Afarmer had an accident and spilled a chemical into his pond. several days later, he notices many dead frogs around the pond. that summer, the number of gnats around the pond was higher than ever. this is because

Frogs are insectivores. If the frogs prey on the gnats and their numbers are decreased, this allows the gnats to proliferate because the competition for survival is lessened. Gnats, being lower on the food chain, have adapted to lay large numbers of eggs due to the environmental pressures under which they evolved (being eaten in large quantities). Therefore, fewer gnats being eaten = more gnats surviving.