Toward a Locational Definition of State Systems of Settlement

Recent information indicates that urbanism is only one of several options providing the means to consolidate, concentrate, and organize the coercive power necessary for state formation. Central Place Theory (CPT) is a model of urban settlement frequently chosen to approach the broader problem of state formation, but its universal applicability is in doubt. In this paper, spatial and functional definitions of urbanism and other concepts (functional center, functional lattice) related to state systems of settlement are derived using locational analytic approaches other than CPT, and their implications are discussed. A typology of state-level settlements is introduced. Advantages of a locational approach to the investigation of settlement systems are suggested.     

Sources of natural resistance to plant viruses: status and prospects

Globally, virus diseases are common in agricultural crops and have a major agronomic impact. They are countered through the deployment of genetic resistance against the virus, or through the use of a range of farming practices based upon the propagation of virus-free plant material and the exclusion of the virus vectors from the growing crop. We review here the current status of our knowledge of natural virus resistance genes, and consider the future prospects for the deployment of these genes against virus infection.     

Semiempirical modeling of abiotic and biotic factors controlling ecosystem respiration across eddy covariance sites

In this study we examined ecosystem respiration (R_ECO) data from 104 sites belonging to FLUXNET, the global network of eddy covariance flux measurements. The goal was to identify the main factors involved in the variability of R_ECO: temporally and between sites as affected by climate, vegetation structure and plant functional type (PFT) (evergreen needleleaf, grasslands, etc.). We demonstrated that a model using only climate drivers as predictors of R_ECO failed to describe part of the temporal variability in the data and that the dependency on gross primary production (GPP) needed to be included as an additional driver of R_ECO. The maximum seasonal leaf area index (LAI_MAX) had an additional effect that explained the spatial variability of reference respiration (the respiration at reference temperature T_ref=15 °C, without stimulation introduced by photosynthetic activity and without water limitations), with a statistically significant linear relationship (r²=0.52, P<0.001, n=104) even within each PFT. Besides LAI_MAX, we found that reference respiration may be explained partially by total soil carbon content (SoilC). For undisturbed temperate and boreal forests a negative control of total nitrogen deposition (N_depo) on reference respiration was also identified. We developed a new semiempirical model incorporating abiotic factors (climate), recent productivity (daily GPP), general site productivity and canopy structure (LAI_MAX) which performed well in predicting the spatio‐temporal variability of R_ECO, explaining >70% of the variance for most vegetation types. Exceptions include tropical and Mediterranean broadleaf forests and deciduous broadleaf forests. Part of the variability in respiration that could not be described by our model may be attributed to a series of factors, including phenology in deciduous broadleaf forests and management practices in grasslands and croplands.     

Migration of wild and captive‐bred Little Bustards Tetrax tetrax: releasing birds from Spain threatens attempts to conserve declining French populations

Populations of the Little Bustard Tetrax tetrax in the farmlands of Europe have declined greatly over the last century. In Western Europe, France now holds the only remaining migratory population, which currently numbers fewer than 300 displaying males. However, the movements of these birds are virtually unknown, in spite of the important implications of this information for the conservation of this species. We identified migratory movements and overwintering areas of French migratory populations, using wild individuals fitted with satellite or radio‐transmitters. Little Bustards completed their migration journey over a relatively short time period (2–5 days), with nocturnal migration flights of 400–600 km per night. All birds overwintered in Iberia. In addition, we tested the consequences of captive rearing on migratory movements. French wild adults and French captive‐bred juveniles behaved similarly with regard to migration, suggesting that hand‐raising does not alter migratory movements. However, birds originating from eggs collected in Spain and reared in western France did not migrate, suggesting a genetic component to migratory behaviour. These results therefore suggest that a conservation strategy involving the release in France of birds hatched from eggs collected in Spain may imperil the expression of migratory movements of the French population. More generally, to maintain the integrity of native populations, the introduced individuals should mimic their migratory movements and behaviour.     

Effects of azadirachtin on oogenesis in Aedes aegypti

ABSTRACT. . Azadirachtin in blood fed to adult female Aedes aegypti through an artificial membrane does not cause feeding inhibition over a wide dose range (0–200 ng/female), and high doses of ingested azadirachtin fail to inhibit or delay oviposition. However, significant, transient retardation of oocyte growth is observed for up to 72 h after feeding. Immature oocytes are observed in 86% of azadirachtin-fed females decapitated 10 h after a blood meal, whereas 96% of decapitated control females contain maturing oocytes. This suggests that azadirachtin delays the release of one or more factors from the head that regulate oogenesis. We propose that adult females overcome the effect of azadirachtin by rapid metabolism rather than by excretion of the compound, since by 2 h after a blood meal, only 0.1% of ingested azadirachtin was recovered from excreta and 5% recovered from the body.     

Histological structure of the cancellous bone layer in Bothriolepis canadensis (Antiarchi, Placodermi)

The Placodermi are extinct basal gnathostomes which had extensive dermal and perichondral bone, but which lacked the endochondral bone which characterizes the more derived bony fishes. Thin sections of bone from a specimen of the antiarch placoderm Bothriolepis canadensis, from the Escuminac Formation (Frasnian, Upper Devonian), Québec, Canada, reveal that part of the cancellous layer in its dermal and endoskeletal bone formed from perichondral bone trabeculae growing around cartilage spheres. The resultant structure mimics that of osteichthyan endochondral bone. The layout and dimensions of this polygonal mosaic patterning of the bone trabeculae and flattened cartilage spheres resemble those of the prismatic layers of calcified cartilage in chondrichthyans. If the lack of endoskeletal bone in chondrichthyans is a derived character, then the structure identified in B. canadensis could represent a 'template' for the formation of prismatic calcified cartilage in the absence of bone.