低緯度的熱帶地區長期以來被認為是生物多樣性較豐富的地方，但科學家卻未能有確切的證據證明此一論點。一項新的研究發現，熱帶地區除了是孕育新物種的生物搖籃外，亦為古老生物留存的生態博物館。
此份報告的主筆作者、芝加哥大學地球物理科學教授賈布隆斯基說：「假如你初次從外太空來到地球，開始隨意觀察此地的生命，至少在人類來到地球之前，你首先會發現的是熱帶地區豐富多樣的生命。這是地球上最驚人的生物多樣性模式。」
該研究團隊為《科學》期刊分析雙殼貝而獲得這份研究資料，雙殼貝綱是包括蛤蠣、扇貝和牡蠣的海洋生物類別，「牠們到處都可生存，」賈布隆斯基表示，「從北極海到熱帶最炎熱的地方，都留下了大量的化石紀錄。」
這項化石紀錄讓研究團對得以追蹤到過去超過150種的雙殼貝，並且判斷牠們在何處開始出現、延續多久，以及分佈和存續的地點。
研究人員發現，不管氣候狀況如何，每隔一段時間皆有持續的模式出現。在整整1100萬年間，研究人員發現在熱帶地區出現的雙殼貝種類，是高緯度的兩倍，此外，只生存在熱帶地區的生物僅30種遭遇滅絕，而生活在在熱帶以外地區，包含各種緯度的生物，有107種已經滅絕。
「發現這個模式很重要，且令人驚喜，」賈布隆斯基說，「顯示出其他動植物也是以這種模式生存的，甚至在陸地上的生物也是。」報告的共同作者、加州大學聖地牙哥分校生物學家羅伊表示，「全世界的生物是網網相連的，這是個地球村，對生物來說也是。」不過，生物演化的洪流為何是從熱帶地區開始的，卻仍舊是個謎。
現在研究團隊將把研究的時間往前推，找出是什麼讓熱帶地區的生物多樣性如此豐富的。他們相信這份報告已說明了加強熱帶地區保育工作的重要性。
羅伊表示，「人類造成熱帶地區生物的滅絕，最終將影響溫帶和高緯度地生物多樣性，這在未來50年雖未必明顯可見，但卻會造成相當長遠的影響。」
The tropics have long been identified as much richer in biodiversity than higher latitudes, but scientists have been unsure why this is the case. A new study answers the question, finding that the tropics are both a cradle of biodiversity, where new species originate, and a biodiversity museum, where old species persist.
"If you came from outer space and you started randomly observing life on Earth, at least before people were here, the first thing you'd see was this incredible profusion of life in the tropics," said the report's lead author, David Jablonski, a professor of geophysical sciences at the University of Chicago. "This is the single most dramatic biodiversity pattern on this planet."
The team acquired its data for the Science study by analyzing bivalves, a class of marine life that includes clams, scallops and oysters. "They live everywhere," Jablonski said. "They're found from the Arctic Ocean to the hottest part of the tropics, and they have left a great fossil record."
The record allowed the research team to track more than 150 bivalve lineages back through time and determine where they started and how long they lasted as well as where they persist and spread.
They found a consistent pattern in each slice of time, regardless of the prevailing climatic conditions. Over the entire 11-million-year period, they found that more than twice as many bivalve lineages started in the tropics than at higher latitudes. Meanwhile, only 30 varieties of organisms that lived only in the tropics went extinct, compared to 107 that lived outside the tropics, or at all latitudes.
"It's a really striking, surprising pattern," Jablonski said. "And it appears that other animals and plants were playing the same game, even on land." "The world is connected," added study coauthor Kaustuv Roy, a biologist at the University of California at San Diego. "It's a global village, even for organisms.” The forces behind the flood of evolutionary activity that flows from the tropics remain a mystery.
The research team will now work to address what drives biodiversity in the tropics by pushing their analysis further back in time. They argue their findings to date strengthen the need to focus conservation efforts on protecting the tropics.
"Human-caused extinctions in the tropics will eventually start to affect the biological diversity in the temperate and high latitudes," Roy added. "This is not going to be apparent in the next 50 years, but it will be a long-term consequence."
