Body size and geographic range do not explain long term variation in fish populations: a Bayesian phylogenetic approach to testing assembly processes in stream fish assemblages.

Stephen J Jacquemin,Jason C Doll

doi:10.1371/journal.pone.0093522

Abstract

We combine evolutionary biology and community ecology to test whether two species traits, body size and geographic range, explain long term variation in local scale freshwater stream fish assemblages. Body size and geographic range are expected to influence several aspects of fish ecology, via relationships with niche breadth, dispersal, and abundance. These traits are expected to scale inversely with niche breadth or current abundance, and to scale directly with dispersal potential. However, their utility to explain long term temporal patterns in local scale abundance is not known. Comparative methods employing an existing molecular phylogeny were used to incorporate evolutionary relatedness in a test for covariation of body size and geographic range with long term (1983 – 2010) local scale population variation of fishes in West Fork White River (Indiana, USA). The Bayesian model incorporating phylogenetic uncertainty and correlated predictors indicated that neither body size nor geographic range explained significant variation in population fluctuations over a 28 year period. Phylogenetic signal data indicated that body size and geographic range were less similar among taxa than expected if trait evolution followed a purely random walk. We interpret this as evidence that local scale population variation may be influenced less by species-level traits such as body size or geographic range, and instead may be influenced more strongly by a taxon’s local scale habitat and biotic assemblages.

Highlights

Attributing stream fish assemblage dynamics to random or deterministic factors is a long standing theme of community ecology [1,2]
The 95% credible interval estimates of the parameters for body size and geographic range overlapped 0 (Table 2), indicating there is no credible evidence to support a relationship with species coefficient of variation given the phylogenetic tree
Long term variation in stream fish population abundances did not covary with body size or geographic range of taxa. This finding is contrary to our initial expectations; we do not interpret this as evidence that White River stream fish assemblages are random or stochastic

Summary

Introduction

Attributing stream fish assemblage dynamics to random or deterministic factors is a long standing theme of community ecology [1,2]. A current paradigm is that assemblages are highly organized by a variety of abiotic and biotic variables dictated by geographic and evolutionary scale [3,4]. Unexplained assemblage variation is typically attributed to random noise or other untested mechanisms. In addition to biotic and abiotic scale dependent factors, body size and geographic range are not necessarily independent of assemblage variation [12]. An inverse relationship between body size and abundance is expected as a function of energetic constraints [13] in both terrestrial [14] and aquatic [15] assemblages/ecosystems. Macroecological studies have demonstrated a relationship between body size and geographic range [16,17]. The expectation is that larger sized individuals are more capable of long range movements and exhibit increased range sizes

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