Competition in Umbra-Perca fish assemblages: experimental and field evidence

Area of Science:

• Ecology
• Aquatic Ecology
• Behavioral Ecology

Background:

• Interspecific competition can increase predation risk for prey species by affecting their growth rates.
• Size-limited predation by gape-limited piscivores is a key factor structuring freshwater fish communities.
• Central mudminnows (Umbra limi) and yellow perch (Perca flavescens) interactions provide a model for studying competition and predation.

Purpose of the Study:

• To investigate the mechanisms and consequences of competition between central mudminnows and yearling yellow perch.
• To determine if competition affects mudminnow feeding success and subsequent growth and condition.
• To assess the field-level impacts of this competition on fish assemblage structure and dominance dynamics.

Main Methods:

• Laboratory experiments simulating foraging under varying densities of competing perch.
• Field surveys of fish size distributions and condition factors in lakes with differing mudminnow-perch assemblage compositions.
• Analysis of mudminnow feeding behavior, activity levels, and patch use in the presence and absence of perch.

Main Results:

• Mudminnow food intake decreased significantly in the presence of yearling perch due to exploitation competition, not interference or predator avoidance.
• Field data showed smaller, poorer-conditioned mudminnows in mixed assemblages compared to mudminnow-only assemblages.
• Perch condition and size were positively influenced by mudminnow presence at lower perch densities, indicating asymmetrical competition.

Conclusions:

• Asymmetrical competition between yellow perch and mudminnows directly impacts mudminnow growth and condition.
• This competition indirectly increases mudminnow predation vulnerability, contributing to perch dominance in mixed-species assemblages.
• Understanding these competitive dynamics is crucial for predicting freshwater fish community structure and population dynamics.