Functional Responses and Additive Multiple Predator Effects of Two Common Wetland Fish

Linton F Munyai,Tatenda Dalu,Gordon O’Brien,Lutendo Mugwedi,Farai Dondofema,Ross N Cuthbert,Ryan J Wasserman

doi:10.3390/w14050699

Abstract

Understanding trophic interactions is essential for the prediction and measurement of structure and function in aquatic environments. Communities in these ecosystems may be shaped by variables such as predator diversity, prey density and emergent multiple predator effects (MPEs), which are likely to influence trophic dynamics. In this study, we examined the effect of key predatory fish in floodplain wetlands, namely Oreochromis mossambicus and Enteromius paludinosus, towards Chironomidae prey, using a comparative functional response (FR) approach. We used single predator species as well as intra- and interspecific paired species to contrast FRs under multiple predator scenarios. Attack rate and handling time estimates from single predator FRs were used to predict multiple predators’ feeding rates, which were compared to observe multiple predators’ feeding rates to quantify potential MPEs. From single fish trials, each species displayed a significant Type II FR, characterized by high feeding rates at low prey densities. Oreochromis mossambicus had a steeper (initial slope, i.e., higher attack rate) and higher (asymptote of curve, i.e., shorter handling time and higher maximum feeding rate) FR, whereas E. paludinosus exhibited lower-magnitude FRs (i.e., lower attack rate, longer handling time and lower feeding rate). In multiple predator scenarios, feeding rates were well-predicted by those of single predators, both in conspecific and interspecific pairs, and thus we did not find evidence for antagonistic or synergistic MPEs. Predator–prey interactions in wetland systems can have significant consequences on the structure and dynamics of ecological communities. In turn, this could have destabilizing effects on resources in tropical wetlands. These results, although experimental, help us understand how trophic interaction among conspecific or interspecific fish species in Austral tropical wetlands might influence their aquatic prey species. This will help us to understand food web dynamics better.

Highlights

Licensee MDPI, Basel, Switzerland.Predator–prey dynamics are central to our understanding of how species interact and are pervasive determinants of community structure [1,2]
For conspecific interactions, feeding rates combined additively across prey density treatments since expected proportions of prey were consumed relative to those upscaled from single predators
Given the evidence that a change in functional response (FR) of individual species may result from multiple predator effects (MPEs) [24], this study further demonstrates how single and multiple predators can cause additive responses in the aquatic system and how intensely they interact with prey within these systems

Summary

Introduction

Predator–prey dynamics are central to our understanding of how species interact and are pervasive determinants of community structure [1,2]. These dynamics in tropical and subtropical wetlands systems have received little scientific interest [3,4]. Floodplain connection to permanent water typically facilitates small-bodied fish presence in their food webs during their hydroperiod [8]. In these shallow systems, small-bodied fish typically represent the top of the aquatic food web, often exploiting the rich productivity associated with wetlands during the wet season [9,10]. Multiple predatory species exploit these environments, but little is known on how predator–predator interactions may facilitate or disrupt predator–

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