Environmental Constraints on the Mechanics of Crawling and Burrowing Using Hydrostatic Skeletons

Mechanics, kinematics, and energetics of crawling and burrowing by limbless organisms using hydrostatic skeletons depend on the medium and mode in which the organism is moving. Whether the animal is moving over or through a solid has long been considered important enough to distinguish crawling and burrowing as different terms, and in fact the mechanics are very different. Crawlers use mechanisms to increase friction to generate thrust while reducing resistive friction. Burrowers in elastic muds extend their burrows by fracture, whereas sands are fluidized by burrowers much larger than grain sizes and smaller burrowers displace individual grains. Gravitational forces depend on how closely the density of the organism matches that of its fluid surroundings, therefore frictional forces depend on whether the organism is moving through air or water and fluidization on whether sands are saturated or unsaturated

The effect of animal movement on line transect estimates of abundance

This work was supported by the University of St Andrews (http://www.st-andrews.ac.uk/; RG, STB, LT) and by a summer scholarship and PhD grant from The Carnegie Trust for the Universities of Scotland (http://www.carnegie-trust.org/) to RG.Line transect sampling is a distance sampling method for estimating the abundance of wild animal populations. One key assumption of this method is that all animals are detected at their initial location. Animal movement independent of the transect and observer can thus cause substantial bias. We present an analytic expression for this bias when detection within the transect is certain (strip transect sampling) and use simulation to quantify bias when detection falls off with distance from the line (line transect sampling). We also explore the non-linear relationship between bias, detection, and animal movement by varying detectability and movement type. We consider animals that move in randomly orientated straight lines, which provides an upper bound on bias, and animals that are constrained to a home range of random radius. We find that bias is reduced when animal movement is constrained, and bias is considerably smaller in line transect sampling than strip transect sampling provided that mean animal speed is less than observer speed. By contrast, when mean animal speed exceeds observer speed the bias in line transect sampling becomes comparable with, and may exceed, that of strip transect sampling. Bias from independent animal movement is reduced by the observer searching further perpendicular to the transect, searching a shorter distance ahead and by ignoring animals that may overtake the observer from behind. However, when animals move in response to the observer, the standard practice of searching further ahead should continue as the bias from responsive movement is often greater than that from independent movement.Publisher PDFPeer reviewe

Terraced Subtropical Farming: Sustainable Strategies for Soil Conservation

47 páginas.- 5 tablas.- 8 figuras.- 208 referenciasTerracing is a soil conservation strategy applied worldwide to prevent erosion and runoff on sloping lands. Orchard terraces can considerably reduce soil loss due to water erosion if they are well planned, correctly constructed and properly maintained. Terraces have to be combined with additional soil conservation practices, of which the most important is the maintenance of a soil cover, especially during the rainy period. On the coastal strip of the provinces of Granada and Malaga (south-eastern Spain), irrigated subtropical fruit species have been introduced and cultivated on terraces with a considerable importance as the only European producer region. The subtropical farming in this zone also has strong socio-economic impact. In the present chapter, land-use changes were analysed in a selected representative watershed over 29 years. According to the findings, formerly, 97.5% of the watershed was devoted to traditional Mediterranean crops; however, after this period, due to abandonment, this area was reduced to 17.6% and increased in subtropical fruit crops (26.6%), shrubland (29.8%) and abandoned cropland (24.6%). The main driving force in land-use change has been intensive irrigation on terraces planted with subtropical crops, which are economically more profitable than traditional rainfed crops, almond and olive, which have been replaced or abandoned. The intensification of subtropical farming in terraces provokes environmental effects, especially those regarding soil and water resources, which need to be minimized. The results support the recommendation of using plant covers on the taluses of subtropical crop terraces in order to control soil erosion and improve the soil quality in the taluses of orchard terraces. In this sense, compared to bare soil, thyme and native spontaneous vegetation plant covers reduced the runoff with 94% and 93% and declined erosion with 71% and 79%, respectively. That is to avoid the collapse of the structure and make more feasible the subtropical fruit cultivation in the study area. Thus, it is possible to mitigate the impact of subtropical farming on terraces by adopting sustainable measures for soil and water conservation.Part of this publication was sponsored by the research project, ‘Impact of deficit irrigation on productivity of subtropical fruit crops: tools for sustainable water stress management’ (PP.AVA.AVA201601.8), and cofinanced by the European Regional Development Fund (ERDF) within the Operational Programme Andalusia 2014–2020 ‘Andalucía is moving with Europe’.Peer reviewe