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Mountain Chains (mountain + chain)
Selected AbstractsGenetic population structure of the net-winged midge, Elporia barnardi (Diptera: Blephariceridae) in streams of the south-western Cape, South Africa: implications for dispersalFRESHWATER BIOLOGY, Issue 1 2003M. J. Wishart SUMMARY 1.,The net-winged midges (Diptera: Blephariceridae), with highly specific habitat requirements and specialised morphological adaptations, exhibit high habitat fidelity and a limited potential for dispersal. Given the longitudinal and hierarchical nature of lotic systems, along with the geological structure of catchment units, we hypothesise that populations of net-winged midge should exhibit a high degree of population sub-structuring. 2.,Sequence variation in the cytochrome c oxidase subunit I (COI) region of the mitochondrial DNA (mtDNA) was examined to determine patterns of genetic variation and infer historical and contemporary processes important in the genetic structuring of populations of Elporia barnardi. The DNA variation was examined at sites within streams, between streams in the same range, and between mountain ranges in the south-western Cape of South Africa. 3.,Twenty-five haplotypes, 641 bp in length, were identified from the 93 individuals sampled. A neighbour-joining tree revealed two highly divergent clades (,5%) corresponding to populations from the two mountain ranges. A number of monophyletic groups were identified within each clade, associated with individual catchment units. 4.,The distribution of genetic variation was examined using analysis of molecular variance (amova). This showed most of the variation to be distributed among the two ranges (,80%), with a small percentage (,15%) distributed among streams within each range. Similarly, variation among streams on Table Mountain was primarily distributed among catchment units (86%). A Mantel's test revealed a significant relationship between genetic differentiation and geographical distance, suggesting isolation by distance (P < 0.001). 5.,Levels of sequence divergence between the two major clades, representing the two mountain ranges, are comparable with those of some intra-generic species comparisons. Vicariant events, such as the isolation of the Peninsula mountain chain and Table Mountain, may have been important in the evolution of what is now a highly endemic fauna. 6.,The monophyletic nature of the catchment units suggests that dispersal is confined to the stream environment and that mountain ridges provide effective physical barriers to dispersal of E. barnardi. [source] Drainage patterns and tectonic forcing: a model study for the Swiss AlpsBASIN RESEARCH, Issue 2 2001A. Kühni ABSTRACT A linear surface process model is used to examine the effect of different patterns of rock uplift on the evolution of the drainage network of the Swiss Alps. An asymmetric pattern of tectonic forcing simulates a phase of rapid retrothrusting in the south of the Swiss Alps (,Lepontine'-type uplift). A domal pattern of tectonic forcing in the north of the model orogen simulates the phase of the formation of the ,Aar massif', an external basement uplift in the frontal part of the orogenic wedge (,Aar'-type uplift). Model runs using the ,Lepontine'-type uplift pattern result in a model mountain chain with a water divide in the zone of maximum uplift and orogen-normal rivers. Model runs examining the effect of ,Lepontine'-type uplift followed by ,Aar'-type uplift show that the initially formed orogen-normal river system and the water divide are both very stable and hardly affected by the additional uplift. This indifference to changes in tectonic forcing is mainly due to the requirement of a high model erosion capacity for the river systems in order to reproduce the exhumation data (high-grade rocks in the south of the Swiss Alps point to removal of a wedge-shaped nappe stack with a maximum thickness of about 25 km). The model behaviour is in agreement with the ancestral drainage pattern of the Alps in Oligocene and Miocene times and with the modern pattern observed in the Coast Range of British Columbia; in both cases river incision occurred across a zone of rapid uplift in the lower course of the rivers. The model behaviour does not, however, explain the modern drainage pattern in the Alps with its orogen-parallel rivers. When the model system is forced to develop two locally independent main water divides (simultaneous ,Lepontine'- and ,Aar'-type uplift), a zone of reduced erosional potential forms between the two divides. As a consequence, the divides approach each other and eventually merge. The new water divide remains fixed in space independent of the two persisting uplift maxima. The model results suggest that spatial and temporal changes in tectonic forcing alone cannot produce the change from the orogen-normal drainage pattern of the Swiss Alps in Oligocene,Miocene times to the orogen-parallel drainage observed in the Swiss Alps today. [source] Relationship among five populations of Bactrocera dorsalis based on mitochondrial DNA sequences in western Yunnan, ChinaJOURNAL OF APPLIED ENTOMOLOGY, Issue 7 2008P. Chen Abstract Genetic variation in the Oriental fruit fly, Bactrocera dorsalis (Hendel), was analysed using five populations from western Yunnan, China, to elucidate the distribution and likely dispersal patterns of this fly. A 503-bp portion of the mitochondrial cytochrome oxidase gene was sequenced from a minimum of seven individuals from each of five fly populations; 25 haplotypes were observed among 57 individuals in these populations. High genetic diversity within populations was detected. Genetic distances between haplotypes reached 1.2%. Mantel tests did not indicate any isolation because of geographic distance. The Ruili (RL) population was significantly isolated from the others (pairwise Fst ranging from 0.10 to 0.21, and average genetic distances being higher than for all other four population comparisons). RL is geographically separated from the other sites by the Gaoligong Mountains. The Liuku (LK) population had a close genetic relationship with the Lujiangba (LJB) population, suggesting that the LK population probably originated from LJB that is located in the same valley to the south. The Baoshan (BS) and Dali (DL) populations were also geographically isolated from the others, not originating from LJB and RL, where the fly is present year-round. The north-south orientation of mountains and valleys in western Yunnan appears to prevent latitudinal gene exchange by dispersing flies and thus divides the five populations into four relatively independent zones, namely BS, DL, LK-LJB and RL. In addition, air currents that generally flow south to north appear to assist dispersing flies, especially in valleys between the mountain chains. [source] SIMM: An integrated forecasting system for the Mediterranean areaMETEOROLOGICAL APPLICATIONS, Issue 4 2007Antonio Speranza Abstract Many ,high-impact' meteorological, marine and hydrological events in the Mediterranean area are characterized by horizontal spatial scales of the order of 10,100 km. Such events are, sometimes, driven by complex dynamical processes involving planetary scale atmospheric flows. Several international programs (ALPEX, POEM, MAP, PYREX, MEDEX) have improved the understanding of some of these processes. However, because of the Mediterranean's geomorphological structure, characterized by mountain chains (e.g. the Alps), semi-enclosed sea basins and small river catchments, many problems remain. It is clear that such problems have to be faced in the context of analysis-prediction systems bridging the gap between global and local scales of motion. These systems should allow for an adequate representation of key dynamical processes at all the relevant scales of motion. The Hydro-Meteorological-Marine System (,Sistema Idro-Meteo-Mare', SIMM) is a first step in developing an integrated system, adequately covering all scales of motion from global to local. A short description of the system is presented, highlighting scientific concepts behind design choices. A summary of the results of verification tests is also illustrated, together with a general evaluation of the whole process in planning, developing and running SIMM in order to assist future updates of the system, currently under development. Copyright © 2007 Royal Meteorological Society [source] Genetic structure of Euclea schimperi (Ebenaceae) populations in monsoonal fog oases of the southern Arabian PeninsulaNORDIC JOURNAL OF BOTANY, Issue 3-4 2007Jörg Meister Euclea schimperi, a widespread Afromontane shrub or tree, occurs in the Arabian Peninsula in fragmented, semi-evergreen or evergreen woodland refugia in wet escarpment localities of the western and southern mountain chains. In the southern coastal mountains, the (semi-) evergreen woodland with E. schimperi is close to its ecological limit and consequently today very rare, with the exception of the monsoonal fog oases of east Yemen and south Oman in the central south coast of the Arabian Peninsula. Due to the steep precipitation gradient from the centre to the western edge in this monsoon affected area, E. schimperi is found in two different habitat types: in continuous woodland belts in the Hawf and Dhofar mountains, and in isolated, scattered woodland patches in the Fartak Mountains. Ten populations (138 individuals) from across the southern Arabian distribution area of the species were analysed using chloroplast microsatellites and AFLP fingerprinting to a) reconstruct the phylogeographical pattern of E. schimperi on the southern Arabian Peninsula and b) to evaluate the consequences of population fragmentation on the genetic diversity harboured in isolated patches vs cohering stands. Phylogeographical reconstructions show that the distribution area of E. schimperi in the southern Arabian Peninsula is characterised by a geographical split that separates the southwestern populations (representated by material from Jabal Eraf and Jabal Uthmar), from the southcentral populations, which themselves are split from each other into a western (Ras Fartak) and an eastern refugium (Hawf/Dhofar). The analysis of the within-population genetic diversity in E. schimperi populations resulted in a slightly, but not significantly higher genetic variation in small and isolated woodland patches (HS=0.302) compared to larger, cohering stands (HS=0.291). [source] | |||||||||||||