Abstract Detail



Ecology

Wu, Yingtong [1].

What determines species range size? Testing niche-breadth and niche-position hypotheses in North and Central American oaks (Quercus spp.).

Introduction: Why some species are widespread while others are rare is a fundamental question in biogeography. Two intrinsic properties of species, niche breadth and niche position, might contribute to variation in species range sizes. The niche-breadth hypothesis posits that broader niche breadth is generally associated with larger geographic range size. The niche-position hypothesis posits that central niche position, presumably encompassing conditions that are common within a landscape, leads to large geographic range size. Testing both hypotheses simultaneously in the same system may improve our understanding of the determinants of species range size. In the meanwhile, we also need to understand the relative importance of soil niches and climate niches in explaining species range size.
Methods: We tested the niche-breadth and niche-position hypotheses in 182 species of North and Central American oaks (genus Quercus). To calculate species niche breadth and niche position, we first generated a MaxEnt niche model for each oak species based on climate and soil variables. We then calculated the niche breadth and niche position using the Outlying Mean Index method. Lastly, we used structural equation modelling, with the incorporation of phylogenetic non-independence, to examine the relationship of species range size (both area of occupancy [AOO] and extent of occurrence [EOO]) to niche breadth and niche position.
Results: Broad climate niche breadth, central climate position and central soil niche position lead to large species geographic range size in oaks, while soil niche breadth does not contribute to species range size. This finding is robust with respect to correction for phylogenetic non-independence. We also found that species range sizes (AOO and EOO), climate niche breadth, climate and soil niche marginality of oak species exhibit phylogenetic lability, relative to evolution modeled by Brownian motion or an Ornstein-Uhlenbeck process.
Conclusion: Both niche breadth and niche position influence the current species range sizes of oaks in the New World, a group that exhibits considerable evolutionary lability in species distributional extent. Understanding how particular mechanisms cause variation in species ranges remains a challenge. 


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Keywords:
range size
ecological niche modelling
oak.

Presentation Type: Poster Time and date to be determined
Number: PEC004
Abstract ID:274
Candidate for Awards:None


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