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201.
Summary The prediction that mothers should invest more in sons than daughters was briefly examined in American bison (Bison bison) by Wolff (1988). He concluded that (a) male calves suckle more than females, (b) cows that had previously produced sons were more likely to be barren, and (c) cows that had male calves became estrous later in the year than other cows. In this paper we present data from two long term studies at different sites to show that Wolff's conclusions are equivocal at best and difficult to reconcile with predictions of the hypothesis because of questionable methods and assumptions.
Offprint requests to: W.C.H. Green 相似文献
202.
Kay Grossmann Thuro Arnold Robin Steudtner Stefan Weiss Gert Bernhard 《Die Naturwissenschaften》2009,96(8):963-974
Low-temperature alteration reactions on uranium phases may lead to the mobilization of uranium and thereby poses a potential
threat to humans living close to uranium-contaminated sites. In this study, the surface alteration of uraninite (UO2) and uranium tetrachloride (UCl4) in air atmosphere was studied by confocal laser scanning microscopy (CLSM) and laser-induced fluorescence spectroscopy using
an excitation wavelength of 408 nm. It was found that within minutes the oxidation state on the surface of the uraninite and
the uranium tetrachloride changed. During the surface alteration process U(IV) atoms on the uraninite and uranium tetrachloride
surface became stepwise oxidized by a one-electron step at first to U(V) and then further to U(VI). These observed changes
in the oxidation states of the uraninite surface were microscopically visualized and spectroscopically identified on the basis
of their fluorescence emission signal. A fluorescence signal in the wavelength range of 415–475 nm was indicative for metastable
uranium(V), and a fluorescence signal in the range of 480–560 nm was identified as uranium(VI). In addition, the oxidation
process of tetravalent uranium in aqueous solution at pH 0.3 was visualized by CLSM and U(V) was fluorescence spectroscopically
identified. The combination of microscopy and fluorescence spectroscopy provided a very convincing visualization of the brief
presence of U(V) as a metastable reaction intermediate and of the simultaneous coexistence of the three states U(IV), U(V),
and U(VI). These results have a significant importance for fundamental uranium redox chemistry and should contribute to a
better understanding of the geochemical behavior of uranium in nature.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
203.
The importance of preserving both protected areas and their surrounding landscapes as one of the major conservation strategies
for tigers has received attention over recent decades. However, the mechanism of how land-use surrounding protected areas
affects the dynamics of tiger populations is poorly understood. We developed Panthera Population Persistence (PPP)—an individual-based
model—to investigate the potential mechanism of the Sumatran tiger population dynamics in a protected area and under different
land-use scenarios surrounding the reserve. We tested three main landscape compositions (single, combined and real land-uses
of Tesso-Nilo National Park and its surrounding area) on the probability of and time to extinction of the Sumatran tiger over
20 years in Central Sumatra. The model successfully explains the mechanisms behind the population response of tigers under
different habitat landscape compositions. Feeding and mating behaviours of tigers are key factors, which determined population
persistence in a heterogeneous landscape. All single land-use scenarios resulted in tiger extinction but had a different probability
of extinction within 20 years. If tropical forest was combined with other land-use types, the probability of extinction was
smaller. The presence of agroforesty and logging concessions adjacent to protected areas encouraged the survival of tiger
populations. However, with the real land-use scenario of Tesso-Nilo National Park, tigers could not survive for more than
10 years. Promoting the practice of agroforestry systems surrounding the park is probably the most reasonable way to steer
land-use surrounding the Tesso-Nilo National Park to support tiger conservation. 相似文献
204.
Recent studies on climate responses in ectothermic (cold-blooded) vertebrates have been few in number and focussed on phenology
rather than morphology. According to Bergmann’s rule, endothermic (warm-blooded) vertebrates from cooler climates tend to
be larger than congeners from warmer regions. Although amphibians are ectothermic vertebrates, weather and climatic conditions
may also impact on their morphology, and thereby affect their survival rates and population dynamics. In this paper, we show,
in a unique long-term study during the period 1963–2003 in an agricultural landscape in western Poland, that the body length
of two water frog parental species (males of both Rana ridibunda and R. lessonae) increased significantly. However, their hybridogenetic hybrid R. esculenta did not show similar changes. A significant relationship with a large-scale climatic factor, the winter North Atlantic Oscillation
index, was found positive for R. ridibunda males and R. lessonae females, and negative for R. esculenta females. Our findings, the first for amphibians, are consistent with other studies reporting that recent climate change has
affected the morphology of animals. However, we also show that changes in amphibian phenotype linked to climate may vary independently
between (even very similar) species. 相似文献