不可思議 鮭魚的性行爲竟然能改變地理形貌

Sex. It drives people to do crazy things. Animals too. They'll make unsettling sounds, perform complex dances, or show off giant plumes of colorful feathers.

性會讓人們做些瘋狂的事情。動物也不例外。它們會發出讓人心緒不寧的聲音、表演複雜的舞蹈、或是炫耀絢麗多彩的羽毛。

And, famously, salmon will swim hundreds of kilometers upstream to get down to business. They also inadvertently rework the landscape.

而最著名的，就是鮭魚會向上遊遊數百千米來解決性的問題。它們在無意中改變了生態景觀。

"Adult salmon spend most of their life out in the ocean and then they come in to freshwater to mate." Washington State University ecologist Alex Fremier. "What the female salmon will do is, she digs a hole in the streambed."

華盛頓大學的生態學家阿萊克斯·弗萊米爾表示：“成年鮭魚一生中大多數時間都在海里，但是當它們交配時要去淡水區。而雌性鮭魚所需要做的就是在河牀上挖一個洞。”

That little hole is called a redd. That's where the salmon lays her eggs. And Fremier says when she builds it, she basically "unpacks" the streambed, making all those loose sands and gravels more mobile.

挖的這個小洞被稱爲redd，就是鮭魚產卵的地方。弗萊米爾稱，當雌性鮭魚建造好這個洞以後，她基本上就是將河牀“解壓”了，讓鬆軟的沙子和碎石更易流動。

High water and flooding events move that sediment, which in turn exposes bedrock to further erosion.

高水位以及汛期會使砂石等沉積物移動，這樣反過來也會增加基岩的腐蝕程度。

"It's quite impressive. We did not expect to have salmon, in some cases, changing the vertical position of a river channel up to 30 percent more than it would have without salmon in it."

“這的確非常震撼。與沒有鮭魚的河道相比，我們沒有想過鮭魚會將河道的垂直距離改變30%左右。”

Fremier hypothesized that salmon not only influence landscape evolution, but that the evolution of salmon as a species itself has a landscape-level impact.

弗萊米爾假設，鮭魚不僅可以影響景觀演化，同時它們自身的進化也會影響自然景觀。

To test the idea, he and colleagues recreated salmon redds in an experimental flume.

爲了驗證這一想法的正確性，弗萊米爾和同事們在實驗水槽中製造了鮭魚的“redd”。

Then they compared findings from the flume with real field observations. They cross-referenced all that data with discoveries from a study that modelled river profile erosion over five million years.

之後，他們將研究結果與實地觀察結果進行比較，並將發現的所有數據和之前模擬的五百萬年前的河流橫斷面的研究進行了對照。

"We were stunned by the fact that it actually had a larger scale effect, given that we account for tectonic uplift, the big floods, like a lot of flood water moving downstream, different conditions of the gravel sizes on the river. I think we were all surprised by the fact that salmon could have such a large effect at that million-year scale."

“隨後我們被這樣一個事實驚呆了，因爲它實際上有一個更大規模的效應。因爲我們還考慮到構造隆起、洪水等因素，比如大量洪水向下遊移動、河流裏不同尺寸條件下的碎石。我想我們都對鮭魚能在這百萬年裏有如此巨大的影響感到驚訝。”