Biogeography of functional trait diversity in the Taiwanese reef fish fauna

Abstract

The richness of Taiwanese reef fish species is inversely correlated to latitude as a direct consequence of the abiotic environment and its effects on benthic habitats. However, to date, no studies have investigated the variations in the diversity of traits (FD) linked with the role of these fishes in the ecosystem. FD is usually considered more sensitive than species richness in detecting early changes in response to disturbances, and therefore could serve as an indicator of ecological resilience to environmental changes. Here, we aim to characterize FD in the Taiwanese reef fish fauna and to document its regional variations. Six traits were used to categorize the 1,484 reef fish species occurring in four environmentally contrasted regions around Taiwan. The number of unique trait combinations (FEs), their richness (FRic), their redundancy (FR), their over-redundancy (FOR), and their vulnerability (FV) were compared among these regions. Overall, 416 FEs were identified. Their number decreased from south to north in step with regional species richness but FRic remained similar among regions. FR and FOR were higher to the south. At the local scale, variations in FEs and FRic are in concordance with the worldwide pattern of FD. High-latitude, impoverished fish assemblages, offer a range of trait combinations similar to diversified tropical assemblages. Increasing diversity in the latter mainly contributes to raising FR and supports already over-redundant entities. High vulnerability makes many combinations highly sensitive to species loss, and was higher at intermediate latitudes when using a fine resolution in trait categories. It suggests that the loss of FEs may first be characterized by an increase in their vulnerability, a pattern that could have been overlooked in previous global scale analyses. Overall, this study provides new insights into reef fish trait biogeography with potential ramifications for ecosystem functioning.

Keywords: Kuroshio; functional diversity; high‐latitude; ichthyofauna; marginality; traits.

Figure 1

(a) The four studied regions around Taiwan. (b) Their respective species richness and number of unique species, unique trait combinations (FEs), range of unique trait combinations (FRic). The y‐axis is the percentage of richness in all bar plots

Figure 2

Distribution of species among unique trait combinations (FEs) with their redundancy (FR), vulnerability (FV), and over‐redundancy (FOR) among regions around Taiwan. FR is the mean number of species among all FEs. FV is the percentage of FEs possessing only one species. FOR is the percentage of species contributing to the over‐representation of some sets of traits (i.e., gray oblique lines). The black stair line corresponds to the distribution of species in FEs in the overall Taiwanese reef fish fauna. The black oblique dashed line area represents the contribution of unique species to FV