The amount of nitrogen in prairie soil sets an upper limit on how much grass can grow there, and so on how many grazers the prairie supports. How is soil nitrogen classified as a limiting factor?

A fungus that grows on the muzzles and wings of hibernating bats spreads through a cave colony and kills most of the bats in it. How is the fungus classified as a limiting factor?

Several things hold down the amount of kelp in a coastal kelp forest. Which of these limiting factors is biotic?

On a rangeland, prairie dogs and cattle eat the same grasses, and the prairie dog population stays smaller where cattle are grazed. How is this factor classified?

A late-summer drought lowers a stream's water level, and a heron eats the fish trapped in the shrinking pools. Which statement classifies these two limiting factors correctly?

Ash from a volcanic eruption settles over a coastal meadow and buries the same fraction of the wildflowers whether the meadow holds 500 plants or 50,000. How is the ash fall classified?

A respiratory virus moves through a deer herd. In years when the herd is small and spread out, few deer are infected; in years when the herd is large and animals feed shoulder to shoulder, most are infected. How is the virus classified?

Which of these limiting factors is density-independent?

As a songbird population on a woodland reserve grows, the number of suitable nest cavities per pair falls, and a larger share of pairs fail to breed each year. What does this show about competition for nest cavities?

Why do ecologists classify predation as a density-dependent limiting factor?

In one dry year a drought kills the same fraction of a jackrabbit population across a whole county. In the same county, a tick parasite spreads through the jackrabbits only where they are crowded. Which classification is correct?

A grassland has steady rainfall, mild temperatures and far more grass and rodents than the foxes there can eat. The rocky outcrop holds only 12 usable dens, and each year only 12 fox pairs raise young. Which factor limits this fox population?

A cave stream stays near 12 degrees Celsius all year, is well oxygenated, and has many empty chambers. Food washed in from the surface is plentiful in spring but scarce in late summer, when salamander numbers fall. Which factor limits this population?

A lake's algae population stays low all summer. A researcher adds phosphate to one fenced-off section of the lake and nothing to a second fenced section. Within two weeks the phosphate section is thick with algae. What does the result show?

A seabird island has bare cliff ledges to spare and fish are abundant offshore, but ship rats reached the island and now eat most of the eggs and chicks each season. Which factor is limiting this seabird population?

A meadow holds a steady population of about 400 rabbits, and the amount of grass is what keeps it there. Hunters remove every fox from the meadow. The grass supply does not change. What is the most likely outcome?

A shallow pond holds about 500 minnows. Each late summer the dissolved oxygen in the water falls and many minnows die. The owner starts adding extra fish food but does not aerate the water. What is the most likely outcome?

A deer herd on a reserve holds steady near 250 animals. Managers clear brush and double the winter browse, which had been the scarcest resource. Predators, disease and weather are unchanged. What is the most likely outcome?

Reindeer released on an island with deep lichen grow rapidly to about 2,000 animals, strip nearly all the lichen, and then the herd crashes to a few dozen. What does this pattern show?

Bacteria in a sealed flask of broth multiply rapidly at first, then level off near 8 million cells and stay there for days. What best explains the leveling off?