Niches in the Anthropocene: passerine assemblages show niche expansion from natural to urban habitats

Abstract

Human‐mediated habitat transformation is increasingly evident around the world. Yet, how this transformation influences species’ niche width and overlap remains unclear. On the one hand, human‐mediated habitat transformation promotes increased species similarity through trait‐based filtering, and an increased prevalence of generalist species with broad niches, resulting in functional homogenization. On the other hand, species that colonize transformed habitats could use empty niches, resulting in decreased species similarity and an expansion of assemblage‐level niche space. Here we explore these two alternatives in eight highly diverse passerine assembles in natural, rural and urban habitats in south and southwest China, a rapidly developing region of the world. Based on stable isotopes, we found that species’ niche width increased from natural to human‐made habitats, but there were no differences in niche overlap among habitats. Therefore, we found evidence for niche expansion, with generalists appearing to use empty niches created by human habitat modification, and with assemblages being comprised of complementary species. Further research is needed to determine whether increased between‐ or within‐individual niche variation is the main driver of niche expansion in transformed habitats.

How to Become a Generalist Species? Individual Niche Variation Across Habitat Transformation Gradients

“…Newbold et al, 2015). Natural habitats were relatively undisturbed and protected forested areas, rural habitats were predominantly agricultural areas or managed forests with low human population density, and urban habitats were humandominated areas inside cities (Liang et al, 2018;Pagani-Núñez et al, 2019; Figure 2). Six common passerines in the area included the Rufous-capped Babbler Stachyris ruficeps, the Gray-checked Fulvetta Alcippe morrisonia, the Common Tailorbird Orthotomus sutorius, the Red-whisked Bulbul Pycnonotus jocosus, the Redbilled Leiothrix Leiothrix lutea and the Scaly-breasted Munia Lonchura punctulata.…”

“…Frogs belonged to three species of the genus Feirana (Swelled-vented Frog F. quadranus, Taihangshan Swelled-vented Frog F. taihangnica and Kangxian Swelled-vented Frog F. kangxianensis) (Figure 3; Fei et al, 2009;Yang et al, 2011). For birds, we sampled a large number of individuals and species (see Pagani-Núñez et al, 2019). We focused, however, on six common species that were present in several habitats and limited sample size to 10 individuals per species (Figure 3).…”

“…While we did record markedly larger TNW in urban than in natural habitats, differences in WIC were negligible and species only showed a non-significant tendency to have larger BIC between these two habitat types. Many studies using different approaches have reported similar patterns of niche expansion across habitat transformation gradients (Bonier et al, 2007;Devictor et al, 2008a;Callaghan et al, 2019;Pagani-Núñez et al, 2019;Palacio, 2019), yet no study had thoroughly addressed how this pattern is a result of changes in different niche characteristics at the individual level. Our study is original in showing this pattern of trophic specialization within species, while previous Results from a set of linear mixed-effects models using the Within-Individual (WIC) and Between-Individual (BIC) niche components, and Individual Specialization (IS = WIC/TNW) in 21 populations of birds and frogs as response variables.…”

“…This loss is not neutral in that predominantly specialized species -those requiring particular habitat or food resources -are disproportionately lost, while environmental generalists -those with less selective habitat or dietary needs -become dominant (Flynn et al, 2009;Ducatez et al, 2018;Sol et al, 2020). A consequence of this process is that species in transformed habitats display broader niches than species in natural habitats (Bonier et al, 2007;Clavel et al, 2011;Coogan et al, 2018;Pagani-Núñez et al, 2019;Palacio, 2019). It is unclear however how this process of population niche expansion translates into the niches of the individual organisms.…”

Climate Change Adaptation in Natural World Heritage Sites: A Triage Approach

“…Human society is now living in the Anthropocene [1][2][3][4][5], encountering far-reaching anthropogenic environmental changes. Climate change has become one of the few most critical challenges we face [6,7].…”