首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
Today, we are going to be continuing our discussion of evolution, specifically how the forces of natural selection and environme
Today, we are going to be continuing our discussion of evolution, specifically how the forces of natural selection and environme
admin
2019-08-27
50
问题
Today, we are going to be continuing our discussion of evolution, specifically how the forces of natural selection and environmental pressures interact. Last time we said that for any species the most important urge is to reproduce and ensure survival of the species. Now any organism has a set amount of energy it can’t devote to the task of reproduction to produce eggs, find a mate, rear its offspring, etc. But different species have different strategies for how they use that energy. Let’s look at two examples to clarify this. For this purpose we’ll compare two aquatic animals: the blue whale and the American shad.
The blue whale reproduces quite slowly. Females don’t reach sexual maturity until they are about ten years old. They take an entire year to give birth, and the calf is dependent on its mother for at least the next 6 months. That means at maximum, blue whales can reproduce once every two years, and it’s often more like every three years. In the context of this low birth rate, every calf is valuable, and a considerable amount of energy is devoted to caring for the calf and ensuring its survival.
The American shad reach sexual maturity in as little as three years. They breed every single year. And in one breeding season a female American shad may lay as many as 300, 000 eggs. Of course, only a tiny fraction of these will survive to become mature shad themselves. After the female shad lays her eggs, she moves back into the ocean leaving her young to fend for themselves.
So blue whales and American shad employ entirely different reproductive strategies that kind of lie on opposite ends of the spectrum. Blue whales invest all of their energy into a small number of offspring, while American shad put their energy into reproducing in huge numbers but with a very low chance of survival into maturity.
Many other species follow one of these two reproductive strategies. Those that fit into the pattern of the blue whale are known as K-strategies, and those that reproduce in large numbers with low chances of survival for individual offspring are known as R-strategies. So what determines whether a species evolves to be a K-strategist or R-strategist? Well, it largely has to do with the environmental pressures that the species faces and how they fit into their overall habit.
Blue whales are the biggest organisms in the ocean, and as such they have no natural predators. What’s more, their large bodies mean that they can build up large reserves of fat to sustain them when food is scarce. As a result, a mature blue whale has a very good chance of survival from year to year. In fact, if a blue whale manages to survive its childhood and reach maturity, it will most likely continue to live until it either dies of disease or old age. What all this means is that the blue whale population tends to be pretty stable. It generally doesn’t experience massive or sudden declines, or at least it didn’t until humans started disrupting its habitat.
American shad lead a much riskier existence. Even when they reach maturity they are preyed upon by a number of larger fish. Moreover, their population is much more susceptible to food shortage and mass starvation. But this is balanced out by the shad’s ability to reproduce quickly, but it can always bounce back.
Which of the following species is most likely to be an R-strategist?
选项
A、The koala.
B、The gorilla.
C、The kangaroo.
D、The polar bear.
答案
D
解析
本题细节定位于第四段第二句话“Blue whales invest all of their energy into a small number of offspring,while American shad put their energy into reproducing in huge numbers but with a very low chance of survival into maturity.”和倒数第三段第二、三句话“Those that fit into the pattern of the blue whale are known as K-strategies…it largely has to do with the environmental pressures that the species faces…”。由此可知,蓝鲸将所有精力都投入到养育数量很少的幼鲸上,而美国鲥鱼的精力投入到大量繁殖上,但其后代的生存率却很低。蓝鲸的繁殖模式被称为K策略,美国鲥鱼的繁殖模式被称为R策略。物种的进化策略在很大程度上与其面临的环境压力有关。据此可以推知,北极熊很可能发展成R策略这种繁殖模式,因此选择D。
转载请注明原文地址:https://kaotiyun.com/show/wbTO777K
0
考博英语
相关试题推荐
Islanguage,likefood,abasichumanneedwithoutwhichachildatacriticalperiodoflifecanbestarvedanddamaged?Judgin
It’sabouttimeparents______thegapsbetweenthemandtheirchildren.
SomeAfricanAmericanshavehadaprofoundimpactonAmericansociety,changingmanypeople’sviewsonrace,historyandpolitic
Whatoursocietysuffersfrommosttodayistheabsenceofconsensusaboutwhatitandlifeinitoughttobe;suchconsensusca
Whatdotheextraordinarilysuccessfulcompanieshaveincommon?Tofindout,welookedforoperations.Weknowthatcorrelation
Writeanessayonthetopic"OnUniversity"accordingtothefollowingoutlineandpresentyourargumentwithsupportingdetails
Everynightshelistenedtoherfathergoingaroundthehouse,lockingthedoorsandwindows.Shelistened;thebackdoorclosed
InsomeCaliforniahousingestates,akeyaloneisinsufficienttogetsomeoneinthedoor;hisorhervoiceprintmustalsobe__
当今世界正在发生广泛而深刻的变化。由于经济全球化与信息化的发展,科学技术迅猛进步,世界变成了“地球村”。各国相互联系,相互依存,利益交融达到了前所未有的程度,需要携手应对的问题越来越多,互利合作的愿望越来越强,从某种意义上讲,世界已是一种“利益共同体”。
随机试题
Ifyou’relikemanypeople,youmayhavedecidedthatyouwanttospendlesstime【C1】________atyourphone.It’sagoodidea:an
Everyfewweeks,outsidethemovietheatreinpracticallyanyAmericantowninthelate1910s,stoodthelife-sizedcard-boardf
血清学指标AFP增高的疾病包括
固定成本与产量的变动无关。()
甲因受贿罪被判处有期徒刑15年,服刑8年后获得假释,在假释考验期内的第3年,故意致人重伤,被判刑6年。根据《刑法》规定,对甲应撤销假释,按照数罪并罚的规定处理,在()范围内适用有期徒刑。
关于债券的风险,下列表述错误的是()。
分析下面的谱例。要求:说明乐句间主要的结构特点。
你负责开一个推介会,向中小企业宣传国家政策和项目,你要重点关注哪些问题?
[1996年]要求结合所学知识分析材料回答问题。材料1恩格斯指出:“就一切可能看出,我们还差不多处在人类历史的开端,而将来纠正我们的错误的后代,大概比我们可能经常以极为轻视的态度纠正其认识错误的前代要多得多,”“科学史就是把这种谬误逐渐消除或是更换为新
A、46.B、50.C、2.D、27.DHowmanypeopleworkintheofficenow?
最新回复
(
0
)