|Year of Publication:
|Q. - G. Zhang, Zhang D. - Y.
|Algal microcosm, complementarity, productivity, selection effect, Species diversity
The importance of species richness for ecosystem productivity has received much atten- tion in recent years, but the consequences of non-random species extinction remain poorly understood. We propose an index, ‘essentiality’, to assess the consequence of extinction of particular species for community biomass production. The essentiality of a species in a given community is the extent to which the functional role of that species is irreplaceable by the remaining species, calculated as the relative difference in yields between communi- ties with and without the focal species. Species with zero essentiality play a completely re- placeable functional role in their communities. Positive essentialities suggest irreplaceable contributions by species to their communities; species with essentiality values even higher than their dominance in the community may exhibit facilitative effects on the other spe- cies. Negative essentialities indicate interference of the focal species with other members of the same community. We applied this index to data from a microcosm experiment, in which five algal species were grown in monocultures and in all possible species combina- tions. Essentiality varied greatly across species. Two species had overall zero essentiality values throughout the experiment, two species had positive essentiality values which were lower than the species’ dominance, and the remaining species had negative essenti- ality. Furthermore, two out of the five species had essentiality values dependent on species richness of communities from which they were lost; essentiality decreased with an in- crease in species richness. The essentiality index provides a straightforward measurement of functional consequences of individual species loss, which complements the existing an- alytical methods by focusing on the detection of facilitation and interference.