Rapoport's rule: time for an epitaph?

The christening of the decline in the geographic extent of species from high to low latitudes as Rapoport's rule was a bold step. Allowing for a variety of potentially significant complications to the interpretation of empirical studies, evidence that this is indeed a general pattern is, at the very least, equivocal. The present taxonomically and regionally biased set of studies lend support to the recent suggestion that the pattern is a local phenomenon being expressed primarily in the Palaearctic and Nearctic above latitudes of 40-50°N. Five hypotheses have been proposed to explain the generation of latitudinal declines in range size where they do occur, with the past heavy emphasis on a climatic variability mechanism being eroded. Evidence is accruing in support of more than one such mechanism. Whatever the generality of the `rule', it has undoubtedly served to stimulate a consideration of the role of spatial variation in range sizes in several areas of research in ecology and evolution.     

Are potential natural vegetation maps a meaningful alternative to neutral landscape models?

Abstract. In this paper, we present a short overview of neutral landscape models traditionally adopted in the landscape ecological literature to differentiate landscape patterns that are the result of simple random processes from patterns that are generated from more complex ecological processes. Then, we present another family of models based on Tuxen’ s definition of potential natural vegetation that play an important role, especially in Europe, for landscape planning and management. While neutral landscape models by their very nature do not take into account vegetation dynamics, nor abiotic constraints to vegetation distribution, the concept of potential natural vegetation includes the effects of vegetation dynamics in a spatially explicit manner. Therefore, we believe that distribution maps of potential natural vegetation may represent an ecological meaningful alternative to neutral landscape models for evaluating the effects of landscape structure on ecological processes.     

The nature of natural: defining natural character for the New?Zealand context

New?Zealand has a long-standing statutory policy goal to preserve the natural character of the coastal environment and various freshwater environments and their margins. In the absence of an authoritative definition, it has not been possible to develop a method to measure natural character and its change, nor the outcomes of the long-standing national policy goal. Here we develop a definition of natural character that is relevant and useful in the New?Zealand environmental, cultural and legal/policy context. Literature-derived interpretations of natural character and equivalent concepts are evaluated as to their potential suitability for developing a biophysical definition of natural character. Using a set of carefully designed criteria a subset of interpretations are condensed into a definition of natural character. The application of this definition is qualified following consideration of the literature addressing human perception and experiences of natural character. Appropriate reference conditions and baselines for evaluating natural character in different contexts are discussed.     

The posttranslational concept of protein folding: how valid is it?

Two concepts of protein folding are known. One of them, the cotranslational concept, states that a protein folds during the synthesis of the polypeptide chain on the ribosome. According to the other, the posttranslational concept, the protein starts to fold just after the synthesis of its polypeptide chain. This article attempts to show that the posttranslational concept is hardly suited to solve the problem of protein folding. In our opinion, polypeptide chains cannot be represented as random coils. They are stiff chain-like macromolecules rather than flexible ones: the single bond rotational barriers of a polypeptide substantially exceed the accepted standard values; even in strong denaturing conditions, a protein possesses a considerable amount of residual folded structures. We believe that the popular "hierarchical" models for the protein folding mechanism are not realistic because the formation of secondary and tertiary structures of proteins occurs simultaneously and cooperatively. The time for the elongation of a polypeptide chain by one amino acid residue during biosynthesis exceeds considerably the time of the formation of alpha-helices and beta-sheets in proteins as well as the time supposed for the spatial structure formation of a native protein during renaturation. Thus, we believe that the mechanism of protein folding in vivo cannot be clarified by denaturation-renaturation experiments. In our opinion, the phenomenon of protein renaturation is no more than the restoration of native protein conformation (which initially forms cotranslationally) disrupted during denaturation, and thus denaturation-renaturation experiments cannot serve as a model to clarify the mechanism of protein folding.     

The role of outcrops in the diversity of Patagonian vegetation: Relicts of glacial palaeofloras?

Outcrops around the world enhance biodiversity as they provide heterogeneous environments and varied habitats for species with different requirements than those living in the surroundings, and in this way they increase alpha and beta diversity. We studied the floristic composition of the vegetation of rock outcrops in northwestern Patagonia, Argentina, and compared them to the surrounding matrix of shrubland and steppe. For this we sampled 50 outcrops and 50 matrix plots close to them, identified all the species present, and analyzed their floristic composition with Detrended Correspondence Analysis (DCA). We also analyzed the floras of the north and south faces of the outcrops. The resulting ordinations were related to geographic gradients of the region. The proportions of alien to native species, different life forms, and phylogenetic groups of the outcrop floras were compared to the matrix with G-tests. Our results showed similar dominant families, life form proportions and percentage of alien species in the outcrops and the surrounding matrix. However, species composition of the outcrops was markedly different. North Patagonian outcrops present several taxa not found in the matrix, especially in their southern, less insolated walls. The previously recorded distribution of most of these exclusive species is found in colder areas further south. Thus, we hypothesize that outcrops could be acting as relicts of cold-adapted glacial paleofloras that were probably more extended during glacial times and retreated south after the last glacial maximum.     

The liver: an organ of the immune system?

The liver stands in a unique position between the gastrointestinal tract and systemic venous system. Its constant exposure to food antigens, bacterial products and potential pathogens through the mesenteric circulation, requires the liver to maintain tolerogenic capabilities while preserving the means to mount effective immune responses. The liver has the unique ability amongst solid organs, to activate na?ve CD8+ T lymphocytes in an antigen-specific manner. However, this activation can be inefficient and lead to apoptosis. This phenomenon is believed to be involved in both, the development of oral tolerance and the induction of tolerance in liver allografts. The liver is the target of both autoimmune diseases and of chronic viral infections and its unique tolerogenic environment has frequently been suggested as a factor in the development of these diseases. A better grasp of the liver's unique immunological processes would lead to a better understanding of immune tolerance mechanisms and their role in the development of autoimmune diseases and chronic viral infections.     

Are patients with potential celiac disease really potential? The answer of metabonomics

Celiac disease (CD) is an autoimmune disorder caused by a permanent sensitivity to gluten in genetically susceptible individuals. Accurate diagnosis of CD at an early stage and its treatment with a gluten-free diet (GFD) are important for optimum treatment and prognosis. Recently, by employing a noninvasive metabonomic approach, we have shown that CD has a well-defined metabonomic signature. Here we address potential CD patients, defined as subjects who do not have, and have never had, a jejunal biopsy consistent with clear CD, and yet have immunological abnormalities similar to those found in celiac patients. Sixty-one overt CD patients at diagnosis, 29 patients with potential CD, and 51 control subjects were examined by (1)H NMR of their serum and urine: out of 29 potential CD patients, 24 were classified as CD and 5 as control subjects. Potential CD largely shares the metabonomic signature of overt CD. Most metabolites found to be significantly different between control and CD subjects were also altered in potential CD. Our results demonstrate that metabolic alterations may precede the development of small intestinal villous atrophy and provide a further rationale for early institution of GFD in patients with potential CD, as recently suggested by prospective clinical studies.     

The 70th anniversary of E.N. Pavlovsky’s concept of natural nidality of human diseases

The concept of the natural nidality of human diseases has significantly changed during the last 70 years, but its essence is preserved. Many “new” infections with natural foci were discovered and their geographical distribution was investigated in detail, and the classification of natural foci was developed. It has been established that epidemic features of transmissible infections depend mainly on types of parasitism of insect, tick and mite vectors.     

The mosaic diversity of field layer vegetation in the natural and exploited forests of Białowieża

The main focus of the study was to find out whether and how the forestry management in the Biaowiea Forest has influenced the mosaic diversity of field layer vegetation and habitat heterogeneity in the temperate hard wood forest (Tilio-Carpinetum). Five belt-transects represent natural and semi-natural old-growths in Biaowiea National Park (BNP), the commercial forest (CF), and secondary stands in the CF. Along the transects, distinct patches of field layer vegetation were identified and delimited, and their species composition was assessed. Along central lines of the transects the environmental data was collected from sample points established at regular intervals: soil pH and the distances to the 4 closest trees, their species, and dbh (diameter at the breast height=135 cm). The group of patches (on average 50 per transect) was subjected to the dichotomous classification in order to identify a number of characteristic types of microphytocoenoses – synusiae. Beta-diversity of the vegetation was expressed with the Simpson diversity index calculated on the basis of areas occupied by synusiae. The most structurally diversified were the transects representing natural old-growths in the BNP. A calculation of similarity coefficients between the transects on the basis of their mosaic composition displayed sharper differences between old-growth and secondary communities in summer than those found in spring. Forestry management has seriously modified the tree species composition in two studied stands, through planting oak or initiating succession. This resulted, both in plantation and pioneer stand, in loss of the main components of natural old-growths: hornbeam (Carpinus betulus), Norway spruce (Picea abies), lime (Tilia cordata) and maple (Acer platanoides). Significantly a wider range of soil pH values in natural old-growths coincided with a higher diversity of herbaceous mosaics comparing to secondary stands. The elimination of spruce (the species being most commonly blown down, projecting an acid canopy shadow) in two studied areas, elimination of dead wood, and destruction of humus layers through ploughing, could contribute to a reduction of specific microenvironments. A lower mosaic diversity of secondary stands coinciding with the unification of environmental conditions along the transects may indicate that forestry management can lead to the disappearance of a highly structural character in natural forest communities.Nomenclature: Flora europaea; Sokoowski (1993).     

The influence of vegetation pattern on the productivity,diversity and stability of vegetation: The case of `brousse tigrée' in the Sahel

Sample sites of `brousse tigrée' and related vegetation types are described for Mali and Niger. Species composition and physical structure of the herbaceous layer as well as woody plant population were recorded at all sites together with data on soils and natural resource management. Herbage yield was measured whereas foliage yield and wood mass were calculated using allometry equation calibrated for each species. `Brousse tigrée' is characterized by the regularly alternating bare-soil stripes with dense linear thickets arranged perpendicularly to the slope. There was no clear superiority in total plant production of `brousse tigrée' when compared to neighbouring site with diffuse vegetation. However, the pattern of `brousse tigrée' tended to favour woody plant yield to the detriment of herbage yield. The number of herbaceous species recorded per site (22–26) was slightly above Sahelian vegetation average despite low number of species per 1-m² quadrat (6–9), bare soil excluded. This species richness reflects the diversity in edaphic niches resulting from the redistribution and local concentration of water resources and shade. The high spatial heterogeneity and species richness of the herbaceous layer in `brousse tigrée' did not attenuate the interannual variation in herbage yield despite low yields. Except for the herb layer, little evidence was found of grazing influence on the vegetation structure and yield a few hundred metres away from livestock concentration points. On the other hand, the clearing of thickets for cropping led to severe soil erosion which threaten the resilience of `brousse tigrée'. These observations and the well-defined climatic, soiland topographic situations under which the `brousse tigrée' occurs invalidate the hypothesis of an anthropic origin of that vegetationpattern.