Draw a vertical food chain (part of a food web) showing that sea urchins eat kelp and that sea otters eat sea urchins.
Use this model to (1) show or explain how a trophic cascade works; and (2) offer an explanation for why otters are considered a keystone species.

Which of the following best illustrates ecological succession?

a. A mouse eats seeds, and an owl eats the mouse.

b. Decomposition in soil releases nitrogen that plants can use.

c. Grasses grow in a deserted field, followed by shrubs and then trees.

d. Imported pheasants increase in numbers, while local quail disappear.

Which of the following could qualify as a top-down control on a grassland community?

a. Limitation of plant biomass by rainfall amount

b. Influence of temperature on competition among plants

c. Influence of soil nutrients on the abundance of grasses versus wildflowers

d. Effect of grazing intensity by bison on plant species diversity

What is a disturbance? Consider the role of fire in a forest. Compare the consequences of high-frequency versus low-frequency fire, and high severity versus low severity of fire.

The most plausible hypothesis to explain why species richness is higher in tropical than in temperate regions is that

a. Tropical communities are younger.

b. Tropical regions generally have more available water and higher levels of solar radiation.

c. Higher temperatures cause more rapid speciation.

d. Diversity increases as evapotranspiration decreases.

Community 1 contains 100 individuals distributed among four species: 5A, 5B, 85C, and 5D. Community 2 contains 100 individuals distributed among three species: 30A, 40B, and 30C. Calculate the Shannon diversity (H) for each community. Which community is more diverse?

About a third of insect species measured are in decline, meaning that their populations are shrinking due to habitat destruction, pollution, and other factors. Predict how this change affects the bee pollination of crops such as apples and almonds.

Suppose that a two-acre lawn on your college's campus is allowed to undergo succession. Describe how species traits, species interactions, and the site's history might affect the community that develops.