Species niche differences promote community temporal stability via the overyielding effect

Background/Question/Methods

Temporal stability is an important property of ecological communities. Three mechanisms (overyielding, the portfolio effect, and the covariance effect) can potentially stabilize communities. A variety of factors can affect these mechanisms and hence influence the stability of communities, but no existing work, to our knowledge, has specifically linked community stability to contemporary species coexistence theory that emphasizes the importance of species niche and fitness differences. Using laboratory microcosms containing bactivorous protist communities, we tested the effects of species niche and fitness differences on community temporal stability.  Microcosms containing paired combinations of six species of bactivorous protists were observed over a six week period.  Protist abundance data were collected, and converted to biovolume data using average individual volumes. Protist species niche differences were quantified by the differences in the bacterial communities that they grazed upon and fitness differences were quantified with mutual invasion experiments that measured the growth rate of one species invading steady-state monocultures of another species. The relationships between the temporal stability of community biovolume and both niche and fitness differences were calculated using regressions.  To determine the mechanisms of stabilization, the summed variances, summed covariances, and total biomass were also related to both niche and fitness differences.

Results/Conclusions

The temporal stability of community biovolume significantly differed among species pairs. Species niche differences, but not fitness differences, had a significant positive relationship with community temporal stability.  A significant positive relationship existed between species niche differences and community biovolume indicating that overyielding contributed to community stability.  However, species fitness differences explained little variation in community biomass, and neither niche or fitness difference was related to summed variances or summed covariances. These results suggest that understanding the mechanisms by which species can coexist can offer additional insight into mechanisms regulating community stability.