Parasitism in a community context: trait‐mediated interactions with competition and predation

Abstract

Abstract. Predation and competition can induce important density-and trait-mediated effects on species, with implications for community stability. However, interactions of these factors with parasitism remain understudied. Here we investigate interactions among competition, predation and parasitism by crossing tadpole density (Bufo americanus), presence of a caged predator (Notophthalmus viridescens), and Echinostoma trivolvis trematodes, experimentally partitioning their effects on tadpole exposure and susceptibility to infection. Predation did not affect E. trivolvis infection but accelerated tadpole development and growth, and decreased activity. The presence of E. trivolvis caused the opposite effects on these three responses and reduced tadpole survival. High conspecific density reduced tadpole survival, growth, and development, and increased tadpole activity. Effects of predation and parasitism on activity were only evident at low tadpole density. High-density mesocosms also had twice the number of E. trivolvis infections as low-density mesocosms, despite a lack of evidence for stress-induced immunomodulation. Instead, this effect was explained by high density delaying tadpole development, which increased both the duration of exposure to cercariae and susceptibility to infection, because tadpoles spent more time in highly susceptible early stages. These results highlight the importance of accounting for trait-mediated effects, host plasticity, and exposure vs. susceptibility in parasite ecology.

Interactive effects of competition and predator cues on immune responses of leopard frogs at metamorphosis

“…However, competition had little or no effect when tadpoles were exposed to predator cues chronically or for only a week early in development. This research, which is only the second study of the effects of both competition and predator cues on immune functions in amphibians (Raffel et al, 2010), shows that stress experienced early in development or chronically throughout development can have lasting effects on skin defenses during highly sensitive life-history stages later in life.…”

“…For example, density-dependent immunosuppression of antibody responsiveness has been found in lizards (Svensson et al, 2001), while density-dependent immune enhancement (in the form of increased melanism) has been found in moths (Hagen et al, 2006). No density-dependent effects on acquired immune functions (leukocyte count and type) were found in a recent study of the effects of competition in American toad tadpoles, Anaxyrus americanus (Raffel et al, 2010). Our results support the density-dependent immune enhancement hypothesis; however, further disease challenges are necessary to test the adaptiveness of this response.…”

“…environmental changes alter critical immune responses against pathogens (Råberg et al, 1998;Carey et al, 1999;Hawley and Altizer, 2011;Raffel et al, 2010;Rollins-Smith et al, 2011). For example, amphibians are declining around the globe, and the emerging infectious diseases caused by ranaviruses and Batrachochytrium dendrobatidis (Bd) are contributing to these trends (Daszak et al, 2003).…”

Parasites of Trinidadian guppies: evidence for sex‐ and age‐specific trait‐mediated indirect effects of predators

“…One of the challenges in this field is to ascribe observed patterns to trait-rather than density-mediated indirect effects (Raffel et al 2010). Extensive work on this system has shown, however, that guppy populations do not differ consistently in density or sex ratio, neither spatially nor temporally (Pettersson et al 2004, Magurran 2005.…”

Evidence for carry-over effects of predator exposure on pathogen transmission potential

“…These phenotypic responses to predation risk are costly and can alter the nature of the interactions with other species, such as pathogens [9]. Predator exposure can modify the key traits that govern host-pathogen interactions through trade-offs between anti-pathogen and anti-predator defences.…”