نتایج جستجو برای: latitude
تعداد نتایج: 16503 فیلتر نتایج به سال:
This discussion of the problem of depopulation in Melanesia limits itself to oudine form and brief treatment. Moreover, it is unwise to be dogmatic about the relative importance of the factors invQlved. Depopulation, wherever it occurs, is a phenomenon of complex derivation and of wide societal relationships, which vary accQrding to locus and are in some cases evanescent. The problem is one tha...
The introduction and rapid spread of Drosophila subobscura in the New World two decades ago provide an opportunity to determine the predictability and rate of evolution of a geographic cline. In ancestral Old World populations, wing length increases clinally with latitude. In North American populations, no wing length cline was detected one decade after the introduction. After two decades, howe...
A more detailed analysis is made of the energy spectrum of the diffuse component of extragalactic gamma rays over the range of 0.3- 10 GeV, obtained fromthe EGRET instrument at the Compton Gamma Ray Observatory. The derived excess energy spectrum of high galactic latitude, b > 60°, using intercept method shows that it is correlated with Virgo cluster (over lsr) and average Virgo intensity i...
Aim Glacial cycles had a major influence on the distribution of high-latitude species, and while genetic consequences of these cycles have been well studied in the Circumpolar North, notably fewer studies have been undertaken in the Antarctic. Here, we use multilocus genetic data from the South Georgia pintail (Anas georgica georgica) as a proxy to study the presence and timing of ice-free refu...
We examine Robert MacArthur's hypothesis that niche breadth is positively associated with latitude (the latitude-niche breadth hypothesis). This idea has been influential and long standing, yet no studies have evaluated its generality or the validity of its assumptions. We review the theoretical arguments suggesting a positive relationship between niche breadth and latitude. We also use availab...
Airborne transport of microbes may play a central role in microbial dispersal, the maintenance of diversity in aquatic systems and in meteorological processes such as cloud formation. Yet, there is almost no information about the abundance and fate of microbes over the oceans, which cover >70% of the Earth's surface and are the likely source and final destination of a large fraction of airborne...
Basic information on where nonnative plant species have successfully invaded is lacking. We assessed the vulnerability of 22 vegetation types (25 sets of four plots in nine study areas) to nonnative plant invasions in the north-central United States. In general, habitats with high native species richness were more heavily invaded than species-poor habitats, low-elevation areas were more invaded...
The rapidly warming temperatures in high-latitude and alpine regions have the potential to alter the phenology of Arctic and alpine plants, affecting processes ranging from food webs to ecosystem trace gas fluxes. The International Tundra Experiment (ITEX) was initiated in 1990 to evaluate the effects of expected rapid changes in temperature on tundra plant phenology, growth and community chang...
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