Black-legged ticks carry Lyme disease, a common illness in the United States. Black-legged ticks live in forests and meadows. The ticks feed on small rodents like chipmunks as they grow. The chipmunks feed on acorns from oak trees. Researchers investigated factors that affect tick populations in their habitats. They recorded the number of black-legged ticks, acorns, and chipmunks in an area over several years. The table below shows their results.