Comparative functional responses predict the predatory impact of the highly invasive fish Cichla kelberi

Abstract

Peacock basses (genus Cichla) are a group of Amazonian predatory fishes that invaded many systems worldwide. Severe ecological impacts have been reported, but no study investigated the functional response of these fishes to variations in prey abundance, a crucial information to determine predator consumption and impact. In this study, we evaluated the functional response of the highly invasive Cichla kelberi toward prey species of different taxonomic groups, and compared it to the response of the wolf fish Hoplias malabaricus, a voracious predator used as baseline. We hypothesized that higher feeding rates drive the predatory impact of the invasive predator. Using a non-replacement experimental setup, we manipulated prey densities (fish and shrimp) in 1000-L mesocosm tanks to quantify the consumption response of each predator during 24 h. Both predators consumed more fish than shrimp, but C. kelberi consumed significantly more than H. malabaricus. We found that C. kelberi consistently displayed higher Type-II functional response than H. malabaricus toward both prey species. There was a non-significant effect of predator species on attack rates, but C. kelberi presented significantly lower handling time values and higher maximum feeding rates. Our findings provide empirical evidence that high individual consumption rates explain the predatory impact of the highly invasive C. kelberi, and predict strong effects on invaded communities.