# Differentiation of Ecological Niches in Trophic Specialists From a Disturbed Lacustrine Ecosystem: Insights from the Sympatric Lake Tana Labeobarbs (Cyprinidae)

## TL;DR

This study examines how fish species in Lake Tana have adapted to human-caused environmental changes by analyzing their diets and ecological niches.

## Contribution

The study uses stable isotope and fatty acid analyses to reveal trophic niche differentiation in Lake Tana labeobarbs under human-induced disturbance.

## Key findings

- Generalized omnivorous labeobarbs occupy one niche, while nonpiscivorous and piscivorous species occupy multiple distinct niches.
- Top predators were most affected by ecosystem disturbances, showing altered and narrowed niches.
- Some species appear to have adapted their diets in response to habitat changes and population declines.

## Abstract

Adaptive radiations of freshwater fishes are based on the partitioning of trophic resources as sympatric forms diverge and end up occupying unique and specialized trophic niches. It remained unknown how these specialists responded to recent human‐induced ecosystem disturbances. Here, we tested how the species with various degrees of tropho‐ecological specializations (generalists vs. specialists) of Lake Tana Labeobarbus spp. flock reacted to the ongoing detrimental human‐induced ecosystem transformation and the resulting drastic population declines. In late 2022, we collected adults of the still remaining species to examine current niche partitioning within the assemblage based on the analyses of muscle stable isotope ratios and fatty acid compositions as time‐ and space‐integrated tropho‐ecological markers. The data revealed one niche for the generalized omnivorous labeobarb, four distinct niches for the nonpiscivorous, as well as three discernible niches for the piscivorous labeobarbs. Of the 11 species caught in the lake, only two pairs showed demonstrably large niche overlap. Of all the species in the Lake Tana species flock, the top (piscivorous) predators were the most strongly affected by the disturbance in ecological parameters, which resulted in altered and narrowed niches. This suggests that most of the endemic labeobarb species still retain their original, stable, and distinct diets and habitat preferences that appeared to have maintained the overall ecological relationships in Lake Tana. We also detected that some species apparently changed their diet, seemingly adapting to human‐induced habitat disturbances and large population declines during the last decades.

Lake Tana harbors the world's most complex adaptive radiation of cyprinids in the world. Although trophic specialization has been proven to drive this diversification, the diet of endemics has been studied using only traditional stomach content analysis. Here we present a study of the trophic differentiation of Lake Tana labeobarbs based on the analysis of muscle stable isotope ratios and fatty acid compositions as the time‐ and space‐integrated tropho‐ecological markers.