Population growth rate and carrying capacity for springtails Folsomia candida exposed to ivermectin.

Forecasting the effects of stressors on the dynamics of natural populations requires assessment of the joint effects of a stressor and population density on the population response. The effects can be depicted as a contour map in which the population response, here assessed by population growth rate, varies with stress and density in the same way that the height of land above sea level varies with latitude and longitude. We present the first complete map of this type using as our model Folsomia candida exposed to five different concentrations of the widespread anthelmintic veterinary medicine ivermectin in replicated microcosm experiments lasting 49 days. The concentrations of ivermectin in yeast were 0.0, 6.8, 28.8, 66.4, and 210.0 mg/L wet weight. Increasing density and chemical concentration both significantly reduced the population growth rate of Folsomia candida, in part through effects on food consumption and fecundity. The interaction between density and ivermectin concentration was "less-than-additive," implying that at high density populations were able to compensate for the effects of the chemical. This result demonstrates that regulatory protocols carried out at low density (as in most past experiments) may seriously overestimate effects in the field, where densities are locally high and populations are resource limited (e.g., in feces of livestock treated with ivermectin).     

Population change and environment in central and eastern Kenya

"This paper, in compiling a case-study of six districts in Central and Eastern Provinces of Kenya, addresses the two poles of theory regarding population, environment, and economy--restricted growth and degradation versus induced change and intensification. The paper presents data on population change, and explores its relevance for changing patterns of resource use and economic opportunity.... Changes in population density between the 1969 and 1979 censuses are compiled, using regions of agroclimatic potential as surrogates for indicators of economic development.... Trends in urbanization are also analysed, to illuminate the dynamics of rural-urban linkages."     

The success of elutriate tests in extended prediction of water quality after a dredging operation under freshwater and saline conditions

Dredging simulation by elutriate tests accurately predicted concentrations of Hg, Cu, Mn and Fe released to the water column from contaminated sediment to within 1 order of magnitude. Hg and Cu concentrations increased by up to 7-fold after dredging, but declined to background concentrations within 48 h. Maximum loadings of Hg and Cu coincided with Fe and total organic carbon (TOC) water column concentrations, suggesting Hg and Cu are adsorbed onto particulates of Fe oxides and organic material. Seasonal changes in redox potential and temperature did not significantly affect metal release from sediments. Saline water did not cause significant increases in contaminant release from sediments to the water column over that observed for freshwater. Water quality standards of 1 µg l^–1 Hg and 28 µg l^–1 Cu as annual averages were not breached by dredging operations. Long-term effects of dredging on Hg and Cu availability, due to deposition of contaminated material as surficial sediments, is, however, of concern.     

Genetic diversity and structure in Pelvetia fastigiata (Phaeophyta: Fucales): does a small effective neighborhood size explain fine-scale genetic structure?

We investigated the genetic diversity and genetic structure of southern California populations of the common intertidal fucoid seaweed Pelvetia fastigiata, (J. Ag.) De Toni by means of allozyme electrophoresis and estimates of genetic neighborhood area and size, which are the first for seaweeds. We predicted that P. fastigiata populations would exhibit relatively low genetic diversity and high genetic structure because the seaweed is monoecious and has limited dispersal of gametes and zygotes. This prediction was supported; genetic diversity indices were all low compared to other seaweeds studied, but high genetic structure was evident particularly within individual reefs. Geospatial statistical analyses (second-order analyses) revealed clustered distribution of glucose-6-phosphate isomerase (GPI) alleles at the scale of 1 to 6 m within three reefs. The rare alleles were distributed only at the landward third of the reefs. Genetic neighborhood area (2.3 m²) and size (133 individuals) were estimated from parent-offspring dispersal distributions of gametes and zygotes from attached thalli and also detached reproductive fragments, which contributed very little to the effective neighborhood size. The neighborhood size was in the small theoretical range in which genetic drift could be responsible for the within-reef genetic structure. This result was equivocal, because the stereotyped distribution of rare alleles on the tips of each reef was highly unlikely to be due to random events (6.9×10^-24). These results emphasize (1) the importance of allele mapping in addition to spatial statistics to elucidate genetic structure, and (2) that interpretation of genetic-structure statistics as evidence for gene flow can be complicated, even when supported with independent estimates of gene flow, if data are lacking on selection and sporadic migration events. The emerging pattern of low levels of polymorphisms in brown seaweeds will limit the use of Wright's F-statistics and will require alternative, more direct techniques for the analysis of mechanisms responsible for population genetic structure.     

ICT reuse in socio-economic enterprises

In Europe, socio-economic enterprises such as charities, voluntary organisations and not-for-profit companies are involved in the repair, refurbishment and reuse of various products. This paper characterises and analyses the operations of socio-economic enterprises that are involved in the reuse of Information and Communication Technology (ICT) equipment. Using findings from a survey, the paper specifically analyses the reuse activities of socio-economic enterprises in the UK from which Europe-wide conclusions are drawn. The amount of ICT products handled by the reuse organisations is quantified and potential barriers and opportunities to their operations are analysed. By-products from reuse activities are discussed and recommendations to improve reuse activities are provided. The most common ICT products dealt with by socio-economic enterprises are computers and related equipment. In the UK in 2010, an estimated 143,750 appliances were reused. However, due to limitations in data, it is difficult to compare this number to the amount of new appliances that entered the UK market or the amount of waste electrical and electronic equipment generated in the same period. Difficulties in marketing products and numerous legislative requirements are the most common barriers to reuse operations. Despite various constraints, it is clear that organisations involved in reuse of ICT could contribute significantly to resource efficiency and a circular economy. It is suggested that clustering of their operations into “reuse parks” would enhance both their profile and their products. Reuse parks would also improve consumer confidence in and subsequently sales of the products. Further, it is advocated that industrial networking opportunities for the exchange of by-products resulting from the organisations’ activities should be investigated. The findings make two significant contributions to the current literature. One, they provide a detailed insight into the reuse operations of socio-economic enterprises. Previously unavailable data has been presented and analysed. Secondly, new evidence about the by-products/materials resulting from socio-economic enterprises’ reuse activities has been obtained. These contributions add substantially to our understanding of the important role of reuse organisations.     

Biodegradation of acrylic acid polymers and oligomers by mixed microbial communities in activated sludge

The biodegradability (mineralization to carbon dioxide) of acrylic acid oligomers and polymers was studied in activated sludge obtained from continuous-flow activated sludge (CAS) systems exposed to mixtures of low molecular weight (Mw < 8000) poly(acrylic acid)s and other watesoluble polymers [poly(ethylene glycol)s] in influent wastewater. Dilute preparations of activated sludge from the CAS units were tested for their ability to mineralize acrylic acid monomer and dimer, as well as a series of model acrylic acid oligomers and polymers (Mw 500, 700, 1000, 2000, and 4500), as sole carbon and energy sources. Complete mineralization of acrylic acid monomer and dimer was observed in low-biomass sludge preparations previously exposed to the polymer mixture, based on carbon dioxide production and residual dissolved organic carbon analyses. Extensive (though incomplete) degradation was also observed for the low molecular weight acrylic acid oligomers (Mw 500 and 700), but degradation dropped off sharply for the 1000, 2000, and 4500 Mw polymers. Radiochemical (¹⁴C) data also confirmed the low degradation potential of the 1000, 2000, and 4500 Mw materials. Degradation of two commercial poly(ethylene glycol)s at 1000 and 3400 Mw was complete and comparable to that of the acrylic acid monomer and dimer. Our results indicate that mixed populations of activated sludge microorganisms can extensively metabolize acrylic acid oligomers of seven units or less. Complete mineralization, however, could be confirmed only for the monomer and dimer material, and carbon mass balance data suggested that the true molecular weight cutoff for complete biodegradation was significantly less than the 500–700 Mw range tested.