Functional redundancy supports biodiversity and ecosystem function in a closed and constant environment

The role functionally redundant species play in ecosystem function has not been adequately investigated. To study this, we examined species richness and an ecosystem function, cellulose decomposition, while environmental conditions were held constant. Our hypotheses were (1) increasing species richness will have no effect on rates of cellulose decomposition and (2) species richness will decline over time in functionally redundant communities. A relatively simple microcosm-based system to manipulate complex microbial interactions was employed. Microcosms containing cellulose as the sole carbon source were inoculated at equal densities with none, one, two, four, or eight species of cellulolytic bacteria. At 5-d intervals for 25 d, community composition and cellulose decomposition were determined. We rejected both of our hypotheses. In a constant environment, greater species richness supported a greater number of individuals and subsequently greater rates of total cellulose decomposition. Furthermore, greater initial species richness maintained greater richness over time. These results provide experimental evidence that functionally redundant species may play an integral role in ecosystem function.