1. GWD-6-Q9 to Q12小树懒为什么要往他妈背上爬 The sloth bear, an insect-eating animal native to Nepal, exhibits only one behavior that is truly distinct from that of other bear species: 树懒作为一种食昆虫的尼泊尔的本土的动物,所展现的只有一种行为与其他的熊类同胞不同: the females carry (5) their cubs (at least part-time) until the cubs are about nine months old, even though the cubs can walk on their own at six months. 雌性的会背着他们的幼兽知道他们大概9个月大,即使它们在6个月的时候就已经可以自己行走了。 Cub-carrying also occurs among some other myrmecophagous (10) (ant-eating) mammals; therefore, one explanation is that cub-carrying is necessitated by myrmecophagy, since myrmecophagy entails a low metabolic rate and high energy expenditure in (15) walking between food patches. 背着幼兽也发生在很多食蚁性的哺乳动物身上;因此,一种解释是背着幼兽对食蚁动物是必需的,因为她们遗传了在行走时低代谢,搞能量消耗。 (16) However, although polar bears’ locomotion is similarly inefficient, polar bear cubs walk along with their mother. 然而,尽管北极熊的移动同样的低效,但是他们的幼兽都是跟着妈妈行走的。 Furthermore, the daily movements of sloth (20) bears and American black bears— which are similar in size to sloth bears and have similar-sized home ranges— reveal similar travel rates and distances, suggesting that if black bear cubs are (25) able to keep up with their mother, so too should sloth bear cubs.长毛熊cub-carrying的一种解释及缺陷 此外,树懒和美国黑熊他们在领地和身体的尺寸上基本相同,他们的每日的移动显示出相似的移动率以及距离,说明,如果黑熊的幼兽能够跟得上他们的妈妈,那么树懒也同样跟得上。 An alternative explanation is defense from predation. Black bear cubs use trees for defense, whereas brown bears (30) and polar bears, which regularly inhabit treeless environments, rely on aggression to protect their cubs. 另一种解释来自于掠夺行为,黑熊的幼兽使用树来作防御,然而,灰熊和北极熊生长于没有树的环境,因此通过进攻来保护他们的幼兽。 Like brown bears and polar bears (and unlike other myrmecophagous mammals, which are (35) noted for their passivity), sloth bears are easily provoked to aggression. 与灰熊和北极熊相似(不像其他那些食蚁哺乳动物以被动性著称),树懒更容易被激怒而采取进攻。 Sloth bears also have relatively large canine teeth, which appear to be more functional for fighting than for foraging. (40) Like brown bears and polar bears, sloth bears may have evolved in an environment with few trees. 树懒还拥有相对来说较大的犬齿,他们的作用更像是为战斗而不是食草。像灰熊以及北极熊一样,树懒也可能已经扩展到那些没有树的环境中去了。 They are especially attracted to food-rich grasslands; although few grasslands (45) persist today on the Indian subcontinent, this type of habitat was once wide- spread there. 他们尤其对食物充足的草原感兴趣:尽管现在在印度的次大陆只保留了很少的草原,但他们的栖息还是曾经在那里传播。 Grasslands support high densities of tigers, which fight and sometimes kill sloth bears; sloth bears (50) also coexist with and have been killed by tree-climbing leopards, and are often confronted and chased by rhinoceroses and elephants, which can topple trees. 草原拥有大量的老虎,他们有时会捕杀树懒;树懒也同样与可以爬树的美洲虎共存或被其捕杀,同时也经常会面对或遭到那些可以倾倒大树的犀牛和大象的追捕。 Collectively these factors probably (55) selected against tree-climbing as a defensive strategy for sloth bear cubs. 所有这些方面可能都决定了树懒选择爬树作为抵御他们的策略。 Because sloth bears are smaller than brown and polar bears and are under greater threat from dangerous animals, (60) they may have adopted the extra precaution of carrying their cubs. 因为树懒比灰熊或是北极熊小很多并且对那些有危险动物的威胁要来得更怕,他们会背起他们的幼兽来作为额外的防范措施。 Although cub-carrying may also be adoptive for myrmecophagous foraging, the behavior of sloth bear cubs, which climb on their (65) mother’s back at the first sign of danger, suggests that predation was a key 尽管,背着幼兽这种树懒的一旦发现危险就第一时间跳上妈妈的背上的行为可能同样被食草的食蚁动物所采纳,但看起来掠夺行为才是最主要的原因。 |