Mass ratio effects underlie ecosystem responses to environmental change

Abstract

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 native tallgrass prairie site. 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, are an important determinant of ecosystem function with environmental change. K E Y W O R D S anthropogenic change, biodiversity, climate change, dominant species, ecosystem function and services, global change ecology, mass ratio hypothesis, non-random species loss 856 | Journal of Ecology SMITH eT al.

Effects of plant functional group removal on CO2 fluxes and belowground C stocks across contrasting ecosystems

“…While the effects of shifts in plant community composition and loss of diversity on C cycling have received growing attention (Chen et al 2016, Li et al 2018, Smith et al 2020), how these effects vary across ecosystems is not well understood. Removal experiments, where the same plant species or functional groups are removed across different environmental settings, have shown that the effect of removals on drivers of C cycling (i.e., soil respiration, litter decomposition rates, net primary productivity) vary along abiotic and biotic gradients, including gradients in ecosystem productivity (Wardle and Zackrisson 2005, Fanin et al 2018) and nutrient availability (Suding et al 2008, McLaren and Turkington 2011).…”

Mowing weakens the positive effects of nitrogen deposition on fundamental ecosystem service of grassland

“…Although the positive effects of N enrichment on forage quality were not mowingdependent as mentioned above, mowing did diminish the positive effects of N enrichment on the quantity of nutrition provided in grasslands. While mass ratio effect is important in driving the quantitative responses of forage production to N addition (Smith et al 2020), our results indicate that it might not be the case for qualityadjusted yield, at least for the stocks of crude protein and crude fat examined here.…”

Predicting species and community responses to global change in Australian mountain ecosystems using structured expert judgement

“…they act as 'foundation species', Ellison & Degrassi 2017), understanding the autecology and dynamics of dominant species in response to global change drivers appears to be a key research need. Indeed, the uncertainty around common species responses highlights that longterm cover/abundance trends need to be quantified if future ecosystem stability is to be understood, a call that has been made repeatedly in the literature (Smith & Knapp 2003;Gaston & Fuller 2007;Gaston 2011;Smith et al 2020). Monitoring species' local abundance may therefore better inform species' extinction risks in alpine areas under global change than monitoring their range (Cotto et al 2017).…”