Final answer:
Sardine numbers are less likely to collapse during an El Niño event because they feed mainly on phytoplankton, which tend to remain more stable in population than zooplankton, the primary food source for anchoveta.
Step-by-step explanation:
During an El Niño event, oceanic conditions change in a way that can significantly affect marine life. Phytoplankton, which are at the base of the ocean food chain, are less sensitive to these changes compared to zooplankton, which are more affected by the altered environmental conditions. Sardines feed mainly on phytoplankton, while anchoveta feed on large zooplankton. Since phytoplankton are less likely to experience a dramatic population decline during El Niño, sardines may have a more reliable food source than anchoveta. Therefore, sardine numbers are less likely to collapse during an El Niño event because their primary food source remains more stable compared to the food source for anchoveta.