Who were the competitors who got extinguished?

Directions: Read the following passage and answer the question that follows:

The ground was full of seeds that cannot rise into seedlings: they rob one another of air, light and water, the strongest robber winning the day and extinguishing his competitors. Year after year, the wild animals with which man never interferes are, on the average, neither more nor less numerous than they were; and yet we know that the annual produce of every pair is from one to perhaps a million young; so that it is mathematically certain that, on the average, as many are killed by natural causes as are born every year, and only those escape which happen to be a little better fitted to resist destruction than those that die. The individuals of a species are like crew of a foundered ship, and none but good swimmers have a chance of reaching the land.