Showing papers by "Augustana College (Illinois) published in 2001"

Grazer-resource interactions in the plankton: Are all daphniids alike?

Abstract: Daphniids have long been considered to be uniquely effective grazers in the planktonic food web of lakes, but whether all daphniid species are equivalent in this functional role is less clear. In particular, a common belief that large-bodied daphniids are more capable than smaller daphniids at controlling phytoplankton abundance has received limited testing. Using whole water column enclosures in a mesotrophic lake, we compared the ability of four common planktonic daphniids (Ceriodaphnia reticulata, Daphnia ambigua, Daphnia mendotae, and Daphnia pulicaria) to exploit a natural assemblage of phytoplankton. We established replicated monocultures of each daphniid species and allowed their populations to reach a carrying capacity determined by resources. We then compared the effects of each daphniid species on phytoplankton biomass, size structure, taxonomic composition and C : N : P stoichiometry. Populations of all four daphniids stabilized at very low birth and death rates, with larger species having a lower density but a higher biomass than smaller species. The seston C : P molar ratio was driven to equally high values (.300) in all treatments; however, daphniid effects on phytoplankton abundance and composition were quite different. The two smaller daphniids were less effective at depressing phytoplankton populations than were the two larger daphniids. This difference was associated with the persistence of a diverse assemblage of digestionresistant green algae in the Ceriodaphnia and D. ambigua treatments but their elimination from the D. mendotae and D. pulicaria treatments. Several lines of evidence, including growth bioassays, that have used juveniles of a clone of D. pulex-pulicaria, suggest that body size was not an adequate explanation for these differences in daphniid species effects on phytoplankton.

Amblygonite-montebrasite solid solutions as monitors of fluorine in evolved granitic and pegmatitic melts

Abstract: The distribution of F between amblygonite (Amb, LiAlPO4F)–montebrasite (Mbr, LiAlPO4OH) solid solutions and metaluminous haplogranitic melt has been calibrated at 585 °C and 200 MPa H2O. The partition coefficient for F between the crystalline phase and melt, D FMbr/melt, is linear between 0 to ~10 wt% F in amblygonite, which contains 13 wt% F at the end-member: ![Formula][1] Values of D FAmb/melt decrease sharply above 10 wt% F in amblygonite as the amblygonite reaches saturation in F at 200 MPa H2O. In natural occurrences, however, the vast majority of primary amblygonite-montebrasite solid solutions contain ~4–7 wt% F, well within the linear range of the calibrated exchange reaction, and the montebrasite-bearing assemblages are among the last to crystallize. If the F contents of the montebrasite are magmatic, then these most-fractionated residual melts of the LCT (Li-Cs-Ta, and mostly peraluminous S-types) rare-element class generally contained up to ~1.0–1.8 wt% F near the end of their crystallization. The modest F contents of pegmatites are consistent with the common association of Li aluminosilicates and with the general paucity of topaz in these occurrences. In topaz-bearing granites of Western Europe, however, high-F amblygonite (~10–11 wt% F) reflects >3 wt% F in melt during crystallization of these magmatic phases. [1]: /embed/tex-math-1.gif

Teenagers, Pregnancy, and Childbearing in a Risk Society How Do High-Risk Teens Differ From Their Age Peers?

Abstract: This article attempts to make a connection between two heretofore analytically distinct discourses on risk. On one hand, it refers to ways in which social work professionals and the like use the term to identify certain categories of teens as high, moderate, or low risk. On the other hand, it refers to the way theorists such as Anthony Giddens and Ulrich Beck described the advent of the risk society as a manifestation of a novel stage in the development of modernity. Theoretical issues are raised in reference to the findings derived from a study on teenage sexuality and pregnancy conducted in a Midwestern metropolitan statistical area of approximately 300,000, paying particular attention to a comparative assessment of the following two groups of interviewees: teen mothers and adolescent women using the services of a family planning clinic.

Microhabitat Use and Activity Patterns of Holbrookia niaculata and Sceloporus u-ndulatus at White Sands National Monument, New Mexico

Abstract: White Sands National Monument (WSNM), New Mexico, was established as a National Park to preserve the biotic and abiotic features of the "white" gypsum dunes environment. The lizards of WSNM are characterized as having special adaptive qualities that enable them to survive in gypsum sand. The lesser earless lizard (Holbrookia maculata) and the eastern fence lizard (Sceloporus undulatus) are white forms of their respective species that reside at the Monument (Ruthven, 1907; Smith, 1943; Lowe and Norris, 1956). At WSNM, Holbrookia maculata is short, stout, and dorsally pallid with fairly well-defined ventro-lateral blotches, and Sceloporus undulatus is medium-sized with a dorsal coloration of pale gray to nearly white with faint black shoulder patches (Smith, 1943). Dixon and Medica (1966) reported food of these lizards, and Dixon (1967) studied their activity and reproduction. MacFarland (1969) found that H. maculata and S. undulatus overlap greatly in daily activity, behavior, and food but differ in substrate preferences in seminatural enclosures at WSNM. Holbrookia maculata at WSNM had lower body temperatures and thermoregulated differently than a population of H. mniaculata from outside the dunes proper (Hager, 2000). Human-induced landscape alterations and increased land management practices threaten taxa adapted to aeolian habitats. Preservation of these organisms requires basic knowledge of their biology. Consequently, my goal was to understand more about the activity patterns and habitat use of H. maculata and S. undulatus in the gypsum dune field at WSNM. To my knowledge, this is the first systematic field study of these two lizards in their natural habitat across an entire activity season. For each species, I evaluated daily and seasonal surface activity and how this activity relates to the lizard's structural environment, use of microhabitats, proximity to vegetation, and population density. These data will allow monument personnel to make more informed management decisions on behalf of these lizards and the biotic resources, in general, and will ultimately contribute toward the preservation of the biodiversity of the gypsum environment. In broad terms, this information sheds more light on community structure in sand dune habitats. White Sands National Monument, New Mexico, (32?45'N; 106?15'W) encompasses approximately 450 km2 of active, moving dunes. Its edges house various

National Styles of Worker Protection in the United States and Japan: The Case of the Automotive Industry

Abstract: This paper compares and contrasts the national styles or approaches to the regulation and management of occupational safety and health distinctive of the United States and Japan within the context of the automotive industries of these two countries. Referring to comparative workplace injury and illness experience and data on safety and health regulatory activities, strengths and weaknesses of the two approaches are considered. It is suggested that an optimal strategy would contain elements of both approaches. Elements of the two approaches that might be adapted cross-nationally are identified and discussed.