GRE写作Issue部分精品素材分享之外来物种

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生物多样性下降的原因

Some characterize loss of biodiversity not as ecosystem degradation but as conversion to trivial standardized ecosystems (e.g., monoculture following deforestation). In some countries lack of property rights or access regulation to biotic resources necessarily leads to biodiversity loss (degradation costs having to be supported by the community).

A September 14, 2007 study conducted by the National Science Foundation found that

biodiversity and genetic diversity are dependent upon each other—that diversity within a species is necessary to maintain diversity among species, and vice versa. According to the lead researcher in the study, Dr. Richard Lankau, “If any one type is removed from the system, the cycle can break down, and the community becomes dominated by a single species.”

外来物种对生物多样性的威胁

The widespread introduction of exotic species by humans is a potent threat to biodiversity. When exotic species are introduced to ecosystems and establish self-sustaining populations, the endemic species in that ecosystem, that have not evolved to cope with the exotic species, may not survive. The exotic organisms may be either predators, parasites, or simply aggressive species that deprive indigenous species of nutrients, water and light. These exotic or invasive species often have features, due to their evolutionary background and new environment, which make them highly competitive; able to become well-established and spread quickly, reducing the effective habitat of endemic species.

As a consequence of the above, if humans continue to combine species from different ecoregions, there is the potential that the world‟s ecosystems will end up dominated by relatively a few, aggressive, cosmopolitan “super-species”.

食品与生态

Many have challenged the notion that there is “vast untapped potential” for reducing humankind‟s dependence on a relatively small number of domesticated plant and animal species. Jared Diamond, based on studies of the domestication of plants and animals, argued that the rarity of species suitable for domestication and their occurrence in just a few parts of the world, determined the limited number of locations in which major civilizations could arise. In recent times there have been many studies of minor food sources, but none of these sources have subsequently become major food crops.

适当技术AT的概念

Appropriate Technology (AT) is technology that is designed with special consideration to the environmental, cultural, social and economic aspects of the community it is intended for. With these goals in mind, AT typically requires fewer resources, is easier to maintain, and has a lower overall cost and less of an impact on the environment.

Proponents use the term to describe technologies which they consider to be suitable for use in developing nations or underdeveloped rural areas of industrialized nations, which they feel cannot operate and maintain high technology. Appropriate Technology usually prefers labor-intensive solutions over capital-intensive ones, although labor-saving devices are also used where this does not mean high capital or maintenance cost.

In practice, it is often something that might be described as using the simplest level of technology that can effectively achieve the intended purpose in a particular location. However, the terminology is not very precise.

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