Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

Mexican mojarra can dominate non-native convict cichlids even when outnumbered.

Abstract

The non-native, aggressive, convict cichlid Amatitlania nigrofasciata is often regarded as a cause for the decline of native Mexican mojarra Cichlasoma istlanum in Mexican rivers. Convict cichlids are assumed dominant in areas they invade. Cooperative territorial defense has been observed in convict cichlids, suggesting that they can dominate Mexican mojarras by coalition. Behavioral observations were recorded and analyzed to experimentally test hierarchical dominance establishment (ES) and maintenance (MN) between uneven numbers of both species. Counts of aggressive interactions (bites, chases, and confrontations) between species were used to measure dominance in ES and MN interactions. More chases and bites were made by Mexican mojarra than convict cichlids in both ES and MN tests. Mexican mojarra attained and maintained dominance against two convict cichlids when competing for food resources via increased antagonistic interactions. Intraspecific confrontations were more common than interspecific confrontations for convict cichlids. Our results offer insight into competition mechanisms potentially occurring in natural settings, suggesting that while convict cichlids may be exploitative and interference competitors to Mexican mojarra, behavioral interactions between these species may not be the sole cause of observed Mexican mojarra population declines in freshwater ecosystems throughout western and southern Mexico.