Global gradients in intertidal species richness and functional groups.

Jakob Thyrring,Lloyd S Peck

doi:10.7554/elife.64541

Abstract

Whether global latitudinal diversity gradients exist in rocky intertidal α-diversity and across functional groups remains unknown. Using literature data from 433 intertidal sites, we investigated α-diversity patterns across 155° of latitude, and whether local-scale or global-scale structuring processes control α-diversity. We, furthermore, investigated how the relative composition of functional groups changes with latitude. α-Diversity differed among hemispheres with a mid-latitudinal peak in the north, and a non-significant unimodal pattern in the south, but there was no support for a tropical-to-polar decrease in α-diversity. Although global-scale drivers had no discernible effect, the local-scale drivers significantly affected α-diversity, and our results reveal that latitudinal diversity gradients are outweighed by local processes. In contrast to α-diversity patterns, species richness of three functional groups (predators, grazers, and suspension feeders) declined with latitude, coinciding with an inverse gradient in algae. Polar and tropical intertidal data were sparse, and more sampling is required to improve knowledge of marine biodiversity.

Highlights

The latitudinal diversity gradient in species richness across ecosystems and various functional groups has been a major research topic that has intrigued scientists since at least Darwin, 1859 and Wallace, 1878
A generalized additive mixed effect model (GAMM) indicated a non-linear relationship among a-diversity and latitude in the northern hemisphere where a-diversity peaked at mid-latitudes between 30 and 55 ̊N ( GAMM, edf = 2.005, p=0.023)
Latitudinal diversity gradients are widely quoted as one of the basic laws in ecology (Lomolino, 2004), studies investigating these patterns on a global scale have largely overlooked intertidal ecosystems, despite their global range and importance as unique environments

Summary

Introduction

The latitudinal diversity gradient in species richness across ecosystems and various functional groups has been a major research topic that has intrigued scientists since at least Darwin, 1859 and Wallace, 1878. Latitudinal gradients in some groups have been shown to be closely related to oceanographic covariates, such as water temperature (Roy et al, 2000), yet mammal richness peaks at high latitudes (Grady et al, 2019), and more species have been reported from polar soft-sediment habitats than at many lower latitudes (Vause et al, 2019). While gradients in species diversity have received most attention, latitudinal changes across different functional groups (evaluated here by food acquisition, see Materials and methods) remain less studied despite their importance for ecosystem functioning.

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