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Lower Altitudes (lower + altitude)
Selected AbstractsSpatial and temporal variations of two cyprinids in a subtropical mountain reserve , a result of habitat disturbanceECOLOGY OF FRESHWATER FISH, Issue 3 2007C.-C. Han Abstract,,, We investigated the variations of population of two cyprinids, Varicorhinus alticorpus and Varicorhinus barbatulus, using long-term survey data (1995,2004) in the subtropical island of Taiwan. Fish abundance data showed that at the mainstem stations, V. barbatulus which used to dominate in the higher altitude had declined significantly, while V. alticorpus that used to occupy only the lower altitude had spread upward. However, at the tributaries, trend of the populations of V. barbatulus were not significantly different over time, while populations of V. alticorpus were absent at higher altitude but began to increase at lower altitude. Environmental parameters revealed that sporadic high turbidity was observed at the mainstem stations, but not at the tributaries. Images taken before and after typhoon also showed habitat destruction by debris flow at the mainstem stations. As some models predicted that suitable fish habitats will shrink because of increasing water temperature due to global warming, we showed that fish distribution may be affected by habitat disturbance due to intensified storms sooner than the actual increase of water temperature. [source] Chemical composition of essential oils of Senecio nutans Sch.-Bip. (Asteraceae)FLAVOUR AND FRAGRANCE JOURNAL, Issue 3 2003Vincenzo De Feo Abstract The essential oils from the aerial parts of Senecio nutans Sch.-Bip., collected in two different localities at 3500 and 4800 m above sea level in the Department of Arequipa, Perù, were obtained by hydrodistillation in 0.16% and 0.18% yields, respectively, related to the fresh weight. The oils were characterized by GC and GC,MS analyses. In the oil from plants at the lower altitude, 21 of 25 components were identi,ed; the oil from the higher altitude site showed the presence of 46 components, 41 of which were identi,ed. Monoterpene hydrocarbons predominated in both oils, with sabinene and , -terpinene as the main constituents. Copyright © 2003 John Wiley & Sons, Ltd. [source] Allometric relationships between lamina area, lamina mass and petiole mass of 93 temperate woody species vary with leaf habit, leaf form and altitudeFUNCTIONAL ECOLOGY, Issue 4 2008Guoyong Li Summary 1The allometric scaling relationship between lamina and lamina support has rarely been examined, such that its significance to plant life-history strategies has not been fully explored and understood so far. We investigated the sizes of leaf lamina and petiole for 93 temperate broad-leaved woody species at two altitudes of a southwestern mountain, and analysed the scaling relationship in relation to leaf habit (evergreen vs. deciduous), leaf form (simple- vs. compound-leaved species), and habitat type (low vs. high altitude). 2Significant allometric scaling relationships were found between petiole mass and lamina mass, and between petiole mass and lamina area, with common slopes of 0·872 and 0·742, respectively, both significantly departed from the value of 1·0. The results of phylogenetic comparative analyses were in accordance with the observed positive scaling relationships. 3The evergreen species were found to have a greater petiole mass than the deciduous at a given lamina area; whilst a contrasting pattern was observed between lamina mass and petiole mass, in which the evergreens had a greater biomass allocation to lamina for the same petiole mass relative to the deciduous. 4The compound-leaved species were observed to be significantly greater in both lamina area and lamina support (including petioles, rachis and petiolules) than the simple-leaved species, whereas the former had a smaller lamina area or lamina mass at a given petiole mass than the latter. 5The plants from the high altitude had less lamina area at a given petiole investment compared to those from the lower altitude, likely due to the large mechanic and transporting requirements of petioles in the species at high altitude. 6Our results indicate that petioles serve as an adverse forcing on the maximization of lamina area and lamina biomass and that the allometric relationship between lamina and lamina support varies with leaf habit, leaf form and habitat. [source] Sex pheromone for monitoring flight periods and population densities of the pine sawfly, Diprion jingyuanensis Xiao et Zhang (Hym., Diprionidae)JOURNAL OF APPLIED ENTOMOLOGY, Issue 7 2005Z. Zhang Abstract:, The pine sawfly, Diprion jingyuanensis Xiao et Zhang, is a serious pest of Chinese pine (Pinus tabulaeformis Carr.) in the northern parts of China. The general biology of this recently described sawfly species is little known and in the present study we used a synthetic pheromone to monitor its flight period and to evaluate the possibility to use pheromone traps as a tool for estimating and predicting population densities. The attractant pheromone of D. jingyuanensis is (1S,2R,6R)-1,2,6-trimethyldodecyl propionate and in this study we used a four-isomer threo-mixture containing the active attractant. Both doses tested, 1 and 2 mg/trap, revealed the same seasonal flight pattern, the higher dosage demonstrating more clear flight peaks. The first flight peak of D. jingyuanensis occurred in mid-June during all 3 years, 1997,1999, and in 1997 and 1998 a second flight peak was also recorded in mid-July. The flight period was similar in time for populations located at higher (1400 m) and lower altitude (1100 m), from early June to late July or early August. Temperature was the main weather factor-affecting trap catches. Diurnal flight activity began at 9.00, peaked at 13.00 and lasted until 20.00. A series of tests with traps in different positions within stands and trees were conducted and the results demonstrated the importance of standardizing the trapping protocol in population monitoring studies. By using traps with 2 mg baits it is possible to detect sawfly occurrence at very low population densities, not detectable by other means. Strong positive correlations between trap catch and relative population density were found in 2000 and 2001, but not in 1998, when only few sites were monitored and the population was in a decreasing phase. The results are promising for future large-scale use of pheromone-based monitoring of D. jingyuanensis. [source] Effects of altitude on spleen volume: Sonographic assessmentJOURNAL OF CLINICAL ULTRASOUND, Issue 4 2007Guner Sonmez MD Abstract Purpose. To use sonography to determine changes that may arise in splenic volume in humans from regions of lower altitude who begin to live in regions of higher altitude. Materials and Methods. The study was conducted in the Turkish province of A,r,, at an altitude of 1750 m and included 108 healthy, nonsmoking, disease-free volunteers who had moved from regions at an altitude lower than 500 m. Length, width, and thickness of the spleen were measured using sonography. Splenic volume was calculated using the following standard ellipsoid formula: length × width × thickness × 0.523. Sonographic assessments were repeated at 3 and 6 months along with other blood tests, including hemoglobin, hematocrit, and platelet levels. Results. The mean ± SD splenic volume was 299 ± 97 cm3 (range, 116,574 cm3). At 3 and 6 months, the splenic volumes decreased significantly compared to their initial values (p < 0.05). An increase in hemoglobin, hematocrit, and platelet count was observed in all subjects. Conclusion. Our data show that splenic volume in healthy individuals who begins to live at high altitudes decreases gradually. © 2007 Wiley Periodicals, Inc. J Clin Ultrasound, 2007 [source] Delayed Selfing in an Alpine Biennial Gentianopsis paludosa (Gentianaceae) in the Qinghai-Tibetan PlateauJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 6 2010Yuan-Wen Duan Delayed selfing could provide ovules with an opportunity to be fertilized as a means of "pollination assurance" before the flowers wilt. It could, thus, be regarded as an adaptation to unpredictable pollinator environments. Within the alpine biennial Gentianopsis paludosa, the showy flowers and herkogamy at the early stage of a flower's life cycle may favor outcrossing. As the flower ages, anthers contact the central stigma due to the elongation of all filaments, resulting in autonomous selfing. Flower visitors are extremely rare in a high altitude population; and examination of the mating system indicates that G. paludosa is self-pollinated under natural conditions in this population. While at the lower altitude, the bumblebee visitation rate is relatively high but possibly unreliable. Stigma receptivity is the highest on the third day of anthesis, and decreases thereafter. Pollen viability is the highest when flowers open, and gradually decreases later. Self-pollination of G. paludosa occurs at the late stage of a flower's lifecycle when stigma receptivity and pollen viability have both decreased, suggesting delayed selfing and assurance of seed production. This delayed selfing could assure seed production under the constraints of pollinator scarcity, but ensure outcrossing when pollinators were available. Such a flexible pollination mechanism is highly adaptive in the alpine environment of the Qinghai-Tibetan Plateau. [source] Bird responses to fire severity and time since fire in managed mountain rangelandsANIMAL CONSERVATION, Issue 3 2010P. Pons Abstract Broom matorrals are subjected to extensive burning in the Pyrenees to improve grazing value, despite being a habitat of conservation interest in Europe. Our aim here is to evaluate the impact of such management practices over the long term, and of fire severity over the short term, on avifauna. Bird-habitat stations were distributed in broom shrublands from a few months to 51 years after fire, at 1400,2100 m a.s.l. Overall, shrub cover was the main habitat variable affecting the bird community composition. The abundance trends of bird species for half a century after fire were varied, but population recovery seemed slower (especially in the Dartford warbler Sylvia undata) than it had been reported at a lower altitude. Three species of European conservation concern (Alauda arvensis, Lullula arborea and Lanius collurio) showed abundance peaks at 10,19 years after fire. This time interval showed the highest species richness, abundance and conservation value, whereas shrub cover continued to increase afterwards. The bird assemblage tended to impoverish with increasing fire severity in the first year after a fire. Our results emphasize: (1) the slow recovery of bird community of burnt mountain shrublands; (2) the need for long-term biodiversity assessments to help improve planning of fire intervals at different altitudes; (3) the relevance of reducing fire severity due to its impact on fauna. [source] Effect of Pedoclimatic Conditions on the Chemical Composition of the Sigoise Olive CultivarCHEMISTRY & BIODIVERSITY, Issue 4 2010Samia Dabbou Abstract The present work focused on the quality and the chemical composition of monovarietal virgin olive oil from the Sigoise variety grown in two different locations in Tunisia, viz., a sub-humid zone (Béjaoua, Tunis) and an arid zone (Boughrara, Sfax). In addition to the quality characteristics (acidity, peroxide value, and the spectrophotometric indices K232 and K270) and the chemical composition (content of fatty acids, antioxidants, and volatile compounds) of the oil, the fruit characteristics of the olives were studied. Except for the content of the majority of the fatty acids, there were significant differences observed in the oil composition of olives that were cultivated in different locations. The content of total phenols and lipoxygenase (LOX) oxidation products was higher for olives grown at the higher altitude, whereas that of , -tocopherol, carotenes, and chlorophylls was higher for olives from the Boughrara region (lower altitude). Moreover, olives produced at the higher altitude showed a higher ripeness index and oil content than those cultivated at the lower altitude. [source] Modelling patterned ground distribution in Finnish Lapland: an integration of topographical, ground and remote sensing informationGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 1 2006Jan Hjort Abstract New data technologies and modelling methods have gained more attention in the field of periglacial geomorphology during the last decade. In this paper we present a new modelling approach that integrates topographical, ground and remote sensing information in predictive geomorphological mapping using generalized additive modelling (GAM). First, we explored the roles of different environmental variable groups in determining the occurrence of non-sorted and sorted patterned ground in a fell region of 100 km2 at the resolution of 1 ha in northern Finland. Second, we compared the predictive accuracy of ground-topography- and remote-sensing-based models. The results indicate that non-sorted patterned ground is more common at lower altitudes where the ground moisture and vegetation abundance is relatively high, whereas sorted patterned ground is dominant at higher altitudes with relatively high slope angle and sparse vegetation cover. All modelling results were from good to excellent in model evaluation data using the area under the curve (AUC) values, derived from receiver operating characteristic (ROC) plots. Generally, models built with remotely sensed data were better than ground-topography-based models and combination of all environmental variables improved the predictive ability of the models. This paper confirms the potential utility of remote sensing information for modelling patterned ground distribution in subarctic landscapes. [source] Vegetation of the Stipa loess steppe in Ningxia (northern China) in relation to grazing intensityGRASSLAND SCIENCE, Issue 3 2007Yingzhong Xie Abstract Large areas of northern and western China are covered with steppe vegetation which is grazed with different intensities. Areas which are not or only slightly grazed are rare and mostly exist in nature reserves. We investigated floristic composition and species diversity of the steppe vegetation of the autonomous region Ningxia Hui with emphasis on the Yunwushan dry steppe nature reserve in relation to grazing intensity; all 77 plots were analyzed using ordination techniques, and the relationship between the variation in species composition and environmental conditions was analyzed. In Ningxia, two types of loess grass steppes prevail: in areas with lower altitudes from approximately 1650,1950 m a.s.l., the Stipa bungeana steppe occurs whereas the Stipa grandis steppe is typical for higher altitudes between 1900 and 2100 m a.s.l. For both vegetation types, three subtypes can be distinguished according to different levels of grazing intensity. With increasing grazing intensity, the number of plant species per plot strongly declines and the typical steppe vegetation types are dominated by Artemisia species (A. frigida in the Stipa grandis community and A. sacrorum in the Stipa bungeana community). In contrast to studies carried out in neighboring areas, in our study area the Artemisia steppes do not represent the final state of degradation. Instead, Convolvulus ammanii dominates in heavily grazed areas of both Stipa steppe types. Detrended correspondence analysis confirms the classification and shows that the heavily grazed subtypes of the Stipa grandis and the Stipa bungeana steppe with Convolvulus ammanii are more similar to each other than the other vegetation types. The first axis of the detrended correspondence analysis is strongly related to the grazing intensity (r = 0.93). Our results show that grazing intensity is an important factor for the differentiation of the steppe grasslands and a severe threat to species diversity. [source] Assessment of climate-change impacts on alpine discharge regimes with climate model uncertaintyHYDROLOGICAL PROCESSES, Issue 10 2006Pascal Horton Abstract This study analyses the uncertainty induced by the use of different state-of-the-art climate models on the prediction of climate-change impacts on the runoff regimes of 11 mountainous catchments in the Swiss Alps having current proportions of glacier cover between 0 and 50%. The climate-change scenarios analysed are the result of 19 regional climate model (RCM) runs obtained for the period 2070,2099 based on two different greenhouse-gas emission scenarios (the A2 and B2 scenarios defined by the Intergovernmental Panel on Climate Change) and on three different coupled atmosphere-ocean general circulation models (AOGCMs), namely HadCM3, ECHAM4/OPYC3 and ARPEGE/OPA. The hydrological response of the study catchments to the climate scenarios is simulated through a conceptual reservoir-based precipitation-runoff transformation model called GSM-SOCONT. For the glacierized catchments, the glacier surface corresponding to these future scenarios is updated through a conceptual glacier surface evolution model. The results obtained show that all climate-change scenarios induce, in all catchments, an earlier start of the snowmelt period, leading to a shift of the hydrological regimes and of the maximum monthly discharges. The mean annual runoff decreases significantly in most cases. For the glacierized catchments, the simulated regime modifications are mainly due to an increase of the mean temperature and the corresponding impacts on the snow accumulation and melting processes. The hydrological regime of the catchments located at lower altitudes is more strongly affected by the changes of the seasonal precipitation. For a given emission scenario, the simulated regime modifications of all catchments are highly variable for the different RCM runs. This variability is induced by the driving AOGCM, but also in large part by the inter-RCM variability. The differences between the different RCM runs are so important that the predicted climate-change impacts for the two emission scenarios A2 and B2 are overlapping. Copyright © 2006 John Wiley & Sons, Ltd. [source] Photosynthetic pathways, spatial distribution, isotopic ecology, and implications for pre-Hispanic human diets in central-western ArgentinaINTERNATIONAL JOURNAL OF OSTEOARCHAEOLOGY, Issue 2 2009C. Llano Abstract In a number of areas around the world researchers have begun to use the isotopic values of subsistence resources as a means of determining diets of human populations. The objective of the present study is to classify the plant species present at distinct altitudes in southern Mendoza Province, Argentina, considering photosynthetic pathways in order to determine their ,13C isotopic signature. This will help to understand the relationships between diets and the isotopic values observed in archaeological human remains. Data compiled from various sources are used to establish the photosynthetic pathways and mean ,13C values. The results indicate that C3 species are dominant at high-altitude settings, and that the few identified C4 species were found primarily at lower altitudes. These results are intended to serve as a foundation for future isotopic studies designed to address relationships among species at different trophic levels. Copyright © 2009 John Wiley & Sons, Ltd. [source] Effect of Altitude on Energy Exchange Characteristics of Some Alpine Medicinal Crops from Central HimalayasJOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 1 2004S. Chandra Abstract To explore the conservation and cultivation of endangered alpine medicinal crops at comparatively lower altitudes, a study on variations in morphological parameters and energy exchange characteristics was conducted on five herbaceous medicinal crops from the alpines of Central Himalayas. Plants of same age were selected from the alpine medicinal crop nursery, Tungnath (3600 m), and were planted at the nurseries at 2100 and 550 m altitudes. After well acclimatization at lower altitudes, plants were examined for morphological and energy exchange studies during their active growth period. The energy balance sheet of these plant species indicates that most of the energy absorbed by the leaves dissipates by re-radiation, transpiration and thermal conductance across leaf surfaces. All species maintained leaf temperature below the surrounding air temperature at all altitudes and therefore gained energy by convection of heat as well as by boundary layer thermal conduction. Leaf-to-air temperature difference, gain of energy by convection of heat and boundary layer thermal conduction was maximum at an altitude of 2100 m in all the species. Boundary layer thermal conductivity, boundary layer thickness, thermal conductivity of the leaf and therefore, total energy absorbed by the leaves of these species increase significantly with decreasing altitude. Leaf thickness significantly decreases with decreasing altitude, which in turn enhances total energy absorption (r = ,0.975, P < 0.005) of the leaves in all the species. The results indicate that all these species absorb higher amount of energy at lower altitudes, which indicates their adaptability to warm temperatures at low altitudes (up to 550 m). Therefore, these species can be cultivated at relatively lower altitudes. However, a proper agronomic methodology needs to be developed for better yields. [source] Seasonality and host utilization of the invasive fruit fly, Bactrocera invadens (Dipt., Tephritidae) in central TanzaniaJOURNAL OF APPLIED ENTOMOLOGY, Issue 9-10 2006M. W. Mwatawala Abstract:, The temporal occurrence of the invasive and economically important pest fruit fly, Bactrocera invadens was studied in three agro-ecological areas of Morogoro Region, central Tanzania, during 2004,2005. Weekly and monthly trappings were carried out with methyl eugenol, protein bait and synthetic food attractant. Bactrocera invadens was permanently present at low and mid-altitudes (380,520 m a.s.l.) with peak periods coinciding with the fruiting season of mango (Mangifera indica) and guava (Psidium guajava). At high altitude (1650 m a.s.l.) its incidence was only temporal and apparently the result of dispersal from lower altitudes after the mango fruiting season. Rearing results showed mango, loquat (Eriobotrya japonica), guava and grapefruit (Citrus × paradisi) to be the favoured commercial host fruits. Other Citrus species, cucurbits, papaya (Carica papaya) and avocado (Persea americana) were less favoured. [source] Species richness, rarity and endemicity on Italian offshore islands: complementary signals from island-focused and species-focused analysesJOURNAL OF BIOGEOGRAPHY, Issue 4 2008Leonardo Dapporto Abstract Aims, To investigate the relative explanatory power of source faunas and geographical variables for butterfly incidence, frequency, richness, rarity, and endemicity on offshore islands. Location, The western Italian offshore islands (Italy and Malta). Methods, Thirty-one islands were examined. Data were taken from our own field surveys and from the literature. Two approaches were undertaken, described as island-focused and species-focused, respectively. Offshore islands were allocated to their neighbouring source landmasses (Italian Peninsula, Sicily and Sardinia,Corsica) and compared with each other for faunal attributes, source and island geography. Generalized linear and stepwise multiple regression models were then used to determine the relationships of island species richness, rarity and endemicity with potential geographical predictors and source richness, rarity, and endemicity (island-focused). Species frequency and incidence were assessed in relation to geographical and source predictors using stepwise linear and logistic regression, and inter-island associations were examined using K-Means clustering and non-metric scaling (species-focused). Results, The analysis reveals firm evidence for the influence of the nearest large landmass sources on island species assemblages, richness, rarity and endemicity. A clear distinction in faunal affinities occurs between the Sardinian islands and islands lying offshore from the Italian mainland and Sicily. Islands neighbouring these three distinct sources differ significantly in richness, rarity and endemicity. Source richness, rarity, and endemicity have explanatory power for island richness, rarity, and endemicity, respectively, and together with island geography account for a substantial part of the variation in island faunas (richness 59%, rarity 60% and endemicity 64%). Source dominates the logistic regression parameters predicting the incidence of island species [13 (38%) of 34 species that could be analysed]; three ecological factors (source frequency, flight period and maximal altitude at which species live) explained 75% of the variation in the occurrence of species on the islands. Species found more frequently on islands occurred more frequently at sources, had longer flight periods, and occurred at lower altitudes at the sources. The incidence of most species on islands (84%) is correctly predicted by the same three variables. Main conclusions, The Italian region of the Mediterranean Sea has a rich butterfly fauna comprising endemics and rare species as well as more cosmopolitan species. Analysis of island records benefited from the use of two distinct approaches, namely island-focused and species-focused, that sift distinct elements in island and source faunas. Clear contemporary signals appear in island,source relationships as well as historical signals. Differences among faunas relating to sources within the same region caution against assuming that contemporary (ecological) and historical (evolutionary) influences affect faunas of islands in different parts of the same region to the same extent. The implications of source,island relationships for the conservation of butterflies within the Italian region are considered, particularly for the long-term persistence of species. [source] Effects of natural disturbance and selective logging on Nothofagus forests in south-central ChileJOURNAL OF BIOGEOGRAPHY, Issue 7 2002William Pollmann Aim Changes in stand structure, floristic composition and tree population dynamics during the last four centuries were described in southern temperate rain forests. The impacts of natural and anthropogenic disturbance since the late 1560s were examined for old-growth and logged forests. Location The study was conducted in montane Nothofagus alpina forests in the Andean Range of south-central Chile. Study sites were located at a range of altitudes between 1000 and 1250 m a.s.l. Methods Temporal variation in species recruitment and annual dendroecological data were used to determine the historical development and disturbance history of three old-growth forests, and three stands after selective logging in the late 1880s to early 1900s. Considering the spatial structure of evergreen vs. deciduous elements, the forests are a mixture of deciduous and evergreen tree species. Results Stem density, maximum stem diameter and basal area differed between the old-growth and logged stands, but species composition did not. At lower altitudes, N. alpina was the dominant canopy species in both old-growth and logged stands, but regeneration of N. alpina was significantly different in these stands. At higher altitudes, N. alpina and N. dombeyi were the dominant canopy species in both old-growth and logged stands, and here regeneration patterns of these Nothofagus species were similar. After selective logging, in mixed forests of shade-intolerant Nothofagus and more shade-tolerant trees (such as Laurelia philippiana) there has been a shift in regeneration from more shade-tolerant resprouting species towards Nothofagus. Major and moderate releases in radial growth, indicative of disturbance, occurred in most of the older trees during the last four centuries, and especially during the last 100 years. Growth rates of N. alpina are higher than those of associated shade-tolerant trees, and apparently increase after disturbances. Main conclusions Results suggest that under disturbance regimes dominated by treefall gaps, and additionally canopy openings by selective logging, maintenance of Nothofagus species appears to be associated with complementary differences in growth rate, sprouting capacity, canopy residence time, and longevity. Such small-scale canopy openings may help explain the relative abundance of N. alpina in montane mixed rain forests in the Andean Range, where the maintenance of Nothofagus species in many stands has been attributed to a high frequency of coarse-scale disturbance. My results serve to emphasize that understanding the species coexistence and forest dynamics in Nothofagus forests may require attention to interspecific differences in life-history characteristics. [source] Breeding biology of ostriches (Struthio camelus) in the Serengeti ecosystem, TanzaniaAFRICAN JOURNAL OF ECOLOGY, Issue 3 2009Flora J. Magige Abstract Ostrich breeding behaviour in the Serengeti ecosystem, Tanzania was investigated for differences in laying dates between low altitude western area (WA) and high altitude eastern area (EA) populations. Ostriches in WA laid eggs significantly earlier than in EA. The differences could be attributed to topography and rainfall pattern. Reliable rains in lower altitudes ensure availability of food that in turn influences the whole process of the reproductive cycle. Clutches were contributed by several females with a nest having up to 38 eggs. We also compared the frequency of observation of predators, ostriches, nests, ,singletons' (single eggs laid randomly) and broods between the two areas. There was no significant difference between WA and EA in 1) ostrich/nest ratio, indicating similar breeding densities; 2) ostrich/predator and predator/nest ratios, indicating that predation pressure was equally high; 3) nest/singleton and predator/singleton ratios, indicating that loss of nests did not vary between areas. However, there were significantly more predators, nests and ostriches compared to broods in EA than in WA, indicating a significantly lower reproductive success in EA. Using metapopulation terminology, ostriches in EA could be regarded as a ,sink' population and those in WA as a ,source' population, but investigations over longer time-periods are needed to further resolve if this is the case. Résumé Le comportement reproducteur des autruches dans l'écosystème du Serengeti, en Tanzanie, a étéétudié pour voir les différences dans les dates de pontes entre les populations de la zone occidentale (WA) à basse altitude et de la zone orientale (EA) à plus haute altitude. Les autruches de la WA pondent significativement plus tôt que celles de l'EA. Les différences peuvent être attribuées à la topographie et au régime de la pluviosité. Les pluies fiables à plus basse altitude garantissent la disponibilité de la nourriture, ce qui influence dès lors tout le processus du cycle reproducteur. Des couvées réunissaient les ,ufs de plusieurs femelles , un nid a eu jusqu'à 38 ,ufs. Nous avons aussi comparé la fréquence d'observations de prédateurs, d'autruches, de nids, de «ingletons» (des ,ufs solitaires pondus au hasard) et de nichées entre les deux zones. Il n'y a pas de différence significative entre WA et EA pour 1) le ratio autruches/nids, ce qui indique des densités de reproduction similaires; 2) le ratio autruches/prédateurs et le ratio prédateurs/nids, ce qui indique que la pression de la prédation est aussi haute des deux côtés; et 3) le ratio nids/singletons et le ratio prédateurs/singletons, ce qui indique que la perte des nids ne variait pas entre les zones. Cependant, il y avait significativement plus de prédateurs, de nids et d'autruches par rapport aux nichées dans l'EA que dans la WA, ce qui indique une réussite de la reproduction significativement plus faible dans la EA. En utilisant la terminologie de la métapopulation, les autruches de la EA peuvent être considérées comme une population «puits» et celles de la WA comme une population «source», mais il faudrait faire des recherches de plus longue durée pour montrer si c'est bien le cas. [source] Changes of taxonomic and trophic structure of fish assemblages along an environmental gradient in the Upper Beni watershed (Bolivia)JOURNAL OF FISH BIOLOGY, Issue 1 2006M. Pouilly The distribution and the diet of 28 fish species were evaluated, during the dry season, in 12 streams of the Upper Beni watershed (Amazon basin, Bolivia). The 12 streams were of similar size (stream width and water depth) but situated on a gradient of altitude in the Andean and sub-Andean areas. The environmental conditions in the stream changed in relation to the altitude. As altitude decreased, slope and water velocity also decreased, while temperature, conductivity, pH and the proportion of pools increased. Although the diets of the species were mainly based on two aquatic autochthonous food resources, invertebrates and sediment, species were classified into five trophic guilds: detritivores, algivores, piscivores, invertivores-omnivores and aquatic specialist invertivores. In all streams invertivores dominated or co-dominated with detritivores. The trophic structure of the assemblages, however, changed in relation to the environmental gradient. The fish species richness increased and the trophic composition became more diverse at lower altitudes, when slope decreased and temperature increased. At the same time, the relative number of invertivore species decreased, whereas the relative number of detritivore, algivore and piscivore species increased. Decreasing altitude appeared to play a role similar to increasing stream size along the longitudinal gradient. This could be explained by geomorphological and temperature variations that may generate environmental conditions favourable to an increase of productivity. [source] | |||||||||||||||||||