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Low Growth Rates (low + growth_rate)
Selected AbstractsDeltas in the Abisko area, northern Sweden: the Abiskojokka delta in lake TorneträskGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 3-4 2002Hans Andrén Several small river deltas are found within the Abisko area. This study deals with the Abiskojokka delta in Lake Torneträsk. The aim is to describe the recent delta and its morphological development since the middle 1960s. In the apex of the delta, bars consist of boulders and cobbles while the mouth,bars are built by pebbles, gravel and to some extent sand. Birch vegetation is found on the sandy levées while willows and sedges dominate the interlevée basins. Mouth bars close to the lake generally lack vegetation. A comparison of the map in the present study with a map from 1965 shows comparatively small changes since 1964. Similar results are achieved when comparing aerial photographs from 1959 and 2000. Thus, the growth of the Abiskojokka delta is rather small compared to several other deltas in the Scandinavian mountains. This low growth rate is a result of upstream lakes trapping the major part of the fluvial sediments. Therefore, most of the delta sediment is redistributed old glaciofluvial material from the terraces within the Abiskojokka valley. Some material might also emanate from the Abiskojokka canyon. Formation of the main part of the delta is probably associated with the lowering of the Torneträsk ice,lakes, during and after the deglaciation of the region. Although some extreme rainstorm events have occurred in the area during recent decades, the effects of these on the delta are small. The result of such events is, however, visible as deposition of sand and silt on the levées after flooding. On the other hand, the shoreline and the mouth bars are continuously changing due to rather high wave energy especially during northerly winds. Along several mouth bars, spits are formed and reformed due to wave action. Minor changes of, and within, the two main distributaries have also been noticed, especially as bank erosion and redistribution of bars. The project will continue with a survey of the distal slope (foreset slope) of the delta as well as a study (including X,ray radiography) of the bottom sediments in Lake Torneträsk close to the delta front. The upstream deltas within this drainage basin as well as other deltas within the Torneträsk region will be studied. [source] Demographic factors and genetic variation influence population persistence under environmental changeJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 1 2009YVONNE WILLI Abstract Population persistence has been studied in a conservation context to predict the fate of small or declining populations. Persistence models have explored effects on extinction of random demographic and environmental fluctuations, but in the face of directional environmental change they should also integrate factors affecting whether a population can adapt. Here, we examine the population-size dependence of demographic and genetic factors and their likely contributions to extinction time under scenarios of environmental change. Parameter estimates were derived from experimental populations of the rainforest species, Drosophila birchii, held in the lab for 10 generations at census sizes of 20, 100 and 1000, and later exposed to five generations of heat-knockdown selection. Under a model of directional change in the thermal environment, rapid extinction of populations of size 20 was caused by a combination of low growth rate (r) and high stochasticity in r. Populations of 100 had significantly higher reproductive output, lower stochasticity in r and more additive genetic variance (VA) than populations of 20, but they were predicted to persist less well than the largest size class. Even populations of 1000 persisted only a few hundred generations under realistic estimates of environmental change because of low VA for heat-knockdown resistance. The experimental results document population-size dependence of demographic and adaptability factors. The simulations illustrate a threshold influence of demographic factors on population persistence, while genetic variance has a more elastic impact on persistence under environmental change. [source] Low threshold GaInAs quantum well lasers grown under low growth rate by solid-source MBE for 1200 nm wavelength rangePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2006M. Ohta Abstract Optical property dependence on growth rates of highly-strained GaInAs quantum wells (QWs) on GaAs was studied by solid-source molecular beam epitaxy (MBE). Noticeable improvement of the photoluminescence (PL) was observed by lowering the growth rate of highly-strained GaInAs. A sample grown at a growth rate of 0.05 µm/h under a low growth temperature and high As pressure showed a high PL intensity and a flat surface in atomic force microscope (AFM) measurements. The lowest threshold current density of 117 A/cm2/well is achieved for GaInAs/GaAs double QW lasers at 1190 nm wavelength. A low growth rate is found to be effective to grow highly-strained GaInAs QWs. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Amino acid budgets in three aphid species using the same host plantPHYSIOLOGICAL ENTOMOLOGY, Issue 3 2001J. P. Sandström Abstract. Nutrient provisioning in aphids depends both on the composition of ingested phloem sap and on the biosynthetic capabilities of the aphid and its intracellular symbionts. Amino acid budgets for three aphid species, Rhopalosiphum padi (L.), Schizaphis graminum (Rondani) and Diuraphis noxia (Mordvilko), were compared on a single host plant species, wheat Triticum aestivum L. Ingestion of amino acids from phloem, elimination of amino acids in honeydew, and the content of amino acids in aphids tissue were measured. From these values, ingestion rates were estimated and compared to honeydew and to estimated composition of aphid proteins. Ingestion rate was lowest in D. noxia due to low growth rate and low honeydew production; intermediate in S. graminum due to higher growth rate and intermediate honeydew production; and highest in R. padi, which had the highest rates for both variables. Both D. noxia and S. graminum induced increases in the amino acid content of ingested phloem. These changes in phloem content, combined with differences in ingestion rates, resulted in large differences among aphids in estimated rates of ingestion of individual amino acids. In honeydew, most essential amino acids were found in low amounts compared with the amounts ingested, especially for methionine and lysine. A few amino acids (arginine, cystine, histidine and tryptophan) were more abundant in honeydew of some aphids, suggesting oversupply. Aphid species differed in the composition of free amino acids in tissue but showed very similar composition in protein, implying similar requirements among the aphids. In R. padi and D. noxia, most essential amino acids were ingested in amounts insufficient for growth, implying dependence on symbiont provisioning. In S. graminum, most amino acids were ingested in amounts apparently sufficient for growth. [source] Population ecology of cave armoured catfish, Ancistrus cryptophthalmus Reis 1987, from central Brazil (Siluriformes: Loricariidae)ECOLOGY OF FRESHWATER FISH, Issue 2 2007E. Trajano Abstract,,, The population ecology of Ancistrus cryptophthalmus (Reis 1987) was studied by mark,recapture technique in caves from the São Domingos karst area, State of Goiás, northeastern Brazil. Total population sizes estimated for Angélica and Passa Três Caves were 20,000 and 1000 individuals, respectively. Densities around 1.0 individuals per m2 in Angélica, Bezerra and São Vicente I Streams, and 0.6 individuals per m2 in the smaller Passa Três Stream may be considered high for cavefish standards, as well as for epigean loricariids. As expected for benthic grazers, cave catfish are highly sedentary. The distribution of size classes did not differ among caves and within the same cave throughout the studied dry seasons; on the contrary, the condition factor decreased throughout this period probably because of the progressive depletion of organic matter available as food. Low proportions of mature individuals, low growth rates (average = 0.5 mm month,1) with cases of negative growth and high longevities (8,10 years) point to a precocial lifestyle, typical of troglobitic species. [source] Limitation of oxygenic photosynthesis and oxygen consumption by phosphate and organic nitrogen in a hypersaline microbial mat: a microsensor studyFEMS MICROBIOLOGY ECOLOGY, Issue 1 2006Rebecca Ludwig Abstract Microbial mats are characterized by high primary production but low growth rates, pointing to a limitation of growth by the lack of nutrients or substrates. We identified compounds that instantaneously stimulated photosynthesis rates and oxygen consumption rates in a hypersaline microbial mat by following the short-term response (c. 6 h) of these processes to addition of nutrients, organic and inorganic carbon compounds, using microsensors. Net photosynthesis rates were not stimulated by compound additions. However, both gross photosynthesis and oxygen consumption were substantially stimulated (by a minimum of 25%) by alanine (1 mM) and glutamate (3.5 mM) as well as by phosphate (0.1 mM). A low concentration of ammonium (0.1 mM) did not affect photosynthesis and oxygen consumption, whereas a higher concentration (3.5 mM) decreased both process rates. High concentrations of glycolate (5 mM) and phosphate (1 mM) inhibited gross photosynthesis but not oxygen consumption, leading to a decrease of net photosynthesis. Photosynthesis was not stimulated by addition of inorganic carbon, nor was oxygen consumption stimulated by organic compounds like glycolate (5 mM) or glucose (5 mM), indicating that carbon was efficiently cycled within the mat. Photosynthesis and oxygen consumption were apparently tightly coupled, because stimulations always affected both processes to the same extent, which resulted in unchanged net photosynthesis rates. These findings illustrate that microsensor techniques, due to their ability to quantify all three processes, can clarify community responses to nutrient enrichment studies much better than techniques that solely monitor net fluxes. [source] Migration Policy and Industrial Structure: The Case of SwitzerlandINTERNATIONAL MIGRATION, Issue 2 2008Leonhard Becker ABSTRACT Structural change in OECD countries, emphasizing knowledge-based sectors, has led to an increasing demand for highly skilled labour. One means of meeting this demand has been to implement a selective immigration policy. Such policies, however, have been criticized for channelling labour into low-producing sectors and occupations, hampering structural change. Proponents of such criticism point to Switzerland's former policy of channelling immigrants into so-called seasonal sectors, a practice abandoned in the early 1990s, as having contributed to Switzerland's low growth rates. To assess this, we here analyse the amended migration policy's effects on skill structure and sectoral distribution of immigration flows using data from the Swiss Census of 1990 and 2000 to determine whether the new policy has led to an immigrant inflow more adapted to the processes of structural change. We find that the share of highly skilled immigrants has increased notably under the new migration policy. Our analysis also shows an important change in the sectoral focus of the new arrival inflow. Not only have fewer immigrants been entering declining sectors, but the majority of migrants arriving under the new policy regime have been absorbed into growing and knowledge-based sectors, meaning they are employed primarily in service and knowledge-intensive sectors. Overall, the analysis provides ample evidence that the current admission policy as ositively contributed to tructural change in Switzerland. [source] To sample or eradicate?JOURNAL OF APPLIED ECOLOGY, Issue 4 2008A cost minimization model for monitoring, managing an invasive species Summary 1Considerable effort is expended by national and local governments to exclude alien species via detection and eradication of invading populations, but these efforts are not necessarily designed in the most economically or biologically efficient manner. 2Using the invasion of the European strain of the gypsy moth Lymantria dispar into the USA as a case study, we develop an analytical model to determine the optimal trap density for detecting isolated infestations. Most models focus on monitoring or eradication costs only; our model considers the costs of both detection and eradication when determining the best monitoring strategy. 3The model assumes that all isolated populations must be located and eradicated by the conclusion of a programme. For programmes lasting longer than 1 year, it is more worthwhile to proactively monitor and manage rather than to wait until the programme is over. 4For a management programme of a given length, optimal trap density is most influenced by the growth rate of the infestation. Optimal trap densities are lowest for infestations with very low growth rates (because they remain small and therefore are less expensive to eradicate) or very high growth rates (because they are easier to detect), and highest for infestations with moderate growth rates (because they are neither inexpensive to eradicate nor easy to detect). 5Our model is useful in setting a baseline level of monitoring for isolated incidents of gypsy moth invasion. Analysis of data in two US states show that actual trap densities are far higher than the optimal densities from the model. The difference suggests risk aversion may play a role in real systems. 6Synthesis and applications. Our model suggests that we can improve the efficiency of detection and eradication programmes for isolated infestations by optimizing detection effort relative to infestation growth rates and management programme duration. It also clearly demonstrates the importance of balancing the costs and benefits of both detection and eradication when developing invasive species monitoring programmes. [source] UNCOUPLING OF SILICON COMPARED WITH CARBON AND NITROGEN METABOLISMS AND THE ROLE OF THE CELL CYCLE IN CONTINUOUS CULTURES OF THALASSIOSIRA PSEUDONANA (BACILLARIOPHYCEAE) UNDER LIGHT, NITROGEN, AND PHOSPHORUS CONTROL1JOURNAL OF PHYCOLOGY, Issue 5 2002Pascal Claquin The elemental composition and the cell cycle stages of the marine diatom Thalassiosira pseudonana Hasle and Heimdal were studied in continuous cultures over a range of different light- (E), nitrogen- (N), and phosphorus- (P) limited growth rates. In all growth conditions investigated, the decrease in the growth rate was linked with a higher relative contribution of the G2+M phase. The other phases of the cell cycle, G1 and S, showed different patterns, depending on the type of limitation. All experiments showed a highly significant increase in the amount of biogenic silica per cell and per cell surface with decreasing growth rates. At low growth rates, the G2+M elongation allowed an increase of the silicification of the cells. This pattern could be explained by the major uptake of silicon during the G2+M phase and by the independence of this process on the requirements of the other elements. This was illustrated by the elemental ratios Si/C and Si/N that increased from 2- to 6-fold, depending of the type of limitation, whereas the C/N ratio decreased by 10% (E limitation) or increased by 50% (P limitation). The variations of the ratios clearly demonstrate the uncoupling of the Si metabolism compared with the C and N metabolisms. This uncoupling enabled us to explain that in any of the growth condition investigated, the silicification of the cells increased at low growth rates, whereas carbon and nitrogen cellular content are differently regulated, depending of the growth conditions. [source] Growth rate constrain morphological divergence when driven by competitionOIKOS, Issue 1 2006Jens Olsson Resource competition has been hypothesized to be important in driving divergence by natural selection. The effect of competition on morphological divergence and plasticity has however rarely been investigated. Since low growth rates might constrain morphological modulation and individual growth rates usually are negatively related to the intensity of competition, there might be a connection between competition, growth rate and morphological divergence. We performed an aquarium experiment with young-of-the-year Eurasian perch (Perca fluviatilis L.) to investigate how individual growth rate affected morphological plasticity induced by contrasting habitat treatments. Furthermore, in a field study of 10 lakes we also related the degree of morphological differentiation between habitats to the intraspecific competitior biomass. In the aquarium experiment we found that morphological plasticity was growth rate dependent in that morphological differentiation between the habitat treatments was confined to high individual growth rates. In the field study we found that morphological differentiation between habitats decreased with increasing intraspecific competitior biomass. Since plasticity is hypothesized to be important in divergence and intraspecific biomass could serve as a proxy for the level of competition, we suggest that our results indicate that morphological divergence might be constrained during periods of intense intraspecific competition due to low growth rates. A possible scenario is that at low growth rates all energy available is used for metabolic maintenance and no surplus energy is therefore available for morphological modulation. [source] Supplementation of tryptophan and lysine in Diplodus sargus larval diet: effects on growth and skeletal deformitiesAQUACULTURE RESEARCH, Issue 10 2009Margarida Saavedra Abstract Amino acids are the building blocks for growth and the major energy source during fish larval stages. Deficient amino acids can be supplemented in the diets, overcoming problems such as low growth rates and skeletal deformities. In this study, three experimental diets were tested: a balance diet supplemented with lysine, a balance diet supplemented with tryptophan and a control with no supplementation. Trials were conducted with Diplodus sargus larvae from 1 to 25 days after hatching (DAH). A microencapsulated diet was introduced at 15 DAH in co-feeding with live feed and from 20 DAH larvae were fed only this diet. The effect of the supplemented diets was assessed in terms of survival, growth rate, skeletal deformities, ammonia excretion and activity of amino acid catabolism enzymes. The results showed a similar survival in all treatments. However, larvae given tryptophan supplementation had a lower weight on 25 DAH. No significant differences were found in ammonia excretion, frequency or type of deformities or enzymatic activity. Tryptophan and lysine supplementation failed to improve larval growth, survival or larval quality. [source] Seedling establishment, mortality, tree growth rates and vigour of Acacia nilotica in different Astrebla grassland habitats: Implications for invasionAUSTRAL ECOLOGY, Issue 3 2002Ian J. Radford Abstract A demographic study was conducted in the northern Australian Astrebla grasslands to determine the importance of habitat type in influencing invasion patterns of Acacia nilotica, an exotic leguminous tree from Africa and Asia. One of the repeated patterns observed for A. nilotica is that denser populations are often associated with riparian habitats. Data available on this species do not enable us to determine which of a number of processes has lead to the formation of this pattern. Several explanations were tested for patterns in tree abundance: (i) that more seedlings emerge in wetter habitats; (ii) that mortality is lower in wetter habitats; (iii) that growth rates are faster in wetter habitats; and (iv) that plants are more vigorous (as indicated by leaf cover, flowering intensity and predation rates) over longer periods in wetter habitats. The study was stratified across three habitat types, perennial and ephemeral riparian and non-riparian, which are characteristic of Astrebla grasslands and differentiated by the availability of water. In addition to testing for habitat-linked differentiation in demography, data were also used to test whether seedling emergence, mortality, growth and vigour varied between sites with cattle versus sheep. The data collected indicated that seedling emergence, determined primarily by livestock dispersal, was likely to be the dominant influence on patterns of A. nilotica invasion. Mortality and growth rates were similar in ephemeral riparian and non-riparian habitats, whereas perennial riparian habitats had more rapid growth rates, which may increase the rate of invasion in these areas. Plant vigour was also greater over longer periods in perennial riparian habitats with greater leaf cover, longer flowering season and fewer insect borer holes. Livestock species were found to have little influence on the demography of A. nilotica plants in this study. Very low growth rates and high mortality in A. nilotica populations are likely to lead to net decline in ephemeral riparian and non-riparian habitats in the long term. The importance of episodic recruitment in the maintenance of A. nilotica populations is discussed. [source] | |||||||||||||