Mass ratio effects underlie ecosystem responses to environmental change

1. Random species loss has been shown experimentally to reduce ecosystem
function, sometimes more than other anthropogenic environmental changes.
Yet, controversy surrounds the importance of this finding for natural
systems where species loss is non-random. 2. We compiled data from 16
multi-year experiments located at a single site in native tallgrass
prairie. These experiments included responses to 11 anthropogenic
environmental changes, as well as non-random biodiversity loss - either
the removal of uncommon/rare plant species or the most common (dominant)
species. 3. As predicted by the mass ratio hypothesis, loss of a dominant
species had large impacts on productivity that were comparable to other
anthropogenic drivers. In contrast, the loss of uncommon/rare species had
small effects on productivity despite having the largest effects on
species richness. 4. The anthropogenic drivers that had the largest
effects on productivity – nitrogen, irrigation, and fire – experienced not
only loss of species but also significant changes in the abundance and
identity of dominant species. 5. Synthesis. These results suggest that
mass ratio effects rather than species loss per se is an important
determinant of ecosystem function with environmental change.