Intraguild Predation: Predatory Networks at the Microbial Scale

Abstract

Microbes live and interact within diverse communities of organisms which are embedded in complex networks of competition, parasitism, and predation. Predatory interactions in microbial communities have been of central interest in microbial ecology and ecological theory (Cohen et al. 2019; Gao et al. 2019; Gause 1934; Karakoç et al. 2017; Miki and Jacquet 2008; Pernthaler 2005), and interactions within microbial foods webs have been recognized as crucial key drivers for energy fluxes and nutrient transfer and recycling (Azam et al. 1983; Clarholm 1985; Sherr and Sherr 2002). It is now well accepted that top-down control by predators is the most important factor for mortality in bacterial communities (Breitbart 2012; Sherr and Sherr 2002). However, we still do not fully understand how diverse these interactions are, to which extent they are affected by environmental changes and how temporal and spatial scales impact their dynamics and their contribution to ecosystem processes. In order to be able to predict the functioning of microbial communities in the context of global change, we need to fully address multispecies predator-prey interactions. This requires integrating research on eukaryotic micro-predators of microbes, i.e. protists, as well as viruses and predatory bacteria, with a specific focus on the combined effect of micro-predators with partially overlapping prey ranges (Johnke et al. 2014). Only then will we be able to comprehensively understand the relevance on top-down control as compared to a resource-driven bottom-up control in different environments and along different scales. One important, but rather neglected, aspect of multiple predation is whether predators which potentially share prey resources also trophically interact with each other, a process which is called intra-guild predation (IGP) (Polis et al. 1989). While IGP has been described and studied in many ecosystems for higher organisms (Arim and Marquet 2004; Vance-Chalcraft et al. 2007), there is still a considerable knowledge gap regarding its relevance to the microbial world. In this chapter, we therefore attempt to first briefly present the key micro-predator groups on the microscale (in particular the protists and viruses, but also bacterial predators), to introduce the basic concept of intraguild predation (IGP) and to summarize several microbial IGP studies. We finally provide an outlook touching on a few selected aspects and techniques which may be very useful in order to address microbial IGP in a context of basic and applied ecology.