Researchers working in Finland propose that the unique light environment of the Earth's polar regions creates conditions that result in circumpolar hybrid zones around the North and the South Poles. These extreme conditions increase the synchrony of reproductive phenology among species, i.e., force all species into a smaller window for reproduction. This will sustain biodiversity in the long term.

The length of the Earth's daylight and night is characterized by year-round equal amount of daylight and night at the Equator, minor seasonal variation moving away from the Equator, and substantial seasonality of day length closer to the Poles. In the far North and far South, inside the Arctic and Antarctic circles, this results in the unique months-long phenomena of the "midnight sun" with 24-hour daylight in the summer and the "polar night" of winter, when the sun does not rise above the horizon for months at a time.

"At the center of our theory is the hypothesis that the extreme light environment of the polar regions creates hybrid zones in both polar regions," says Saikkonen.

Researchers Kari Saikkonen and Marjo Helander collect plant samples in Antarctica on King George Island. Credit: Kari Saikkonen

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