Effects of ocean acidification, temperature and nutrient regimes on the appendicularian Oikopleura dioica: a mesocosm study

Increasing pCO₂ is hypothesized to induce shifts in plankton communities toward smaller cells, reduced carbon export rates and increased roles of gelatinous zooplankton. Appendicularians, among the most numerous pan-global “gelatinous” zooplankton, continuously produce filter-feeding houses, shortcutting marine food webs by ingesting submicron particles, and their discarded houses contribute significantly to carbon fluxes. We present a first mesocosm-scale study on the effects of temperature, pCO₂ and bloom structures on the appendicularian, Oikopleura dioica. There were effects of temperature and nutrients on phytoplankton communities. No shifts in functional phytoplankton groups, nor changes in particle sizes/morphotypes, known to impact appendicularian feeding, were observed under manipulated pCO₂ conditions. However, appendicularian abundance was positively correlated with increased pCO₂, temperature and nutrient levels, consistent with hypotheses concerning gelatinous zooplankton in future oceans. This suggests appendicularians will play more important roles in marine pelagic communities and vertical carbon transport under projected ocean acidification and elevated temperature scenarios.     

The boll weevil‐cotton plant complex

The boll weevil, Anthonomus grandis Boheman was introduced from Mexico into the United States about 1892. More than three‐fourths of all insect losses to cotton in this country have been attributed to this insect, and it is generally agreed that cotton cannot be profitably grown in areas where it occurs without adequate control measures. This review summarizes the chemically oriented research conducted on this plant‐insect complex during the past seventy years with emphasis on the program conducted since 1962 at the Boll Weevil Research Laboratory.

Of plant‐insect relationships, host plant resistance, feeding stimulants, plant attractants, and plant constituents are discussed. Insect‐insect relationships treated include insecticides, chemosterilants and hormones, sex attractants, and insect constituents. The development of an integrated program for the attempted eradication of this insect is also discussed.     

Determination of pentachlorophenol in human urine using solid phase extraction and GC‐MS analysis with stable isotope dilution

A method for the determination of pentachlorophenol (PCP) in human urine was developed. Urine samples were fortified with ¹³C₆‐IabeIed PCP and hydrolyzed with sulfuric acid prior to extraction. The urine samples were then passed through preconditioned solid phase extraction cartridges containing octadecylsilane adsorbent. The PCP was subsequently eluted from the cartridge with ethyl acetate and converted to pentachloroanisole prior to GC‐MS analysis. GC‐MS quantitation was performed using the technique of stable isotope dilution. Percent recoveries averaging 100, 97, and 111% were obtained for replicate urine samples fortified with approximately 2, 20, and 200 ng/mL of PCP, respectively. The method detection limit was estimated to be 0.2 ng/mL.     

Quantifying the importance of local niche-based and stochastic processes to tropical tree community assembly

Although niche-based and stochastic processes, including dispersal limitation and demographic stochasticity, can each contribute to community assembly, it is difficult to quantify the relative importance of each process in natural vegetation. Here, we extend Shipley's maxent model (Community Assembly by Trait Selection, CATS) for the prediction of relative abundances to incorporate both trait-based filtering and dispersal limitation from the larger landscape and develop a statistical decomposition of the proportions of the total information content of relative abundances in local communities that are attributable to trait-based filtering, dispersal limitation, and demographic stochasticity. We apply the method to tree communities in a mature, species-rich, tropical forest in French Guiana at 1-, 0.25- and 0.04-ha scales. Trait data consisted of species' means of 17 functional traits measured over both the entire meta-community and separately in each of nine 1-ha plots. Trait means calculated separately for each site always gave better predictions. There was clear evidence of trait-based filtering at all spatial scales. Trait-based filtering was the most important process at the 1-ha scale (34%), whereas demographic stochasticity was the most important at smaller scales (37-53%). Dispersal limitation from the meta-community was less important and approximately constant across scales (-9%), and there was also an unresolved association between site-specific traits and meta-community relative abundances. Our method allows one to quantify the relative importance of local niche-based and meta-community processes and demographic stochasticity during community assembly across spatial and temporal scales.     

Warming modifies trophic cascades and eutrophication in experimental freshwater communities

Climate warming is occurring in concert with other anthropogenic changes to ecosystems. However, it is unknown whether and how warming alters the importance of top-down vs. bottom-up control over community productivity and variability. We performed a 16-month factorial experimental manipulation of warming, nutrient enrichment, and predator presence in replicated freshwater pond mesocosms to test their independent and interactive impacts. Warming strengthened trophic cascades from fish to primary producers, and it decreased the impact of eutrophication on the mean and temporal variation of phytoplankton biomass. These impacts varied seasonally, with higher temperatures leading to stronger trophic cascades in winter and weaker algae blooms under eutrophication in summer. Our results suggest that higher temperatures may shift the control of primary production in freshwater ponds toward stronger top-down and weaker bottom-up effects. The dampened temporal variability of algal biomass under eutrophication at higher temperatures suggests that warming may stabilize some ecosystem processes.     

On the estimation of phosphorus from the Niagara River to Lake Ontario

A predictive or model based approach to making inferences about the loading of a contaminant from a point source is presented and illustrated by estimating the total phosphorus, TP, loading from the Niagara River to Lake Ontario for the years 1967 to 1982. Information about explanatory variables and/or autodependence among successive observations can be easily included in the model and this allows more accurate inferences to be made. The results of the application to the Niagara River show a major decrease in TP loadings has occurred during the study period.     

Plant-available zinc and lead in mine spoils and soils at the mines of Spain, Iowa

To investigate the forms of Zn and Pb and their plant availability in mine spoil long after its abandonment, we studied seven sites in the Mines of Spain, near Dubuque, IA. Ores of Zn and Pb were mined from dolomitic limestone primarily during the 19th century, and there had been no subsequent remediation of metals-contaminated spoil. From both mine spoil and undisturbed areas, we collected root-zone soil samples as well as samples of the dominant ground-level, native plants, aniseroot [Osmorhiza longistylis (Torr.) DC.] and black snakeroot (Sanicular marilandica L.). We determined Zn and Pb concentrations in both the plant tissue and in the soil samples after strong-acid digestion, and we fractionated the solid-phase forms of Zn, Pb, and P in the soil samples by using sequential extraction. Concentrations of total Zn and Pb were 10- to 20-fold greater in the spoil than in the undisturbed soils. Plants growing in the mine spoil had Zn concentrations two to four times greater and Pb concentrations more than 26 times greater than did plants growing in the undisturbed soils. The highest concentrations of Zn and Pb were in the CBD-extractable and the residual fractions in both undisturbed and mine spoil samples. Although the mine spoil contained large amounts of P, Zn, and Pb were available for uptake by the two plant species in amounts proportional to Zn and Pb concentrations in the rooting zone.     

Topographic, bioclimatic, and vegetation characteristics of three ecoregion classification systems in North America: comparisons along continent-wide transects

Ecoregion classification systems are increasingly used for policy and management decisions, particularly among conservation and natural resource managers. A number of ecoregion classification systems are currently available, with each system defining ecoregions using different classification methods and different types of data. As a result, each classification system describes a unique set of ecoregions. To help potential users choose the most appropriate ecoregion system for their particular application, we used three latitudinal transects across North America to compare the boundaries and environmental characteristics of three ecoregion classification systems [Küchler, World Wildlife Fund (WWF), and Bailey]. A variety of variables were used to evaluate the three systems, including woody plant species richness, normalized difference in vegetation index (NDVI), and bioclimatic variables (e.g., mean temperature of the coldest month) along each transect. Our results are dominated by geographic patterns in temperature, which are generally aligned north-south, and in moisture, which are generally aligned east-west. In the west, the dramatic changes in physiography, climate, and vegetation impose stronger controls on ecoregion boundaries than in the east. The Küchler system has the greatest number of ecoregions on all three transects, but does not necessarily have the highest degree of internal consistency within its ecoregions with regard to the bioclimatic and species richness data. In general, the WWF system appears to track climatic and floristic variables the best of the three systems, but not in all regions on all transects.     

An ecosystem approach to population management of ungulates

Harvest objectives for wild ungulates have traditionally been based on population models that do not consider ecosystem effects of ungulate herbivory, nor interactions between native and domestic ungulate species. There is a need for ecosystem models to allow wildlife managers to evaluate potential ecosystem effects of management scenarios. The utility of the SAVANNA simulation model for estimating elk population objectives within an ecosystem context was demonstrated for North Park, Colorado, USA. Effects of different elk population levels were evaluated for range condition, elk and cattle forage, elk and cattle condition, forage and condition of mule deer and moose, plant production, and plant community composition. Analyses were based on 30-year simulation runs using variable, historical weather. Another set of analyses utilized stochastic weather patterns. For management scenarios using the historical climate pattern, increasing elk populations caused biomass reductions of palatable plant species, particularly on areas of high winter density, where mean leaf biomass of palatable shrubs declined from 26.97 g/m2 at 0 elk to 20.82 g/m2 at 4000 elk (3.73 elk/km2), a 23% decline. At population levels of 5000 elk (4.68 elk/km2) or greater, elk body condition declined sharply following a severe winter. The availability of palatable browse on critical winter range was likely the limiting factor. However, when random climate patterns were simulated for the same scenarios, the threshold level for density-dependent effects varied with climate, ranging from 2000 to 10,000 elk. We suggest that elk population levels from 4000 to 5000 animals represent a conservative population objective for the North Park elk herd. Also, increasing elk population levels appears to intensify intraspecific competition among elk, far more than interspecific competition with cattle. Resolution of elk-cattle conflicts is likely to be facilitated by managing elk distribution, rather than overall elk population levels.