Vegetation patterns on Mount Everest as influenced by monsoon and föhn

The vegetation of Mt Everest is described by means of the dominant plant formations and characteristic features of biotopes. Climatic data givenin connection with weather observations show evidence that the extreme asymmetry of the altitudinal vegetation belt on the south and north slope is induced by heavy rainfall on the south slope and the desiccating effect of the Himalaya föhn in the valleys of the north slope. Biotope shift from hypsozonal distribution on the south slope to extrazonal distribution on the north slope is described, the patterns of the actual timber line are discussed in order to reconstruct the natural upper forest limit, and regressive plant successions during the last 400 years of man's impact are summarized. The dominant vegetation pattern of the alpine belt is compared with that in the European Alps. On the arid north slope alpine steppe communities occur up to 5 500 m. The highest altitudinal vegetation belt and the highest plant communities at 5 960 m are dominated by periglacial processes. The highest records of flowering plants (6 100/6 200 m) and lichens (7 400 m) are discussed in light of the present knowledge on high-altitude vegetation ecology.     

Scales and costs of habitat selection in heterogeneous landscapes

Summary Two scales of habitat selection are likely to influence patterns of animal density in heterogeneous landscapes. At one scale, habitat selection is determined by the differential use of foraging locations within a home range. At a larger scale, habitat selection is determined by dispersal and the ability to relocate the home range. The limits of both scales must be known for accurate assessments of habitat selection and its role in effecting spatial patterns in abundance. Isodars, which specify the relationships between population density in two habitats such that the expected reproductive success of an individual is the same in both, allow us to distinguish the two scales of habitat selection because each scale has different costs. In a two-habitat environment, the cost of rejecting one of the habitats within a home range can be expressed as a devaluation of the other, because, for example, fine-grained foragers must travel through both. At the dispersal scale, the cost of accepting a new home range in a different habitat has the opposite effect of inflating the value of the original habitat to compensate for lost evolutionary potential associated with relocating the home range. These costs produce isodars at the foraging scale with a lower intercept and slope than those at the dispersal scale.Empirical data on deer mice occupying prairie and badland habitats in southern Alberta confirm the ability of isodar analysis to differentiate between foraging and dispersal scales. The data suggest a foraging range of approximately 60 m, and an effective dispersal distance near 140 m. The relatively short dispersal distance implies that recent theories may have over-emphasized the role of habitat selection on local population dynamics. But the exchange of individuals between habitats sharing irregular borders may be substantial. Dispersal distance may thus give a false impression of the inability of habitat selection to help regulate population density.     

Environmental networks,compensating life histories and habitat selection by white-footed mice

Summary Analysis of 6 years' data on a population of free-living white-footed mice documents both phenotypic and environmental control of litter size. Litter size was positively correlated with maternal body size. Maternal size depended upon both seasonal and annual variation. Paradoxically, the proportion of small versus large litters varied among habitats independently of the effects of body size. The result is an influence of habitat on life history that yields patterns of reproduction and survival opposite to the predictions of demographic theory. The habitat producing the largest litters had a relatively high ratio of adult/juvenile survival. Litter size was small in the habitat where the adult/juvenile survival ratio was smallest. All of these anomalous patterns can be explained through density-dependent habitat selection by female white-footed mice. Life-history studies that ignore habitat and habitat selection may find spurious correlations among traits that result in serious misinterpretations about life history and its evolution.     

Increased working capacity with hyperoxia in humans

The purpose of the study was to examine the influence of oxygen-breathing on maximal oxygen uptake (VO2max) and submaximal endurance performance. Six young women and five men rode a cycle-ergometer while breathing compressed air (normoxia, NOX) or a 55% O2 in N2 mixture (hyperoxia, HOX). The VO2max increased significantly by 12% (P less than 0.01) with HOX in the women but not in the men (+4%; nonsignificant). Maximal heart rate was also increased with HOX in the women but not in the men. Endurance time during work to exhaustion at 80% of normoxic VO2max was 41% longer in HOX than in NOX (P less than 0.025) with no significant difference between the men and the women. The variation among individuals was large. The oxygen uptake and respiratory quotient were not different in the two endurance tests, but pulmonary ventilation (VE) and blood lactate concentration were lower in HOX than in NOX, especially during the latter part of the task. Plasma base deficit (BDpl) increased initially by 3.5 mmol.l-1 during HOX and then stabilized. In NOX, a continuous increase was seen and the change was more than twice as large. Relative to BDpl, VE was higher in HOX than in NOX indicating a more efficient ventilatory compensation of the metabolic acidosis. The reduced ventilatory demand and lower metabolic acidosis in HOX in combination with lower relative exercise intensity may have contributed to the longer time to exhaustion. However, the pattern of individual variation suggested that other mechanisms were also involved.     

Upstream migratory behaviour in landlocked Arctic charr

Synopsis Extensive upstream migration of landlocked Arctic charr during spring floods was recorded in several tributaries of an oligotrophic lake in north-west Sweden. Migration was confined to a period of about two weeks and residence in most creeks was of short duration. Only fish migrating to two small productive lakes remained in the new habitat over the summer. Repeated annual migrations were only recorded in the creek leading to these lakes and no straying was observed among repeat migrants. Water temperatures provided the primary cues for initiation and direction of migration, although an ability to detect productive habitats by odour was indicated. Creek size, feeding opportunities during migration and conspeeific odour were subordinate guiding factors.     

Importance of communal foraging grounds outside the reed marsh for breeding great reed warblers

Foraging habitat selection of breeding great reed warblers was studied at a shore of Lake Biwa. The foraging grounds of parent warblers during the nesting period were not restricted to the breeding territory of the reed marsh, their nestling habitat. The paddy field outside the reed marsh was used communally by them throughout the breeding season. Females with early stage nestlings did not visit the paddy field whereas when nestlings were older than 3 days, more than half of their total food was collected there. Females with nests adjacent to the paddy field tended to exploit the paddy field more often than those with nests distant from it. Monogamously mated females tended to exploit the paddy field more often than polygynously mated females. Food collected in the paddy field was larger than that in the reed marsh and parent birds were prepared to travel longer distances to exploit the rich source of food in the paddy field. The importance of the communal foraging ground outside the reed marsh as a background of the polygynous mating system of this species is discussed.     

Complementarity of genes for resistance to greenbug [Schizaphis graminum (Rondani)], biotype E,in sorghum [Sorghum bicolor (L.) Moench]

Summary Gene complementarity among various sources of resistance to greenbug biotype E was assessed. Analysis of the F₂ generation of crosses between susceptible and resistant parents (mating 1) and among sources of resistance (mating 2) suggested that resistance in sorghum to greenbug biotype E was complexly inherited and, to some extent, dependent on the nature of both the resistant and susceptible parents. Positive transgressive segregation in the F₂ generations of both matings was found to be due to effective plus factors, contributed by both parents in a cross, which complemented each other. The number of plus factors ranged from one to two in the susceptible parents and from two to five in the resistant parents of mating 1, and from one to five in the parents of mating 2. The consistently significant reciprocal effects shown by Sarvasi and PI264453 indicated that these sources had major factors for resistance in their cytoplasms, which were expressed in all their crosses. The results from this study indicated that the sources of resistance complemented each other to give increased number of F₂ segregates with increased resistance. Thus, it should be possible to increase and diversify resistance of sorghum to greenbug biotype E by accumulating different, effective plus factors from various sources through recurrent selection.Contribution No. 90-106-J from the Kansas Agricultural Experiment Station, Kansas State University, Manhattan, KS 66506, USA     

Spatial and temporal localization of FGF receptors in Xenopus laevis

Summary Mesoderm formation is a result of cell-cell interactions between the vegetal and animal hemisphere and is thought to be mediated by inducing peptide growth factors including members of the FGF and TGF superfamilies. Our immunochemical study analyses the distribution of FGF receptors coded by the human flg gene during embryogenesis of Xenopus laevis. Immunostaining was detected in the dorsal and ventral ectoderm and also in the marginal zone of early cleavage, blastula and gastrula stages. Signals were very strong in the mid and late blastula (stage 8 and 9) and declined slightly in the early gastrula (stage 10). A dramatic decrease was observed up to the late gastrula (stage 11⁺). In stage 13 embryos, immunostaining was only found in cells around the blastopore. Isolated ectoderm cultured in vitro showed a similar temporal expression and decrease of the signal as the normal embryos. These results indicate that receptor expression is independent of the interaction of the animal cells with the vegetal part of the embryo. Of interest is the fact that the signal cannot only be found at or near the cell surface but also within the cell. This suggests the presence of an intracellular isoform of the receptor resulting from the endogenous expression of splice variants and the internalization of transmembrane receptor. Taken together our results suggest that the loss of competence (for bFGF around stage 10) is not directly correlated with the presence of receptors. The possible roles of heparan sulphate glucosaminoglycans (low affinity receptors) and control mechanisms in the intracellular signalling pathway downstream of the receptor level should be taken into consideration.     

The sinking ark: pollution and the worldwide loss of biodiversity

Humans are making increasing demands on natural ecosystems. One recent study has concluded that our species is consuming or diverting some 40% of the net photosynthetic productivity of our planet. Many habitats are being converted to simpler systems which provide more harvestable goods to people. As a result, genetic diversity, species and whole ecosystems are disappearing; some scientists suggest that as many as 25% of the world's species could be lost in the next several decades.The sinking ark is usually characterized in terms of pollution, habitat loss, poaching, introduced species and illegal trade in wildlife products, but these are symptoms rather than causes. At a more fundamental level, many of the same factors which have enabled pollution to become such a problem have also been responsible for the loss in biodiversity; the most important factor is that the effects of pollutants on biodiversity have been considered an externality, an unintended side effect of industrial activity which brought measurable benefits to people. Development activities which have depleted biodiversity have proven profitable only because the real costs have been hidden.Keeping the ark afloat will require the Five-I Approach: investigation (learning how natural systems function); information (ensuring that the facts are available to inform decisions); incentives (using economic tools to help conserve biodiversity); integration (promoting a cross-sectoral approach to conserving biodiversity); and international support (building productive collaboration for conserving biodiversity).