# Functional Trait Divergence in Feeding Ecology Between Two Closely Related Upeneus Species in the Beibu Gulf: An Ecological Morphology Analysis

## TL;DR

This study shows how two closely related fish species in the Beibu Gulf use different feeding strategies and body shapes to coexist and avoid competition.

## Contribution

The study reveals novel insights into niche differentiation and adaptive evolution through functional trait and trophic niche analysis in closely related goatfish species.

## Key findings

- U. tragula has higher functional richness and trophic diversity compared to U. sulphureus.
- Morphological differences correlate with distinct feeding strategies and habitat preferences in the two species.
- Stable isotope analysis confirms divergent diets, with U. sulphureus feeding on cephalopods and U. tragula on benthic invertebrates.

## Abstract

Closely related species coexisting in the same habitat often undergo niche differentiation or morphological adaptations to reduce interspecific competition and secure sufficient resources, particularly when their ecological niches overlap. Such differentiation may manifest as niche expansion or enhanced morphological adaptations to improve competitive advantages in resource utilization. This study focused on
Upeneus sulphureus
and
Upeneus tragula
in the Beibu Gulf, using functional trait analysis, stable isotope techniques, and morphological comparisons to explore their functional niche differentiation and resource utilization strategies. Functional richness analysis showed that
U. tragula
had significantly higher functional richness (22.33%, n = 38) than
U. sulphureus
(11.64%, n = 67), with low functional niche overlap (27.91%), indicating significant divergence in resource utilization. Trophic niche analysis further revealed that
U. tragula
had significantly higher trophic diversity (CD) and core niche breadth (SEAc) than
U. sulphureus
, indicating broader resource utilization capabilities and adaptability. The results revealed significant differences in functional traits between
U. sulphureus
and
U. tragula
:
U. sulphureus
has a robust body, longer pectoral fins and snout, and a larger oral gape, exhibiting lower δ13C (−18.38‰ ± 0.35‰) and δ15N (13.31‰ ± 0.47‰) values (p < 0.05), primarily feeding on cephalopods. In contrast,
U. tragula
has a streamlined body, larger eye diameter, and longer barbels, displaying higher δ13C (−15.23‰ ± 0.96‰) and δ15N (15.36‰ ± 0.38‰) values (p < 0.01), primarily preying on small benthic invertebrates. These morphological differences are closely related to the feeding strategies and habitat preferences of the two goatfish species, reflecting their ecological adaptive divergence. This study reveals that
U. sulphureus
and
U. tragula
achieve coexistence through functional trait and trophic niche differentiation, providing important insights into species adaptive evolution and resource allocation mechanisms in ecosystems.

This research not only provides new insights into the niche differentiation and adaptive evolution of closely related species but also offers significant evidence for understanding resource allocation mechanisms within ecosystems.