Green lacewings are used to control aphids, which are pests of many crops. A population of 1000 green lacewings is released into a farmer’s field. The graph shows the change in the population over time. The graph plots a population of green lacewings over ten years. The population grows slowly over the first three years. Then from year 3 to 7, the population increases greatly. From year 8 to year 10, the population stabilizes. What is the most likely explanation for the approximately constant population of the lacewings after the eighth year?