估计是原文的出处,由于太长,我就节选了相关的内容,应该只多不少,耐心看看, 蓝色的段落是和原文内容重复很多的地方, HIGHLIGHT的地方是出了题的, 同样考过这篇文章的也帮忙看看,还有哪处是考点,回帖通知我.
The Monarch butterfly, Danaus plexippus (L.) (Lepidoptera: Danaidae), is a migrant which colonizes Canada each year in the late spring to breed, re-populating its range from its overwintering grounds. There are two distinct populations: a small western one found in Canada only in British Columbia, which overwinters in California, and a much larger eastern population, found east of the Rocky Mountains throughout the rest of Canada, which overwinters in central Mexico. The Monarch varies greatly in abundance and distribution from place to place and from year to year in Canada but, since the Monarch breeds in Canada and the northern U.S., having from one to three generations depending on latitudinal location and other edaphic factors, it generally becomes more common as the summer progresses. Monarchs are most often noticed when they assemble to begin the fall migration south. The large eastern population is most abundant in Ontario due in large part to the low latitude and modifying effect of the Great Lakes on the climatic regime. Eastern Canada provides a significant proportion of the fall migrants that overwinter in Mexico.
The distribution of the Monarch in Canada is determined largely by the distribution of its obligate larval hostplants, the Milkweeds (Asclepias sp.; Asclepiadaceae). There is little doubt that land use changes over the last 200 years have greatly aided the expansion of milkweeds, especially the Common Milkweed, A. syriaca, in the east and Showy Milkweed, A. speciosa, in the west, thus increasing the available range of the Monarch. For example, there has been a demonstrable increase in the abundance and distribution of Monarchs in Ontario over the last 5 decades. A number of conservation issues may affect this distribution greatly in the coming years. These issues include further land use changes, global warming and the concomitant increase in carbon dioxide and low-level ozone, weed control legislation and programs which have direct effects on hostplant availability as well as indirect effects on the habitat as a whole due to herbicide and pesticide spraying, and the spread of invasive alien plant species which alter open habitats and may compete as inappropriate larval hosts.
Of major importance also is the ongoing degradation and destruction of the overwintering roosts in Mexico, as well as future conservation efforts by the United States. All of the breeding Monarchs which make their way to eastern Canada each year have bred in the southern U.S. - the butterflies which reach Canada are one or two generations removed from those that overwintered in Mexico. International cooperation between these three nations is essential to encourage the continuation of the "endangered phenomenon" that is the migration of the Monarch butterfly. International cooperation can provide benefits through protection of the overwintering sites in Mexico and California and through protection of the spring and autumn migratory pathways through the United States. Their protection has a direct impact on the numbers of Monarchs that return to Canada each spring, in turn, Canadian conservation efforts have far-reaching effects on recruitment to the overwintering roosts.
Monarchs from the eastern North American population are most common in southern Ontario and possibly southwestern Quebec where the larval hostplants are most abundant.
The western population of Monarchs breeds in Canada only in the interior of British Columbia between the Rocky and Coastal mountain ranges up to about 52° N latitude with occasional strays being recorded from further north and from the Victoria/Vancouver area where they've been reported to breed on garden milkweeds
Land use changes in Ontario and most southern regions of Canada over the last 200 years have likely served to increase the range of Milkweeds, especially those species such as A. syriaca and A. speciosa which grow in open situations. There is no doubt that Monarch ranges have increased over the last 50 years. Urquhart & Urquhart (1979a) give the breeding range of the Monarch in Ontario during the years 1937-1940 as Kingston to Goderich (approx. 44° N) and south with low numbers breeding in Barrie and Midland to the north. By 1975 they found that the Monarch was commonly breeding along the north shore of Lake Huron from Sudbury to Sault Ste. Marie (47° N) and in Thunder Bay and that in 1977 Monarchs were considerably more common at Sault Ste. Marie than they were at Toronto (Urquhart & Urquhart 1979a). Similarly Urquhart & Urquhart (1979a) reported no breeding in B.C. or Alberta with only scattered larvae recorded through Saskatchewan and Manitoba in the 1940-44 period. More recent records show that breeding does occur in B.C. and Alberta (C. Guppy, pers. comm.; Bird et al. 1995) and that they are now more common in Saskatchewan and Manitoba (Hooper 1973; Klassen et al. 1989). This recent range expansion may slow somewhat but is expected to continue.
The western populations, based on counts at overwintering roosts, have declined over the last five years (Marriott 1994a; 1994b; 1995) possibly due to a Neogregarine protozoan parasite (Leong et al. 1992; Marriott 1993; 1995; Brower et al. 1995). Swengel's (1995) analysis of 4th of July Butterfly Count data shows that both the western and the eastern populations fluctuate dramatically from year to year, often coinciding with major widespread climatic perturbations, but found that no significant increase or decrease in the numbers of Monarchs censused persisted for more than two years. New (1991) and Gaston & McArdle (1993) note that insects whose populations fluctuate dramatically are more likely to become endangered if some catastrophic event occurs at a low point in the natural population cycle. Brower (1995) and others fear that the ongoing degradation and destruction of Mexican overwintering sites may constitute just such a catastrophic event (Wells et al. 1983; Pyle 1983; Brower & Malcolm 1989; Malcolm 1993).
Monarchs, like all butterflies, have four distinct stages in their life cycle: egg, larvae or caterpillar, pupae or chrysalis and imago or adult butterflies. Mated adult females lay their eggs on a variety of Milkweeds. The egg stage in Monarchs lasts about 4 days, larvae grow and develop through 5 instars (growth stages) in approx. 15 days and the pupal stage lasts from 9 to 15 days (Urquhart 1987). Adult butterflies live 2-6 weeks in the summer broods and up to 8 months in the migratory stage. Monarchs are most vulnerable to a wide variety of mortality sources in the larval and pupal stages.
Monarchs obtain cardenolides (cardiac glycosides) - bitter, emetic compounds akin to digitalis - from their Asclepiadaceous hostplants which serve to protect them to some degree from their own predators (Brower 1984). The bold coloration of both larvae and adults advertises their unpalatability in such a way as to "train" their predators to avoid them (Brower 1984; Dempster 1984). Each different kind of Milkweed has a characteristic profile of cardenolides (a chemical "fingerprint") as do the butterflies that feed on them (Roeske et al. 1976). The concentration of cardenolides declines with age so that unpalatable butterflies become progressively more palatable as they age (Malcolm et al. 1993; Alonso-Meija & Brower 1994).
Spring migration into Canada depends greatly on the weather conditions experienced in any particular year but generally butterflies arrive in late May/early June in southern Ontario and in mid-June to early July throughout the rest of the country. Fall migration from southern Ontario is very well documented (Urquhart 1987; Walton 1993; Brenner 1993; Wormington 1994; D. Davis, pers comm.) by the tagging programs which eventually enabled the discovery of the Mexican overwintering sites (Urquhart 1987). Numbers can be very high (Wormington, 1994, estimates that as many as 96,000 butterflies moved through Point Pelee National Park in the space of a few hours on September 6, 1993) but more typically range from 100 - 500 butterflies per day (Brenner 1993; D. Davis, pers. comm.). Data on migration through other provinces is scarce.
The Monarch butterfly is the only current example of what has come to be known as an "endangered phenomenon" (Wells et al. 1993; Pyle 1983; Brower & Malcolm 1989; Malcolm 1993). The scope of the migration undertaken by this species - where the return trip to the overwintering roosts is accomplished by butterflies that are five generations removed from those that made the re-colonization trip north the preceding spring (akin to a person having to find the origin of their great-great-great grandparent with no intergenerational information transfer!) - is truly a phenomenon.
Of major importance also is the ongoing degradation and destruction of the overwintering roosts in Mexico, as well as future conservation efforts by the United States. All of the breeding Monarchs which make their way to eastern Canada each year have bred in the southern U.S. - the butterflies which reach Canada are one or two generations removed from those that overwintered in Mexico.
楼主辛苦。估计考完试大家都成了monarch butterfly的专家了，呵呵。
巨崇拜啊！！
感谢得不知如何表达
顶,
辛苦
楼主真是太好了，呵呵，I know you will be SOMEONE someday.
楼主真是好人啊
谢谢了
崇拜+感激中....
that's what i am talking about.. 
上场文章还是要看,不过看完楼主这个,就不用慌啦!
8月的兄弟姐妹,要发扬CD的优秀传统,就像楼主一样!
赞一个，辛苦了！
太棒了！顶！！！
lz,你真的太好了，感动，谢谢
顶顶顶!
真是个大好人太愿我能遇到这题
下周就考了，万分感动！
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