Predator identity and the nature and strength of food web interactions

Abstract

Summary1. Most trophic interaction theory assumes that all predators are an abstract form of risk to which prey respond in a quantitatively similar manner. This conceptualization can be problematic because recent empirical work demonstrates that variation in the responses of prey to different predators can play a key role in structuring communities and regulating ecosystem function. 2. Predator identity -the species specific response of prey to a predator -has been proposed as an ultimate mechanism driving the relative contribution of indirect effects in food webs; however few studies have explicitly tested this hypothesis. 3. This study explores the impact of predator identity on direct consumptive (CE) and nonconsumptive effects (NCEs), and on the relative contribution of indirect, density and traitmediated effects in trophic cascades within host-parasitoid communities. 4. We systematically compared the individual, host-parasitoid-plant interactions of two actively foraging parasitoid species with disparate foraging styles, one aggressive and one furtive, a common aphid host and plant. Our results demonstrate that the degree of risk aversion by prey to each particular predator species (i.e. predator identity) is a key factor driving the nature and strength of direct and indirect transmission pathways. 5. Both parasitoid species, in general, had a negative impact on plants. The magnitude of the aphid anti-predator dispersal response was positively correlated with plant infestation and plant damage. The qualitative effect of predator-induced infestation of new plants superseded the quantitative effects of predator-mediated reductions in aphid numbers. 6. The greatest indirect impact on plants was generated by the aggressively foraging parasitoid, and the strength of the aphids anti-predator response (a NCE) antagonistically traded-off with CEs due to an increased investment in attempting to capture risk-sensitized prey. In contrast, the furtive parasitoid did not elicit a strong anti-predator response, had little indirect impact on plants, but generated very high CEs due to the advantage of ovipositing into a sedentary prey population. 7. Our data suggest the responses of prey to different predatory cues may be an important mechanism driving the relative contribution of transmission pathways in trophic cascades. We conclude that predator identity is a key factor influencing the nature and strength of food web interactions.

The importance of intraguild predation in predicting emergent multiple predator effects

“…However, to manipulate the presence and absence of IGP, these studies also simultaneously varied the richness (Finke and Denno 2004) and composition (Finke and Denno 2005) of predator communities. Predators are not necessarily equivalent (Ramos andVan Buskirk 2012, Schneider andBrose 2013), and if we are to understand the impacts of IGP per se in multipredator systems, studies must be conducted without modifying the carnivore community or changing predator identity (sensu Henry et al 2010) by altering habitat domain or hunting mode. The importance of these predator characteristics in shaping MPEs was shown in a study of numerous generalist arthropod carnivores that consume planthoppers (Woodcock and Heard 2011); the interaction between habitat domain and hunting mode was a significant predictor of MPEs for prey and their resource.…”

Using optimality models to improve the efficacy of parasitoids in biological control programmes

“…In this case, parasitoid females could adopt any of three strategies: (1) specialist: accept only the most profitable hosts, (2) generalist: accept all encountered hosts, and (3) expanding specialist: accept only the most profitable host at first and switch to a generalist diet once the most profitable host is sufficiently depleted. The optimal strategy for a forager is to adopt the expanding specialist strategy, while adjusting the moment it switches from a specialist to a generalist diet based on the patch residence time (Henry et al, 2010). Such adjustment of the model would explain cases where partial preferences are expressed, a behaviour not explained by the original model (Jones, 1990).…”

Evidence for specificity in symbiont-conferred protection against parasitoids

“…The two wasp species have very different parasitism techniques [46]. Aphidius species attack quickly, laying each egg in less than a second but causing considerable disruption to the aphid colony; Aphelinus are furtive and cause minimal disturbance to their hosts, but oviposition takes several minutes [33,34,46].…”

“…Aphidius species attack quickly, laying each egg in less than a second but causing considerable disruption to the aphid colony; Aphelinus are furtive and cause minimal disturbance to their hosts, but oviposition takes several minutes [33,34,46]. The goal of the experimental design was to allow enough time for all aphids in the dish to be parasitized but to minimize superparasitism.…”