The biomass density of cockles was highest in muddy patches at the start of winter, and birds aggregated in patches that switched from being muddy at the start of winter to being sandy at some point during the winter. We argue that sediment type influences foraging costs experienced by the birds, so birds avoid feeding in muddy patches unless the fine sediment is removed from a patch, as happens during winter storms. When this happens a high biomass density of cockles suddenly becomes available and the birds aggregate in such patches. The rate of biomass loss was greatest in patches used intensively by birds for feeding, suggesting that the birds' aggregative response influences cockle mortality. We discuss the implications of our results for ideal free models. [source] Single- or multistage regulation in complex life cycles: does it make a difference?OIKOS, Issue 2 2000Barbara Hellriegel Data on the different stages of complex life cycles are often rather unbalanced, especially those concerning the effects of density. How does this affect our understanding of a species' population dynamics? Two discrete three-stage models with overlapping generations and delayed maturation are constructed to address this question. They assume that survival or emigration in any life stage and/or reproduction can be density dependent. A typical pond-breeding amphibian species with a well-studied larval stage serves as an example. Numerical results show that the population dynamics resulting from density dependence at a single (e.g. the larval) stage can be decisively and unpredictably modified by density dependence in additional stages. Superposition of density-dependent processes could thus be one reason for the difficulties in identifying density dependence in the field. Moreover, in a simulated source-refuge system with habitat-specific density-dependent dispersal of juveniles density dependence in multiple stages can stabilize or destabilize the dynamics and produce misleading age structures. From an applied perspective this model shows that excluding multistage regulation prematurely clearly affects our ability to predict consequences of human impacts. [source] A green fluorescent protein-based screening method for identification of resistance in anthurium to systemic infection by Xanthomonas axonopodis pv. dieffenbachiaePLANT PATHOLOGY, Issue 5 2007W. Elibox Resistance of cultivars of Anthurium andraeanum to systemic infection by Xanthomonas axonopodis pv. dieffenbachiae, the causal organism of bacterial blight disease of anthurium, was investigated using a bioengineered bacterial strain containing p519ngfp plasmid. Successful infection establishment in anthurium was found to be cultivar and inoculum density dependent, but independent of plant age. Injection of cut petioles (stage-2 leaf) with 100 µL inoculum (109 CFU mL,1) resulted in 100% infection establishment in susceptible cultivars on a repeatable basis, and differentiated between various levels of observed field resistance. Time to death (weeks) and proportion of dead plants best differentiated between levels of resistance and cultivars were placed in four groups based on these criteria. The susceptible group (32 cultivars) rapidly declined within 6,12 weeks of inoculation (WAI) and resulted in 100% plant death; the moderately resistant group (10 cultivars) declined within 12 WAI, but resulted in less than 100% plant death; the resistant category had less than 100% plant death with a slow decline taking over 20 weeks; and the highly resistant category (15 cultivars) showed 0% infection. The correlation coefficient between green fluorescent protein (GFP)-fluorescence and eventual death of plants was 0·90, indicating that the final death of individual plants can be reasonably well predicted based on GFP-fluorescence data at 5 WAI. Hence GFP data at 5 WAI can be used for early detection of latently infected plants and may assist screening for resistance in segregating populations of anthurium. [source] Effect of stocking density on the growth performance and yield of Nile tilapia [Oreochromis niloticus (L., 1758)] in a cage culture system in Lake Kuriftu, EthiopiaAQUACULTURE RESEARCH, Issue 13 2008Ashagrie Gibtan Abstract This research was conducted to investigate the effect of stocking density on the growth performance and yield of Oreochromis niloticus in cage culture in Lake Kuriftu. The treatments had stocking densities of 50 (50F), 100 (100F), 150 (150F), and 200 (200F) fish per m,3. All treatments were in duplicate. Juveniles with an average weight of 45. 76±0.25 g were stocked in the treatments. The fish were fed a composite mixture of mill sweeping, cotton seed, and Bora food complex at 2% of their body weight twice per day using feeding trays for 150 days in powdered form. The growth performance of O. niloticus was density dependent. The final mean weight of O. niloticus ranged 147.76±0.28,219.71±1.42 g and the mean daily weight gain was 0.69±0.01,1.15±0.02 g day,1. Fish held in cages with lower density were heavier than the ones held at higher densities, and showed higher weight gain and daily weight gain. The most effective stocking density, in terms of growth parameters, was 50 fish m,3. The gross yield (4.5,20.55 kg cage,1) showed a significant difference with increasing stocking density (P<0.05). Moreover, the apparent food conversion ratio (2.48,7.22) was significantly affected by stocking density (P<0.05). However, survival rate was not affected by stocking density (P>0.05). It can be concluded that the most effective stocking densities were at 50 fish m,3 cage for larger size fish demand in a short period and 200 fish m,3 for higher gross production with supplementary feed. [source] Nursery rearing of the Asian catfish, Clarias macrocephalus (Günther), at different stocking densities in cages suspended in tanks and pondsAQUACULTURE RESEARCH, Issue 13 2002Ruby F Bombeo Abstract Growth and survival of hatchery-bred Asian catfish, Clarias macrocephalus (Günther), fry reared at different stocking densities in net cages suspended in tanks and ponds were measured. The stocking densities used were 285, 571 and 1143 fry m,3 in tanks and 114, 228 and 457 fry m,3 in ponds. Fish were fed a formulated diet throughout the 28-day rearing period. Generally, fish reared in cages in ponds grew faster, with a specific growth rate (SGR) range of 10.3,14.6% day,1, than those in cages suspended in tanks (SGR range 9,11.3% day,1). This could be attributed to the presence of natural zooplankton (copepods and cladocerans) in the pond throughout the culture period, which served as additional food sources for catfish juveniles. In both scenarios, the fish reared at lower densities had significantly higher SGR than fish reared at higher densities. In the pond, the SGR of fish held at 228 and 457 m,3 were similar to each other but were significantly lower than those of fish held at 114 m,3. The zooplankton in ponds consisted mostly of copepods and cladocerans, in contrast to tanks, in which rotifers were more predominant. Per cent survival ranged from 85% to 89% in tanks and from 78% to 87% in ponds and did not differ significantly among stocking densities and between rearing systems. In conclusion, catfish nursery in cages suspended in tanks and ponds is density dependent. Catfish fry reared at 285 m,3 in tanks and at 114 m,3 in ponds had significantly faster growth rates than fish reared at higher densities. However, the desired fingerling size of 3,4 cm total length for stocking in grow-out culture can still be attained at stocking densities of 457 m,3 in nursery pond and 571 m,3 in tanks. 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