Patchiness in food resources drives fish abundances in emergent macrophytes under field and experimental conditions

Abstract

The basic tenet of optimal foraging theory is that animals will select habitats that provide the greatest energy return (of food resources) per unit effort spent searching to optimize their fitness. Fish living in variable environments may use specific cues that indicate optimal feeding patches relative to poorer quality patches. To examine whether carp gudgeons (Hypseleotris spp.) preferentially select habitat patches based on food resource availability, we examined their habitat use in emergent macrophyte stands (the giant rush, Juncus ingens). We tested the hypothesis that carp gudgeons selected patches based upon food availability in a floodplain billabong and experimental billabongs. Under field conditions, finescale associations between carp gudgeons and giant rush demonstrated patch-specific differences in their prey (chironomid) density that were positively associated with fish abundance. Furthermore, the amount of biofilm within a patch was positively associated with the density and biomass of chironomids. Experimental evidence demonstrated that carp gudgeon patch selection was independent of stem density and based upon prey density. Carp gudgeons track their food resources through time, thus maximizing their feeding returns in both natural and experimental systems.

The use of fatty acids to identify food sources of secondary consumers in wetland mesocosms

“…In addition, the gudgeons appeared to target different taxa in the different habitat types, Chironomidae from the plankton and Chydoridae from the benthos and avoided Ostracoda and Daphniidae/Macrothricidae in both habitat types. Western carp gudgeons are known to eat Daphnidae, Chironomidae and to a lesser extent ostracods and chydorids (Meredith et al 2003;Balcombe and Humphries 2006;Balcombe and Closs 2016). Through their dietary preferences gudgeons can alter the assemblage structure of zooplankton (Ning et al 2010) but it is unclear if this is the case for benthos.…”