Trophic Cascades and Ecosystem Dynamics

The video session from UCLA explains trophic cascades, breaking down the concept into manageable parts. It defines trophic levels within a food chain and describes how changes at different levels can impact the entire ecosystem. Two types of control are discussed: top-down, where predators influence the ecosystem, and bottom-up, where changes in primary producers affect the food chain. Examples include sea otters and kelp for top-down control, and plankton and kittiwakes for bottom-up control. The video concludes by summarizing the importance of understanding these ecological processes.

What does the term 'trophic' refer to in the context of trophic cascades?

• A water cycle

• A food chain

• A weather pattern

• A type of ecosystem

In a top-down control scenario, what happens when the top predator is removed?

• The ecosystem remains unchanged

• The prey population migrates

• The prey population increases

• The prey population decreases

Which organism is at the top of the food chain in the top-down control example?

• Sea otters

• Kelp

• Sea urchins

• Phytoplankton

What is the primary effect of reducing phytoplankton in a bottom-up control scenario?

• Increase in zooplankton

• Decrease in zooplankton

• No change in the ecosystem

• Increase in herring

In the bottom-up control example, which organism directly consumes phytoplankton?

• Zooplankton

• Kittiwakes

• Herring

• Sea otters

How does bottom-up control affect the abundance of organisms at each trophic level?

• It causes an increase at each level

• It causes a decrease at each level

• It causes random fluctuations

• It causes no change

What is a key difference between top-down and bottom-up controls?

• Top-down affects all levels below the top predator

• Bottom-up affects only the bottom level

• Bottom-up affects only the middle levels

• Top-down affects only the top predator

Which type of control typically results in an alternation in abundance at each trophic level?

• Top-down control

• Bottom-up control

• Neither top-down nor bottom-up control

• Both top-down and bottom-up control

What is the overall impact of a trophic cascade on an ecosystem?

• It only affects the top predator

• It stabilizes the ecosystem

• It has no impact

• It causes a chain reaction of changes

What is the main focus of the video on trophic cascades?

• To discuss plant growth

• To simplify the concept of trophic cascades

• To describe weather patterns

• To explain the water cycle