Trophic Cascades and Keystone Species in Ecosystems

The video discusses trophic cascades, where changes at the top of a food chain affect lower levels. It explains direct and indirect effects, using sea otters and kelp forests as examples. The impact of wolves in Yellowstone is highlighted, showing how their reintroduction balanced the ecosystem. Keystone species, like sea otters and wolves, are crucial for maintaining ecosystem stability.

What is a trophic cascade?

• A type of waterfall formation

• A method of energy transfer in plants

• A series of changes in a food web caused by the addition or removal of a top predator

• A process where nutrients are recycled in an ecosystem

How do sea otters indirectly affect kelp forests?

• By eating kelp directly

• By controlling the population of sea urchins that eat kelp

• By providing shelter for fish

• By increasing water temperature

What happens to kelp ecosystems when sea otters are removed?

• Kelp forests thrive and expand

• Kelp forests are destroyed due to uncontrolled sea urchin populations

• Sea urchin populations decrease

• Fish populations increase

Why were wolves eradicated in Yellowstone in the early 20th century?

• They were considered a threat to livestock

• They were causing river pollution

• They were damaging the forest

• They were overpopulated

What was one major consequence of removing wolves from Yellowstone?

• Improvement in fish habitats

• Increase in beaver populations

• Decrease in elk populations

• Destruction of vegetation in valleys

How did the reintroduction of wolves affect the elk population in Yellowstone?

• The elk population remained the same

• The elk population increased

• The elk population moved to other regions

• The elk population decreased significantly

What role do beavers play in the ecosystem after the reintroduction of wolves?

• They decrease the fish population

• They prevent birds from nesting

• They increase the speed of river flow

• They help create slow-flowing water areas by building dams

What is a keystone species?

• A species that is the most abundant in an ecosystem

• A species that migrates frequently

• A species that has a disproportionately large effect on its environment

• A species that is at the bottom of the food chain

Which of the following is an example of a keystone species?

• Rabbit

• Hawk

• Grass

• Sea otter

Why is the starfish considered a keystone species in Pacific tide pools?

• It is the largest predator in the tide pools

• It cleans the water in the tide pools

• It helps maintain the balance of species in the tide pools

• It provides food for all other species