Bird species richness is associated with phylogenetic relatedness, plant species richness, and altitudinal range in Inner Mongolia.

Chenxia Liang,Gang Feng,Jie Yang,Lingfeng Mao,Guisheng Yang,Xingfeng Si,Jens‐Christian Svenning

doi:10.1002/ece3.3606

Abstract

Bird species richness is mediated by local, regional, and historical factors, for example, competition, environmental heterogeneity, contemporary, and historical climate. Here, we related bird species richness with phylogenetic relatedness of bird assemblages, plant species richness, topography, contemporary climate, and glacial‐interglacial climate change to investigate the relative importance of these factors. This study was conducted in Inner Mongolia, an arid and semiarid region with diverse vegetation types and strong species richness gradients. The following associated variables were included as follows: phylogenetic relatedness of bird assemblages (Net Relatedness Index, NRI), plant species richness, altitudinal range, contemporary climate (mean annual temperature and precipitation, MAT and MAP), and contemporary‐Last Glacial Maximum (LGM) change in climate (change in MAT and change in MAP). Ordinary least squares linear, simultaneous autoregressive linear, and Random Forest models were used to assess the associations between these variables and bird species richness across this region. We found that bird species richness was correlated negatively with NRI and positively with plant species richness and altitudinal range, with no significant correlations with contemporary climate and glacial–interglacial climate change. The six best combinations of variables ranked by Random Forest models consistently included NRI, plant species richness, and contemporary‐LGM change in MAT. Our results suggest important roles of local ecological factors in shaping the distribution of bird species richness across this semiarid region. Our findings highlight the potential importance of these local ecological factors, for example, environmental heterogeneity, habitat filtering, and biotic interactions, in biodiversity maintenance.

Highlights

Because Random Forest models could effectively capture interactions and nonlinear relationships, and do not require the data to follow strict assumptions, for example, homoscedasticity and normality in errors (Breiman, 2001), they were implemented for the multiple-variable analyses, aiming to find the combination of variables most associated with bird species richness
Random Forest analyses showed that the six combinations of variables most associated with bird species richness consistently included phylogenetic relatedness of bird assemblages, plant species richness, and contemporary-Last Glacial Maximum (LGM) change in mean annual temperature (MAT), indicating that contemporary-LGM change in MAT was not significantly correlated with bird species richness, it may still play a supplementary role in predicting distribution of bird species richness (Table 2)
Consistent with these studies, we found that bird species richness in Inner Mongolia increases with altitudinal range (Figure 1)

Summary

| MATERIALS AND METHODS

Geographic distribution of species diversity and its drivers at broad scales is an important topic in ecology and biogeography (Brown, 2014; Currie, 1991; Fine, 2015). Because Random Forest models could effectively capture interactions (e.g., in this study correlation between MAP and change in MAP is 0.76, and correlation between MAT and change in MAT is −0.70) and nonlinear relationships, and do not require the data to follow strict assumptions, for example, homoscedasticity and normality in errors (Breiman, 2001), they were implemented for the multiple-variable analyses, aiming to find the combination of variables most associated with bird species richness. Random Forest analyses showed that the six combinations of variables most associated with bird species richness consistently included phylogenetic relatedness of bird assemblages, plant species richness, and contemporary-LGM change in MAT, indicating that contemporary-LGM change in MAT was not significantly correlated with bird species richness, it may still play a supplementary role in predicting distribution of bird species richness (Table 2)

| DISCUSSION

| CONCLUSIONS

Findings

CONFLICT OF INTEREST