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941.
942.
Eva S. Stangler Stefan Jarau Michael Hrncir Ronaldo Zucchi Manfred Ayasse 《Chemoecology》2009,19(1):13-19
Foragers of several species of stingless bees deposit pheromone spots in the vegetation to guide recruited nestmates to a
rich food source. Recent studies have shown that Trigona and Scaptotrigona workers secrete these pheromones from their labial glands. An earlier report stated that species within the genus Geotrigona use citral from their mandibular glands for scent marking. Since convincing experimental proof for this conjecture is lacking,
we studied the glandular origin of the trail pheromone of Geotrigona mombuca. In field bioassays, newly recruited bees were diverted by artificial scent trails that branched off from the natural scent
trail deposited by their nestmates only when they were baited with extracts from the foragers’ labial glands. Compounds extracted
from the mandibular glands, however, did not release trail following behavior. This demonstrates that the trail pheromone
of G. mombuca is produced in the labial glands, as in Trigona and Scaptotrigona. Furthermore, in chemical analyses citral was identified exclusively in the foragers’ mandibular glands, which disproves
its supposed role as a trail pheromone. The labial glands contained a series of terpene- and wax type esters, with farnesyl
butanoate as major constituent. We, therefore, postulate that the trail pheromone of G. mombuca is composed of a blend of esters. 相似文献
943.
A series of field surveys were carried out on two permanent pools of the upper Glenelg River in SW Victoria, Australia. One was representative of the wider and deeper pools while the other was representative of the more-narrow and shallower pools. Both pools showed a typical seasonal cycle of warm, brackish, oxygen-poor, summer conditions and cool, oxygen-rich, low-salinity, winter conditions. The summer salinity increases were larger than expected, suggesting possible saline groundwater inflow from unidentified springs. Both pools contained anoxic water in their deeper sections but this was permanent only in the deeper pool. A simple model of the flushing rate of such anoxic pools subject to flows, such as environmental flow releases, was developed, based on an energy balance between the potential energy required to lift the anoxic layer and the kinetic energy derived from the river flow. The results were tested against and in agreement with the field measurements. The model also suggests that the anoxic layers are resilient to all but the largest environmental flows. 相似文献
944.
Barbara Neumann Michael Lütz Beatrice Schüpbach Erich Szerencsits 《Regional Environmental Change》2009,9(3):197-207
Spatial modelling of environmental indicators has been well established in landscape ecology and in nature conservation on
regional and national scales over the recent past. Yet, using spatial information as a basis for the coordination of environmental
measures on a trans-national European level reveals several shortcomings and hindrances, ranging from data quality issues
and methodological aspects to discussions on how to define ecological indicators across Europe. This paper analyzes the potential
of spatial modelling for the development and implementation of agri-environmental measures as part of rural development policies,
discussing critical aspects of spatial environmental modelling as well as chances, trends and demands. 相似文献
945.
Consumer-based ocean conservation efforts focus attention on seafood that is produced in an “eco-friendly” manner. However, many species can be produced either in aquaculture operations or harvested within wild capture fisheries, and each mode of production differs in their environmental impacts as well as their energy requirements. Complicating the assessment of eco-friendly seafood is the fact that seafood is a global commodity, the suppliers of which utilize a variety of methods to distribute the product from producer to consumer (e.g. ship, truck, airplane). Like the modes of production, these various modes of distribution differ in their energy intensity. This analysis assesses the overall energy requirements of production and distribution (EP&D) of seafood to evaluate how the energy costs of distribution influence the total energy cost of seafood produced by different methods. This paper develops the concept of energy isolines as a tool to assess EP&D. Isolines are a graphical method to succinctly integrate multiple distance assessments so that the best sourcing option can be determined. The isolines are then used to assess how the energy cost of distribution functions as a component of the overall energy cost, and how this influences the EP&D of a product originating from two different sources with inherently different energy costs of production. Using scallops and salmon as examples, this analysis has revealed that an “eco-friendly” seafood commodity (one produced with less energy) produced far from its destination market could have a higher total EP&D compared to a local, less “eco-friendly” product (that takes more energy to produce). Finally, this paper evaluates strategies to minimize the overall EP&D of seafood. Overall, further work on energy audits of seafood focused the need to maintain a global perspective to determine seafood with the lowest overall energy cost of production and distribution. 相似文献
946.
947.
948.
Scott Elliott Gerald E. Streit Jeffrey S. Gaffney James E. Bossert Michael Brown Jon Reisner Laurie A. McNair 《Environmental science and pollution research international》1999,6(2):103-105
The nerve agent sarin has recently been deployed by terrorists in a major city. The molecule is volatile and made its way
to many victims by passing as vapor through a highly reactive medium. Here we estimate rates and pathways for the removal
of gas phase sarin from a generalized urban atmosphere. Only information from the open scientific literature is used. By structure
reactivity comparisons with the organophosphorus pesticides, hydroxyl radical hydrogen abstraction may occur in as little
as one hour. Decomposition of side chains after hydroxyl attack leads to organic oxygenates which preserve the phosphonofluoridate
and so toxicity. The aqueous aerosol surface is contacted in minutes and offers access to a range of dissolved nucleophiles.
Substitution displaces the fluoride leaving group, giving safe phosphoric acid analogs. Because of uncertainties in the electron
distribution and in aqueous decay mechanisms, the time constants must be viewed as lower limits. 相似文献
949.
Abstract: Matrix population models have entered the mainstream of conservation biology, with analysis of proportional sensitivities (elasticity analysis) of demographic rates becoming important components of conservation decision making. We identify areas where management applications using elasticity analysis potentially conflict with the mathematical basis of the technique, and we use a hypothetical example and three real data sets (Prairie Chicken [ Tympanuchus cupido ], desert tortoise [ Gopherus agassizii ], and killer whale [ Orcinus orca ]) to evaluate the extent to which conservation recommendations based on elasticities might be misleading. First, changes in one demographic rate can change the qualitative ranking of the elasticity values calculated from a population matrix, a result that dampens enthusiasm for ranking conservation actions based solely on which rates have the highest elasticity values. Second, although elasticities often provide accurate predictions of future changes in population growth rate under management perturbations that are large or that affect more than one rate concurrently, concordance frequently fails when different rates vary by different amounts. In particular, when vital rates change to their high or low values observed in nature, predictions of future growth rate based on elasticities of a mean matrix can be misleading, even predicting population increase when the population growth rate actually declines following a perturbation. Elasticity measures will continue to be useful tools for applied ecologists, but they should be interpreted with considerable care. We suggest that studies using analytical elasticity analysis explicitly consider the range of variation possible for different rates and that simulation methods are a useful tool to this end. 相似文献
950.
Travis C. Glenn †‡ Wolfgang Stephan and Michael J. Braun† 《Conservation biology》1999,13(5):1097-1107
Abstract: The Whooping Crane ( Grus americana ) is an endangered bird that suffered a severe population bottleneck; only 14 adults survived in 1938. We assessed the genetic effect of this human-caused bottleneck by sequencing 314 base pairs ( bp) of the mitochondrial DNA control region from cranes that lived before, during, and after this bottleneck. The maximum length of DNA amplifiable from museum specimens was negatively correlated with age, and only 10 of 153 specimens yielded the entire 314 bp sequence. Six haplotypes were present among the prebottleneck individuals sequenced, and only one of these persists in the modern population. The most common modern haplotype was in low frequency in the prebottleneck population, which demonstrates the powerful effect of genetic drift in changing allele frequencies in very small populations. By combining all available data, we show that no more than one-third of the prebottleneck haplotypes survived the human-caused population bottleneck. High levels of variation of substitution rates among nucleotide sites prevented us from estimating the prebottleneck population size. Our data will be incorporated into the captive breeding program to allow better management decisions regarding the preservation of current genetic diversity. These data offer the first glimpse into the genetic toll this species has paid for human activities. 相似文献