AP Biology Unit 8: Ecology

What Unit 8 covers

Unit 8 is ecology, from single organisms up to whole ecosystems: how organisms respond to their environment, including behavior and communication; how energy flows through trophic levels, and how carbon, nitrogen, phosphorus and water cycle through ecosystems; how populations grow, exponentially or logistically, and what limits them; how species interact in communities; why biodiversity matters; and how disruptions such as invasive species and human activity change ecosystems.

Where students slip

• Energy flows through an ecosystem and is lost as heat at each level; matter is recycled.
• Arrows in a food web point the way energy moves, from the organism eaten to the one that eats it.
• About 10% of the energy at one trophic level reaches the next, on average. It is a rule of thumb, not a fixed law.
• Density-dependent factors such as competition and disease bite harder as a population grows. Density-independent ones, such as a flood or a frost, don't depend on its size.
• A keystone species has an effect far larger than its numbers suggest. It is often not the most common species.