Animal species produce more offspring when their supply of food goes up. Some animals appear able to anticipate unusual food abundance. Red squirrels eat seeds from pinecones, a food source that sometimes has very large crops. Researchers collected data on an index of the abundance of pinecones and the average number of offspring per female over 16 years. The least-squares regression line calculated from these data is:
predicted offspring = 1. 4146 + 0. 4399 (cone index)
