The problem and promise of scale dependency in community phylogenetics

The problem of scale dependency is widespread in investigations of ecological communities. Null model investigations of community assembly exemplify the challenges involved because they typically include subjectively defined "regional species pools." The burgeoning field of community phylogenetics appears poised to face similar challenges. Our objective is to quantify the scope of the problem of scale dependency by comparing the phylogenetic structure of assemblages across contrasting geographic and taxonomic scales. We conduct phylogenetic analyses on communities within three tropical forests, and perform a sensitivity analysis with respect to two scaleable inputs: taxonomy and species pool size. We show that (1) estimates of phylogenetic overdispersion within local assemblages depend strongly on the taxonomic makeup of the local assemblage and (2) comparing the phylogenetic structure of a local assemblage to a species pool drawn from increasingly larger geographic scales results in an increased signal of phylogenetic clustering. We argue that, rather than posing a problem, "scale sensitivities" are likely to reveal general patterns of diversity that could help identify critical scales at which local or regional influences gain primacy for the structuring of communities. In this way, community phylogenetics promises to fill an important gap in community ecology and biogeography research.     

Diagnostic indicators of elevated nitrogen deposition

Tissue N content of mosses, which has been shown to be an indicator of enhanced N, was studied at a range of locations dominated either by wet or dry deposited and oxidised and reduced forms of N. Tissue N responded differently to wet and dry deposited N. For a 1 kg ha(-1) y(-1) increase in N deposition, tissue N increased by 0.01% at wet deposition sites but by 0.03% at sites dominated by dry deposited NH3. Tissue N at wet deposition sites responded more to concentrations of NO3- and NH4+ in precipitation (r(2) 0.63) than to total N deposition (r(2) 0.27), concentration explaining 66% of the variation in tissue N, wet deposition 33%. The study clearly concludes that tissue N concentration in mosses provides a good indication of N deposition at sites where deposition is dominated by NH3, and is also valuable in identifying vegetation exposed to large concentrations of NH4+ or NO3-, in wet deposition dominated areas, such as hilltops and wind exposed woodland edges.     

QUANTIFICATION OF ACTINIDE MIGRATION PATHWAYS AT ROCKY FLATS,COLORADO1

ABSTRACT: Migration of plutonium, americium, and uranium (actinides) in the environment at the Rocky Flats Environmental Technology Site (RFETS) is the subject of ongoing studies to develop effective strategies for cleanup and regulatory closure of the Department of Energy facility. The Actinide Migration Evaluation pathway analysis quantified actinide transport processes to validate a qualitative conceptual model of environmental actinide transport. Major actinide transport mechanisms evaluated include surface water, ground water, airborne, and biological pathways. Relative quantities of actinide movement via different pathways were compared in terms of actinide loads delivered off the RFETS, using a combination of monitoring data, predictive transport models and results from historic RFETS studies. Results indicate air and surface water constitute the dominant transport mechanisms for plutonium and americium. In ground water, shallow alluvial flow is a limited pathway for plutonium and americium because of the low aqueous solubility of these actinides and their tendency to sorb to soil. However, localized flow in shallow alluvium is a more significant pathway for uranium movement, because of the relatively higher solubility of uranium (VI) species, though isotopic ratios indicate much of the uranium is from natural sources. Biological transport of actinides by mammals, birds, fish, and arthropods is small compared to the other pathways.     

Simulated Responses of a Forest-Interior Bird Population to Forest Management Options in Central Hardwood Forests of the United States

I used estimates of carrying capacity, survival, fecundity, and edge effects to simulate the responses of a forest-interior bird population to selection cutting clearcutting, and no timber harvest. I also modeled population sensitivity to changes in fecundity, survival, K , and edge relationships. Because model parameters are based on scant data, results should he regarded as hypotheses to be further investigated or measures of the relative impact or sensitivity (given model assumptions). Simulated population size was greater with no timber harvest than with clearcutting and greater with clearcutting than with group selection when edge effects were included in the model. Without edge effects, population levels were only slightly lower under group selection than under no timber harvest, and greater than clearcutting. Edge effects had only a small impact on population levels under clearcutting. Clearcut size did not have much effect on population levels, but longer and shorter rotation ages resulted in higher and lower population levels, respectively. The model was very sensitive to declines in mean fecundity and survival, suggesting that factors affecting mean demographic rates could be more important than local edge effects. Some methods of timber harvest may be compatible with the conservation of forest-interior birds, but better demographic data and information on habitat suitability of selectively cut forests and young even-aged stands is needed to adequately evaluate management options.     

Distribution and abundance of choanoflagellates (Acanthoecidae) in the coastal cold ocean of Newfoundland, Canada

Water samples from six bays were taken over a 5-year period (1988 to 1992) to determine the distribution and abundance of loricate choanoflagellates in coastal Newfoundland, and to assess the impact that these organisms might have on this cold ocean food web. Scanning electron microscopy was used to study the morphology of these flagellates, allowing us to identify 11 species of loricate choanoflagellates. Parvicorbicula socialis (Meunier) Deflandre was the most abundant species (80 × 10³ cells l⁻¹), particularly during the spring diatom bloom. Single-cell species, such as Bicosta spini fera (Throndsen) Leadbeater and Calliacantha natans (Grontved) Leadbeater, were found more commonly after the spring diatom bloom in the summer months. Many of the single-cell choanoflagellates were attached to bacteria-rich microaggregates and debris in the water column and in unpoisoned sediment traps. The P. socialis cell flux was calculated to be 5.3 × 10⁶ cells m⁻² d⁻¹ in late May sediment traps. P. socialis in the upper 100 m of the water column was removing 0.3% of the standing crop of bacteria each day (April/May), and the equivalent of 7.4% of the daily bacterial production over the water column. Diel studies of P. socialis in Conception Bay suggest that the sharp decline in population numbers observed in midnight samples may be related to the high number of grazing zooplankton observed during the same period. Pelagic tunicate and zooplankton fecal pellets were found to contain large numbers of choanoflagellate costae, thus providing a direct link from the microbial loop to the macrozooplankton. Received: 17 March 1997 / Accepted: 9 May 1997     

Measurement of filtration rates by infaunal bivalves in a recirculating flume

A flume system and protocol for measuring the filtration rate of infaunal bivalves is described. Assemblages of multi-sized clams, at natural densities and in normal filter-feeding positions, removed phytoplankton suspended in a unidirectional flow of water. The free-stream velocity and friction velocity of the flow, and bottom roughness height were similar to those in natural estuarine waters. Continuous variations in phytoplankton (Chroomonas salinay) cell density were used to measure the filtration rate of the suspension-feeding clam Potamocorbula amurensis for periods of 2 to 28 h. Filtration rates of P. amurensis varied from 100 to 580 liters (gd)^-1 over a free-stream velocity range of 9 to 25 cm s^-1. Phytoplankton loss rates were usually constant throughout the experiments. Our results suggest that suspension-feeding by infaunal bivalves is sensitive to flow velocity.     

Ultraviolet irradiation of municipal wastewater: Evaluation of effects on organic constituents

A comparison of chromatograms derived from the UV-absorbing and oxidizable constituents present in primary and secondary municipal wastewater effluents indicates that exposure to UV irradiation at disinfection levels results in only slight chemical changes. The most pronounced chemical effects to nonvolatile organic constituents in wastewater effluents have been observed at irradiation levels in excess of those necessary for disinfection. Aliquots of effluents before and after exposure to varying levels of UV irradiation were concentrated by lyophilization prior to liquid chromatographic (LC) analysis. Anion-exchange chromatographic techniques utilizing a modified ultraviolet detector coupled in series with a cerate oxidative monitor provided excellent resolution and sensitivity in the determination of chemical changes occurring in the effluents as a result of exposure to different irradiation levels. The total coliform counts for each irradiated effluent were determined by the membrane-filter technique to evaluate the effectiveness of UV irradiation as a disinfection process for municipal wastewaters. Changes in biochemical oxygen demand (BOD), chemical oxygen demand (COD), total organic carbon (TOC), and total Kjeldahl nitrogen (TKN) at different levels of exposure to UV irradiation are presented. The results of these determinations and the gas chromatography/mass spectrometry data characterizing the observed chemical changes are discussed.