分蜂所产生的后果

１有关分蜂的解释目前有几个不同的假设。这些假设是由Ｈｏｇｇ（１９９７）和Ｇｕｅ（１９９８）总结的。幼虫食物假说这一假说认为蜂群中幼蜂过剩会产生过剩的幼虫食料 ,因而导致蜂群产生王台。幼虫拥挤假说认为过多的幼虫给蜂王造成可用于产卵的空间太小 ,因此 ,导致蜂群产生王台 ;同时又认为过于拥挤的蜂群造成蜂群通风不良 ,箱内ＣＯ２ 含量上升。内勤蜂的劳动假说认为蜂群中内勤蜂的数量远远超过外勤蜂的数量。蜂王外激素分布假说这一假说认为 ,随着工蜂数量的迅速增加 ,蜂王物质在箱内的分布呈下降趋势。群内食料过于充分假说当蜜蜂…     

Evidence that Minor Sprout Damage Can Lead to Significant Reductions in Gluten Strength of Winter Wheats

Seventeen winter wheat lines were grown in triplicate plots at Warsaw, Painter, and Blacksburg, VA, during the 1999–2000 growing season. Hagberg falling numbers, protein content, farinograms, sedimentation volumes, and total glutenin content were determined for flours derived from 153 harvested wheat samples. Over three inches (8.2 cm) of rain fell during the week before harvest in Blacksburg, resulting in falling numbers of 100 for Recital and 137 for Heyne, two severely sprouted Blacksburg wheat samples, and falling numbers <250 in three other Blacksburg wheats. There were no significant differences across locations in falling numbers of four wheat lines, and one line had significantly greater falling numbers in Blacksburg than in Warsaw or Painter. All 18 Blacksburg flours had a significantly higher mixing tolerance index (MTI) and shorter departure times (DT) than corresponding Warsaw flours. Weaker gluten strength of Blacksburg flours suggestss that all 18 Blacksburg wheats were sprout‐damaged and contained active proteases. However, according to falling number data, five of these Blacksburg wheats were sprout‐free with falling numbers >400. These data indicate that Hagberg falling number should not be used as the sole criteria for determining the degree of sprout damage in wheat because it does not quantify, nor always accurately reflect changes in protein composition and quality due to grain weathering.     

Impact of Agronomic and Storage Practices on Acrylamide in Processed Potatoes

Acrylamide is a probable carcinogen found in processed potato products. The compound is formed at elevated temperatures by the Maillard reaction from two primary precursors - reducing sugars (fructose and glucose) and asparagine. Significant advances have been made in reducing acrylamide formation by selecting varieties with low precursor concentrations through conventional breeding or genetic modification techniques. However, acrylamide in many of the traditional varieties processed for fries or chips is sometimes found at elevated levels. Both agronomic and storage practices can significantly influence glucose, fructose, and asparagine concentrations and therefore the potential to form acrylamide during processing. This summary of a symposium presentation given at the 99th Annual Potato Association of American Meeting is to provide a general overview of previous studies that have examined the effects of agronomic factors such as nutrient and water management and storage factors such as temperature and duration on acrylamide precursors and/or acrylamide in processed potato products. A better understanding of how these factors affect acrylamide precursors is a first step in minimizing acrylamide formation during processing and improving the quality of processed potato products.     

Distribution,abundance and growth of juvenile salmonids off the coast of Oregon and Washington,summer (1980)

Juvenile salmonids (< 50 cm) were sampled by purse seine off the Pacific coast from Tillamook Bay, Oregon, to Copalis Head, Washington, during the period May through September (1980). Temporal distribution and abundance of the major Columbia River species were determined. Spring chinook salmon (Oncorhynchus tshatuytscha) and steel head (Salmo gairdneri) were present only during early cruises and were distributed almost entirely in the Columbia River plume and the sample area to the north. Coho salmon (O. kisutch) and fall chinook salmon were distributed more uniformly throughout the sampling area and were relatively abundant throughout the sampling period. Concentrations of fish were found only within 28 km of the shore. A number of fish that had been marked before or during their outmigration from the Columbia River system were recaptured. It appeared possible that with concentrated sampling in areas with high fish abundances, sufficient numbers of marked juvenile salmonids could be captured to provide relative survival estimates between different stocks of Columbia River fish.     

The value of recreational fishing in Sweden – Estimates based on a nationwide survey

A nationwide recreational fishing survey in Sweden was used to estimate the benefits of recreational fishing in Sweden. The survey targeted the Swedish population and, consequently, the sample contained a large fraction of zero fishing days. To consider this, a zero-inflated Poisson model was used in the estimations. Swedes fished about 15.6 million days in 2013, of which two-thirds were spent on inland fishing, and one-third on marine and coastal fishing. Expected consumer surplus per fishing day varied with the season; SEK 193 for winter fishing, SEK 787 for summer fishing and SEK 95 for autumn fishing. Although about 70 per cent of total fishing days were spent on inland fishing, the weighted consumer surplus per fishing day in marine and coastal areas were higher. The results also demonstrated strong positive effects of increases in expected catch per day on number of fishing days demanded and consumer surplus, which have important implications for fishery policies directed at recreational fishing.     

Re‐introduction of structurally complex wood jams promotes channel and habitat recovery from overwidening: Implications for river conservation

相似文献   

Ontogeny of the stress response in chinook salmon, Oncorhynchus tshawytscha *

Whole body concentrations of cortisol were determined via radioimmunoassay in chinook salmon, Onchorynchus tshawytscha, during early development in both stressed and non-stressed fish to determine when the corticosteroidogenic stress response first appeared. Progeny from both pooled and individual females were examined to determine if differences existed in offspring from different females. Levels of cortisol were low in eyed eggs, increased at hatch, decreased 2 weeks later and then remained constant thereafter. Differences in cortisol between stressed and control fish were found 1 week after hatch and persisted for the remainder of the study. The magnitude of the stress response, or relative amount of cortisol produced, generally increased from the time when it was first detected, but a decrease in the ability to elicit cortisol was seen 4 weeks after hatching. Cortisol content of separate progeny from two individual females showed a similar pattern to that seen in pooled eggs. Our results indicate that chinook salmon are capable of producing cortisol following a stressful event approximately 1 week after the time of hatching. The decrease in endogenous cortisol content seen 2 weeks after hatching, and the decrease in the magnitude of the stress response seen 4 weeks after hatching may be comparable to developmental events documented in mammals where corticosteroid synthesis is inhibited to neutralize possible detrimental effects of these hormones during critical periods of development. This revised version was published online in August 2006 with corrections to the Cover Date.     

A delay-differential model for representing small pelagic fish stock dynamics and its application for assessing alternative management strategies under environmental uncertainty

We present a novel adaptation of the classic discrete delay-difference model, a continuous delay-differential model (cDDM), which can adequately represent population dynamics of stocks that turn over rapidly and continuously over time (e.g., small pelagic fish, small tunas, and shrimps). We used the Northern-Central Peruvian anchoveta stock (Engraulis ringens, Engraulidae) as a case study for implementing the cDDM and conducted a management strategy evaluation (MSE) through stochastic optimization in policy space (SOPS). Our results showed that cDDM integrated with SOPS efficiently searches optimum and near-optimum harvest control rules (HCR) and is an alternative to pre-setting arbitrary HCRs as in traditional MSE. The cDDM showed comparable stock biomass and recruitment estimate reconstructions to more complex stock assessment models described for anchoveta. We concluded that the anchoveta stock is sustainably managed and is an example of adaptive fisheries management under high ocean-climate variability and uncertainty. Contrary to fishery textbooks, the anchoveta's collapse was not entirely due to the 1972 El Niño (EN) but a recruitment failure preceding EN. Our reconstructions revealed that low recruitment (or recruitment failure) could still occur at high stock biomass. Anchoveta's stock biomass is larger than pre-collapse, likely due to favourable environmental conditions (a cooling trend) and management, despite more frequent and stronger EN events. SOPS quickly revealed that harvest strategies with large base biomass (>5 mmt) lead to higher interannual stock variability and would not produce substantial increases in long-term yield. Alternative HCRs with lower base biomass, while adjusting for productivity regimes, have similar long-term yields without affecting the long-term average stock.     

ATP-driven exchange of histone H2AZ variant catalyzed by SWR1 chromatin remodeling complex

The conserved histone variant H2AZ has an important role in the regulation of gene expression and the establishment of a buffer to the spread of silent heterochromatin. How histone variants such as H2AZ are incorporated into nucleosomes has been obscure. We have found that Swr1, a Swi2/Snf2-related adenosine triphosphatase, is the catalytic core of a multisubunit, histone-variant exchanger that efficiently replaces conventional histone H2A with histone H2AZ in nucleosome arrays. Swr1 is required for the deposition of histone H2AZ at specific chromosome locations in vivo, and Swr1 and H2AZ commonly regulate a subset of yeast genes. These findings define a previously unknown role for the adenosine triphosphate-dependent chromatin remodeling machinery.