Subsidy‐stress and multiple‐stressor effects along gradients of deposited fine sediment and dissolved nutrients in a regional set of streams and rivers

1. Stream managers need to understand relationships between multiple stressors and ecological responses. We examined responses of benthic invertebrates and algae along two land‐use‐related stressor gradients of concern in running waters. Our correlative study of the consequences of augmented deposited fine sediment and nutrient concentrations was conducted in a regional set of streams and rivers monitored by a water management authority in New Zealand and incorporated a wide range of catchment geologies and stream orders. 2. We used multiple linear regression analysis and an information‐theoretic approach to select the best predictive models for our biological response variables by testing multiple competing hypotheses that include nonlinear subsidy‐stress relationships and interactive effects between the two stressors. 3. Patterns consistent with a subsidy‐stress response to increasing dissolved inorganic nitrogen concentration were found for the relative abundances of the common invertebrate genera Pycnocentrodes and Deleatidium and for the relative abundance of total individuals in the EPT orders (Ephemeroptera, Plecoptera, Trichoptera). 4. Fine sediment seemed the more pervasive stressor, apparently counteracting and overwhelming any initial subsidy effect of increased nutrients, and accounting for more of the variance in biological response variables. Relationships with high nutrient concentrations were weaker and modelled with less certainty, probably reflecting the indirect modes of action of nutrients compared to those underlying sediment effects. Nevertheless, in several cases, the models indicated that nutrients interacted synergistically with fine sediment, lending further weight to the conclusion that managers need to address both stressors to achieve the best outcomes.     

AUTONOMY AND AUTHENTICITY OF ENHANCED PERSONALITY TRAITS

There is concern that the use of neuroenhancements to alter character traits undermines consumer's authenticity. But the meaning, scope and value of authenticity remain vague. However, the majority of contemporary autonomy accounts ground individual autonomy on a notion of authenticity. So if neuroenhancements diminish an agent's authenticity, they may undermine his autonomy. This paper clarifies the relation between autonomy, authenticity and possible threats by neuroenhancements. We present six neuroenhancement scenarios and analyse how autonomy accounts evaluate them. Some cases are considered differently by criminal courts; we demonstrate where academic autonomy theories and legal reasoning diverge and ascertain whether courts should reconsider their concept of autonomy. We argue that authenticity is not an appropriate condition for autonomy and that new enhancement technologies pose no unique threats to personal autonomy.     

A dye-binding induced conformational transition of poly-(methacrylic acid) by Auramine O in aqueous solutions. I. Experimental results

Binding of auramine O to poly-(methacrylic acid) (PMA) has been established over a large range of C⁰_p/C⁰_d values using spectroscopic methods (UV absorption and visible fluorescence emission spectra), equilibrium and sedimentation dialysis, potentiometric and viscosimetric titrations. All the results show qualitative agreement with those obtained previously with the system crystal violet-PMA although the binding seems to be less strong for auramine O than for crystal violet. From dialysis experiments binding isotherms were obtained at three different degrees of neutralization α'; at α' = 0.10 the results could be fitted to a Langmuir isotherm but at α' equal to 0.40 and 0.65 deviations with respect to such an isotherm occur. The results of potentiometric and viscosimetric titrations confirm that the conformational transition which the dye-free PMA exhibits upon ionization is affected by the dye binding. The region in which the conformational transion occurs is broadened and is less sharply defined in the presence of auramine O.     

Ecology and systematics of mangrove crabs of the genus Perisesarma (Crustacea: Brachyura: Sesarmidae) from East Africa

East Africa has a reduced mangrove crab species richness when compared to Asian mangroves. To date, only one species of Perisesarma de Man, 1895 has been reported in East Africa, despite more than 30 years of mangrove research in this region. Based on morphology, colour, mtDNA and behaviour, we describe a new species of Perisesarma from Kenya, P. samawati sp. nov. Surprisingly, when comparing molecular data from other species within this genus, P. samawati sp. nov. and the sympatric P. guttatum (A. Milne Edwards, 1869) are not sister species. Some aspects of the ecology of P. guttatum and P. samawati sp. nov. are compared and the differences discussed. Additionally, we compare P. samawati sp. nov. with the ecological literature of a possible sister species P. eumolpe de Man, 1895 from Malaysian mangroves. Our findings suggest that the new species is an ecologically important species in East African mangroves.  © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society , 2004, 141 , 435–445.     

Estimation of prediction error variances via Monte Carlo sampling methods using different formulations of the prediction error variance

Calculation of the exact prediction error variance covariance matrix is often computationally too demanding, which limits its application in REML algorithms, the calculation of accuracies of estimated breeding values and the control of variance of response to selection. Alternatively Monte Carlo sampling can be used to calculate approximations of the prediction error variance, which converge to the true values if enough samples are used. However, in practical situations the number of samples, which are computationally feasible, is limited. The objective of this study was to compare the convergence rate of different formulations of the prediction error variance calculated using Monte Carlo sampling. Four of these formulations were published, four were corresponding alternative versions, and two were derived as part of this study. The different formulations had different convergence rates and these were shown to depend on the number of samples and on the level of prediction error variance. Four formulations were competitive and these made use of information on either the variance of the estimated breeding value and on the variance of the true breeding value minus the estimated breeding value or on the covariance between the true and estimated breeding values.     

Response of benthic invertebrates to natural versus experimental disturbance in a Swiss prealpine river

1. The crucial point of disturbance experiments in streams is the extent to which they can simulate a natural spate. Ideally, disturbance experiments should proceed side by side with a phenomenological study to allow a direct comparison. In the present study conducted in a prealpine Swiss river, the River Necker, fortuitous events made such a comparison possible. 2. In summer 1994, we took Surber samples one day before and on several sampling dates after a major flood (recurrence interval ≈ 5 years), which was followed by a long period of uniform discharge in a river characterized by frequent spates. Beginning 19 days after this flood, patches of the stream bed (≈ 9 m²) were physically disturbed by kicking and raking. 3. The degrees of reduction in the total number of individuals and the dominant taxa were similar after both types of disturbance, as were the recolonization patterns of Rhithrogena spp., Leuctra spp. and Hydracarina. Chironomidae, Baetis spp., Simuliidae, Pentaneurini and Corynoneura/Thienemanniella spp. showed a distinct lag phase after the flood before recolonization began, whereas there was no such lag phase after the experiment. Therefore, the time needed to recover to pre-flood densities was longer for these taxa. Nevertheless, recolonization rates and patterns after the lag phase were similar to those after the experimental disturbance. 4. Size-class measurements indicated that recruitment from egg hatching may have been more important after the flood than after the experimental disturbance for Rhithrogena spp., but not for Chironomidae, Baetis spp., Simuliidae, Pentaneurini and Leuctra spp. Invertebrate drift was probably the most important pathway of recolonization after both types of disturbance. 5. Our experiment allowed a realistic simulation of several important effects of the large flood on the invertebrate community. Smaller spates that induce substratum movement at a spatial scale similar to our experimental plots are much more common than large floods in the River Necker. For these spates, our experiment should provide an even more realistic simulation of natural disturbance.     

Air-surface exchange measurement in heterogeneous regions: extending tower observations with spatial structure observed from small aircraft

Strategies to assess long-term atmosphere-ecosystem exchange of CO₂ and H₂O must deal not only with time trends but also with spatial variability. Flux towers efficiently measure time trends, but only at discrete sites, always limited in number. Representativeness of these sites and the causes of spatial variation between sites are difficult to investigate from tower data alone. Such issues are better addressed with flux measurements from moving vehicles, particularly aircraft. Recent technological advancements in aircraft and instrumentation now allow mobile flux measurement with enhanced precision, greater ease, and lower cost. Results are presented which illustrate the importance of spatial variability, and some suggestions are given for assessment of flux-tower representativeness. Unfortunately, airborne observations of the kind presented here are practical only during a part of the daylight hours in brief intensive field campaigns. Extrapolation of spatial-structure information derived from these measurements to night-time or to long-term averages thus remains problematic. For the foreseeable future this extrapolation will require models that faithfully simulate both space and time characteristics of H₂O and CO₂ exchange. The development and validation of such models will be greatly enhanced by the increased availability of measurements from moving vehicles, which record spatial as well as temporal structure.