“Playing out Liem’s Paradox: opportunistic piscivory across Lake Tanganyikan cichlids”

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Jimena Golcher-Benavides and Catherine E. Wagner (Aug 2019)

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Researchers report diet switching by morphologically specialized cichlids as consequence of unusual concentrations of clupeids

Liem’s Paradox (1980) in wild cichlid species from Lake Tanganyika. (Credit: Jimena Golcher-Benavides)

Cichlid fishes are celebrated for their often extreme feeding adaptations and unique feeding strategies: Lobochilotes labiatus extracts invertebrates from rock crevices using its enlarged lips, Perissodus microlepis’s feeding on scales from other fishes is linked to their striking mouth asymmetry, Tropheus duboisi crops algae growing on the rocky substrate using teeth located at the jaw-edges of their subterminal mouths. Karel Liem (1980) first noted that cichlid fishes are not only remarkable dietary specialists, but also can act as jacks-of-all-trades. However, evidence for the dietary flexibility of cichlids comes from laboratory studies, and it is unclear whether cichlid fishes in the wild actually feed on resources other than the ones they have adaptations for. We report field observations of dietary switching by multiple cichlid species in Lake Tanganyika as a consequence of a transient school of juvenile sardines; and discuss this evidence in the framework of Liem’s paradox. Robinson and Wilson (1998) solved Liem’s paradox by demonstrating that extreme dietary specializations can theoretically be maintained as long as they do not preclude the ability to exploit other broadly accessible food resources. Rare pulses of “easy prey” could determine the fate of endemic species with small population size across ecosystems.


Abstract

Trophic specialization is a key feature of the diversity of cichlid fish adaptive radiations. However, Liem (1980) observed that even species with highly specialized trophic morphologies have dietary flexibility, enabling them to exploit episodic food resources opportunistically. Evidence for dietary flexibility comes largely from laboratory studies, and it is unclear whether cichlid fishes undergo diet shifts in the wild. We report observations of diet switching by multiple cichlid species in Lake Tanganyika as a consequence of unusual concentrations of schooling juvenile clupeid fishes. Fish species with varying degrees of trophic specialization converged on a single prey: juvenile sardines that are also endemic to Lake Tanganyika (Stolothrissa tanganicae and Limnothrissa miodon). We provide evidence for cichlid species acting as jacks-of-all-trades and discuss this evidence in the framework of Liem’s classic paradox: that trophic specialization does not preclude dietary flexibility.