When I initially think of a microbial population, I would start by defining the parameters of a population unit by a single species or even a strain of a species given the type of microbial organism. Morphological characteristics of a population could be seen in colony formation or the physical dispersal of a population. This would include pigmentation, size, shape, margin type or elevation if I was focused on bacteria. If looking at other organisms like fungi, I would describe other three dimensional aspects like how hyphal development and pathways spread throughout a specific environment. I could take these visual characteristics a step farther by looking at microbes with increased magnification and resolution, and describe cellular morphological traits that aren’t seen at lower magnification. Then I’d move to describing the ways that cells interact with each other in cell to cell communication, how they interact with their environment, how they use resources, how they respond to resource deficit or environmental changes, like changes in temperature and pH, how they respond to waste or toxic build up whether that be from their own metabolic processes or from environmental factors or just how a population is characterized over time.
Shifting to the characteristics of a microbial community, the questions and aspects are the same as when examining and observing a microbial population, except the parameters of a specific species or strain are lifted and I would focus on multiple species, strains or organisms within a specific environment. The definition of the environment becomes more important. A simple environment might just be a specific place or substrate type – maybe we are looking at a microbial community in a square tract of soil. You can then redefine your environment by considering a community in soil over a specific period of time or after that soil has been supplemented with a specific mineral or solution. With different environmental pressures, cues or changes, how do the metabolisms of a group change? Again, the questions are the same. What morphological traits can be observed at different magnifications when different species exist in a shared space? How do they interact with each other? How do they interact with their environment? How and what kind of communication takes places?
The main difference for me between characterizing a population versus a community is just looking at a group of different microbial species or strains in an environment together rather than a single microbial species or strain in a particular environment. I think the only caveat that comes with this differentiation is with respect to bacterial communities. Since generation time is so quick and the potential for mutation and genetic shifts to evolve is also so quick (compared to our/human perception of time), different strains might develop in a single population, and at what point do such genetic changes lend to distinguishing between a single population and a community?
