Population eruptions

INTERACTIONS / LEVELS OF SCALE CONSTRAINTS ON POPULATION ERUPTIONS... 

Many conifer-bark beetle-fimgal systems possess elements of the terpene-based dynamics shown in Figures 4.3 and 4.9. However, most species do not undergo extensive population eruptions. We do not have a clear understanding of the circumstances under which various competing processes will dominate, and hence whether the landscape-level outcomes will be canopy thiiming, gap formation, or forest conversion. We consider this question by evaluating results from two other systems. 

To link these various scales, it is necessary to recognize both that each level of conifer - bark beetle - fungal interaction is characterized by a discrete threshold, and that the outcome at each level depends on feedback among multiple variables (Table 4.4). For example, a beetle can either enter or not enter a tree. However, that discrete outcome is determined by monoterpene and phenolic concentrations and composition, beetle age, the number of rejections already made by a beetle, beetle lipid content, beetle density on the plant surface, beetle genotype, beetle population phase, and presumably other factors. Similar relationships characterize thresholds at the levels of aggregation, host establishment, and population eruption (Table 4.4). 

Lava was extruded with a well mixed population of bubbles so that their initial mass distribution is not a function of vertical position in the flow. This is typically the case in effusive eruptions that produce fluid lava (rather than ash). 

Not all of tlie recent major accidents liave been "man-made. There liave been numerous tragic floods, landslides, volcanic eruptions, and eartliquakes. One such earthquake struck central Guateimila on Februaiy 4, 1976, killing more than 24,000 people and injuring another 50.000. As much as one-sixth of the country s population may ha c been left homeless. The death toll makes this the second worst disaster in Western Hemisphere history, e.xceeded only by the 1970 Peruvian earthquake that took between 50.000 luid 70,000 lives. 

The effects of volcanic emissions on climate were noted by no less a person than Benjamin Erankhn. While hving in Erance, he commented on the persistent haze, dimming of the sun, and unusually cold summer of 1783 and speculated that a volcanic eruption might have been the cause (Franklin, 1789). Although he was not aware of a massive fissure in Iceland at the time, his observation was correct. On Iceland an eruption rained ash that caused death of grass and starvation of hvestock and killed 25% of the population from the resulting famine. 

Health concerns regarding VA have focused primarily on respiratory effects in heavily exposed populations such as short-term respiratory irritation and longer-term development of pneumoconiosis. The potential toxicity of crystalline silica in the ash has been of particular concern (Baxter et al, 1999 Wilson et al, 2000 CDC, 1986 Vallyathan et al, 1983a,b Baxter et al, 1983). These studies indicate that the potential toxicity of VA can vary between different ash eruptions from a given volcano and between different volcanoes. The variability is probably due to difference in the crystalline silica content and in the proportion of respirable particles. 

Here one can easily see how the eruption or extraction of mites from the skin would lead to the belief that they are themselves a morbid product of the body. And Aristotle explicitly says that flesh must be the matter out of which such insects come. Even such a seemingly incorruptible matter as snow has its characteristic living product. When old snow turns red, Aristotle says Hist. an. 552b6-8), it can generate small insects. It is said that this observation of insect-populated algae growing on snow was not remarked again until 1778, by the Swiss naturalist Horace-Benedict de Saussure. 

In general, a contaminant or potentially hazardous material may be presented to the population in one of several ways. It may be uncovered by natural processes such as water erosion or a volcanic eruption or it may be brought to the surface by man-made activities such as mining or quarrying. Alternatively, it may be a new problem in that it is a completely novel synthetic compound not encountered before in nature, or it may be a natural product which is now, owing to man s intervention, produced in quantities not previously seen. 

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