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In low-intensity grazing systems, patch grazing leads to a mosaic structure of short (frequently defoliated) and tall (rarely defoliated) patches, with the stocking rate determining the proportion of these patch types on the pasture. Little is known about the long-term effects of patch grazing on the productivity of contrasting sward height patches developed under varying stocking rates. On a 12-year low-intensity cattle pasture we investigated aboveground net primary productivity (ANPP) and its seasonal variation in different patch types (‘short’, ‘medium’ and ‘tall’) under three stocking rates (‘moderate’, ‘lenient’ and ‘very lenient’) over two years. Additionally, we determined stocks of soil phosphorus, potassium and magnesium as well as soil pH. ANPP was affected by an interaction of patch type and stocking rate and ranged from less than 300 g/m2 in short patches under very lenient stocking to more than 1,000 g/m2 in medium patches under moderate stocking. In contrast with observations at the start of the experiment, ANPP in short patches was similar to or less than that in medium and tall patches. As topsoil phosphorus and potassium stocks were lowest in short patches, this indicates a long-term redistribution of nutrients by grazing animals, which limits short-patch productivity. Productivity of medium patches increased with stocking rate, and soil potassium concentration showed a similar trend, pointing towards enhanced nutrient cycling under more intensive stocking. We conclude that nutrient redistribution may lead to increasing trade-offs between ecological and agronomic aims in long-term low-intensity grazing systems. 相似文献
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Jozef H. Blom Konrad Dabrowski James Ebeling 《Journal of the World Aquaculture Society》2000,31(1):115-118
Abstract.— Despite a large economical value of the ornamental fish trade, little information is available on the dietary ascorbic acid requirements of these species. Ascorbic acid requirements of fishes of the cichlid family appear to vary widely. Juvenile angelfish, a widely produced ornamental cichlid, were maintained on diets containing graded levels of ascorbyl monophosphate. Liver ascorbic acid concentrations after 96 d of feeding were significantly reduced in groups receiving 120 mg or less ascorbic acid equivalents/kg diet. However, no differences in growth or mortality between groups were found, and no external signs of ascorbic acid deficiency were observed, indicating a high resistance of this species against prolonged ascorbic acid deficiency. Based on the long possible life span of angelfish in the aquarium, we proposed a conservative dietary ascorbic acid requirement of 360 mg/ kg diet, necessary to maintain maximum tissue storage of this vitamin. 相似文献
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R. E. Ciereszko Konrad Dabrowskl A. Ciereszko J. Ebeling J. S. Ottobre 《Journal of the World Aquaculture Society》1997,28(4):344-356
The involvement of photoperiod and temperature in the regulation of reproductive processes was investigated in female yellow perch. Initially, all fish kept indoors were exposed to the same water temperature (22°C) and photoperiod (15L:9D). By the end of August, following the first sampling, fish were submitted to different photothermal regimes. Group A3 was maintained under photothermal conditions characteristic for southern Ohio. Group B3 was submitted to a condensed light/temperature regime designed to accelerate photothermal changes. The mean gonadosomatic index in group A3 gradually increased throughout the experiment. Gonadosomatic index in group A3 was higher than that in group B3 from February through April. The highest plasma concentrations of estradiol in group A3 occurred in November and December and exceeded those in group B3. Plasma concentrations of testosterone in group A3 were highest in December and tended to be higher in October and April than in other months. There was no difference in plasma testosterone between groups A3 and B3 except in March when concentrations of this androgen were extremely high in group B3. Ovulation occurred earlier in B regime fish in comparison to that of A regime fish. However, egg quality of fish from regime B was lower than that of fish from regime A. We conclude that the condensed photothermal cycle is not an entirely effective method of inducing out-of-season spawning in female yellow perch. These data suggest that although the compression of the photothermal cycle slightly accelerated spawning, it also caused disturbances in patterns and levels of plasma steroids, diminished ovarian and hepatic growth, and reduced the quality of eggs. Thus, temperature and/or photoperiod may have only a modifying effect on the onset of perch spawning, but these environmental cues seem to markedly influence earlier stages of gonadal growth and development. 相似文献
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Bela H. Buck Michael W. Ebeling Tanja Michler-Cieluch 《Aquaculture Economics & Management (Blackwell Science)》2013,17(4):255-281
More than 50% of the annual worldwide harvest of mussels is produced in Europe. The mussel cultivation in Germany is based on an extensive on-bottom culture and depends entirely on natural resources for food, spat and space. Due to stakeholder conflicts and a lack of spat availability, mussel farmers tend to move offshore where space is not limited and adequate settlement guaranteed. Newcomers – the offshore wind farmers – are covering large areas in the German Bight which in contrast give the opportunity to use these areas in a multifunctional way by accepting mussel cultivation within the wind farms. This study compiles the basic data for offshore mussel cultivation in close vicinity to a designated offshore wind farm in the open sea of the German Bight and employs different case-scenario calculations to illustrate the impact of changing parameter values on overall profitability or non-profitability of this activity. Primary focus is placed on the production of consumer mussels but seed mussel cultivation is also taken into consideration. We show that production of consumer mussels with longline technology is sufficiently profitable even under the assumption of substantial cost increases. This is especially true, if existing capacities could be used. The cultivation of seed mussels depends on the possibility of using existing equipment. A substantial increase of seed mussel prices to at least 0.6 €, given the main cost categories remaining constant, turns this alternative into substantial profitability. This study concludes with providing some recommendations on how favorable terms or actions could further improve profitability of offshore mussel cultivation. Altogether, our results are intended to shed some light on business management topics that future offshore mariculture operators such as traditional mussel farmers should follow in order to be efficient. 相似文献
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Roy J. Pence Manuel S. Viray Waiter Ebeling Donald A. Reierson 《Pesticide biochemistry and physiology》1975,5(1):90-100
Blood from cockroaches stressed by having their mouthparts sealed or by being dehydrated by contact with silica aerogel, administered into the opened wounds of freshly excised honey bee abdomens, produced neuromuscular reaction that was monitored and recorded as characteristic myograms. When blood became too viscous or unobtainable during the terminal stages of stress, coxal muscle was substituted. Abdomens used for assay were also used for toxicological studies, comparing their survival time with untreated abdomens. Intact and decapitated cockroaches were equally desiccated by contact with silica aerogel to determine if presence or absence of the coordinating center had any bearing on stress. Fragments of coxal muscle from the intact cockroaches deactivated 10 bee abdomens in 15 hr while coxal muscle from the decapitated cockroaches deactivated only one out of 10 abdomens. Blood from cockroaches poisoned by oral administrations of boric acid solution was readily available, clear, and free-flowing, and produced myograms showing periods of lethargy followed by deep convulsions. Portions of these myograms resembled symptoms of lethargy and convulsions produced by boric acid solution when it was administered directly into the bee abdomens. 相似文献
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W. Ebeling D.A. Reierson R.J. Pence M.S. Viray 《Pesticide biochemistry and physiology》1975,5(1):81-89
American cockroaches, Periplaneta americana (L.), and German cockroaches, Blattella germanica (L.), ingested large quantities of powder (silica aerogel and boric acid) in the process of preening their appendages. Their crops were greatly distended by the powder, but the denticles of the armarium of the proventriculus permitted the movement of only very small quantities of silica aerogel into the remainder of the alimentary tract. Boric acid likewise passed the armarium in very small quantities and apparently only in solution.There was no significant difference in the rate of mortality of both species of cockroaches confined with deposits of silica aerogel SG-68, whether their mouthparts were sealed with paraffin wax or left unsealed. Ingested powder did not increase the rate of water loss. Cockroaches with unsealed mouthparts died more rapidly on deposits of boric acid than those with sealed mouthparts, as might be expected of a toxic compound. However, cockroaches with sealed mouthparts were strikingly affected by boric acid, indicating cuticular penetration by that compound. Penetration within the integument, in the gross body contents, in the alimentary tract, and in the feces was confirmed by a boric acid flame test. 相似文献
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