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Altitudinal Variations (altitudinal + variation)
Selected AbstractsAltitudinal variation in behavioural thermoregulation: local adaptation vs. plasticity in California grasshoppersJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 4 2005J. SAMIETZ Abstract We investigated the adaptive significance of behavioural thermoregulation in univoltine populations of the grasshopper Melanoplus sanguinipes along an altitudinal gradient in California using laboratory tests of animals raised under different temperatures. Trials consisted of continuous body temperature measurements with semi-implanted microprobes in a test arena, and observation and simultaneous recording of behavioural responses. These responses included mobility, basking and orientation of the body axes (aspect angle) towards a radiation source. Mobility and basking are determined by the altitudinal origin of the parental generation and not by the temperature treatments. With increasing altitude, individuals tend increasingly to raise body temperatures via mobility and increased basking. In contrast, body orientation towards the radiation source is influenced by the temperature treatments but not by the altitude of origin. Individuals experiencing higher temperatures during rearing show a lower tendency to lateral flanking. We conclude that body orientation responses are not adapted locally. In contrast other components of the behavioural syndrome that increase body temperature, such as mobility and basking, are adaptive in response to local selection pressure. The thermoregulatory syndrome of these grasshoppers is an important contribution to life-history adaptations that appropriately match season lengths. [source] Floristic diversity in fragmented Afromontane rainforests: Altitudinal variation and conservation importanceAPPLIED VEGETATION SCIENCE, Issue 3 2010Christine B. Schmitt Abstract Question: How does the floristic diversity of Afromontane rainforests change along an altitudinal gradient? What are the implications for conservation planning in these strongly fragmented forest areas that form part of the Eastern Afromontane Biodiversity Hotspot? Location: Bonga, southwestern Ethiopia. Methods: Based on evidence from other montane forests, we hypothesized that altitude has an effect on the floristic diversity of Afromontane rainforests in southwestern Ethiopia. To test this hypothesis, detailed vegetation surveys were carried out in 62 study plots located in four relatively undisturbed forest fragments situated at altitudes between 1600 m and 2300 m. Floristic diversity was evaluated using a combination of multivariate statistical analyses and diversity indices. Results: Ordination and indicator species analyses showed gradual variations in floristic diversity along the altitudinal gradient with a pronounced shift in species composition at ca. 1830 m. Upper montane forest (>1830 m) is characterized by high fern diversity and indicator species that are Afromontane endemics. Lower montane forest (<1830 m) exhibits a greater diversity of tree species and a higher abundance of the flagship species Coffea arabica. Conclusions: Our results provide crucial ecological background information concerning the montane rainforests of Ethiopia, which have been poorly studied until now. We conclude that both forest types identified during this study need to be considered for conservation because of their particular species compositions. Owing to the high degree of forest fragmentation, conservation concepts should consider a multi-site approach with at least two protected areas at different altitudinal levels. [source] Morphological and genetic differentiation in Isodon umbrosus by altitudinal variation in bumblebee pollinator assemblagesPLANT SPECIES BIOLOGY, Issue 1 2010IKUMI DOHZONO Abstract The corolla tube length of the bumblebee-pollinated plant Isodon umbrosus shows conspicuous geographical variation, corresponding with the proboscis length of its bumblebee pollinators across its distributional range. We hypothesized that altitudinal variation in the pollinator assemblage is a principal factor mediating morphological and genetic differentiation among I. umbrosus populations. We examined determinants of the morphological and genetic differentiation of Isodon umbrosus by analyzing floral morphology and allozyme variation across the distributional range. A reanalysis of previous data confirmed that altitude was a good indicator of pollinator assemblages. Corolla tube length was highly variable among the 15 study populations, and genetic differentiation among the populations (GST = 0.360) was also highly significant. The differentiation in corolla tube length was explained by altitudinal difference, a proxy of the difference in pollinator assemblages. Genetic differentiation among populations also tended to be affected by the same factor, but statistical support was weak. To better understand the mechanisms responsible for morphological and genetic differentiation in I. umbrosus, we need to investigate altitudinally different populations over a narrower geographical scale. [source] Stable isotopes in the source waters of the Yamuna and its tributaries: seasonal and altitudinal variations and relation to major cationsHYDROLOGICAL PROCESSES, Issue 17 2002Tarun K. Dalai Abstract Water samples from the Yamuna and its tributaries, one of the major river systems draining the Himalaya, have been analysed for their stable oxygen and hydrogen isotopes during three seasons (summer, monsoon and post-monsoon). The data show clear seasonal and altitudinal variations; waters from higher altitudes and those collected during monsoon season are characterized by relatively depleted isotopic composition. Regression analysis of ,D,,18O data of samples collected during summer and monsoon seasons shows that the slope of the best-fit lines are nearly identical to those of precipitation at New Delhi for the same period. The similarity in their slopes suggests that the isotopic composition of precipitation contributing water to these rivers are reasonably well preserved in both monsoon and non-monsoon seasons, however, during the non-monsoon period both rainfall and river waters carry signatures of evaporation. The ,deuterium excess' in river waters during the three seasons though overlap with each other, the values during October are higher. This can be understood in terms of recycled moisture contributions to precipitation. The ,altitude effect' for ,18O in these waters is determined to be 0·11, per 100 m, a factor of about two less than that reported for the Ganga source waters from similar altitudinal range. The variability in altitude effects in rivers draining the Himalaya seems to be controlled by the ,amount effect' associated with the monsoon. The significant spatial variability in altitude effect in these river basins, which are a few hundred kilometers apart, suggests that reconstruction of palaeoelevation in the Himalaya, based on ,18O-altitude gradients, would depend critically on its proper assessment in the region. This study has established a relationship between total cation abundance and ,18O in waters of the Yamuna mainstream; total cations (corrected for cyclic components) double for a 1·4 km decrease in altitude as the Yamuna flows downstream. Copyright © 2002 John Wiley & Sons, Ltd. [source] Long-term snow climate trends of the Swiss Alps (1931,99)INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 7 2003Martin Laternser Abstract The mean snow depth, the duration of continuous snow cover and the number of snowfall days in the Swiss Alps all show very similar trends during the observation period 1931,99: a gradual increase until the early 1980s (with insignificant interruptions during the late 1950s and early 1970s) followed by a statistically significant decrease towards the end of the century. Regional and altitudinal variations are large; high altitudes show only slight changes, and the trends become more pronounced at mid and low altitudes. At any particular time the southern part of the Alps often has different conditions than the north. Shorter snow duration is mainly caused by earlier snow melting in spring than by later first snowfalls in autumn. Trends for heavy snowfall events are somewhat different: at elevations above 1300 m a.s.l. a very weak increasing trend towards heavier snowfalls has persisted since the 1960s, and only low altitudes below 650 m a.s.l. show a marked drop since the early 1980s, indicating that heavy winter precipitation to an increasing degree falls in the form of rain instead of snow. A literature review confirms that, throughout the temperate and subpolar Northern Hemisphere, a similar general pattern of temporal snow variations occurred during the 20th century. Copyright © 2003 Royal Meteorological Society [source] | |||||||||||||