In a hypothetical situation, a bacterium lives on the surface of a leaf where it obtains nutrients from the leaf's nonliving waxy covering, which the leaf continually produces. The plant is not hurt or harmed by this feeding. Once the number of bacteria reaches a critical mass, they inhibit the growth of other microbes that damage the plant. Occasionally, these bacteria can gain access to the interior of the leaf, for example, if there is weather-related leaf breakage the exposes the plant's interior tissues. If this occurs, the bacteria feed on the plant's living tissue, causing minor damage. What sequences best describes the ecological roles played by the bacterium in this situation?