Martha Foley talks with Dr. Curt Stager about how carbon cycles through the atmosphere and the bodies of all living things - why we need it to live, and how it also threatens the planet.

Our atmosphere is about 80 percent nitrogen. Martha Foley and Dr. Curt Stager explore the ways this common element and necessary component of all life forms interacts with the biosphere.

Researchers have found that variations in the wingspan of cliff swallows has a measurable impact on their survival in a human-dominated environment. In this week's Natural Selections, Dr. Curt Stager and Martha Foley discuss how cliff swallows living in a high traffic area have adapted to survive the conditions.

Static electricity plays a role in getting pollen to come loose from the blossom and to stick to the pollinator. According to a recent study using petunias and bumblebees, British researchers observed that the flowers increase their electrical charge in response to the presence of pollinating insects.The charge peaks in intensity just before the potential pollinator begins feeding on nectar, and decreases after they go away.Martha Foley and naturalist Curt Stager discuss this unique example of "flower power."

Plants have many strategies for manipulating animals to do their bidding. Some flowers focus the attention of their pollinators with a familiar pick-me-up: caffeine. Martha Foley and Dr. Curt Stager discuss the natural world.

One of the features of a hard winter can be loud spooky booming noises. These may be cryoseisms or "icequakes," caused when masses of ice expand and contract until they reach a breaking point. The sound signals the release of large amounts of energy.Lake ice can also make alarming noises; some expert skaters can accurately estimate the thickness of the ice from the pitch of the noise.Ice expansion within trees and within homes can also add to winter jitters. Martha Foley and Curt Stager listen to the winter.

Martha Foley and Dr. Curt Stager discuss the hottest and coldest places on earth. Death Valley is no longer the hottest. Libya takes (or bakes) the cake these days. The lowest, as you would expect, is in Antarctica. How cold? You don't want to know.

Spiders from big to tiny use their webs to snag and trap prey in fascinating ways. One spider even reels in tiny gnats that come to "roost" on the web. The silky constructions are wonders of engineering and construction. They're also highly specialized, spider to spider. Martha Foley and Curt Stager talk about spiders and the tangled webs they weave.

Dr. Curt Stager and Martha Foley talk about porcupines: why (and how) they climb trees and why it can be a dangerous job. Plus, what to do when one lives under (and gnaws on) your porch.Get up close, but not too close, to porcupines.

Tall trees may be the kings of the forest, but there is another kingdom of forest life that passes unnoticed. Dr. Curt Stager and Martha Foley talk about the arboreal network of fungus.