Evenness effects mask richness effects on ecosystem functioning at macro‐scales in lakes

Abstract

Biodiversity–ecosystem functioning (BEF) theory has largely focused on species richness, although studies have demonstrated that evenness may have stronger effects. While theory and numerous small‐scale studies support positive BEF relationships, regional studies have documented negative effects of evenness on ecosystem functioning. We analysed a lake dataset spanning the continental US to evaluate whether strong evenness effects are common at broad spatial scales and if BEF relationships are similar across diverse regions and trophic levels. At the continental scale, phytoplankton evenness explained more variance in phytoplankton and zooplankton resource use efficiency (RUE; ratio of biomass to resources) than richness. For individual regions, slopes of phytoplankton evenness–RUE relationships were consistently negative and positive for phytoplankton and zooplankton RUE, respectively, and most slopes did not significantly differ among regions. Findings suggest that negative evenness effects may be more common than previously documented and are not exceptions restricted to highly disturbed systems.

Phytoplankton Diversity Effect on Ecosystem Functioning in a Coastal Upwelling System

“…Again, this result concurs with previous findings documenting a negative relationship between phytoplankton evenness and the production of zooplankton biomass per unit of phytoplankton biomass in lakes (Filstrup et al, 2014). However, it differs from Filstrup et al (2019) who found a nonsignificant role of phytoplankton richness in driving zooplankton resource use efficiency in lakes.…”

“…A simultaneous detection of a positive and negative effect of richness and evenness, respectively, on ecosystem function as the one observed here, was shown also by others either in fresh (Filstrup et al, 2019) or marine (Napoleón et al, 2014) waters. However, there are contrasting results on the relative contribution of the two effects, that is, the differences between the strength of the relationships.…”

“…Overall, our models indicated that taxonomic richness consistently had much stronger effects on both phytoplankton and zooplankton RUE. This result contrasts with what has been observed in lakes, where evenness explained more variance in phytoplankton and zooplankton RUE than richness leading the authors to suggest that it might be the distribution of taxa rather than their number, the main driver of ecosystem function in lakes (Filstrup et al, 2019). Coastal upwelling ecosystems are highly heterogeneous and contain an enormous species richness rapidly changing with the environmental conditions.…”

“…indicate that certain dominant species, or group of species, would exhibit specific traits that would give them certain physiological advantages allowing for a more efficient exploitation of resources, that is, a selection effect (Filstrup et al, 2019).…”

Spatiotemporal dependency of resource use efficiency on phytoplankton diversity in Lake Taihu

“…RUE is directly affected by climate, abiotic and biotic attributes in terrestrial and aquatic ecosystems (Hodapp et al 2019), such as warming (Bestion et al 2018), nutrient (Verbeek et al 2018), and biodiversity (Gagic et al 2015). Phytoplankton diversity is frequently revealed to be an important driver of phytoplankton RUE in artificial or natural communities (Cardinale et al 2006(Cardinale et al , 2012, as it can enhance the available RUE at higher levels of species richness or at lower levels of evenness through complementary or selecting effects (Filstrup et al 2019). However, the direction and strength of the dependency of RUE on phytoplankton diversity remains largely unquantified across spatial and temporal scales, especially in freshwater ecosystems (Olli et al 2014;Hodapp et al 2019).…”