Taxonomic Distinctness of Demersal Fishes of the California Current: Moving Beyond Simple Measures of Diversity for Marine Ecosystem-Based Management

Nick Tolimieri,Marti J Anderson,Simon Thrush

doi:10.1371/journal.pone.0010653

Abstract

BackgroundLarge-scale patterns or trends in species diversity have long interested ecologists. The classic pattern is for diversity (e.g., species richness) to decrease with increasing latitude. Taxonomic distinctness is a diversity measure based on the relatedness of the species within a sample. Here we examined patterns of taxonomic distinctness in relation to latitude (ca. 32–48 °N) and depth (ca. 50–1220 m) for demersal fishes on the continental shelf and slope of the US Pacific coast.Methodology/Principal FindingsBoth average taxonomic distinctness (AvTD) and variation in taxonomic distinctness (VarTD) changed with latitude and depth. AvTD was highest at approximately 500 m and lowest at around 200 m bottom depth. Latitudinal trends in AvTD were somewhat weaker and were depth-specific. AvTD increased with latitude on the shelf (50–150 m) but tended to decrease with latitude at deeper depths. Variation in taxonomic distinctness (VarTD) was highest around 300 m. As with AvTD, latitudinal trends in VarTD were depth-specific. On the shelf (50–150 m), VarTD increased with latitude, while in deeper areas the patterns were more complex. Closer inspection of the data showed that the number and distribution of species within the class Chondrichthyes were the primary drivers of the overall patterns seen in AvTD and VarTD, while the relatedness and distribution of species in the order Scorpaeniformes appeared to cause the relatively low observed values of AvTD at around 200 m.Conclusions/SignificanceThese trends contrast to some extent the patterns seen in earlier studies for species richness and evenness in demersal fishes along this coast and add to our understanding of diversity of the demersal fishes of the California Current.

Highlights

Species are distributed neither uniformly nor randomly across the globe
We examined two measures of diversity: average taxonomic distinctness (AvTD or D+) and variation in taxonomic distinctness (VarTD or L+) [30]
When the degrees of freedom for the smoothed term were near their minimum value, we examined whether the trend was described sufficiently by a linear regression using Akaike’s information criterion (AIC) and analysis of deviance between the two models

Summary

Introduction

Large-scale patterns in biodiversity have interested ecologists since at least the time of Wallace and Darwin [1,2]. Understanding these large-scale patterns helps us to develop hypotheses regarding how communities and ecosystems are organized on both ecological and evolutionary time scales [2,3]. Biodiversity is a key concept for conservation and management, and is fundamental for ecosystem-based approaches [8,11,12]. Large-scale patterns or trends in species diversity have long interested ecologists. The classic pattern is for diversity (e.g., species richness) to decrease with increasing latitude. Taxonomic distinctness is a diversity measure based on the relatedness of the species within a sample. We examined patterns of taxonomic distinctness in relation to latitude (ca. 32–48 uN) and depth (ca. 50–1220 m) for demersal fishes on the continental shelf and slope of the US Pacific coast

Methods

Results

Conclusion