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.
Methods
Data were downloaded from the Konza Prairie LTER website (http://lter.konza.ksu.edu) or obtained directly from investigators.