Spindle disturbances in human-hamster hybrid (A(L) ) cells induced by the electrical component of the mobile communication frequency range signal

The production of spindle disturbances in a human–hamster hybrid (A_L) cell line by an electromagnetic field (EMF) with field strength of 90 V/m at a frequency of 900 MHz was studied in greater detail. The experimental setup presented allows investigating whether either the electrical (E) and/or the magnetic (H) field component of EMF can be associated with the effectiveness of the spindle‐disturbing potential. Therefore, both field components of a transversal electromagnetic field (TEM) wave have been separated during exposure of the biological system. This procedure should give more insight on understanding the underlying mechanisms of non‐thermal effects of EMF. A statistical comparison of the proportions of the fractions of ana‐ and telophases with spindle disturbances, obtained for five different exposure conditions with respect to unexposed controls (sham condition), showed that only cells exposed to the H‐field component of the EMF were not different from the control. Therefore, the results of the present study indicate that an exposure of cells to EMF at E‐field strengths of 45 and 90 V/m, as well as to the separated E component of the EMF, induces significant spindle disturbances in ana‐ and telophases of the cell cycle. Bioelectromagnetics 32:291–301, 2011. © 2010 Wiley‐Liss, Inc.     

General patterns of niche construction and the management of 'wild' plant and animal resources by small-scale pre-industrial societies

Niche construction efforts by small-scale human societies that involve 'wild' species of plants and animals are organized into a set of six general categories based on the shared characteristics of the target species and similar patterns of human management and manipulation: (i) general modification of vegetation communities, (ii) broadcast sowing of wild annuals, (iii) transplantation of perennial fruit-bearing species, (iv) in-place encouragement of economically important perennials, (v) transplantation and in-place encouragement of perennial root crops, and (vi) landscape modification to increase prey abundance in specific locations. Case study examples, mostly drawn from North America, are presented for each of the six general categories of human niche construction. These empirically documented categories of ecosystem engineering form the basis for a predictive model that outlines potential general principles and commonalities in how small-scale human societies worldwide have modified and manipulated their 'natural' landscapes throughout the Holocene.     

Predicted disappearance of coral-reef ramparts: a direct result of major ecological disturbances

Two coral cays near La Parguera, Puerto Rico, have large, exposed coral ramparts composed almost entirely of loose pieces of elkhorn coral Acropora palmata (88% of horizontal transects, 98% of vertical transects). The total volume of elkhorn coral in the ramparts of the two cays was estimated at 3600 and 12 800 m³. The present volume of living elkhorn coral on these two reefs was estimated at 7 and 14 m³ and previous volumes at 11 000 and 34 900 m³. White-band disease was found on 8.5% of living elkhorn colonies. Lang’s boring sponge Cliona langae covered 10.8% of the total transect area, overgrowing both dead and living corals. White-band disease and coral-reef bleaching have drastically reduced the populations of elkhorn coral, thus, skeletal coral materials to replenish the plate ramparts are severely reduced, disrupting the process of forming and maintaining these coral reef ramparts. We predict that the next series of major storms striking these prominent cay ramparts will remove them. These disappearances will represent a quick, obvious and permanent consequence of global disturbances. Loss of cay ramparts will modify the environments on and around Atlantic coral reefs. Ramparts may be similarly lost from Indo-Pacific reefs. The lack of any other indisputable definitive indicators of long-term, major disturbances on coral reefs makes the distinct loss of coral-reef ramparts an important physical sign.     

Cryptic barriers to dispersal within a lake allow genetic differentiation of Eurasian perch

Gene flow between coexisting or nearby populations normally prevents genetic divergence and local adaptation. Despite this, there are an increasing number of reports of sympatric sister taxa, indicating potential divergence and speciation in the face of gene flow. A large number of such reported cases involve lake-dwelling fish, which are expected to run into few physical barriers to dispersal within their aquatic habitat. However, such cases may not necessarily reflect sympatric speciation if cryptic dispersal barriers are common in lakes and other aquatic systems. In this study, we examined genetic differentiation in perch (Perca fluviatilis L.) from nine locations in a single, small lake (24 km(2)), using microsatellites. We detected significant genetic differentiation in all but two pairwise comparisons. These patterns were not consistent with divergence by distance or the existence of kin groups. Instead, they suggest that cryptic barriers to dispersal exist within the lake, allowing small-scale genetic divergence. Such an observation suggests that allopatric (or parapatric) divergence may be possible, even in small, apparently homogenous environments such as lakes. This has important consequences for how we currently view evidence from nature for sympatric speciation.     

Tree rings reveal a growth-decline event in A.D. 1875–1883 in a Tibetan plateau juniper forest

Forest declines under global warming have received much attention in studies of forest ecology, yet such events in periods before climate warming have been less studied because of shortage in documentation of past decline events. Here we used dendroecological techniques to identify forest decline events in the past five and a half centuries for a juniper forest near Lhasa of Tibet, China. Data of tree ring-widths were obtained from 42 relatively old trees after sample collection, measurement and crossdating. Radial growth of these trees was significantly and positively correlated with total precipitation in May and June. Persistent and severe growth reductions, lasting for at least eight years, were identified for each sample. We found that greater than 35% of the trees exhibited persistent and severe growth reductions in the interval A.D. 1875–1883, suggesting a growth decline event in the forest. This growth decline was the most severe event in the past five and half centuries. The weakened Indian monsoon in A.D. 1875–1878, which would result in extreme and prolonged droughts at spatially large scale in the monsoon zone, was most likely the driving force for the forest decline event discovered in this study. Our results suggested that future risk of juniper forest declines in central Tibetan plateau will be related to extreme droughts which could be amplified by warming. The study highlighted the importance of examining growth trajectory of individual trees in assessing forest health in a long perspective.     

Effectiveness of Ditch Blockage for Restoring Hydrologic and Soil Processes in Mountain Peatlands

Drained peatlands are a global concern due to alterations of the water and carbon cycle, loss of habitat, and increased fire frequency. However, methods for restoring drained sloping peatlands are limited and poorly tested. Therefore, we measured water table dynamics, CO₂ fluxes, and soil properties at four sloping fens that were restored (1–20 years post‐restoration) with the installation of small check dams in ditches that had drained the sites for a century. Restoration had a positive effect on water tables, increasing from approximately 45 cm below the surface to approximately 15 cm below the surface during the summers. Restoration also benefited CO₂ fluxes, as the mean net ecosystem exchange was greatest in the restored areas (?2.19 g CO₂ m^?2 hour^‐1) compared to the unrestored drained areas (?1.28 g CO₂ m^?2 hour^?1), while in reference areas it was ?1.74 g CO₂ m^?2 hour^?1. Drainage also caused significant changes to the peat soil including: 25% reduction in soil organic matter (lost between 1.4 to 3.6 kg/m²), increased bulk density, decreased porosity, and reduced saturated hydraulic conductivity. Restoration did not affect these parameters, even 20 years after restoration. This study suggests that although natural water table levels have been reestablished and the process of carbon sequestration improved, the physical properties of the most disturbed, near surface peat soils do not mimic reference conditions 20 years post‐restoration.     

Invaders' control on post-disturbance succession in coastal mangroves

Aims In recent years, coastal mangroves have been frequently affected by large disturbances (cyclones, hurricanes, flooding and tsunamis) and post-disturbance vegetation is often dominated by small stature mangrove, mangrove-associate and non-mangrove species potentially affecting ecosystem functioning. Knowledge on the processes of mangrove vegetation development and recovery (succession) following normal and large disturbances will benefit practitioners in designing robust ecosystem management/restoration plans. Here we propose a conceptual model of disturbance-mediated succession in mangroves.Methods Based on field observations and species' life history traits, we develop conceptual models of mangrove succession under normal disturbance regime and recently experienced increased frequency of large disturbances. We evaluate our conceptual models by conducting a scenario testing experiment.Important findings We suggest two predominant processes affecting mangrove succession after disturbance: propagule limitation due to damage of seed producing mature trees and dispersal barrier resulting from biological invasion associated with large disturbance. We argue that large disturbances affect mature trees more than the small-stature non-tree (shrubs, herbs and climbers) species creating a larger propagule shortage for mangrove tree species than non-tree species. Secondly, large disturbances facilitate invasion of free-floating aquatics, which may interfere with the flow-facilitated propagule dispersal and seedling establishment of mangrove species. In a scenario testing experiment, we have shown that similar levels of disturbance impact vegetation development and recovery differently depending on the presence or absence of invasive species. We conclude that since biological invasion is one of the major drivers of post-disturbance mangrove succession, the dimension of biological invasion should be included in prediction, management and restoration of mangrove forests.     

Postfire Soil N Cycling in Northern Conifer Forests Affected by Severe, Stand-Replacing Wildfires

Severe, stand-replacing fires affect large areas of northern temperate and boreal forests, potentially modifying ecosystem function for decades after their occurrence. Because these fires occur over large extents, and in areas where plant production is limited by nitrogen (N) availability, the effect of fire on N cycling may be important for long-term ecosystem productivity. In this article, we review what is known about postfire N cycling in northern temperate and boreal forests experiencing stand-replacing fires. We then build upon existing literature to identify the most important mechanisms that control postfire N availability in systems experiencing severe, stand-replacing fires compared with fires of lower severity. These mechanisms include changes in abiotic conditions caused by the opening of the canopy (for example, decreased LAI, increased solar radiation), changes in ground layer quantity and quality (for example, nutrient release, permafrost levels), and postfire plant and microbial adaptations affecting N fixation and N uptake (for example, serotiny, germination cues). Based on the available literature, these mechanisms appear to affect N inputs, internal N cycling, and N outputs in various ways, indicating that severe fire systems are variable across time and space as a result of complex interactions between postfire abiotic and biotic factors. Future experimental work should be focused on understanding these mechanisms and their variability across the landscape.     

A simulation framework for modeling anthropogenic disturbances in habitat networks

Anthropogenic disturbances, like roads, increase the landscape fragmentation and affect wildlife migration and biodiversity. Such disturbances often prevent migration of wildlife due to increased barriers and mortality effects.

The aim of our simulation based approach is to assess the landscape permeability considering anthropogenic disturbances. The developed framework SimapD imposes an abstract view of a habitat network, based on an undirected graph. The simulation is done by an individual-oriented approach, where individuals explore the idealized network. Based on the information gained during the simulation, an overall network permeability index is calculated, which can be used to compare different scenarios of landscape development. Disturbances are represented by sub-models, from which appropriate resistance and mortality rates can be deduced. In this paper this is demonstrated by the construction of a fuzzy road kill model for the federal state of Baden-Wuerttemberg, Germany. The utilization of the network permeability index and a comparison to other fragmentation measures is shown by an exemplary application.