TABLE 2 

Definitions of the various terms used throughout this articlea

TermDefinition
βNTIβ-Nearest taxon index, which uses phylogenetic information to
assemble random populations of microorganisms to measure
whether compared communities are more or less different than
random chance; differentiates deterministic and stochastic
processes
RCBCRaup-Crick (Bray-Curtis), which builds null communities
probabilistically based upon OTU abundances within a
sample to determine whether communities are more or
less different than random chance alone; differentiates
stochastic processes
Variable selectionThe result of communities being more different than would be
expected by random chance alone (e.g., geochemical conditions
are very different between samples); deterministic process
Homogenizing selectionThe result of communities being less different than would be
expected by random chance alone (e.g., geochemical
conditions are identical/different between samples);
deterministic process
Dispersal limitationIndicates populations between samples are unable to interact,
due to separation by either time or space; stochastic process
Homogenizing dispersalIndicates populations between samples are freely able to interact,
potentially due to significant hydrological connectivity;
stochastic process
Ecological driftOccurs when communities are as different as random chance
alone; primarily occurs due to random mutations or variations
in generation times
UndominatedIndicates no single ecological process is capable of explaining
the observed results
CohesionA metric that measures the complexity/interconnectedness of a
given community as measured by the degree of cocorrelation
Positive cohesionThe cohesion result for those community members that were
positively correlated; unknown interpretation
Negative cohesionThe cohesion result for those community members that were
negatively correlated; potentially significantly related to
community turnover and complexity
InterconnectednessA term used to reference the degree of negative cohesion within
a community
  • a See Zhou and Ning (37) and Herren and McMahon (28) for greater detail.