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Jeff A Johnson Heather RL Lerner Pamela C Rasmussen David P Mindell 《BMC evolutionary biology》2006,6(1):65-12
Background
Populations of the Oriental White-backed Vulture (Gyps bengalensis) have declined by over 95% within the past decade. This decline is largely due to incidental consumption of the non-steroidal anti-inflammatory veterinary pharmaceutical diclofenac, commonly used to treat domestic livestock. The conservation status of other Gyps vultures in southern Asia is also of immediate concern, given the lack of knowledge regarding status of their populations and the continuing existence of taxonomic uncertainties. In this study, we assess phylogenetic relationships for all recognized species and the majority of subspecies within the genus Gyps. The continuing veterinary use of diclofenac is an unknown but potential risk to related species with similar feeding habits to Gyps bengalensis. Therefore, an accurate assessment of the phylogenetic relationships among Gyps vultures should aid in their conservation by clarifying taxonomic uncertainties, and enabling inference of their respective relatedness to susceptible G. bengalensis. 相似文献3.
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King Frederick D.; Cucci Terry L.; Townsend David W. 《Journal of plankton research》1987,9(2):277-289
Ammonium regeneration by micro- (35153 µm) andmacrozooplankton (> 153 µm) was determined in the Gulfof Maine by measuring the activity of the excretory enzyme glutamatedehydrogenase (GDH) in various size fractions. GDH maxima weregenerally observed to correspond to the depth of the chlorophyllmaximum as previously reported in the Gulf of Mexico and inthe vicinity of the Nantucket Shoals. GDH activity of the microzooplanktonwas considerably lower than the macrazooplankton, suggestingthe microzooplankton made only a minor contribution (111%) to the total ammonium regenerated. These results were confirmedby biomass estimates made from counts of individual species.Ammonium excretion by both zooplankton fractions was estimatedto supply 531 % of the nitrogen requirements for primaryproduction, with an estimated 5963% supplied by the verticaltransport of nitrate (new nitrogen) into the euphoric zone. 相似文献
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Frederick Errington is Aaaociate Professor of Anthropology, at Keene State College, New Hampshire. Deborah Gewertz is Professor of Anthropology, at Amherst College, Massachusetts. 相似文献
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Synopsis The bloater, Coregonus hoyi, deposits its eggs on deep sediments (70–100 m in Lake Michigan), where its eggs and embryos can be exposed to epibenthic
predators. We investigated the vulnerability of early life intervals of bloaters to predation by mysids, Mysis relicta, which are mostly epibenthic by day and planktonic at night. Bloaters were raised from spawn in the laboratory and presented
to field-collected mysids in laboratory predation trials. Eggs were not ingested by the mysids. Embryonic bloaters were vulnerable
to predation by mysids only during the interval between hatching and swim up, usually 1–24 h under laboratory conditions.
The mysids required about a day of exposure to this novel prey before they were able to kill significant numbers of the bloater
embryos by making successive attacks with their thoracic legs. In experiments with experienced (2 and 3 days with bloater
embryos) mysids, a functional response between embryo density and mysid predation rates was apparent. Temperature and the
presence of alternative prey (zooplankton) did not alter the ‘kill rate’ (about 2.5 embryos mysid-1d-1) of experienced mysids at high bloater densities (>4 bloaters/mysid). However, more embryos were partially, rather than completely,
ingested at 4 versus 9° C and in the presence of zooplankton. 相似文献
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Three axenic and rhizosphere microorganism-inoculated shortgrass steppe plant species were evaluated for possible differences in residual organic carbon and nitrogen present as sugars, organic acids and amino acids. IntroducedAgropyron cristatum was compared toA. smithii andBouteloua gracilis, which are dominant species in the native shortgrass steppe. These plants, grown for 90 days in root growth chambers, showed differences in residual organic carbon and nitrogen per gram of root, and rhizosphere microbe presence resulted in additional changes in these compounds. The root biomass ofB. gracilis was significantly increased with microbes present. TheAgropyron species had significantly lower amino acid levels with microbes present, while under the same conditions, theB. gracilis showed significant decreases in residual sugars. Based on the amino acids, sugars and organic acids, the C/N ratio of the sterileA. cristatum was higher than forB. gracilis. Rhizosphere microbe presence did not result in changes in these C/N ratios. These results suggest thatA. cristatum, with microbes present, will have lower levels of amino acids present, whileB. gracilis, with a lower C/N ratio, will have sugars used to a greater extent by the rhizosphere microbes. This resulted in the higher levels of residual soluble organic C and N in the rhizosphere ofB. gracilis, in comparison with the introducedA. cristatum. These differences may be critical in influencing the course of nutrient accumulation and plant competition in short-grass steppe communities, and in understanding basic aspects of plant-rhizosphere microorganism interactions. 相似文献
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Summary Two alternative estimators of individual tree leaf area (A1) area are used to derive estimates of leaf-area index (L) for 40 plots in Pinus contorta Dougl. stands. One estimator of A1 is based on the common assumption of a constant ratio between A1 and sapwood cross-sectional area at breast height (As). The second estimator of A1 accounts for tree-to-tree variation in the relation between A1 and As. The apparent relationship between stand growth and leaf-area index is strongly dependent on the way leaf area is estimated. When L is derived from a constant A1As ratio, stand growth appears to be strongly correlated with L. However, when L is based on estmates of A1 that account for tree-to-tree variation in the A1 — As relation, stand growth is seen to be only weakly related to L. Stand structure, quantified as percent live-crown, accounts for a great deal of the observed variation in leaf-area efficiency. These contrasting relationships illustrate the importance of unbiased estimates of L in interpreting the link between stand-level processes and leaf area.Utah Aggriculural Experiment Station Journal Paper No. 3333 相似文献