Author's Intent Practice Test

One of the most influential niche constructors is the earthworm, an organism found almost everywhere on the planet. A scientist only concerned with evolution would predict that, in order to live on land, earthworms would have to significantly change. Earthworms didn’t change their physiology a great amount, however; instead, they changed the soil to make it more like the ocean in order to survive. Land with earthworms is less compacted, is more nutrient rich, and is better mixed than land without them – resulting in a moist environment in which the worms can thrive.

1 Niche constructors are particularly important in colonizing new environments. One of the easiest ways to measure this effect on evolution has been in the effect that the number of earthworms has on soil fertility, a measure of how hospitable an environment is to plant growth. Even the least fertile soil has around 62 worms per square meter, and as the number of worms increases so does soil fertility. As worms move through the different layers of soil, they eat, digest, and excrete massive amounts of organic matter. They leave their excretions behind in the form of nutrient-rich droppings known as casings. As these casings decompose, they release nutrients into the soil. This process not only moves nutrients from one layer of the soil to another but also converts the nutrients to forms that plants can absorb and process more easily. Because it is easier for plants to get the proper nutrients, plants don’t have to invest time and energy into making better root systems to gather nutrients. As result, plants have, over time, lost some of these mechanisms – a form of evolution.

Which of the following provides the most effective transition from the previous paragraph?