Around 115 miles east of Medellín, in Colombia, sits the enormous hacienda built by the drug lord Pablo Escobar—who had his own personal zoo, which included hippos. When Escobar’s empire fell, most of the exotic animals were safely relocated—except for the hippos, who eventually escaped.
“So he brought four from a zoo in the U.S. to Colombia, and they lived at his ranch. And they’ve grown slowly but steadily.”
Jonathan Shurin, ecologist from the University of California in San Diego.
The original population of four in 1981 is estimated to be at least 80 now. Hippos have a tremendous influence on their native ecosystems in Africa, so Shurin wanted to see how they might be affecting their new ecosystem in Colombia.
“It shouldn’t be a surprise to anybody that hippos poop in the water in South America, just as they do in Africa.”
Hippos on both continents wallow in ponds and lakes, where their droppings release a tremendous amount of nutrients into the water.
“That imported material stimulates photosynthesis of algae and aquatic plants and also microbial bacterial production—bacteria that are living off of the organic matter that’s imported.”
And that’s where the hippos can cause ecological trouble. If there is too much photosynthesis occurring, then the water becomes full of oxygen during the daytime. But at night, when the sun goes down, and the plants and algae stop releasing oxygen into the water, a phenomenon called eutrophication occurs. All the creatures that consume oxygen keep consuming it, and the overall amount of oxygen dissolved in the water becomes critically low.
“The oxygen dropping low enough—you can have all the fish sort of croaking and going belly-up.”
The researchers also say the situation provides a unique glimpse into the way that massive mammals like mammoths and mastodons, long extinct in the New World, may have influenced their habitats prior to their extinction.
But they also note that unless we can somehow curtail their population growth, the hippo population could explode in the next couple of decades—at which point, they will disrupt larger and wilder river systems. The study is in the journal Ecology. [Jonathan B. Shurin et al., Ecosystem effects of the world’s largest invasive animal]
Lethal control isn’t a popular management strategy among people who love hippos or see them as a valuable tourism attraction. But the question is when, not if, the hippos become detrimental to Colombian ecology—which means that folks should be thinking about the best way to solve the problem now, when there are fewer than a hundred hippos to manage and not thousands.
—Jason G. Goldman
【参考译文】
在哥伦比亚麦德林以东约115英里处，坐落着大毒枭巴勃罗-埃斯科瓦尔（Pablo Escobar）建造的巨大庄园，他有自己的私人动物园，其中包括河马。当埃斯科瓦尔的帝国衰落时，大多数异国动物都被安全地重新安置，但河马除外，它们最终逃脱了。
"因此，他把四只河马从美国的一个动物园带到了哥伦比亚，它们住在他的农场里。而且它们已经缓慢但稳定地成长。"
乔纳森-舒林，来自圣地亚哥加利福尼亚大学的生态学家。
1981年最初的4个种群，现在估计至少有80个。河马对它们在非洲的本土生态系统有着巨大的影响，因此舒林想看看它们可能如何影响它们在哥伦比亚的新生态系统。
"对任何人来说，河马在南美洲的水里拉屎都不应该是一个惊喜，就像它们在非洲一样。"
两大洲的河马都在池塘和湖泊中打滚，它们的粪便会向水中释放大量的营养物质。
"这些进口物质刺激了藻类和水生植物的光合作用，也刺激了微生物细菌的生产--这些细菌依靠进口的有机物质而生存。"
而这正是河马可能造成生态麻烦的地方。如果有太多的光合作用发生，那么水在白天就会充满氧气。但是到了晚上，当太阳下山时，植物和藻类停止向水中释放氧气，就会出现一种叫做富营养化的现象。所有消耗氧气的生物不断消耗它，溶解在水中的氧气总量变得极低。
"氧气下降到足够低的程度--你可以让所有的鱼都呱呱坠地，变得肚皮朝天。"
研究人员还说，这种情况提供了一个独特的视角，让我们看到像猛犸象和乳齿象这样在新世界早已灭绝的大型哺乳动物在灭绝前可能对其栖息地的影响。
但他们也指出，除非我们能以某种方式遏制它们的人口增长，否则河马的数量可能会在未来几十年内爆发--届时，它们将扰乱更大和更野性的河流系统。该研究发表在《生态学》杂志上。[乔纳森-B-舒林等人，世界上最大的入侵动物的生态系统效应] 。
在热爱河马或将其视为有价值的旅游景点的人们中，致命的控制并不是一个受欢迎的管理策略。但问题是河马何时，而不是是否会对哥伦比亚的生态造成损害--这意味着人们现在就应该考虑解决问题的最佳方法，因为此时需要管理的河马不到一百只，而不是成千上万只。
-Jason G. Goldman
