A great many factors can influence the size of a population of a certain species located within a certain area. What can these factors be and how do they influence one another?
A population of a species filling a certain niche in an area does not exist in a vacuum. They are involved within the greater biological community in which various species interact with each other on a whole host of different levels. For example, if the certain species we are looking at are primary consumers in the habitat then they are dependent upon the number of edible plant resources available in the area. The point at which the resources stop being enough to support additional growth of the population is known as the carrying capacity of that area. In other words, the population can only grow so much before demand outstrips the supply and in extreme cases can lead to the decline of the species. The population of predators, (or secondary consumers and so on) disease, loss of habitat, and reproductive issues such as the loss of genetic variation can all have effects on the population size of a certain species.
During the time period of (roughly) 1955-1975, the United States was involved in the Vietnam War during which more than 58,000 American servicemen lost their lives. The war eventually ended with the failure of the United States to keep the North Vietnamese from overrunning the south mostly due to the negative public approval of increased military intervention. What other factors made the United States unable to completely stop the advances of the NVA and Viet Cong?
The loss of the Vietnam War can be traced to very many different causes. However, it is generally agreed that a combination of bombing supply routes that could be easily re-routed by the enemy such as the Ho Chi Minh trail, the emphasis of body count instead of territorial gains by U.S. commanders, and the ability of the enemy such as the Viet Cong to hide in plain sight among the civilians and others led to the collapse of a feasible victory in the conflict.
Metaphors are one of the most powerful tools in writing for creating meaning by directly comparing two things that someone wouldn't normally associate together. Besides this, what other facts about metaphors make them so powerful and thus be used throughout the history of literature?
Metaphors generally use more 'concrete' words as in regular verbs or nouns than many other types of literary devices. The use of these words in the comparison of different things instead of more abstract words such as adverbs and adjectives is more powerful because the association is directly made into the reader's head. It is akin to 'showing' the reader the meaning of the piece rather than just telling.