In a grassland, grass is eaten by grasshoppers, grasshoppers by mice, and mice by hawks. Why does this grassland support far fewer hawks than grasshoppers?

Fallen oak leaves and a dead deer on a forest floor are broken down by fungi and bacteria. What does this activity do for the forest?

Look at the stream food web. Which organism receives energy along two different paths?

A farmer spreads manure from her cows onto a field, and the corn there grows taller than corn in an untreated field. What does this show about matter in an ecosystem?

The carbon atoms in a rabbit's muscles came from the plants that the rabbit ate.

Along a rocky coast, sea otters eat sea urchins, and sea urchins graze on kelp. Hunters remove nearly all the otters from one stretch of coast. What most likely happens to the kelp there?

Zebra mussels arrive in a lake and filter enormous amounts of plankton from the water. What is the most likely change in the population of native fish that feed on plankton?

Wolves are removed from a valley. Elk then browse heavily on young willows along the streams. Beavers in that valley cut willow stems to build dams. What most likely happens to the beaver population?

An orchard owner sprays a chemical that kills most of the bees visiting his apple trees. The trees still flower normally that spring. What is the most likely effect on the apple harvest?

Black-footed ferrets feed almost entirely on prairie dogs. Ranchers poison the prairie dogs across a large area of grassland. What is the most likely change in the ferret population there?

A lava flow from a volcano cools into bare rock, covering a hillside where a forest once stood. How would you classify the community change that begins on that rock?

A farm field is abandoned and weeds and grasses take it over within a year. Which community is most likely to occupy the field next, before a mature oak forest develops?

Beach grass is the first plant to take hold on a bare sand dune. How does it change the dune for the species that arrive later?

A fire burns through a pine forest but leaves the soil and buried seeds in place. The site must now start over with lichens breaking down bare rock.

Two grasslands face the same drought. Grassland A has three grass species; Grassland B has twelve. The drought kills the one grass species that grows in both. Which grassland is more likely to keep feeding its bison herd?

A new fungus attacks one variety of wheat. One farm is planted entirely with that variety; a nearby prairie holds dozens of native plant species. What is the most likely outcome?

A storm damages a coral reef. Reefs with many species of coral and fish usually recover faster than reefs with only a few. Which reasoning best explains this?

The table shows measurements from one pond. Which factor best explains the fish deaths recorded in July?

The graph shows a deer herd introduced to an island that has no predators. Growth slows and then levels off. What does the level part of the graph represent?

Researchers add nitrogen fertilizer to one meadow plot and the plants grow three times taller. On an identical plot they add extra water only, and growth does not change. What had been limiting plant growth?