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

Dan Liang,Yang Liu,Chao He,Shengnan Yang,Wen Bo Liao,Junhua Hu,Emilio Pagani-Núñez,Eben Goodale

doi:10.3389/fevo.2020.597450

Dan Liang, Yang Liu + Show 6 more

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Species in transformed habitats, frequently labeled as environmental generalists, tend to show broader niches than species in natural habitats. However, how population niche expansion translates into changes in the niches of individual organisms remains unclear, particularly in the context of habitat transformation. Niche expansion could be a product of individuals having broader niches, greater distances among individuals’ niches, or a combination of both processes. This would challenge the traditional conceptions on niche dynamics, which emphasize the role played by individual specialization (IS). Here, using stable isotopes, we computed total niche width (TNW), its within- and between-individual components (WIC and BIC), and IS (the ratio WIC/TNW), in 13 populations of 6 bird species and 8 populations of 3 frog species in natural and transformed habitats. We confirmed that species had broader niche width in transformed than in natural habitats, yet population niche expansion across habitats was mainly a product of increased distance between individuals. Within each habitat type, increases in TNW were linked to increases in WIC for all habitat types, while relationships between TNW and BIC were found in transformed but not in natural habitats. Hence, both increased individual niche width and increased distance among individuals were apparent within habitats, particularly in transformed ones, where increases in WIC dominated. Neither across or within habitats was niche expansion associated with increasing IS. Therefore, our results overturn traditional conceptions associated with the niche variation hypothesis and illustrate that niche expansion is not invariably associated with increased IS, because the distance between individual’s niches (BIC) can increase, as well as the breadth of those niches (WIC).

Highlights

Habitat transformation is one of the main drivers of biodiversity loss (Newbold et al, 2015)
Total niche width (TNW) of a population is composed by the sum of its within-individual component (WIC) and betweenindividual component (BIC) (Roughgarden, 1972, 1974), while individual specialization (IS) is computed as the ratio between WIC and TNW (Bolnick et al, 2003; Araújo et al, 2011), and increases as this ratio decreases
The niche variation hypothesis (NVH) predicts that TNW is positively correlated with IS (Van Valen, 1965), meaning that increases in TNW are mostly associated with increasing IS (Cachera et al, 2017; Maldonado et al, 2017)

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Introduction

Habitat transformation is one of the main drivers of biodiversity loss (Newbold et al, 2015). The niche variation hypothesis (NVH) predicts that TNW is positively correlated with IS (Van Valen, 1965), meaning that increases in TNW are mostly associated with increasing IS (Cachera et al, 2017; Maldonado et al, 2017). This is because when TNW increases, IS is likely to increase too, because TNW would increase at a higher rate than WIC. This seems a realistic assumption, as generalist populations are often composed of individuals only using a subset of the total population niche (Araújo et al, 2011; Layman et al, 2015; Pagani-Núñez et al, 2015)

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