首页
登录
职称英语
Non-indigenous (non-native) species of plants and animals arrive by way of t
Non-indigenous (non-native) species of plants and animals arrive by way of t
游客
2024-01-01
29
管理
问题
Non-indigenous (non-native) species of plants and animals arrive by way of two general types of pathways. First, species having origins outside the United States may enter the country and become established either as free-living populations or under human cultivation-for example, in agriculture, horticulture, aquaculture, or as pets. Some cultivated species subsequently escape or are released and also become established as free-living populations. Second, species of either US or foreign origin and already within the United States may spread to new locales. Pathways of both types include intentional as well as unintentional species transfers. Rates of species movement driven by human transformations of natural environments as well as by human mobility-through commerce, tourism, and travel-greatly exceed natural rates by comparison. While geographic distributions of species naturally expand or contract over historical time intervals (tens to hundreds of years), species-ranges rarely expand thousands of miles or across physical barriers such as oceans or mountains.
Habitat modification can create conditions favorable to the establishment of non-indigenous species. Soil disturbed in construction and agriculture is open for colonization by non-indigenous weeds, which in turn may provide habitats for the non-indigenous insects that evolved with them. Human-generated changes in fire frequency, grazing intensity, as well as soil stability and nutrient levels similarly facilitate the spread and establishment of non-indigenous plants. When human changes to natural environments span large geographical areas, they effectively create passages for species movement between previously isolated locales. The rapid spread of the Russian wheat aphid to fifteen states in just two years following its 1986 arrival has been attributed in part to the prevalence of alternative host plants that are available when wheat is not. Many of these are non- indigenous grasses recommended for planting on the forty million or more acres enrolled in the US Department of Agriculture Conservation Reserve Program.
A number of factors perplex quantitative evaluation of the relative importance of various entry pathways. Time lags often occur between establishment of non-indigenous species and their detection, and tracing the pathway for a long-established species is difficult. Experts estimate that non-indigenous weeds are usually detected only after having been in the country for thirty years or having spread to at least ten thousand acres. In addition, federal port inspection, although a major source of information on non-indigenous species pathways, especially for agriculture pests, provides data only when such species enter via closely-examined routes. Finally, some comparisons between pathways defy quantitative analysis-for example, which is more "important": the entry path of one very harmful species or one by which many but less harmful species enter the country? [br] Which of the following statements about species movement is best supported by the passage?
选项
A、Human factors affect species movement rates more than its long-term amount.
B、Natural expansions of species account for their slow natural contractions.
C、Natural environments created by human activities contribute much to species movement.
D、Long-range movement of species depends on the geographic extent of human mobility.
答案
D
解析
转载请注明原文地址:https://tihaiku.com/zcyy/3325154.html
相关试题推荐
Athirdfossilformationcontainingbothsoft-bodiedandhard-bodiedanimals
Onlyrecentlyhaveinvestigatorsconsideredusingtheseplantstocleanups
Muchoftheresearchonnutrientdeficienciesisbasedongrowingplantshyd
Muchoftheresearchonnutrientdeficienciesisbasedongrowingplantshyd
Ecologistshavestudiedthefourchipmunkspeciesthatoccurontheeastern
Themostaggressiveofthefoureastern-slopespeciesisthelodgepolechipm
Themostaggressiveofthefoureastern-slopespeciesisthelodgepolechipm
Theanswer,inoneword,isaggression.Chipmunkspeciesactivelydefendthe
Ecologistshavestudiedthefourchipmunkspeciesthatoccurontheeastern
Ecologistshavestudiedthefourchipmunkspeciesthatoccurontheeastern
随机试题
平面图所示的两个建筑从上至下分别是( )。 A.赖特设计的流水别墅和密斯·范
A. B. C. D.
央行采取降低准备金率政策,其政策效应是( )。A.商业银行体系创造派生存款的能
用分段沉淀法分离三萜皂苷的主要依据是混合物中各组分A.极性不同B.基本骨架不同C
各种运输方式内外部的各个方面的构成和联系,就是( )。 A.运输系统
材料在自然状态下单位体积所具有的质量称为( )。A.孔隙率 B.空隙率 C
在证券市场上,投机者的投机活动是具有双重作用的活动,它有积极意义,也有消极意义,
以下属于期货价差套利种类的有( )。A.跨期套利 B.跨品种套利 C.跨市
根据折算标准的不同,汇率的标价方法可分为()。A.直接标价法 B.美元标价法
男,60岁,有慢性支气管炎病史,患肺心病10年,发现高血压5年。突然出现气急、大
最新回复
(
0
)