In a study of tropical forests it was found that while the species of trees that is most common in a particular forest also reproduces the most, trees of the species that is rarest there tend to survive longer. This pattern holds regardless of which species of trees is the most common and which is the rarest. Which one of the following, if true, most helps to explain why trees of the rarest species tend to survive longer than trees of the most common species? ['The study tracked preexisting tree species but did not introduce any new species to the tropical forests.', 'Older trees tend to reproduce the least.', 'The trees of the common species have more competition for the resources they need than do the trees of the rare species.', 'The survival of the trees of the rarer species enables tropical forests to recover more easily from moderate destruction.']