  High-throughput sequencing techniques such as metagenomic and
metatranscriptomic technologies allow cataloging of functional characteristics
of microbial community members as well as their taxonomic identity. Such
studies have found that a community's composition in terms of ecologically
relevant functional traits or guilds can be conserved more strictly across
varying settings than taxonomic composition is. I use a standard ecological
resource-consumer model to examine the dynamics of traits relevant to resource
consumption, and analyze determinants of functional composition. This model
demonstrates that interaction with essential resources can regulate the
community-wide abundance of ecologically relevant traits, keeping them at
consistent levels despite large changes in the abundances of the species
housing those traits in response to changes in the environment, and across
variation between communities in species composition. Functional composition is
shown to be able to track differences in environmental conditions faithfully
across differences in community composition. Mathematical conditions on
consumers' vital rates and functional responses sufficient to produce
conservation of functional community structure across taxonomic differences are
presented.
