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森林的河流
 离开水的河豚,后背上落了一只鸟. (Photo by R. Butler)
更多的河豚图片.
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写 Rhett Butler. 翻译 Che Fei
07/12/2007
流动的草地
流动的植物与被水淹没的植物相比,优势在于能够照射到阳光而起能很容易的从白水河中获取营养.而被淹没的植物在暗淡的河水中很难获得足够的阳光来进行充分的光和作用.
在一些地区,漂浮的草地由小树,灌木和藤本植物形成了独特的生态系统.这些草地在面积上超过一平方英里而且成了大多数脊椎动物和无脊椎动物的家园.一种很有名的漂浮草地的居住者,世界上最大的啮齿类动物--河豚. 河豚看起来像50kg的猪,经常被看见在漂流的草地上吃草或者在河边休息.尽管它看起来不像会游泳的,其实他游泳能力非常强,因为它有带蹼的脚.它们通常是10-15个个体聚集在一起生活,而且是晚上活动.它们的数量因为过度的捕猎有所减少,但幸好他们有比较高的繁殖率而且现在已经有可持续发展计划了.
另一种发现的事和在漂流的草地上生活的动物是海牛.海牛, 被认为是大象的后代,是古代传说中美人鱼的来源.尽管它们长度可达15英尺,而且比较矮胖,但是经常还是有水手弄错把它们当成美丽的少女,因为它们一半像鱼,一半像人.海牛在海洋生态系统和弗罗里达州的Orinico到亚马逊流域的淡水生物栖息地都有发现.海牛是一种行动缓慢,没有危险的生物,它们把大多数时间用来睡觉,而且要消耗大量的草和水生植物.在洪涝季节,大量的水生植物和草很容易获得,海牛每天吃的量超过110磅（50kg）.当洪水退去的时候,食物缺少了,海牛主要依靠它积攒的脂肪而且降低新陈代谢的速率.有趣的事,海牛有很好的牙齿更新替换机制,因为它的牙齿被它经常吃的食物里面的二氧化硅磨损.因为它们的体型比较大,成年的海牛没有天敌,但是尽管如此它们如今由于人类的打猎,使它们居住地的丧失,水上船的航行以及人类的其他行为使它们陷入了危险之中.
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亚马逊的睡莲,巴西 1999. (Photo by R. Butler). |
发现在亚马逊流域和其它热带水域有大量的睡莲,它们聚集形成了比较小的流动草地. 亚马逊睡莲中最华丽的事王莲.测量的直径是4英尺,它可以承受一个小孩的重量.亚马逊睡莲有着比较异常的授粉周期.巨大的白色花朵,有的大小如一只门板,在黄昏时候以很快的速度开放.这些花朵释放出奶油糖果的气味而且刺激引起花朵中央的温度升高使之比周围的温度要高.香味结合高温吸引圣甲虫聚集到花朵中央.当夜晚来临的时候,花朵就闭上了,把这些甲虫就困在里面了.到黎明的时候,花朵会变成粉红色,甲虫开始吃花朵内部的东西.到傍晚的时候,花朵变成了带微红的深紫色,重新开放,甲虫们带着花粉飞走了,去寻找下一朵睡莲花.通过这种方式,它们把花粉从第一朵带走,并给下一朵授粉..
一种常见的睡莲居住鸟类是 水雉,它有一种本领就是用它们很长的足部可以在水面上跑或者在植物上漂浮,这可以把它们的体重充分的分散使它们不会下沉.水雉在漂浮的植物上筑巢,当它们的蛋或者幼体受到威胁时,成年的鸟假装挥动翅膀来分散捕食者的注意力,其实它们不会飞 .
在高水位和低水位时,漂浮的或者淹没的植物为居住的脊椎动物和无脊椎动物提供果实或种子.漂浮草地的一平方英里的淹没根部区域可以支撑超过5万个的无脊椎动物个体.这些包括昆虫(尤其是幼虫),软体蠕虫,蛛形动物和甲壳类动物.
复习题:
[打印版]
续: 河边的生物
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