Parasites as Prey

Abstract

Parasites are usually considered to use their hosts as a resource for energy. However, there is increasing awareness that parasites can also become a resource themselves and serve as prey for other organisms. Here we describe various types of predation in which parasites act as prey for other organisms: (1) predation of nonhosts on infected hosts (concomitant predation), (2) predation on free‐living parasite life cycle stages, (3) predation on ectoparasites in form of grooming or cleaning and (4) predation or hyperparasitism by other parasites. In many cases, these types of predation significantly reduce the numbers of parasites and thus affect parasite population dynamics. In contrast, predation on parasites is often beneficial for the hosts as they are released from parasite burden. Finally, when parasites act as prey they may contribute to the nonhost predator's diet, in some cases constituting a significant proportion of energy intake. Key Concepts: There is increasing awareness that parasites can become a resource themselves by serving as prey for other organisms. Predation on parasites can have significant effects on parasite population dynamics, for example, by interfering with the transmission of infective stages. For hosts, parasite predation may result in a reduced parasite burden, the so‐called dilution effect. When nonhosts prey on parasites or infected prey, this may have an effect on their energy uptake by mediating the energetic value of their prey. Future studies on the levels of predation on parasites in food webs will increase our understanding of disease dynamics as well as the topology and functioning of food webs.

Cercarial behaviour alters the consumer functional response of three‐spined sticklebacks

“…Kuris et al., 2008; Soldánová et al., 2016) prior to infecting their second intermediate or final hosts in either a two‐ or three‐host life cycle (Combes et al., 1994; Morley, 2012). However, cercariae may also encounter non‐host organisms, whereby the parasite's functional role may change to that of a prey resource (Goedknegt et al., 2012; Johnson et al., 2010; Thieltges et al., 2008). Cercariae typically fall into the meso‐zooplankton size range (0.2–2 mm), and given their abundance, they thus represent a noteworthy and easily digestible glycogen and lipid nutritional resource for aquatic predators akin to zooplankton (Johnson et al., 2010; McKee et al., 2020).…”

Tri-trophic interactions of a predator-parasite-host assemblage in New Zealand

“…estimates that 70% of all trophic interactions are parasitic and the antagonistic relationships between parasites and their hosts determine population and community structure in natural ecosystems (Pimm 1979;Pimm 1980a;Paine 1980;Pimm et al, 1991;Polis et al, 1997;Thompson et al, 2007;Lafferty et al, 2008;Chase 2013). Parasites require hosts for nutrition, shelter and, ultimately, survival (Tscharntke 1992;Lafferty et al, 2008;Johnson et al, 2010;Goedknegt et al, 2012;Friman & Buckling 2013) depending on their ecological networks for development, transmission and overall fitness (Lafferty et al, 2008).…”

“…With the recent inclusion of parasites as consumers in food webs, emerging evidence suggests parasites are also a specific food source for predators (Johnson et al 2010;Goedknegt et al 2012;Thieltges et al 2013). The consumption of parasites is often accidental, occurring when parasites are consumed as a bi-product of their host being predated (Goedknegt et al 2012). However, deliberate predation of parasites' free-living life stages also occurs (Goedknegt et al 2012).…”

“…The consumption of parasites is often accidental, occurring when parasites are consumed as a bi-product of their host being predated (Goedknegt et al 2012). However, deliberate predation of parasites' free-living life stages also occurs (Goedknegt et al 2012). Parasites that have specific predators face the same selection pressures as free-living organisms when it comes to the evolution of anti-predator adaptations.…”

“…In turn, parasites rely solely on their hosts for nutrition, shelter and ultimately fitness (Tscharntke 1992;Lafferty et al 2008;Johnson et al 2010;Goedknegt et al 2012;Friman & Buckling 2013). Hosts vary dramatically in their characteristics, particularly between sexes, yet only recently has host sex been considered an underlying mechanism of susceptibility to parasites (Goble & Konopka 1973;Alexander & Stimson 1988;Bundy 1988).…”