Vue d'ensemble sur la végétation de la turquie

Sans résuméReçu par la rédaction le 15.XI.1953.     

Patterns of species ranges, speciation, and extinction

The exact nature of the relationship among species range sizes, speciation, and extinction events is not well understood. The factors that promote larger ranges, such as broad niche widths and high dispersal abilities, could increase the likelihood of encountering new habitats but also prevent local adaptation due to high gene flow. Similarly, low dispersal abilities or narrower niche widths could cause populations to be isolated, but such populations may lack advantageous mutations due to low population sizes. Here we present a large-scale, spatially explicit, individual-based model addressing the relationships between species ranges, speciation, and extinction. We followed the evolutionary dynamics of hundreds of thousands of diploid individuals for 200,000 generations. Individuals adapted to multiple resources and formed ecological species in a multidimensional trait space. These species varied in niche widths, and we observed the coexistence of generalists and specialists on a few resources. Our model shows that species ranges correlate with dispersal abilities but do not change with the strength of fitness trade-offs; however, high dispersal abilities and low resource utilization costs, which favored broad niche widths, have a strong negative effect on speciation rates. An unexpected result of our model is the strong effect of underlying resource distributions on speciation: in highly fragmented landscapes, speciation rates are reduced.     

Predictability of baroreflex sensitivity induced by phenylephrine injection via frequency domain indices computed from heart rate and systolic blood pressure signals during deep breathing

Diminished baroreflex sensitivity (BRS) is related to increased risk of sudden cardiac death in myocardial infarction patients and can be used as an indicator for risk level. The BRS is traditionally estimated invasively using vasoactive drugs, such as phenylephrine injection. This method has been widely accepted as a standard in clinical research. Due to its clinical importance, alternative BRS assessment methods have been investigated over the years to eliminate the use of drugs. In this study, the BRS obtained by drug-based (pharmacological) assessment was predicted from a subset of non-pharmacological indices computed from heart rate and systolic pressure signals. In the first phase of a two-phase experimental paradigm, 16 subjects were asked to perform two deep breathings with a 2-min delay in between. In the second phase, the BRS was measured by phenylephrine injection. Indices computed from the first phase describing the spectral and time domain properties of the heart rate and systolic pressure signals were used as predictors to estimate the pharmacological BRS of each subject. In addition to individual spectrum of beat-to-beat interval and systolic blood pressure, indices from cross-spectrum were also computed and evaluated as predictors. A leave one out method was employed to estimate the generalization capacity of the system and explore subset of indices, which gives the highest correlation between pharmacological and predicted BRS. Two predictors provided the highest correlation (r = 0.87, p = 1.16 × 10⁻⁵) with pharmacological BRS. The algorithm selected consistently normalized cross-power about the Mayer frequency and average magnitude square coherence in the high frequency band as predictors. These results indicate that the pharmacological BRS can be estimated from the combination of non-pharmacological spectral indices computed from beat-to-beat interval and systolic blood pressure signals obtained during deep breathing and therefore may eliminate the use of drugs.     

Die Verwüstung der Artemisia-Steppe bei Karapinar in Zentralanatolien

Zusammenfassung Die trockenste Region in der zentralanatolischen Steppe ist das Karapinar-Gebiet. Die klimatischen Verhältnisse dieses Gebietes wurden vergleichend erörtert. Bodenprofile der zwei für dieses Gebiet charakteristischen Pflanzengesellschaften wurden auch nach ihrer chemischen und physikalischen Beschaffenheit untersucht. Die Pflanzengesellschaft der Sandwüste wurde beschrieben. Die weitaus vorherrschende und wohl auch ursprüngliche Pflanzengesellschaft in diesem Gebiet ist dieArtemisia fragrans-Steppe. Sie ist durch Überweidung stark degradiert und befindet sich in Umwandlung zur Wüste. Ursache und Verlauf der Verwüstung in jüngster Zeit wurde eingehend geschildert.

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Summary The driest region in the central anatolian steppe (Turkey) is the area around the town Karapinar. The climate of this area is compared to others in central Anatolia. Soil profiles for two plant associations, characteristic for this area, are investigated as to their chemical and physical properties.The author describes the plant association of the sand desert. The dominant and probably original plant association in this area is theArtemisia fragrans-Steppe. It is very much degraded by intensive sheep grazing, and is being transformed into desert.Factors involved in this process in recent times are dealt with.

     

Conservation biogeography in North-east India: hierarchical analysis of cross-taxon distributional congruence

Distributional similarity (congruence) between phylogenetically independent taxonomic groups has important biogeographical as well as conservation implications. When multiple groups show congruence, one or two of them can be used as surrogates of diversity in others; thus, simplifying some of the challenges of area prioritization for conservation action. Here we test for congruence in complementarity between amphibians, reptiles and birds across seven tropical rainforest sites in the Eastern Himalaya and Indo-Burma global biodiversity hotspots. The results show that while frogs and lizards are strongly congruent with each other, birds as a whole do not show congruence with either of them. However, certain bird subgroups delineated on the basis of broad ecological niche and life history attributes are significantly congruent with both frogs and lizards. Multiple Mantel regression between environmental variable and species distribution dissimilarity matrices indicate that along with differential response to between-site ecological differences, inherent life-history characteristics shared by certain groups contributes to observed patterns of congruence. Our analyses indicate that examining biologically distinct subsets of larger groups can improve the resolution of congruence analyses. This approach can refine area-prioritization initiatives by revealing fine-scale discordances between otherwise concordant groups, and vice versa. Given that monetary resources do not always allow inclusion of multiple groups in biodiversity inventorying efforts, performing such analyses also makes economic sense because it can provide better resolution even with single-group data. In the context of conservation in North-east India, the results highlight the biogeographical complexity of the region, and also point at future priorities for biodiversity inventorying and conservation prioritization, both in terms of areas as well as taxonomic groups.     

Evolutionary dynamics through multispecies competition

Disruptive selection, emerging from frequency-dependent intraspecific competition can have very exciting evolutionary outcomes. One such outcome is the origin of new species through an evolutionary branching event. Literature on theoretical models investigating the emergence of disruptive selection is vast, with some investigating the sensitivity of the models on assumptions of the competition and carrying capacity functions’ shapes. What is seldom modeled is what happens once the population escapes its effect via increase phenotypic or genotypic variance. The expectation is mixed: disruptive selection could diminish and ultimately disappear or it could still exist leading to further speciation events through multiple evolutionary branching events. Here, we derive the conditions under which disruptive selection drives two subpopulations that originated at a branching point to other points in trait space where each subpopulation again experiences disruptive selection. We show that the general pattern for further branchings require that the competition function to be even narrower than what is required for the first evolutionary branching. However, we also show that the existence of disruptive selection in higher dimensional systems is also sensitive to the shapes of the functions used.