Attempts to explain why certain microbial communities resist colonization by foreign strains have generated a fragmented literature, and no unifying account of resistance has commanded general assent. A framework grounded in the dynamics of unconsumed substrate may nonetheless reconcile most of the competing proposals and dissolve much of the inconsistency that has accumulated across independent investigations. The framework's central claim is that a community becomes more vulnerable to colonization whenever the supply of unconsumed substrate rises.

The heterogeneity of mechanisms by which substrate can be released may account for the absence of stable ecological predictors of resistance. The framework specifically implies that no necessary link should obtain between a community's taxonomic richness and its susceptibility to colonization, since near-total substrate consumption can occur in both diverse and depauperate communities. Whitfield and Osei, however, reported a positive association between taxonomic richness and colonization success. This result may be an artifact rather than a refutation: taxonomically diverse communities are frequently substrate-poor at baseline and therefore disproportionately responsive to anthropogenic substrate inputs.

The passage is chiefly devoted to

A. evaluating the empirical track record of a proposed framework
B. accounting for the failure of a unifying theoretical account to emerge
C. recommending a candidate resolution to a theoretical stalemate
D. deriving testable consequences from a proposed framework
E. cataloguing the methodological obstacles that complicate a body of research



The author would most likely endorse which of the following assessments of the results from prior investigations?

A. Many of the results directly contradict predictions that follow from a substrate-based account of vulnerability.
B. If unconsumed substrate dynamics were taken into account, much of the apparent inconsistency across the results would prove explicable.
C. The apparent inconsistencies are produced by the practice of forcing the results into an inadequate general theory.
D. No general theory has emerged because the studies have failed to measure the magnitude of colonization events with sufficient precision.
E. The results suggest that vulnerability to colonization is generally lower than would be predicted from the frequency of foreign strains in natural settings.



According to the author, the substrate-dynamics framework may resolve the "inconsistency" in prior findings because

A. it shows that a single circumstance can generate divergent outcomes across communities.
B. it does not presuppose that every reported result is an instance of the phenomenon the framework is designed to explain.
C. it predicts that modest differences in experimental design can produce outsized differences in observed outcomes.
D. it rests on a statistical regularity rather than on the premise that the results reflect an underlying causal process.
E. it explains why comparable outcomes may be preceded by quite different circumstances on different occasions.