Effects of species evenness can be derived from species richness – ecosystem functioning relationships

Abstract

Although species richness effects on ecosystem functioning have been studied thoroughly in countless experiments, the effects of the other side of diversity – species evenness – remain less identified, especially at high species richness. Due to the large number of different model ecosystems that need to be created, the explanatory power of the experimental approach for evenness is indeed limited. We show here that experimental studies on the influence of species richness on ecosystem functions contain hidden information on the influence of species evenness. Both the effects of maximum and minimum evenness, and of a key set of intermediate evenness levels, can be derived from species richness – ecosystem function curves, and that for every richness level, by using communities with low species richness as the equivalent of highly uneven communities with higher richness. We show that evenness effects on ecosystem functioning have the same direction as richness effects, however with increasing effect sizes at higher richness levels. We validated our technique for a wide range of ecosystem functions and applied it to the species richness – community biomass data from an existing biodiversity experiment. Our approach could provide a fast and easy alternative to resource‐intensive experiments in which evenness is experimentally varied, as we can build on the elaborate existing literature on species richness to assess its effects.

Litter-Induced Reduction in Ecosystem Multifunctionality Is Mediated by Plant Diversity and Cover in an Alpine Meadow

“…Our study revealed that the litter mass manipulation significantly impacted the species richness and plant functional group evenness, thus impacting the ecosystem multifunctionality (Figure 4). The finding that has also been observed in several previous studies, where the species richness modulated by community attributes (e.g., spatial pattern; Maestre et al, 2012a) or climate (Jing et al, 2015) altered ecosystem multifunctionality, and the same direction as evenness effects (Lembrechts et al, 2018). In contrast, Soliveres et al (2014) have reported no effect of species richness or evenness on ecosystem multifunctionality.…”

Compensatory responses can alter the form of the biodiversity–function relation curve

“…Our findings are in broad agreement with previous hypotheses which state that the potential or probability for compensatory dynamics countering the consequences of biodiversity loss will depend on the level of functional redundancy within a system [80,81], but they acknowledge the importance of species that exhibit low or different effect trait values in maintaining ecosystems as circumstances change. Ultimately, the net ecosystem response is a multiple of the role of which species survive and the population response to perturbation, including the sequence of species loss [82].…”

“…However, understanding variability in species responses to abiotic and biotic change [77], as well as the context-dependent contributions they make to ecosystem functioning over time [59,78,79], will help to refine the likelihood of various ecological outcomes against specific scenarios. Here, biomass compensation had a positive effect on sediment reworking in even communities, especially at intermediate levels of species richness, while incidences of over-compensation were particularly pronounced at high levels of species richness [80]. For uneven communities, functioning was only maintained when extinctions were random or ordered by rarity.…”

Biodiversity alleviates the decrease of grassland multifunctionality under grazing disturbance: A global meta‐analysis

“…In addition, although species richness can largely explain the variations in ecosystem functions, species evenness has been considered to reflect the diversity effect more effectively than richness in species-rich systems (Assaf et al, 2011;Lembrechts et al, 2018).…”