Complex interactions between native and invasive fish: the simultaneous effects of multiple negative interactions

Area of Science:

• Ecology
• Invasive Species Biology
• Conservation Biology

Background:

• Invasive species interactions with native species can lead to extinction or coexistence.
• Relative body size influences the number and type of simultaneous negative interactions (competition, predation).
• Native species may face constraints in trading fitness components, potentially leading to extinction spirals.

Purpose of the Study:

• To investigate the impact of invasive western mosquitofish (Gambusia affinis) on native least chub (Iotichthys phlegethontis).
• To determine how body size influences the interactions and survival of least chub juveniles.
• To assess the combined effects of predation and competition on least chub fitness.

Main Methods:

• Field experiment: Replicate enclosures with varying densities of mosquitofish and different sizes of least chub juveniles in a desert spring ecosystem.
• Laboratory experiments: Assessed least chub mortality from mosquitofish predation, aggressiveness, and habitat selection in the presence of mosquitofish.

Main Results:

• Mosquitofish significantly reduced least chub survival by one-third; small juveniles had zero survival in high-density treatments.
• Predation by large mosquitofish caused 69.7% mortality of least chub in laboratory trials.
• Least chub exhibited reduced aggression, selected protected habitats, and reduced movement when exposed to mosquitofish.

Conclusions:

• Simultaneous interactions with invasive mosquitofish, driven by body size differences, create a 'vice' for least chub juveniles.
• Competition from mosquitofish reduces least chub growth, prolonging vulnerability to predation and increasing extinction risk.
• Management strategies should consider size-dependent interactions to mitigate invasive species impacts on native populations.