Stable isotope food-web analysis and mercury biomagnification in polar bears ( Ursus maritimus )

Mercury (Hg) biomagnification occurs in many ecosystems, resulting in a greater potential for toxicological effects in higher-level trophic feeders. However, Hg transport pathways through different food-web channels are not well known, particularly in high-latitude systems affected by the atmospheric Hg deposition associated with snow and ice. Here, we report on stable carbon and nitrogen isotope ratios, and Hg concentrations, determined for 26, late 19th and early 20th century, polar bear ( Ursus maritimus ) hair specimens, collected from catalogued museum collections. These data elucidate relationships between the high-latitude marine food-web structure and Hg concentrations in polar bears. The carbon isotope compositions of polar bear hairs suggest that polar bears derive nutrition from coupled food-web channels, based in pelagic and sympagic primary producers, whereas the nitrogen isotope compositions indicate that polar bears occupy > fourth-level trophic positions. Our results show a positive correlation between polar bear hair Hg concentrations and δ 15 N. Interpretation of the stable isotope data in combination with Hg concentrations tentatively suggests that polar bears participating in predominantly pelagic food webs exhibit higher mercury concentrations than polar bears participating in predominantly sympagic food webs.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73930/1/j.1751-8369.2009.00114.x.pd

A taxonomic backbone for the global synthesis of species diversity in the angiosperm order Caryophyllales

The Caryophyllales constitute a major lineage of flowering plants with approximately 12500 species in 39 families. A taxonomic backbone at the genus level is provided that reflects the current state of knowledge and accepts 749 genera for the order. A detailed review of the literature of the past two decades shows that enormous progress has been made in understanding overall phylogenetic relationships in Caryophyllales. The process of re-circumscribing families in order to be monophyletic appears to be largely complete and has led to the recognition of eight new families (Anacampserotaceae, Kewaceae, Limeaceae, Lophiocarpaceae, Macarthuriaceae, Microteaceae, Montiaceae and Talinaceae), while the phylogenetic evaluation of generic concepts is still well underway. As a result of this, the number of genera has increased by more than ten percent in comparison to the last complete treatments in the Families and genera of vascular plants” series. A checklist with all currently accepted genus names in Caryophyllales, as well as nomenclatural references, type names and synonymy is presented. Notes indicate how extensively the respective genera have been studied in a phylogenetic context. The most diverse families at the generic level are Cactaceae and Aizoaceae, but 28 families comprise only one to six genera. This synopsis represents a first step towards the aim of creating a global synthesis of the species diversity in the angiosperm order Caryophyllales integrating the work of numerous specialists around the world

Introduction to Organic Chemistry

xiii;ill.;384hal.;22c

Introduction to Organic Chemistry

New Yorkxiii, 384 P.: illus.; 24 c

Introduction to Organic Chemistry

xiii;ill.;384hal.;26c

Methylenecyclobutene and related substances

Methylenecyclobutene was synthesized by a modification of the Willstatter cyclobutene synthesis, with the use of the Hofmann reaction to introduce the intracyclic double bond. A novel feature of the synthesis was the use of anthracene as a blocking group for the exocyclic double bond during the malonic-ester ring closure. 4,4-Dimethylmethylenecyclobutene was synthesized from pinene, and 3-phenylmethylenecyclobutene was obtained by condensation of allene and phenylacetylene. The structures of the methylenecyclobutene dibromides and of the polymers formed by three different mechanisms were investigated. The results were shown to be consistent with the predictions of simple molecular orbital theory. 3-Methylenetrimethylene oxide was synthesized and its structure investigated by electron diffraction. The structures of the dibromides of methylenecyclobutane were determined and found to be consistent with a carbonium-ion mechanism for bromine addition

Introduction to organic chemistry

viii, 323 p.; 21 cm

Displacement Reactions at Bridgeheads of Bridged Polycarbocyclic Systems

A bridged ring system is defined as one in which two rings have three or more atoms in common. Those ring atoms which are bonded to three other ring atoms are called bridgehead atoms. Bridgehead displacements will be taken to include all reactions in which one atom attached to a bridgehead carbon atom is replaced by another atom, regardless of mechanism, and in which the ring skeleton remains unaltered. The available literature to June, 1954, is covered in this review