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[en] Current methods for isolating radiation-sensitive mammalian cell mutants are extremely laborious and time consuming. The authors have developed a fundamentally new procedure combining the culture of clonally-derived cell aggregates (spheroids) with viable flow cytometric analysis and sorting. Essentially, each spheroid serves as a three-dimensional colony which can be individually assayed and manipulated. This method has several potential advantages over current procedures: rapid isolation of large numbers of individual clones; automated sensitivity analysis; rapid separation of sensitive clones; and recovery of surviving cells directly from the tested spheroids. This method also eliminates slow-growth clones which are not actually sensitive. The flow method can potentially screen 107 clones in one day, a 1,000-fold improvement. Several of the individual techniques critical to this procedure have been demonstrated: generation of >108 clonar spheroids; flow sorting of spheroids into a uniformly-sized population; continued uniform growth after sorting; decreased spheroid growth after radiation exposure; and recovery of viable cells from irradiated spheroids. Using radiation sensitive and resistant cells, the authors are verifying the seperation of rare sensitive clones from a predominantly resistant background
[en] Small mammals were live-trapped in burned and unburned segments of a bitterbrush-cheatgrass community during the years 1974-1979. Results indicate that the shrub-dominated unburned area supports about three times as many small mammals as the cheatgrass-dominated burned area. Species composition was similar in both areas with the exception of one ground squirrel (Spermophilus townsendii) captured on the unburned area. Other species caught were the Great Basin pocket mouse (Perognathus parvus), deer mouse (Peromyscus maniculatus), northern grasshopper mouse (Onychomys leucogaster), and the western harvest mouse (Reithrodontomys megalotis)
[en] Highlights: • We evaluated the impacts of accomplished urban structure shift on connectivity. • We developed an approach combining counterfactual analysis with landscape graphs. • What Nanjing might look like if it was a monocentric structure was revealed. • The polycentric structure facilitates bird's dispersal, but not for forest mammals. • Urban structure shift might not necessarily cause connectivity decline. Many studies have been conducted to evaluate the effects of different urban structures on landscape connectivity, and most of them rely on the comparison approach or ex-ante scenario analysis. However, we still lack an ex-post method to capture the consequences of accomplished urban structure shift (from monocentric to polycentric), which is guided by the land use planning. To fill this gap, we develop an ex-post evaluation approach which integrates counterfactual analysis and landscape graphs. Counterfactual analysis is combined with cellular automata simulation model, to uncover what the city might look like, if it had continued to expand in a monocentric structure; and the landscape graphs enable us to reveal the possible landscape connectivity in actual and counterfactual scenarios. We select Nanjing city as the study area and 4 target species, to delve into the varying impacts of the urban structure shift on different taxonomic groups. Our case study demonstrates that: (1) the impact of urban structure shift is more relevant to the long disperser; (2) the actual landscape (polycentric) would facilitate the bird's dispersal, while (3) forest mammals have higher connectivity in the counterfactual scenario (monocentric), and the possible reasons are discussed. Finally, we demonstrate that the urban structure shift might not necessarily cause the connectivity decline, on condition that the key connectivity providers are identified by integrating ecological network analysis into the land use planning, and well preserved in the shift.
[en] The objective of this project is to provide DOE with improved methods to assess risks from contaminants to wildlife populations. The current approach for wildlife risk assessment consists of comparison of contaminant exposure estimates for individual animals to literature-derived toxicity test endpoints. These test endpoints are assumed to estimate thresholds for population-level effects. Moreover, species sensitivities to contaminants is one of several criteria to be considered when selecting assessment endpoints (EPA 1997 and 1998), yet data on the sensitivities of many birds and mammals are lacking. The uncertainties associated with this approach are considerable. First, because toxicity data are not available for most potential wildlife endpoint species, extrapolation of toxicity data from test species to the species of interest is required. There is no consensus on the most appropriate extrapolation method. Second, toxicity data are represented as statistical measures (e.g., NOAEL s or LOAELs) that provide no information on the nature or magnitude of effects. The level of effect is an artifact of the replication and dosing regime employed, and does not indicate how effects might increase with increasing exposure. Consequently, slight exceedance of a LOAEL is not distinguished from greatly exceeding it. Third, the relationship of toxic effects on individuals to effects on populations is poorly estimated by existing methods. It is assumed that if the exposure of individuals exceeds levels associated with impaired reproduction, then population level effects are likely. Uncertainty associated with this assumption is large because depending on the reproductive strategy of a given species, comparable levels of reproductive impairment may result in dramatically different population-level responses. This project included several tasks to address these problems: (1) investigation of the validity of the current allometric scaling approach for interspecies extrapolation an d development of new scaling models; (2) development of dose-response models for toxicity data presented in the literature; and (3) development of matrix-based population models that were coupled with dose-response models to provide realistic estimation of population-level effects for individual responses
[en] Understanding the patterns and processes involved in intraspecific lineages diversification in time and space is the aim of phylogeography. The comparison of those phylogeographic patterns among co-distributed species shows insights of a community history. Here I review the concepts and methodologies of comparative phylogeography, an active research field that has heterogeneous analytical methods. In order to present a framework for phylogeography in the neotropics, I comment the general phylogeographic patterns of the birds from this region. this review is based on more than 100 studies conducted during the last 25 years and indicate that despite different co-distributed species seem to share some points in their phylogeographic pattern they have idiosyncratic aspects, indicating an unique history for each one.
[en] For the avifauna, environmental conditions in northern latitudes obviously have been changing to the better, primarily in the northern hemisphere, so that bird species have been expanding towards the northern face of the earth. This has been observed by ornitologists who came to realize that more species than before remained for longer periods in their northern breeding grounds, with reproduction rates increasing and mortality during the winter seasons declining. Most of the trends observed are significant, although there also are some species whose number in traditional living environments is declining. The positive trends are attributed to the recent global warming. Should this process continue, it is expected to cause considerable shifts in the bird population, from subtropical regions up to the polar regions. At our latitudes, the populations of non-migratory birds are expected to grow, while those of birds migrating over long distances should decline. This might reduce the diversity in species over a given period, but experts expect that this will be followed by growing and lasting diversity at our latitudes. (orig./CB)
[de]Fuer die Avifauna haben sich in hoeheren geographischen Breiten, vor allem der Nordhemisphaere, Umweltverhaeltnisse derart verbessert, dass sie die Ausbreitung vieler Vogelarten nach Norden ermoeglichen, vielen Arten laengere Anwesenheit im Brutgebiet erlauben und den Zugumfang reduzieren, und wiederum bei vielen Arten, die Fortpflanzung beguenstigen sowie die Wintermortalitaet reduzieren. Diese Trends sind grossenteils signifikant, obwohl auch viele Arten, vor allem Langstreckenzieher und Offenlandbrueter, starke Bestandsrueckgaenge zeigen. Die positiven Trends sind offenbar die Folge der Klimaerwaermung. Sollte sich diese globale Klimaerwaermung fortsetzen, so ist mit starken Umschichtungen der Avifauna in weiten Bereichen von den Subtropen bis in polare Regionen zu rechnen. In unseren mittleren Breiten ist die Zunahme von Standvoegeln und die Abnahme vor allem von Langstreckenziehern zu erwarten. Mittelfristig ist dabei ein Rueckgang der Artenvielfalt wahrscheinlich; langfristig duerfte die Formenvielfalt eher wieder zunehmen. (orig.)