Influence of tidal regime,diurnal phase,habitat and season on feeding of an intertidal crab

The relationship between diet and feeding activity of intertidal crabs, and environmental cycles (tidal, daily and seasonal), habitat and level of the intertidal zone (high/low) was studied using Neohelice granulata (Brachyura, Varunidae) as a model. This is a semi‐terrestrial burrowing crab occupying different habitats in the Southwestern Atlantic coasts and estuaries from bare low intertidal mudflats to high intertidal salt marshes, and from fine, organic matter rich sediment to very coarse sediment with low content of organic matter. The study was carried out in two contrasting habitats of three sites with diverse sets of physical and biological conditions. Diet and feeding of adult N. granulata were indirectly studied through the proportion of food items and the presence/absence of food in crab stomachs, respectively. This species has a dual mode of feeding: predominantly herbivorous (live plants or plant litter in salt marshes) or deposit feeder (superficial sediment and detritus in mudflats), but the quantity and quality of ingested food varies among habitats and sites. A trend to omnivory (including algae and conspecifics) was detected in relation to low quality of resources. Feeding activity modulated by a complex interaction of factors varied according to spatial and/or temporal changes in some natural cycles. Males and non‐ovigerous females fed preferably after dark and during submersion periods, but also after emersion periods if mudflat sediment remained wet; salt marsh crab feeding is somewhat independent of light and tidal cycles. Ovigerous females almost never fed. Both diet and feeding activity of this crab seem to be flexible traits adapted to different combinations of physical and biological factors.     

Iberian Plio‐Pleistocene biochronology: micromammalian evidence for MNs and ELMAs calibration in southwestern Europe

A multivariate biochronological analysis of the Plio‐Pleistocene Iberian rodent fossil record is presented. Among more than 300 fossil sites, 49 sites have been selected. The ordination of the fossil sites selected from the Iberian Peninsula has been achieved by the appearance event ordination method. After calibration of this ordination with geochronological dates at some of the localities, numerical dates are proposed for all the localities studied. Hence, mammal fossil sites non‐datable by other means (palaeomagnetism, radiometric dating, etc.) have been dated with a relatively high degree of confidence. Final results allow dating of boundaries between the Plio‐Pleistocene European Land Mammal Ages (ELMAS) or the Mammal Neogene (MN) units. These boundaries agree with previous studies using magnetostratigraphical calibration of these scales. Copyright © 2004 John Wiley & Sons, Ltd.     

Estimation of tree water stress from stem and soil water monitoring with time‐domain reflectometry in two small forested basins in Spain

Soil‐tree water relationships were studied using time domain reflectometry (TDR) in two small forested basins in Spain. The stem water content of two Mediterranean Quercus species (Quercus pyrenaica and Quercus rotundifolia) was measured using previously constructed species‐specific equations. To monitor soil moisture, a TDR station network was used in both cases. Sixteen Q. pyrenaica and six Q. rotundifolia individuals were selected to install two TDR probes in their trunks (at 20 and 120 cm above the ground) to monitor stem water content. Stem and soil water contents were measured fortnightly. The stem water content of both species showed a similar temporal trend for the period studied. A spring maximum (0·654 cm³ cm^?3 for Q. pyrenaica and 0·568 cm³ cm^?3 for Q. rotundifolia) was found to be associated with high transpiration and no soil moisture deficit, and a late‐summer minimum (0·520 cm³ cm^?3 for Q. pyrenaica and 0·426 cm³ cm^?3 for Q. rotundifolia) was associated with the end of the dry season. This drop in stem water content occurs when the available water in the soil decreases. This seasonal difference presumably reflects water withdrawn from stem storage to support the transpirational demands of the tree. Since plant water stress results in reduced stem water content and since this drop can be measured by TDR, it may be concluded that this technology offers a suitable tool for detecting plant water stress. Copyright © 2007 John Wiley & Sons, Ltd.     

Implausibility of Hydrostatic Funnels Constituting the Sun’s Upper Transition Region

Over the past thirty years, two bodies of literature have developed in parallel presenting mutually exclusive views of the Sun’s upper transition region. One model holds that the Sun’s upper-transition-region plasmas are confined primarily in hydrostatic funnels with a substantial backheating component. The other model holds that discrete structures, which are effectively isolated from the corona, predominate in the Sun’s upper transition region. Purveyors of the latter position have recently begun to present near-resolved observations of discrete structures. The funnel scenario, in contrast, has only been addressed by modeling unresolved upper transition region emission. To address this paradox we have constructed hydrostatic funnel models and tested them against a wider set of solar observations than previously performed. We reproduce the results of the previous analyses, yet find that the hydrostatic funnels are unable to self-consistently match the wider set of observations against which we test the models. We show that it is not possible for a class of funnels having peak temperatures in the transition region or in the corona to match the observations. We conclude that it is implausible that a class of hydrostatic funnels constitutes the dominant emitting component of the Sun’s upper-transition-region plasmas as has been suggested.     

Integration of LiDAR data for the assessment of activity in diachronic landslides: a case study in the Betic Cordillera (Spain)

In the procedures to minimize diachronic landslides, data on their temporal evolution and destructive capacities are necessary. For that purpose, remote-detection techniques proved to be highly useful for quantifying the ongoing change in the relief, as well as in comparisons between digital terrain models achieved by Light Detection and Ranging. The methodology presented in this paper includes the supervised merging and comparison of sequential scans, acquired within nearly annual intervals from an irregular terrain, which improves the quality of the results highlighting ground changes. This approach is based on the processing of digital terrain models from point clouds acquired by Terrestrial Laser Scanning to quantify and interpret the landslide displacements. In parallel, it is supported by Global Navigation Satellite Systems, the use of artificial targets and a refined data processing to minimize the uncertainty and improve the precision of the results. This is applied to a large translational slide affecting phyllite rocks in a IV-V degree of weathering settled on the southern slope of Sierra Nevada (south-eastern Spain). During the monitoring period (2008–2010), the slide remained inactive until 2009, followed by a reactivation with displacements in the range ?1.80 to 1.20 m along the period 2009–2010, where negative values are downwards from the reference model (2009). The accumulated relative standard deviation between data sets was on the order of 7.5 cm, whereas the threshold to determine a terrain displacement (also avoiding changes due to erosion-accumulation processes) was of 10 cm. When applying this methodology to Airborne Laser Scanning datasets for the years 2008 and 2010, covering zones hidden to the line of sight of the terrestrial technique, a reactivation with similar deformation pattern was found useful to validate the findings, although the detail of changes and quantitative results did not match exactly due to the different accuracy and resolution of both techniques. The reactivation of the slide coincided with a period of intense rains, pointing to this as the triggering factor, with a precipitation threshold of roughly 1000 mm in a period of 4 months, only reached on one occasion throughout in the historical record.     

Teaching Numerical Groundwater Flow Modeling with Spreadsheets

Mathematical Geosciences - The use of spreadsheets for numerical groundwater flow modeling is not a novelty; however, its potential in the classroom has not been emphasized enough. This Teachers...     

Phenology ofMedicago minimaandErodium cicutariumin semi-arid Argentina

The phenology ofMedicago minimavar.minimaandErodium cicutariumwas studied at two different field sites in the Calden District (approx. 10 million ha), a temperate semi-arid phytogeographical region in central Argentina. One site had been protected from wild and domestic herbivores for the 6 previous years. The other adjacent site had been exposed to continuous grazing by cattle for several decades. A phenological key was made for each species in 1988, and this key was improved during the 1989 growing season when phenological observations were made every 1–3 weeks.The growth cycle ofM. minimaandE. cicutariumwas similar at the two studied sites. Initiation of the cycle occurred in autumn and appeared to be associated with soil water availability. Phenological patterns were very dynamic at the reproductive stage in both species. This stage started earlier and was faster inE. cicutariumthan inM. minima. The end of the growing season occurred during late spring, concomitant with high maximum air temperatures. Our results suggest that these species hasten their development when air temperature increases and soil water availability decreases. This could be an important strategy in these species which allows them to persist as seeds, and produce a new generation under favourable environmental conditions.