Diminishing influence of negative relationship between species richness and evenness on the modeling of grassland α-diversity metrics

Abstract

Species richness and evenness have been widely used to investigate the spatiotemporal variation of α-diversity. However, some studies have indicated that a negative relationship exists between species richness and evenness. The question is how the differing sensitivity of α-diversity metrics and interactive behavior between richness and evenness affect the modeling of α-diversity variation. Here, we explored the response of species diversity, represented by three Hill numbers (i.e., species richness, exponential of Shannon index – expShannon, and inverse of Simpson index – invSimpson) focusing on the abundance of rare and common species, and Pielou index underlining the evenness of a community, to α-diversity variation through structural equation modeling (SEM). The model scheme integrated three categories of variables, spectral variation hypothesis (SVH), community pattern, and vertical structure, along the precipitation gradient spanning three steppes, including meadow steppe, typical steppe, and desert steppe. Our results showed that there were large differences in species richness across the three steppes, with v-shaped patterns emerging along the gradient (low-point in the typical steppe). Differences between steppes were diminished in the expShannon or invSimpson indices, though the v-shaped patterns persisted. The Pielou index showed the opposite pattern, with the peak in the typical steppe. Accordingly, a negative relationship between species richness and Pielou index was found across the three steppes. The concurrent increases in annual species number and dominant species abundance in response to precipitation variations led to the negative relationship. As a result, the SEM fitness on expShannon and invSimpson indices over the region was substantially diminished by the negative relationship. Overall, community pattern better explained the variation in species richness, invSimpson and Pielou indices. The performance of SVH differed among α-diversity metrics due to the collinearity with the variables of community pattern and vertical structure. This study emphasizes the variability of α-diversity metrics in response to environmental change. Particularly, distinguishing the asynchronous behaviors between species richness and evenness is paramount to account for α-diversity variation over heterogeneous ecosystems.

Influences of the Integrated Rice-Crayfish Farming System with Different Stocking Densities on the Paddy Soil Microbiomes

“…Our study highlighted the significant impacts derived from varying stocking densities of the red claw crayfish in the integrated rice-crayfish farming systems on the diversities and compositions of soil bacterial communities. Specifically, the high stocking densities of red claw crayfish in integrated rice-crayfish farming could significantly lower the Simpson and Pielou_J indices during the mid-phase of cultivation, indicating reduced diversity and evenness among soil bacteria [43,44]. This effect, however, gradually diminished towards the end of the cultivation period.…”

Added Biochars Promoted Nitrogen and Phosphorus Removal from Ecological Ditches at Low Temperature

“…The Simpson index combines species richness and diversity, with larger values indicating higher species diversity. The Pielou index indicates homogeneity, with larger values indicating greater homogeneity [49].…”

“…16, x FOR PEER REVIEW 9 of 13 values indicating higher species diversity. The Pielou index indicates homogeneity, with larger values indicating greater homogeneity[49].…”

Precipitation variation: a key factor regulating plant diversity in semi-arid livestock grazing lands

“…Grasslands provide a variety of habitats for organisms and harbor a large proportion of the world's plant and animal life forms (Cleland et al, 2013;Petermann and Buzhdygan, 2021;Yan et al, 2023). However, these ecosystems were facing unprecedented threats from climate change and human activities.…”