Outstanding Questions
Several outstanding questions and subsequent discussion points remain
after our synthesis. First, are there important environmental factors or
interactions among environmental drivers specific to microbial taxa
(e.g., soil pore size) that were not captured in previous studies? If
so, can these explain some of the cases where microorganisms follow
macroecological patterns but where the proposed causal mechanism for
macroorganisms seems inapplicable? Second, how should we conceptualize
traits of microorganisms, such as body size, to compare with
macroorganisms? So far, microbial body size has been measured as cell
size, but extensions to sporocarp or colony size could better reflect
ideas of resource allocation and use underlying some theories of
macroecology. Third, how do the evolutionary rates of microbial
speciation and extinction affect our interpretation of macroecological
rules, such as those associated with the Metabolic Theory of Ecology or
the dynamic equilibrium theory of island biogeography? For example, are
biologically diverse islands hotspots for speciation or cold spots for
extinction, or are patterns relating to island biogeography theory
solely driven by ecological dispersal trajectories? Finally, how does
temporal turnover of microbial communities influence our
conceptualization of macroecological patterns that are inferred from
single time point studies? Are macroecological patterns of
microorganisms consistent intra- and inter-annually? Data from
multi-year studies may address most of these questions and can allow
assessment of ecological and evolutionary turnover in microbial
communities in a variety of habitats.