Patterns of functional diversity along latitudinal gradients of species richness in eleven fish families

Aim: As we enter an era of major biodiversity shifts, understanding large-scale biodiversity patterns has become crucial for ecological and conservation purposes. Often, conservation priorities are based on concepts derived largely from species richness, yet recent work shows that different facets of biodiversity are also crucial for proper ecosystem continuity, function and services. One facet of biodiversity increasingly relevant to conservation is functional diversity. Here, we aim to improve our understanding of large-scale patterns of biodiversity by testing the hypothesis that species richness can also accurately estimate functional diversity along the latitudinal gradient of species richness in fish. Location: Marine environments. Time period: Contemporary. Major taxa studied: Eight hundred and forty-two species within 11 fish families: Acanthuridae, Blenniidae, Chaetodontidae, Gobiidae, Labridae, Lutjanidae, Pleuronectidae, Pomacanthidae, Pomacentridae, Scombridae and Sparidae. Methods: Using geometric morphometrics to calculate morphological diversity, a proxy for functional diversity, we estimated the expected functional diversity for a given number of species and compared it with the observed functional diversity in fish families along latitudes. We then fitted a broken-stick regression model with estimates of functional diversity over absolute degree of latitudes to locate latitudes where significant shifts in functional diversity occur. Results: We found that species richness typically over- or underestimated functional diversity along the latitudinal gradient of species richness in the evaluated fishes. We also showed that for most families investigated, there was a pattern of stable functional diversity from the equator through the tropics that shifted, with a mean inflection point occurring at absolute latitude 31.7 +/- 10.1 degrees. We suggest that this pattern might be linked to changes in environmental factors such as global temperature and/or habitat availability beyond tropical latitudes; however, these concepts require more study. Main conclusions: This analysis shows the importance of considering functional diversity further, in combination with other biodiversity metrics, when developing conservation priorities and policies.

Automated summary

This study examines the relationship between species richness and functional diversity in fish. It finds that species richness cannot accurately estimate functional diversity. In most fish families, there is a pattern of stable functional diversity from the equator through the tropics that shifts at around absolute latitude 31.7 degrees. This analysis demonstrates the importance of considering functional diversity in conservation priorities and policies.