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751.
Bee-pollinated plants are frequently dichogamous: e.g. each flower has a discernable male and female phase, with only the
male phase offering a pollen reward. Pollen-collecting bees should therefore discriminate against female-phase flowers to
maximise their rate of pollen harvest, but this behaviour would reduce plant fitness due to inferior pollination. Here, we
test the hypothesis that flowers use pollen-mimicking floral guides to prevent flower-phase discrimination. Such floral guides
resemble pollen in spectral reflection properties and are widespread among angiosperm flowers. In an array of artificial flowers,
bumblebees learned less well to discriminate between flower variants simulating different flowering phases when both flower
variants carried an additional pollen-yellow guide mark. This effect depended crucially on the pollen-yellow colour of the
guide mark and on its spatial position within the artificial flower. We suggest that floral guides evolved to inhibit flower-phase
learning in bees by exploiting the innate colour preferences of their pollinators. 相似文献
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Sutter K Jung K Krauss GJ 《Environmental science and pollution research international》2002,9(6):417-421
The assessment of pollution in aquatic systems necessitates an accurate indication of toxicity of heavy metals for organisms and ecosystems. We used the stable nitrogen isotope 15N to estimate the influence of the heavy metals Cd, Pb and Zn on the synthesis of nitrogen-containing fractions in the aquatic moss Fontinalis antipyretica. This method permits conclusions concerning inhibitory effects of these heavy metals on the assimilation of nitrogen and the biosynthesis of amino acids and proteins. The moss was exposed to metal concentrations of 25-500 microM over a period of 5-10 days. 15N abundance of exposed plants was compared with that of control plants. Similar to a loss of vitality determined using a fluorometric assay, a decrease of the 15N abundance in the N fractions of Fontinalis antipyretica was measured in dependence on the metal concentration. Nevertheless, the individual inhibition by the distinct metals was different, so that the following order of toxicity was derived: Cd > Pb > Zn. 相似文献
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This article focuses on developing a sustainable tourism in small Caribbean islands, defined here as those that have populations
of fewer than 500,000. Such islands share a very fragile ecology and a high dependence on tourism. They differ in their degree
of tourist penetration and visitor density and the related degree of environmental degradation.
To explain the link between tourism intensity and ecological vulnerability, the so-called “destination life-cycle model” is
presented. This suggests that islands pass through three primary stages of tourist development low-density exploration, rapid
growth and consolidation, and high-density maturation involving the substitution of man-made for natural attractions.
A broad empirical test of the model is performed through a quantitative examination of the tourism characteristics and visitor
densities of a cross section of 23 small Caribbean islands. The three basic stages or tourism styles are identified: low-impact
emerging areas, high-density mass-market mature destinations, and rapidly growing intermediate islands in between. Some broad
strategies consistent with the systems framework for a sustainable tourism with moderate densitites are briefly explored.
An earlier version of this article was presented to Caribbean Conservation Association Conference on Economics and the Environment.
Barbados, West Indies, 6–8 November, 1989. 相似文献