Life Sciences

The largest tree in the world is a giant sequoia (Sequoiadendron giganteum) in California's Sequoia National Park. Called General Sherman, the tree is about 52,500 cubic feet (1,487 cubic meters) in volume. That's the equivalent of more than half the volume of an Olympic-size swimming pool, commonly considered to be 88,500 cubic feet (2,506 cubic meters). General Sherman is also tall, standing 274.9 feet (83.8 meters) high. Incredibly, this enormous tree started as a small seed, merely 4–5 mm (0.16–0.20 in) long and 1 mm (0.04 in) wide. This begs the question, where did General Sherman gets its mass?

The location of Aspen forests and the behavior of rivers changed in Yellowstone National Park after wolves were reintroduced. Wolves are predators at the top of the food chain; however, their impact on ecosystems extends well beyond the simple predator/prey relationships they have with animals like elk and deer. Wolves provide balance to ecosystems through this idea of a “trophic cascade”, which means that what happens at the top of the food chain effects what happens at all other tropic levels. The reintroduction of wolves into Yellowstone National Park in 1995 has dramatically changed the park, in terms of population dynamics, organism behavior, the regeneration of vegetation, and even the behavior of rivers and streams.

Walking in deciduous forests in early spring, you may notice a strange phenomenon. Around the base of tree trunks are perfectly circular "thaw circles." The reason for these circles is heat - as the spring sun warms the forest, the dark tree trunks absorb more heat than the highly reflective snow around them. As this heat radiates out, it uniformly melts the nearby snow in a ring around the tree. Some small plants seem to use this phenomenon to get a jump on the spring growing season and grow close to tree trunks. Scientists are currently testing this hypothesis and estimate that these plants may get as much of a 20% increase in their growing season by sprouting in these thaw circles.

The 1988 forest fires in Yellowstone impacted the plants, animals, and soils of the forest ecosystem. The fires burned live plants and trees as well as debris on the ground releasing nutrients into the soil. Climate impacted the amount of moisture in the ecosystem. Nutrients and moisture in the soil are used by seeds to re-establish vegetation in the burnt forest. Before the fires, the tree community was made up of lodge pole pine trees and quaking aspen. These trees left behind seeds and root structures buried in the soil. The first plants to re-establish after a fire were grasses and wildflowers. The lodge pole pine and quaking aspen are adapted to fire and are able to slowly re-establish themselves years after a fire. Fire also creates new habitats for animals and insects. If an ecosystem has soil before a disturbance it goes through secondary succession after the disturbance. If an ecosystem does not have soil and soil forms the ecosystem goes through primary succession.

Alexandria is a teenage girl in St. Louis, Missouri, who is living with sickle cell anemia. She is one of approximately 72,000 Americans currently living with the disease that can cause, among other symptoms, anemia, episodes of pain, delayed growth, and frequent infections. Sickle cell anemia was caused by a substitution mutation in the DNA of a child living thousands of years ago in Africa and has been passed down ever since. This mutation had altered the child’s hemoglobin, the molecule in red blood cells that carries oxygen through the body. It was not harmful; there are two copies of every gene, and the child’s other hemoglobin gene was normal. The child survived, had a family and passed down the mutation to future generations. Some dependents of that child, like Alexandria, received two copies of the mutated gene which causes them to have sickle cell disease. This leads to the question: Why has this disease been passed down through thousands of generations even though it can have such deleterious effects?

Peter and Rosemary Grant have been studying the finches on Daphne Major in the Galapagos Islands since 1973. During that time, they found concrete evidence of natural selection, the driving force of evolution. In 1977, a severe drought killed off many of Daphne’s finches, setting the stage for the Grants’ first major discovery. During the dry spell, large seeds became more plentiful than small ones. Birds with bigger beaks were more successful at cracking the large seeds. As a result, large finches and their offspring triumphed during the drought, triggering a lasting increase in the birds’ average size. The Grants had observed evolution in action.

The lampsilis mussel lives in the Missouri River. The mantle flesh that spills out of the females' shells is not only shaped like a fish, but moves like one, every so often twitching with a flip of its “tail.” When a predatory fish like a bass attacks the lure, the mussel fires its larvae in the fish's gills. Here the parasitic young attach and drain nutrition from their host before ejecting and settling on the riverbed. Typically lampsilis species mimic the small fish prey of the largemouth bass. The lures are incredibly lifelike and even sport eyespots for extra trickery. A large amount of variation exists among the population of mussels with varieties mimicking different types of fish. When a bass falls for the lure, the mussel releases a cloud of larvae, some of which attach to the gills of the bass where they stay until they are ready to drop off and complete their life cycles. Amazingly, the mussels have developed these life-like lures even though they themselves have no eyes and have never seen the fish they are mimicking.