Is proximity to the North Atlantic Drift and the Continental Shelf Current sustaining freshwater European eel populations in western Scotland?

1. We report on freshwater resident eel numbers in western Scotland based on two time series of data, independent of each other, spanning 28 years and that do not rely upon fisheries information. 2. Data from eel captures on trash screens of a pumping station (1982–2003) on Loch Lomond and electrofishing data from a stream in Lochaber, the Allt Coire nan Con (1989–2010), are compared with similar time series eel population data from elsewhere in the British Isles and more widely in Europe. 3. Over the period of the study, indices of eel numbers from across Europe declined by between 72 and 95%; in stark contrast, neither time series from western Scotland showed evidence for decline between 1982 and 2010. 4. We provisionally conclude that freshwater populations in western Scotland are being maintained by regional processes directly related to the proximity of the leading edge of the North Atlantic Drift and the Continental Shelf Current and the direction of prevailing winds.     

Factors Affecting Golden-Cheeked Warbler Nest Survival in Urban and Rural Landscapes

ABSTRACT We evaluated hypotheses concerning temporal, landscape, and habitat effects on nest survival of golden-cheeked warblers (Dendroica chrysoparia) in an urban and a rural landscape during the breeding seasons of 2005 and 2006 in central Texas, USA. We found support for temporal effects of year and cubic effect of date and included them in candidate models that evaluated habitat and landscape effects. Nest survival was lower in 2006 than in 2005 and decreased nonlinearly as the breeding season progressed. We found support for edge effects with decreased nest survival nearer edges and in areas with increased open edge density (wooded habitat abutting open habitat) or decreased trail density. However, confidence intervals for the model-averaged odds ratios overlapped 1.0 for all edge variables. Overall daily survival rate was 0.964 (95% CI = 0.949-0.975), resulting in a 25-day period survival of 0.398 (95% CI = 0.269-0.524). Period survival in Austin's urban landscape (0.399, 95% CI = 0.270-0.526) was similar to survival in Fort Hood's rural landscape (0.396, 95% CI = 0.261-0.528). Both landscapes likely support self-sustaining populations based on reasonable assumptions for adult survival and number of nesting attempts. We suggest that some large urban preserves can provide breeding habitat of comparable quality to rural locations and recommend protecting large parcels (>100 ha) of breeding habitat with limited fragmentation and reducing the amount of wooded edge abutting open habitat to ensure nest survival regardless of their landscape context.     

Groundwater change forecasts widespread forest dieback across an extensive floodplain system

1. Regulation of rivers for human demands has led to extensive forest dieback on many floodplains. If these important ecosystems are to be maintained under future drier climates, we need accurate tools for predicting forest dieback. In the absence of spatially explicit flooding histories for many floodplains, changes in groundwater conditions may be a good indicator of water availability and, therefore, an important environmental indicator. 2. Eucalyptus camaldulensis forests of Australia are an acute example of forest dieback, with 70% of the Victorian Murray River floodplain dying back. We quantified the relationship between forest dieback and ground water across this extensive floodplain (c. 100 000 ha of forest over 1500 km of river length). 3. A combination of extensive ground surveys, remotely sensed data and modelling methods was used to predict forest dieback at the time of the survey and in the past. This approach provides a valuable tool for accurately monitoring forest condition over large spatial scales. Forest dieback was estimated to have increased from 45 to 70% of the floodplain between 1990 and 2006. 4. Accurate groundwater data (depth and salinity) over a 20‐year period were obtained for 289 bores and summarised using nonlinear regression. Groundwater depth and salinity were strong predictors of stand condition. This suggests that changes in groundwater conditions could be used to signal areas vulnerable to forest dieback and prioritise the limited water available for managed flooding. 5. In the upper Murray, where ground water is predominantly fresh (<15 mS cm^?2), dieback increased with increasing groundwater depth. In contrast, the condition of stands in the lower Murray improved with increases in groundwater depth due its high salinity (>30 mS cm^?2). These regional differences in response of the same tree species to groundwater conditions show that our understanding of the drivers of forest dieback is best achieved at spatial and temporal scales representative of the problem.     

Effects of wildfire and permafrost on soil organic matter and soil climate in interior Alaska

The influence of discontinuous permafrost on ground‐fuel storage, combustion losses, and postfire soil climates was examined after a wildfire near Delta Junction, AK in July 1999. At this site, we sampled soils from a four‐way site comparison of burning (burned and unburned) and permafrost (permafrost and nonpermafrost). Soil organic layers (which comprise ground‐fuel storage) were thicker in permafrost than nonpermafrost soils both in burned and unburned sites. While we expected fire severity to be greater in the drier site (without permafrost), combustion losses were not significantly different between the two burned sites. Overall, permafrost and burning had significant effects on physical soil variables. Most notably, unburned permafrost sites with the thickest organic mats consistently had the coldest temperatures and wettest mineral soil, while soils in the burned nonpermafrost sites were warmer and drier than the other soils. For every centimeter of organic mat thickness, temperature at 5 cm depth was about 0.5°C cooler during summer months. We propose that organic soil layers determine to a large extent the physical and thermal setting for variations in vegetation, decomposition, and carbon balance across these landscapes. In particular, the deep organic layers maintain the legacies of thermal and nutrient cycling governed by fire and revegetation. We further propose that the thermal influence of deep organic soil layers may be an underlying mechanism responsible for large regional patterns of burning and regrowth, detected in fractal analyses of burn frequency and area. Thus, fractal geometry can potentially be used to analyze changes in state of these fire prone systems.     

Distributions of lizard species across edges delimiting open‐forest and sand‐mined areas

Abstract The distributions of lizards across habitat edges delimiting open‐forest and regenerating sand‐mined areas as a function of distance from the edge were studied at Tomago, New South Wales, Australia. Pitfall‐trapping was used to survey lizards across the northern edges of four forest fragments, to determine if lizards displayed characteristic responses across the edge, and whether these could be explained by the different habitat conditions. At each site, 11 equally spaced drift fences (each parallel to the edge) were arranged in a transect running perpendicular to the edge, and stretching 50 m into each habitat type. Captures of Amphibolurus muricatus (Agamidae) decreased substantially across the edge from the mine‐path to the forest so that it was identified as a mine‐path specialist lizard species. Captures of two skink species decreased across the mine‐path before reaching the edge, and were not caught (Ctenotus taeniolatus) or were seldom caught (Ctenotus robustus) in the forest, so they were identified as mine‐path specialist, edge avoiding, lizard species. Captures of Lampropholis delicata (Scincidae) increased across edges into the forest, consistent with the expectation for a forest specialist. Regression analyses indicated the responses to edges of three lizard species (A. muricatus, C. robustus and C. taeniolatus) were negatively correlated with canopy cover (probably due to its influence on temperature, as captures of A. muricatus and C. robustus were also correlated positively with mean daily temperature). In addition, the response of C. robustus correlated negatively with a vegetation factor (dense, even vegetation in the first 50 cm from ground level). The response of L. delicata correlated positively with understorey height. We have identified edge response strategies for four species of lizards across edges delimiting temperate open‐forest and mined areas, and identified habitat and microclimate variables that may have driven these responses.     

Cultural and insecticidal control of Thrips tabaci on onions in the Sudan

Onion thrips (Thrips tabaci) is the major pest of onions in the Sudan. In the Gezira Scheme onions are normally transplanted between October and January when the thrips population is very low. Later, thrips commence to breed. Early transplanted onions were well established before infestations became severe and, without the need for insecticidal control, produced significantly higher yields. Onions transplanted later, when thrips began to multiply, produced lower yields. Depending on the duration and intensity of infestation three to five sprays applied at fortnightly intervals were required to control thrips on the late transplanted crop. The effect of spray frequency on the development and yield of onions was investigated and the response found to be solely due to the extent of thrips control achieved. The toxicant itself had no effect on growth. Although the leaves were unaffected by the various treatments, spraying when most thrips were present increased fresh and dry leaf weights, bulb weight and, in the Hudeiba cultivar, the proportion of flowering plants. With the late-transplanted crop, light infestations led to yield losses of at least 39% whilst severe thrips attacks reduced the crop by 57%.     

Molecular Weight Determination of Nucleic Acids by Gel Electrophoresis in Non-aqueous Solution

IN most areas of research concerned with the structure, function and synthesis of nucleic acids the measurement of molecular weights plays an inescapable part. There are many instances of problems hinging on a rather precise knowledge of the molecular weight of a nucleic acid; examples of particular current interest concern both animal and viral messengers, which are larger than can be accounted for by the total protein message that they encode and ribosomal-RNA, the molecular weight of which bears on the question of the stoichiometry of ribosomal components. Unfortunately the classical methods of molecular weight determination present great difficulties. The quantities of material required are frequently outside the range of feasibility. Moreover, the non-ideality in these highly charged molecules and polydispersity^1,2 resulting from contamination with minor cellular components, or commonly products of nuclease degradation (as well as the need to determine the partial specific volume), combine to make molecular weight measurement a major research undertaking. The remarkable spread of published values for widely studied RNA species reflects these problems.