Suppose scientists noticed that several tundra plant species were declining in number. At the same time, they noticed that certain plant-eating insect species increased greatly in number, but two species of migratory birds that eat mice, spiders, and other small animals were declining. What one factor might account for all of these observations? Arctic mice were eating more plants.

Wolf spiders had almost completely disappeared.

Temperature changes were affecting the birds’ feeding patterns.

Some sort of disease was spreading across the tundra.