Final answer:
The common scales in ecology are organismal, population, community, and ecosystem ecology, arranged hierarchically from least to most inclusive, encompassing the study of individual organisms to the interactions within entire ecosystems.
Step-by-step explanation:
The common levels of scale in ecology are organismal ecology, population ecology, community ecology, and ecosystem ecology. These levels are organized hierarchically from the least inclusive, which is the individual organism, to the most inclusive, which is the ecosystem. So, when we look at the question options provided, the correct answer is: d) a and b. This is because both a) Individual and population, and b) Community and ecosystem are scales studied in ecology. At the organismal ecology level, ecologists examine how individual organisms interact with their environments. In population ecology, the focus is on the number of individuals of a species in an area and how and why this number changes over time. Community ecology delves into the interactions within and among different species in an area. Lastly, ecologists looking at an ecosystem investigate not just the living species but also the nonliving parts of the environment like air, water, and soil.