Answer:
The ecologist's study of the population of bacteria at the bottom of a pond would likely include several levels in the structural hierarchy of life, such as the individual level (individual bacteria), the population level (all the bacteria in the pond), and the community level (the bacteria and other organisms living in the pond).
However, the study may not include higher levels in the structural hierarchy of life, such as the ecosystem level (the pond and all its biotic and abiotic components) or the biome level (the larger geographical area with similar climate and vegetation). Therefore, the level that the study would likely not include is the biome level.