Какое адаптивное значение имеет у животных зимняя или летняя спячка?

The economy of the United States is the world's largest single national economy. The United States' nominal GDP was estimated to be $16.6 trillion in June 2013,[1] approximately a quarter of nominal global GDP.[2] Its GDP at purchasing power parity is also the largest of any single country in the world, approximately a fifth of the global total.[2] The United States has a mixed economy[22][23] and has maintained a stable overall GDP growth rate, a moderate unemployment rate, and high levels of research and capital investment. Its five largest trading partners are Canada, China, Mexico, Japan, and Germany.The US has abundant natural resources, a well-developed infrastructure, and high productivity.[24] It has the world's sixth-highest per capita GDP (PPP).[2] The U.S. is the world's third-largest producer of oil and second-largest producer of natural gas. It is the second-largest trading nation in the world behind China.[25] It has been the world's largest national economy (not including colonial empires) since at least the 1890s.[26] As of 2010, the country remains the world's largest manufacturer, representing a fifth of the global manufacturing output.[27] Of the world's 500 largest companies, 132 are headquartered in the US, twice that of any other country.[28] The country is one of the world's largest and most influential financial markets. About 60% of the global currency reserves have been invested in the US dollar, while 24% have been invested in the euro. The New York Stock Exchange is the world's largest stock exchange by market capitalization.[29] Foreign investments made in the US total almost $2.4 trillion, which is more than twice that of any other country.[30]American investments in foreign countries total over $3.3 trillion, which is almost twice that of any other country.[31] Consumer spending comprises 71% of the US economy in 2013.[32] The labor market has attracted immigrants from all over the world and its net migration rate is among the highest in the world. The U.S. is one of the top-performing economies in studies such as the Ease of Doing Business Index, the Global Competitiveness Report,[33] and others. The US is ranked first globally in the IT industry competitiveness index. только цифры в скобках не пиши