Studying Ancient Insects Opens The Window On Biodiversity
Brett Smith for redOrbit.com – Your Universe Online
Global climate has shifted countless times during the course of Earth´s history and a group of Canadian scientists has found the biodiversity patterns of today´s tropical mountain regions were present in British Columbia about 50 million years ago.
According to the team´s report in Palaeogeography, Palaeoclimatology, Palaeoecology, their findings confirm a theory about modern species diversity across mountain ranges, and provide further evidence that global biodiversity was greater in ancient times than it is today.
The mountain range biodiversity theory was posited by Daniel Janzen, an evolutionary biologist at the University of Pennsylvania, about 45 years ago. He theorized biodiversity from site to site across mountain ranges in the tropics should be greater than the same geological formations found in temperate climates.
Because of the great difference between summer and winter in temperate regions, Janzen concluded various species would have a wider temperature tolerance, and the temperature fluctuations would also provide an overlap of temperatures between the cooler mountain passes and the warmer valley bottoms during certain times of the year.
This confluence of factors results in a wide window for temperate species to migrate across mountainous regions, Janzen said. Conversely, the relatively small temperature fluctuations across the seasons in the tropics allow for a very narrow opportunity for species to navigate mountainous regions.
These concepts led Janzen to conclude that ecological communities across tropical mountains should be quite unique from each other. Previous research on modern communities supports Janzen´s theories.
However, Simon Fraser University (SFU) biologists Bruce Archibald and Rolf Mathewes, along with Brandon University biologist David Greenwood, decided to examine ancient insect fossils to see if Janzen´s theory applied to northwestern North America.
When these fossils were created 50 million years ago, the Earth was dominated by a tropical climate that stretched from the equator to the Arctic. Because of this low variation in temperatures year-round, the pattern of biodiversity in modern tropical mountains as described by Jenzen should have extended well into Canada.
In the study, the team studied five orders of fossil specimens from Horsefly River, and Driftwood Canyon, British Columbia, Canada; and near Republic, Washington. They were able to identify between 468 and 470 species in the 702 specimens they examined.
“We found that insect species changed greatly across British Columbia´s and Washington State´s ancient mountain ranges, like in the modern tropics,” said Archibald, “exactly as Janzen´s seasonality hypothesis predicted.”
Besides reinforcing Janzen´s theory, the new study also supports the idea of a tropical climate that once existed in modern Canada.
“Sometimes it helps to look to the ancient past to better understand how things work today,” Archibald said in a statement.
The study´s results also support the notion that the ancient Earth had a much greater level of biodiversity than it currently does today. Previous research has suggested climate change forces have historically driven this level of diversity down. Ice ages or other periods of global cooling could have wiped out many species, but some studies have shown an uptick in carbon dioxide levels and global temperatures could have led to mass extinctions as well.