medium · Gre Verbal

Naturalist: On our island, the population of a ground-nesting seabird collapsed after rats arrived on shipping vessels a decade ago, since rats prey on the birds' eggs. We recently eradicated every rat from the island. Therefore, the seabird population will now recover to its former size. Which of the following, if true, most seriously weakens the naturalist's prediction? Select the single best answer.

1. During the decade the rats were present, an invasive vine spread across the island's beaches and now blankets nearly all of the open ground the seabirds require for nesting.
2. The rats were eradicated using a specialized baiting method that is also routinely relied upon to control invasive rat populations on several other comparable islands.
3. The same ground-nesting seabird species also continues to breed successfully on a handful of distant offshore islands that the invasive rats had never managed to reach at any point.
4. Some of the very shipping vessels that had originally carried the invasive rats onto the island a decade ago continue, even now, to call regularly at the island's small working harbor.
5. During the years they were established, the rats occasionally preyed upon the eggs of several other resident bird species on the island in addition to those of the ground-nesting seabird.

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