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721.
Kristina?D.?RothleyEmail author Charlene?Rae 《Environmental Modeling and Assessment》2005,10(2):107-113
In this paper we apply graph theory in a reserve selection exercise to explore the tradeoffs between maintaining connectivity and minimizing the total area of a protected area network. Rather than focus on a single organism, we used a multi-species approach and looked at the tradeoff curves for organisms with varying dispersal abilities. We first generated the tradeoff curves using a graph-based metric to determine the importance of individual patches for maintaining connectivity. We then performed an analogous set of analyses using patch size as a surrogate measure of importance. 相似文献
722.
Distribution of actinomycetes in oil contaminated ultisols of the Niger Delta (Nigeria) 总被引:1,自引:0,他引:1
J.P.Essien 《环境科学学报》2000,12(3):296-302
The distribution of actinomycetes in oil contaminated sandy loam ultisols of the Niger Delta region of Nigeria was studied to aid in understanding the effect of hydrocarbons on indigenous microbial population in tropical soils. The average total counts of actinomycetes in all the oil samples analysed was 103 cfu/g. Higher counts of actinomycetes were observed during the dry season than during the wet season. The counts of hydrocarbonoclastic actinomycetes correlated positively with the total count of actinomycetes.The actinomycetes were generally restricted to the top soil(0-10 cm soil depth) although a seemingly deeper(down to 40 cm soil depth) distribution was noticed in the dry season. The isolates included oil degrading species of Actinoplanes, Norcadia,Streptomyces and Streptosporangium. Their high oil utilization ability indicates their positive potential and role in the bioremediation of oil-spilled soils. 相似文献
723.
Supplementing the nutrient requirement of crops through organic manures plays a key role in sustaining soil fertility, and crop productivity and reducing use of fossil fuels. Field experiments were conducted for 2 years at two different locations (i.e. Lucknow and Pantnagar) in Uttar Pradesh, India. The objectives of the study were to assess the herb and essential oil yields of Japanese mint (Mentha arvensis cv. Hy 77), and its nutrient accumulation under single and combined applications of organic manures and inorganic fertilizers (NPK). Changes in physical and chemical characteristics of the soils (Fluvisols, Mollisols) were also determined. Eight treatments comprising different combinations of NPK through inorganic fertilizers and farm yard manure (FYM) were compared. The distilled waste of mint after extraction of essential oil was recycled to soils in the plots to supplement the nutritional requirement of the succeeding mustard crop (Brassica juncea cv. Pusa Bold). Herb and essential oil yield of mint were significantly higher with combined application of organic and inorganic sources of nutrients as compared to single applications. Accumulation of N and P was at par under full inorganic and combined supply whereas, K accumulation was higher with the former. Soil organic C and pH after harvest of mint did not significantly differ among the treatments, but the level of mineralizable N, Olsen-P and NH4OAc extractable K were higher in soil with integrated supply of nutrients. Significant increase in soil water stable aggregates, organic C, available NPK and microbial biomass, and decrease in soil bulk density were observed with waste recycling over fertilizer application. These benefits were reflected in the seed and stubble yield of mustard which succeeded mint. This study indicates that combined application of inorganic fertilizers with organics helps in increasing the availability of nutrients and crop yield and provides a significant effect to the succeeding crop. Similarly, recycling crop residues reduces the need for fossil fuel based fertilizer, and helps in sustaining and restoring soil fertility in terms of available nutrients and major physical and chemical characteristics of the soil. 相似文献
724.
This study investigated the influence of cat urine odour in suppressing development and fertility in Campbell's hamster males.
Exposure to this odour from postnatal day 11 until day 45 (sexual maturation) resulted in reduced sex organ weights, reduced
testosterone levels and in an increase in abnormalities of the synaptonemal complex in both sex chromosomes and autosomes.
Subsequent breeding experiments revealed a significant decrease in litter size. All these data indicate a severe effect of
predator odour on the breeding success of potential prey species. It is assumed that these effects are caused by the sulphurous
compounds in the urine; however, the underlying mechanisms are not yet known.
Received: 31 January 2000 / Accepted in revised form: 6 June 2000 相似文献
725.
Honeybees, Apis spp., maintain elevated temperatures inside their nests to accelerate brood development and to facilitate defense against predators.
We present an additional defensive function of elevating nest temperature: honeybees generate a brood-comb fever in response
to colonial infection by the heat-sensitive pathogen Ascosphaera apis. This response occurs before larvae are killed, suggesting that either honeybee workers detect the infection before symptoms
are visible, or that larvae communicate the ingestion of the pathogen. This response is a striking example of convergent evolution
between this "superorganism" and other fever-producing animals.
Received: 2 September 1999 / Accepted in revised form: 28 February 2000 相似文献
726.
There are numerous reports of invertebrates that are visual mimics of ants, but no formal reports of mimicry of an ant, by
an ant. Two endemic Australian ants, Myrmecia fulvipes and Camponotus bendigensis are remarkably similar in colour and size; both are generally black but have red legs and golden gasters. The density and
hue of the pubescence of each ant's gaster are relatively uncommon in ants, but are very rare when combined with the black
forebody and red legs. The ants are similarly sized but are smaller than other species closely related to M. fulvipes. The range of C. bendigensis lies entirely within that of M. fulvipes, and both species excavate ground nests in open woodland. Finally, workers of both species are crepuscular and forage solitarily.
These data suggest that the relatively benign formicine C. bendigensis is a Batesian mimic of the formidable myrmeciine M. fulvipes.
Received: 9 August 1999 / Accepted in revised form: 22 December 1999 相似文献
727.
A survey is given on fluid-dynamic effects caused by the structure and properties of biological surfaces. It is demonstrated
that the results of investigations aiming at technological applications can also provide insights into biophysical phenomena.
Techniques are described both for reducing wall shear stresses and for controlling boundary-layer separation. (a) Wall shear
stress reduction was investigated experimentally for various riblet surfaces including a shark skin replica. The latter consists
of 800 plastic model scales with compliant anchoring. Hairy surfaces are also considered, and surfaces in which the no-slip
condition is modified. Self-cleaning surfaces such as that of lotus leaves represent an interesting option to avoid fluid-dynamic
deterioration by the agglomeration of dirt. An example of technological implementation is discussed for riblets in long-range
commercial aircraft. (b) Separation control is also an important issue in biology. After a few brief comments on vortex generators,
the mechanism of separation control by bird feathers is described in detail. Self-activated movable flaps (=artificial bird
feathers) represent a high-lift system enhancing the maximum lift of airfoils by about 20%. This is achieved without perceivable
deleterious effects under cruise conditions. Finally, flight experiments on an aircraft with laminar wing and movable flaps
are presented. 相似文献
728.
Chemical synapses are highly specialized cell–cell junctions designed for efficient signaling between nerve cells. Distinct
cytoskeletal matrices are assembled at either side of the synaptic junction. The presynaptic cytomatrix at the active zone
(CAZ) defines and organizes the site of neurotransmitter release from presynaptic nerve terminals. The postsynaptic density
(PSD) tethers neurotransmitter receptors and the postsynaptic signal transduction machinery. Recent progress in the identification
and characterization of novel CAZ and PSD components has revealed new insights into the molecular organization and assembly
mechanisms of the synaptic neurotransmission apparatus. On the presynaptic side, Bassoon and Piccolo, two related giant proteins,
are crucially involved in scaffolding the CAZ. On the postsynaptic side, two families of multi-domain adaptor proteins, the
MAGuKs (membrane-associated guanylate kinase homologs) and the ProSAP (proline-rich synapse-associated protein, also termed
Shank) family members are thought to be major organizing molecules of the PSD. 相似文献
729.
The Mormon cricket, Anabrus simplex, is one of just a few species of katydids (or bushcrickets, Orthoptera: Tettigoniidae) that, like migratory locusts, appear
to have solitary and migratory morphs. Using radio telemetry we studied movements of individuals of two morphs of this flightless
species. Individuals within each migratory band had similar rates of movements along similar directional headings whereas
solitary individuals moved little and showed little evidence of directionality in movement. Our results also add to other
recent radio-telemetry studies showing that flightless insects of 1–2 g in mass can be tracked successfully using these methods.
Received: 28 February 2000 / Accepted in revised form: 19 June 2000 相似文献
730.
High-performance permanent magnets 总被引:2,自引:0,他引:2
High-performance permanent magnets (pms) are based on compounds with outstanding intrinsic magnetic properties as well as
on optimized microstructures and alloy compositions. The most powerful pm materials at present are RE–TM intermetallic alloys
which derive their exceptional magnetic properties from the favourable combination of rare earth metals (RE=Nd, Pr, Sm) with
transition metals (TM=Fe, Co), in particular magnets based on (Nd,Pr)2Fe14B and Sm2(Co,Cu,Fe,Zr)17. Their development during the last 20 years has involved a dramatic improvement in their performance by a factor of >15 compared
with conventional ferrite pms therefore contributing positively to the ever-increasing demand for pms in many (including new)
application fields, to the extent that RE–TM pms now account for nearly half of the worldwide market. This review article
first gives a brief introduction to the basics of ferromagnetism to confer an insight into the variety of (permanent) magnets,
their manufacture and application fields. We then examine the rather complex relationship between the microstructure and the
magnetic properties for the two highest-performance and most promising pm materials mentioned. By using numerical micromagnetic
simulations on the basis of the Finite Element technique the correlation can be quantitatively predicted, thus providing a
powerful tool for the further development of optimized high-performance pms. 相似文献