Landscape heterogeneity and fire behavior: scale-dependent feedback between fire and grazing processes

Fire and grazing are ecological processes that frequently interact to modify landscape patterns of vegetation. There is empirical and theoretical evidence that response of herbivores to heterogeneity is scale-dependent however the relationship between fire and scale of heterogeneity is not well defined. We examined the relationship between fire behavior and spatial scale (i.e., patch grain) of fuel heterogeneity. We created four heterogeneous landscapes modeled after those created by a fire–grazing interaction that differed in grain size of fuel patches. Fire spread was simulated through each model landscape from 80 independent, randomly located ignition points. Burn area, burn shape complexity and the proportion of area burnt by different fire types (headfire, backfire and flankfire) were all affected by the grain of fuel patch. The area fires burned in heterogeneous landscapes interacted with the fuel load present in the patch where ignition occurred. Burn complexity was greater in landscapes with small patch grain than in landscapes with large patch grain. The proportion of each fire type (backfire, flankfire and headfire) was similar among all landscapes regardless of patch grain but the variance of burned area within each of the three fire types differed among treatments of patch grain. Our landscape fire simulation supports the supposition that feedbacks between landscape patterns and ecological processes are scale-dependent, in this case spatial scale of fuel loading altering fire spread through the landscape.     

Principal economic effects of cormorant predation on catfish farms

Substantial economic losses of farmed catfish to fish‐eating birds such as the double‐crested cormorant, Phalacrocorax auritus, continue to be reported on U.S. catfish farms. An economic analysis was conducted of the on‐farm effects of both the increased expenditures to scare fish‐eating birds from catfish farms and of the value of the catfish that were consumed by cormorants. A survey was conducted of U.S. catfish farmers in the Delta region of Mississippi and Arkansas, to obtain farm‐level data on expenditures to scare birds. Estimations of the lost revenue from catfish consumed by cormorants were developed from a concurrent study on cormorant distribution, abundance, and diet in the region. The economic effects of bird predation in terms of both fish consumption and management costs were evaluated across three farm sizes and nine catfish production practices. Catfish farmers spent on average $704/ha ± $394/ha to scare birds, making bird‐scaring costs one of the top five costs of raising catfish. The greatest cost components of scaring birds were manpower (39% of all bird‐scaring costs) and the variable and fixed costs of trucks used to scare birds (34% of all bird‐scaring costs). Losses were greater on hybrid than channel catfish fingerling ponds. Industry‐wide, the value of catfish losses averaged $47.2 million (range of $25.8–$65.4 million). Total direct economic effects (including both the increased costs to scare birds and the revenue lost from fish consumed by cormorants despite bird‐scaring attempts) averaged $64.7 million (ranging from $33.5 to $92.6 million). Profitability improved by 4% to 23% across the farm size/production strategies analyzed upon removal of the economic effects from bird predation, with greater effects occurring on smaller‐scale farms. One‐third of the farm size and production scenarios analyzed changed from being unprofitable to showing a profit in the absence of such negative economic effects associated with bird depredation. Overall, the combined effects of increased farm expenditures to scare birds from farms and the value of the catfish lost to predation by cormorants caused substantial negative economic effects on catfish farms.     

Evidence for acclimation of N cycling to episodic N inputs in anthropogenically-affected intertidal salt marsh sediments

Nitrate removal was compared in anthropogenically-impacted and unimpacted salt marsh sediments in microcosms using the acetylene block technique and ¹⁵N natural abundance measurements. Potential denitrification rates were greater at the impacted site than the unimpacted site at all added NO₃⁻ concentrations (233, 467, or 700 μg N g dw⁻¹). Although the change in concentration of NH₄⁺ over time was small (69-104 μg N g dw⁻¹), the δ¹⁵N of accumulated NH₄⁺ increased significantly (0.26-13.22‰), and was more enriched for all NO₃⁻ treatments in the impacted sediments than the unimpacted site. The impacted site may be acclimated to episodic N inputs, and based on concentrations and ¹⁵N natural abundance had greater denitrification and N cycling than the unimpacted site.     

Costs and Risk of Catfish Split‐pond Systems

Split ponds are recently developed pond‐based aquaculture systems that allow intensification of catfish aquaculture. Successful industry‐wide adoption of newly developing technologies like split‐pond systems will depend upon their productivity and cost efficiencies. Costs and production performance of the following three split‐pond design scenarios were monitored in Arkansas and Mississippi: (1) research design developed at the Thad Cochran National Warmwater Aquaculture Center, Stoneville, Mississippi; (2) waterwheel design tested on commercial catfish ponds; and (3) screw‐pump design tested on commercial catfish ponds. An economic engineering approach using standard enterprise budget analysis was used to develop estimates of breakeven prices (BEPs) ($/kg) for producing foodsize hybrid catfish (♂Ictalurus furcatus × ♀Ictalurus punctatus) for each scenario. Estimates of BEPs of hybrid catfish raised in split ponds ranged from $1.72 to $2.05/kg. The cost of catfish production in split ponds was sensitive to yield, fish prices, and feed prices. Annual net cash flows from both commercial split‐pond systems were high and sufficient to make the investment profitable in the long run. Feed price, feed conversion ratio, and yield contributed the most to downside risk of split ponds.     

Production Characteristics, Water Quality, and Costs of Producing Channel Catfish Ictalurus punctatus at Different Stocking Densities in Single-batch Production

Channel catfish Ictalurus punctatus farming is the largest component of aquaculture in the USA. Culture technologies have evolved over time, and little recent work has been conducted on the effects of stocking density on production characteristics and water quality. Twelve 0.1‐ha ponds were stocked with 13‐ to 15‐cm fingerlings (16 g) at either 8600, 17,300, 26,000, or 34,600 fish/ha in single‐batch culture with three replicates per treatment. Fish were fed daily to apparent satiation with a 32% floating commercial catfish feed. Nitrite‐N, nitrate‐N, total ammonia nitrogen (TAN), total nitrogen, total phosphorus, chemical oxygen demand (COD), Secchi disk visibility, chlorophyll a, chloride, total alkalinity, total hardness, pH, temperature, and dissolved oxygen (DO) were monitored. Ponds were harvested after a 201‐d culture period (March 26, 2003 to October 13, 2003). Net yield increased significantly (P < 0.05) as stocking density increased, reaching an average of 9026 kg/ha at the highest density. Growth and marketable yield (>0.57 kg) decreased with increasing stocking density. Survival was not significantly different among densities. Mean and maximum daily feeding rates increased with density, but feed conversion ratios did not differ significantly among treatments (overall average of 1.42), despite the fact that at the higher stocking densities, the feeding rates sometimes exceeded 112 kg/ha per d (100 lb/ac per d). Morning DO concentrations fell below 3 mg/L only once in a 34,600 fish/ha pond. Concentrations of chlorophyll a, COD, nitrite‐N, and TAN increased nominally with increasing feed quantities but did not reach levels considered problematic even at the highest stocking densities. Breakeven prices were lowest for the highest stocking density even after accounting for the additional time and growth required for submarketable fish to reach market size. While total costs were higher for the higher density treatments, the relatively higher yields more than compensated for higher costs.     

Risk maps for targeting exotic plant pest detection programs in the United States

In the United States, pest risk maps are used by the Cooperative Agricultural Pest Survey for spatial and temporal targeting of exotic plant pest detection programs. Methods are described to create standardized host distribution, climate and pathway risk maps for the top nationally ranked exotic pest targets. Two examples are provided to illustrate the risk mapping process: late wilt of corn (Harpophora maydis) and the giant African land snail (Achatina fulica). Host risk maps were made from county‐level crop census and USDA Forest Inventory and Analysis data, respectively. Climate risk maps were made using the North Carolina State University–USDA APHIS Plant Pest Forecasting System (NAPPFAST), which uses a web‐based graphical user interface to link climatic and geographic databases with interactive templates for biological modelling. Pathway risk maps were made using freight flow allocation data sets to move commodities from 7 world regions to 3162 US urban areas. A new aggregation technique based on the Pareto dominance principle was used to integrate maps of host abundance, climate and pathway risks into a single decision support product. The maps are publicly available online ( http://www.nappfast.org ). Key recommendations to improve the risk maps and their delivery systems are discussed.     

Neuromagnetic evidence of spatially distributed sources underlying epileptiform spikes in the human brain

Neuromagnetic measurements were performed on 17 subjects with focal seizure disorders. In all of the subjects, the interictal spike in the scalp electroencephalogram was associated with an orderly extracranial magnetic field pattern. In eight of these subjects, multiple current sources underlay the magnetic spike complex. The multiple sources within a given subject displayed a fixed chronological sequence of discharge, demonstrating a high degree of spatial and temporal organization within the interictal focus.     

Growth of Stocker Channel Catfish to Large Market Size in Single-Batch Culture

Catfish farmers increasingly are producing fish larger than the traditional size of 0.45-0.57 kg/fish in order to meet processing plant requirements for larger fish. Production of larger channel catfish Ictalurus punctatus in multiple-batch culture has been investigated in a few studies, but the impact of understocked fingerlings on growth of carry-over fish is unknown. The present study was conducted to quantify growth, feed conversion ratio, net daily yield, and net and total yield of stocker channel catfish grown in single-batch, one-season culture to mean individual weights of 0.60, 0.72, 0.91, or 1.17 kg/fish. Channel catfish (mean weight = 0.26 kg/fish) were stocked into 12 0.1-ha ponds at 11,115 fish/ha. Fish were fed a 32% crude protein floating extruded feed once daily to apparent satiation. When the average weight of the fish population reached the target weight, three randomly selected ponds were harvested. Fish growth was linear in all treatments. Growth rates were similar for fish grown to 0.60, 0.72, and 0.91 kg/fish, and significantly lower ( P < 0.05) than for fish grown to 1.17 kg. Variation in individual fish weight increased linearly with increased duration of culture period. Feed conversion ratio averaged 1.9 and did not differ significantly among treatments. The percentage of the fish population at harvest that fell within the 0.57 to 2.04 kg-size range preferred by processing plants increased from 56.6 to 98-5% as the mean weight at harvest increased from 0.60 to 1.17 kg/fish.     

微量营养素可提高防病作用

微量元素和维生素在动物组织和细胞中是以功能性化学复合物存在的 ,不同的组织具有特定的浓度。要维持组织功能和结构的完整性 ,保证动物生长、健康和生产性能不受损害 ,组织中的微量元素和维生素浓度必须维持在一定的水平。微量元素和维生素缺乏、过高或不平衡都会导致其在体组织和体液中的存在形式和浓度变化 ,一旦高于或低于临界值 ,会引起生化变化 ,生理功能和结构损害 ,损害程度与微量营养素缺乏和中毒的程度、持续时间及动物个体有关 ,最有效的方法是在日粮中提供适当的微量营养素。微量营养素不足、中毒和比例不平衡。可能会出现代谢…