Effects of functional diversity loss on ecosystem functions are influenced by compensation

Abstract

Abstract.Understanding the impacts of biodiversity loss on ecosystem functioning and services has been a central issue in ecology. Experiments in synthetic communities suggest that biodiversity loss may erode a set of ecosystem functions, but studies in natural communities indicate that the effects of biodiversity loss are usually weak and that multiple functions can be sustained by relatively few species. Yet, the mechanisms by which natural ecosystems are able to maintain multiple functions in the face of diversity loss remain poorly understood. With a long-term and large-scale removal experiment in the Inner Mongolian grassland, here we showed that losses of plant functional groups (PFGs) can reduce multiple ecosystem functions, including biomass production, soil NO 3 -N use, net ecosystem carbon exchange, gross ecosystem productivity, and ecosystem respiration, but the magnitudes of these effects depended largely on which PFGs were removed. Removing the two dominant PFGs (perennial rhizomatous grasses and perennial bunchgrasses) simultaneously resulted in dramatic declines in all examined functions, but such declines were circumvented when either dominant PFG was present. We identify the major mechanism for this as a compensation effect by which each dominant PFG can mitigate the losses of others. This study provides evidence that compensation ensuing from PFG losses can mitigate their negative consequence, and thus natural communities may be more resilient to biodiversity loss than currently thought if the remaining PFGs have strong compensation capabilities. On the other hand, ecosystems without well-developed compensatory functional diversity may be much more vulnerable to biodiversity loss.

Grazing effect on grasslands escalated by abnormal precipitations in Inner Mongolia

“…Moreover, our study indicated that the effects of grazing intensities on perennial grasses (both bunch and rhizome grasses) were not linear in the nondrought year. This might have occurred because perennial grasses—as dominant PFGs in the typical steppe on the Mongolian Plateau (Li et al., ; Ma et al., ; Pan et al., )—are resistant to grazing because of their acquisitive‐conservative competition for resources (Bai et al., ; Zheng et al., ). This is also likely because the dominant PFGs were more highly sensitive to changes in environmental variation than to grazing intensities (Milchunas et al., 1993).…”

“…Because species richness was tallied as the total number of species in the whole of PFGs, a change in any one of the relative species abundance of PFGs would have primarily altered the comparison of the other PFGs in the plant community. Additionally, these contributions of PFGs on species richness appeared to be associated with climatic conditions (Li et al., ; Pan et al., ; Yan et al., ), and were highly identity‐dependent in grazed grasslands (Díaz et al., ; Lavorel et al., ; Noy‐Meir, ; Su et al., ). Another possible reason behind the negative correlation may be that plant species or PFGs have strong interactions (competition or facilitation) under grazing or drought conditions (Maestre et al., ; Milchunas et al., ), suggesting that interactions with PFGs could play a major role in maintaining plant species richness.…”

“…Grazing can damage the canopy directly (McNaughton, ; Milchunas et al., ; Noy‐Meir, ; Su et al., ). However, the drought substantially reduced the annual and biennial plants, which are sensitive to the variation in rainfall (Yan et al., ), and consequently caused an increase in perennial plants, which are taller and bigger (Li et al., ; Ma et al., ; Pan et al., ), or more stress‐tolerant (Bai et al., ; Zheng et al., ; i.e., indirectly increased height).…”

Consequences of biodiversity loss diverge from expectation due to post-extinction compensatory responses

“…Whilst the effect of various attributes of biodiversity on ecosystem functioning, including evenness49, dominance50, and functional traits51 have been studied, the relative importance of compensatory mechanisms in natural ecosystems and the concept of compensation as a whole has largely been ignored despite evidence for the occurrence of compensation in natural systems52. Importantly, our simulations reveal that the mixing depth of sediment-dwelling invertebrate communities will depend on how compensatory behaviour is expressed, and the extent to which the functional attributes of compensating species affect bioturbation.…”

Predicting ecosystem vulnerability to biodiversity loss from community composition

“…When the contributions of species to ecosystem function are driven by dominance rather than because of their unique effect traits, biomass compensation should mitigate the impact of changing species composition on ecosystem function (Davies et al 2011, Pan et al 2016). Changes in species composition can alter ecosystem function even if compensatory dynamics cause total biomass to remain stable, because of functional trait differences between species.…”