A taxonomic, functional, and phylogenetic perspective on the community assembly of passerine birds along an elevational gradient in southwest China

Abstract

Integrating multiple facets of biodiversity to describe spatial and temporal distribution patterns is one way of revealing the mechanisms driving community assembly. We assessed the species, functional, and phylogenetic composition and structure of passerine bird communities along an elevational gradient both in wintering and breeding seasons in the Ailao Mountains, southwest China, in order to identify the dominant ecological processes structuring the communities and how these processes change with elevation and season. Our research confirms that the highest taxonomic diversity, and distinct community composition, was found in the moist evergreen broadleaf forest at high elevation in both seasons. Environmental filtering was the dominant force at high elevations with relatively cold and wet climatic conditions, while the observed value of mean pairwise functional and phylogenetic distances of low elevation was constantly higher than expectation in two seasons, suggested interspecific competition could play the key role at low elevations, perhaps because of relative rich resource result from complex vegetation structure and human‐induced disturbance. Across all elevations, there was a trend of decreasing intensity of environmental filtering whereas increasing interspecific competition from wintering season to breeding season. This was likely due to the increased resource availability but reproduction‐associated competition in the summer months. In general, there is a clear justification for conservation efforts to protect entire elevational gradients in the Ailao Mountains, given the distinct taxonomic, functional, and phylogenetic compositions and also elevational migration pattern in passerine bird communities.

Functional community assembly and turnover along elevation and latitude

“…Correspondingly, environmental filtering dominates in less benign tropical highlands as well as across most of the elevational gradient in temperate and polar regions, characterized by the strong selective force of their harsher winters. This mirrors earlier findings on the increasing role of abiotic contraints leading to phylogenetic clustering (32–34) and faster rates of speciation (24) at high elevations. Contrary to our predictions, however, we find increasing functional overdispersion toward the highlands in temperate and arctic regions.…”

Global functional and phylogenetic structure of avian assemblages across elevation and latitude

“…Our results confirm our expectation of strong latitudinal variation in elevational gradients in functional diversity and structure. Consistent with previous findings (Graham et al ., 2009; Machac et al ., 2011; He et al ., 2018), we find a prominence of functional overdispersion and high functional distinctiveness in more productive and stable environments (i.e. tropical low elevations).…”

“…Mountain systems harbour exceptionally high biodiversity, but the lack of truly global characterisations of functional diversity along elevation for different taxonomic groups hinders understanding of potential ecosystem‐level consequences of biodiversity loss for mountainous ecosystems. Spatially restricted transect‐level studies (Graham et al ., 2009; Machac et al ., 2011; Pigot et al ., 2016; He et al ., 2018) suggest that lowlands tend to harbour more functional diversity than their species richness would suggest, resulting in functional overdispersion among community members. Correspondingly, functional diversity in the highlands has been suggested to decline below the levels suggested by species richness, resulting in trait similarity (i.e.…”

“…Correspondingly, functional diversity in the highlands has been suggested to decline below the levels suggested by species richness, resulting in trait similarity (i.e. functional clustering; Sydenham et al ., 2015; Xu et al ., 2017; He et al ., 2018). Consensus about the generality of these patterns, however, remains elusive and variation among mountain ranges and hemispheres has been reported (Montaño‐Centellas et al ., 2020).…”

Treeline ecotones shape the distribution of avian species richness and functional diversity in south temperate mountains

“…Fewer studies have focused on the influence of heterogeneity on diversity in temperate mountain ecosystems where high seasonality and low species richness should reduce the intensity of inter-specific competition relative to tropical mountains 13 , 16 , 17 . Hypothetically lower levels of competition in temperate mountain ecosystems could enable coexistence among bird species with similar ecological niches 18 , resulting in large elevational ranges that reflect a broader spectrum of habitat and resource use (i.e. habitat generalists) 19 , 20 .…”