An investigation of avoidance by Antarctic krill of RRS James Clark Ross using the Autosub-2 autonomous underwater vehicle     

Andrew S. Brierley  Paul G. Fernandes  Mark A. Brandon  Frederick Armstrong  Nicholas W. Millard  Steven D. McPhail  Peter Stevenson  Miles Pebody  James Perrett  Mark Squires  Douglas G. Bone  Gwyn Griffiths 《Fisheries Research》2003,60(2-3):569-576

The autonomous underwater vehicle (AUV) Autosub-2 was deployed on eight missions ahead of RRS James Clark Ross in the northern Weddell Sea and in the Bransfield Strait, Southern Ocean, to assess avoidance of the research vessel by Antarctic krill Euphausia superba. The AUV was equipped with the same type of scientific echosounder as the research vessel (Simrad EK500 operating at 38 and 120 kHz) and measured the density of krill along transect acoustically (g m⁻² wet mass) prior to the ship’s arrival. We hypothesised that if krill avoided the ship, perhaps in response to radiated noise, then the ship should detect less krill than the AUV which is known to have much lower noise levels than the ship. We were unable to detect any significant difference between the density of krill detected by the ship or the AUV, either at the transect level or at finer scales within transects. We conclude, therefore, that avoidance by krill of RRS James Clark Ross will not significantly bias acoustic estimates of krill abundance by this vessel.  相似文献   

Fate of lower Mississippi river habitats associated with river training dikes     

F. Douglas Shields 《水产资源保护:海洋与淡水生态系统》1995,5(2):97-108

• 1 Regions of reduced velocity adjacent to spur dikes along the Lower Mississippi River are valuable aquatic habitats. Similar zones along other large rivers have been converted to terrestrial habitats by sediment deposition.
• 2 Repetitive hydrographic surveys of 26 representative groups of dikes are examined to determine the direction and rates of change.
• 3 Since the dikes were constructed, the aquatic volume and area of associated low-velocity habitats have been reduced by 38% and 17%, respectively. Examination of time series shows that most changes occur shortly after construction, and after initial adjustment, habitat area and volume fluctuate about a condition of dynamic equilibrium.
• 4 Sedimentation rates were most rapid for dike fields constructed on the inside of bends to prevent chute development. Dike fields built to force or maintain thalweg crossings exhibited erosion rather than deposition.

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Incorporation and metabolism of (n-3) and (n-6) polyunsaturated fatty acids in phospholipid classes in cultured rainbow trout (Salmo gairdneri) cells     

Douglas R. Tocher 《Fish physiology and biochemistry》1990,8(3):239-249

The incorporation and metabolism of various (n-3) and (n-6) polyunsaturated fatty acids supplemented to the culture medium was investigated in the rainbow trout cell line, RTG-2. The distribution, and the occurrence and relative extent of further desaturation and elongation of the incorporated acids was determined in individual phospholipid classes by analysis of the fatty acid compositions. RTG-2 cells exhibited Δ6 and Δ5 desaturase activities whereas Δ4 desaturase activity was almost totally absent. The percentage of precursor acids was greatest in the phosphatidic acid/cardiolipin fraction (PA/CL), suggesting a role for possibly PA in the initial incorporation of these acids into the phospholipid pool. The compositional data indicated that individual intermediates and products of the desaturation pathways were associated with specific phospholipid classes probably via mechanisms depending upon the specificities of the acylating enzymes. The composition of phosphatidylinositol (PI) and the tightly controlled mechanisms for generating/maintaining it are consistent with a role for this phospholipid in providing precursor fatty acid for eicosanoid synthesis.  相似文献   

Production of second generation penaeid shrimp,Penaeus stylirostris,from Mexico     

Ausbon Brown  Douglas Tave  T.D. Williams  M.J. Duronslet 《Aquaculture (Amsterdam, Netherlands)》1984,41(1):81-84

The life cycle of the penaeid shrimp, Penaeus stylirostris, was completed in captivity with the production of F₂ generation nauplii. Over one million F₂ generation nauplii were harvested from the F₁ generation represented by laboratory-reared adult shrimp. The studies were completed in a laboratory simulated, tropical environment for maturation and spawning, and in pond systems located in a temperate environment for growout of the F₁ generation.  相似文献   

Identification of windbreaks in Kansas using object-based image analysis,GIS techniques and field survey     

Kabita Ghimire  Mike W. Dulin  Robert L. Atchison  Douglas G. Goodin  J. M. Shawn Hutchinson 《Agroforestry Systems》2014,88(5):865-875

Windbreaks are valuable resources in conserving soils and providing crop protection in Great Plains states in the US. Currently, Kansas has no up-to date inventory of windbreaks. The goal of this project was to assist foresters with future windbreak renovation planning and reporting, by outlining a series of semi-automated digital image processing methods that rapidly identify windbreak locations. There were two specific objectives of this research. First, to develop semi-automated methods to identify the location of windbreaks in Kansas, this can be applied to other regions in Kansas and the Great Plains. We used a remote sensing technique known as object-based image analysis (OBIA) to classify windbreaks visible in the color aerial imagery of National Agriculture Imagery Program. We also combined GIS techniques and field survey to complement OBIA in generating windbreak inventory. The techniques successfully located more than 4500, windbreaks covering an approximate area of 2500, hectares in 14 Kansas counties. The second purpose of this research is to determine how well the results of the automated classification schemes match with other available windbreak data and the selected sample collected in the field. The overall accuracy of OBIA method was 58.97 %. OBIA combined with ‘heads up’ digitizing and field survey method yielded better result in identifying and locating windbreaks in the studied counties with overall accuracy of 96 %.  相似文献   

Connectivity,habitat, and flow regime influence fish assemblage structure: Implications for environmental water management in a perennial river of the wet–dry tropics of northern Australia     

Bradley J. Pusey  Michael Douglas  Julian D. Olden  Sue Jackson  Quentin Allsop  Mark J. Kennard 《水产资源保护:海洋与淡水生态系统》2020,30(7):1397-1411

1. Environmental water management seeks to balance competing demands between the water needed to sustain human populations and their economic activities and that required to sustain functioning freshwater ecosystems and the species they support. It must be predicated on an understanding of the environmental, hydrological, and biological factors that determine the distribution and abundance of aquatic species.
2. The Daly River of the wet–dry tropics of northern Australia consists of a perennially flowing main stem and large tributaries, as well as many small to large naturally intermittent tributaries, and associated off‐channel wetlands. Increased groundwater abstraction to support irrigated agriculture during the dry season threatens to reduce dry‐season flows that maintain perenniality and persistence of freshwater fishes.
3. Fish assemblages were surveyed at 55 locations during the dry season over a 2‐year period with the goal of establishing the key landscape‐scale and local‐scale (i.e. habitat) drivers of fish species distribution.
4. Longitudinal (upstream/downstream) and lateral (river/floodplain) gradients in assemblage structure were observed with the latter dependent on the position in the river landscape. Underlying these gradients, stream flow intermittency influenced assemblage composition, species richness, and body size distributions. Natural constraints to dispersal were identified and their influence on assemblage structure was also dependent on position within the catchment.
5. Eight distinct assemblage types were identified, defined by differences in the abundance of species within five groups differing in functional traits describing body size, spawning requirements, and dispersal capacity. These functional groups largely comprised species widely distributed in northern Australia.
6. The results of the study are discussed with reference to the environmental flow needs of the Daly River and other rivers of northern Australia. The findings may also be applied to environmental flow management in savannah rivers elsewhere.

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Ecological consequences of invasive lake trout on river otters in Yellowstone National Park     

William R. Wengeler  Douglas A. Kelt  Michael L. Johnson 《Biological conservation》2010,143(5):1144-1153

The introduction of lake trout (Salvelinus namaycush) to Yellowstone Lake in Yellowstone National Park has contributed to a significant decline in the endangered Yellowstone cutthroat trout (Oncorhynchus clarki bouvieri), leading to concern over the persistence of this subspecies but also to piscivorous predators in this community. We assessed the impact of lake trout on a key piscivore, the river otter (Lontra canadensis) in two lakes in Yellowstone National Park. Yellowstone Lake continues to support a native cutthroat trout population, although the recent introduction of lake trout has dramatically impacted the cutthroat trout population. Nearby Lewis Lake has an entirely introduced fish fauna of lake trout, brown trout (Salmo trutta), and Utah chub (Gilia atraria) but lacks cutthroat trout. Analysis of otter scat from Yellowstone Lake implicated trout (lake or cutthroat trout) as a major prey item (57% of scat), whereas stable isotopes identified longnose suckers (Catostomus catostomus) as the primary prey there (58% of diet). By contrast, scat from Lewis Lake implicated minnows, presumably Utah chub, as the primary prey for otters occupying that lake (86%), while stable isotopes implicated brown trout (64%) over both lake trout and Utah chub (36% combined). Our data establish the importance of alternative prey to otters and suggest that lake trout-induced reductions in cutthroat trout may not be catastrophic for otter populations here. These data do not necessarily exonerate lake trout, as their impact on other species, most notably grizzly bears (Ursus arctos) and piscivorous birds, has been documented to be substantial, and further data on the nutritional value of alternate prey are required to confirm or refute a working hypothesis that otter populations will continue to thrive in the face of the lake trout invasion.  相似文献   

Use of surface plasmon resonance (SPR) to study the dissociation and polysaccharide binding of casein micelles and caseins     

Thompson AK  Singh H  Dalgleish DG 《Journal of agricultural and food chemistry》2010,58(22):11962-11968

Tests were made to determine whether surface plasmon resonance (SPR) could be used as a technique to study the dissociation properties of bovine casein micelles or of sodium caseinate and the interactions between these protein particles and different polysaccharides. Surfaces of bound micelles or caseinate were made, and the changes in refractive index of these layers were used to define changes in the structures of the chemisorbed material. The technique appears to have some potential for studying details of the dissociation of casein micelles and of the binding of different polysaccharides to caseins.  相似文献   

Death from anthropogenic causes is partially compensatory in recovering wolf populations     

Dennis L. Murray  Douglas W. Smith  Curtis Mack  Joe Fontaine  Michael Jiminez  Thomas J. Meier  James Holyan 《Biological conservation》2010,143(11):2514-2524

There is substantial interest in how mortality rates affect animal populations, but mechanisms explaining when and under what circumstances particular causes of death incur demographic responses are far from clear. In theory, small or expanding populations should experience additive mortality from anthropogenic causes of death, but whether such effects are homogenous across a population or expressed only in certain high-risk individuals is open for debate. We used competing risks models to analyze mortality patterns among radio-collared wolves (Canis lupus, n = 711) from three populations in northwestern United States (1982-2004), and evaluated the degree to which anthropogenic mortality was additive vs. compensatory to natural demographic processes. Almost 80% (n = 320) of wolves dying of known fates were killed by anthropogenic causes (legal control, illegal killing, harvest in Canada, vehicle collision), and additive effects of anthropogenic mortality were most pronounced in northwestern Montana where wolf exposure to humans and livestock was high compared to either the Greater Yellowstone Area or central Idaho, where anthropogenic risk was lower. In contrast, risk from natural hazards was lower in northwestern Montana than in the other areas, implying some degree of compensatory mortality from anthropogenic risk. Animals recruited to the study following human-wolf conflict had markedly higher anthropogenic risk than those recruited for standard monitoring purposes, and juvenile wolves as well as dispersers, succumbed to higher anthropogenic risk. Multivariate models revealed that increasing wolf population density promoted higher anthropogenic risk and reduced natural risk, indicating that partially-compensatory effects of anthropogenic mortality actually became increasingly additive with population density. The observed compensatory mortality and hazard heterogeneity in our study implies that demographic responses to mortality risk may be complex and more subtle than previously thought; the density-dependent effect of anthropogenic mortality portends a stabilizing influence of humans on recovering wolf populations. We conclude that future assessment of the role of anthropogenic mortality should include individual-based hazard estimation as a complement to traditional population-level approaches.  相似文献   

Modeling the spatial structure of topical forests     

Jo  o L. F. Batista  Douglas A. Maguire 《Forest Ecology and Management》1998,110(1-3):293-314

The spatial structure of tropical forest stands under different management conditions was modeled as a series of different spatial point processes. Spatial patterns were first assessed by K-function analyses to help choose a point process appropriate for observed patterns. The homogenous Neyman–Scott process accurately described live tree distribution in clear cut areas, where tree patterns tended to be aggregated. Parameters were estimated by minimizing Diggle's modified least squares criterion, and goodness-of-fit was assessed by comparison to confidence envelopes constructed by Monte Carlo simulation. Parameter estimates can be interpreted to help understand the ecological processes influencing re-colonization of disturbed areas. The inhomogeneous Poisson process was investigated for simulating the spatial pattern of ingrowth trees in lower canopy strata. The intensity function of this process was inversely proportional to variables representing canopy density. As assessed by Monte Carlo generation of confidence envelopes, the inhomogeneous Poisson process successfully portrayed the influence of canopy structure on understory plant distribution in most stands. Tree mortality was modeled as a thinning process in which the probability of individual tree mortality was conditional on subject tree attributes and competitive environment. The thinning function took the form of a generalized linear model with a binomial error distribution and logit link function. In most stands, tree neighborhood variables were powerful predictors of mortality, but they were not important predictors in all plots. This suggests that the surrounding forest structure of a subject tree has considerable influence on its morality, but competition is not the sole cause of tree morality in tropical forests.  相似文献