Does Intraguild Predation Enhance Predator Performance? A Stoichiometric Perspective

Abstract

Ecological stoichiometry provides a novel context for elucidating the occurrence of intraguild predation. Recent data show that predators on average have a higher nitrogen content and lower C:N ratio than potential herbivorous prey. Thus, many predators may be nitrogen limited, and intraguild predation may allow them to increase their nitrogen intake and growth by supplementing a diet of herbivores with more nitrogen-rich intraguild prey. We tested this hypothesis using an assemblage of salt-marsh-inhabiting arthropods. First, we determined the nitrogen content and C:N ratio of taxa in four trophic groups (plants, herbivores, omnivores, and predators). Second, we fed an intraguild predator, the wolf spider Pardosa, one of three diets (herbivores, intraguild prey, or an alternating mix of the two) and measured spider survival, growth, capture rate, and biomass and nitrogen intake.In general, body nitrogen content increased and C:N ratio decreased from lower to higher trophic levels for marsh-inhabiting species, with predators having a higher nitrogen content and lower C:N ratio than herbivores. Performance experiments showed that in one case Pardosa ingested more biomass and nitrogen and grew faster on a diet of intraguild prey (the planthopper egg predator Tytthus) than on a diet of herbivores (the planthopper Prokelisia dolus). This occurred because Pardosa captured more Tytthus than Prokelisia and not because Tytthus (a stoichiometric exception) was higher in nitrogen content. In another case, Pardosa grew slower on a diet of intraguild prey (the web-building spider Grammonota) than on a planthopper diet even though Grammonota was more nitrogen rich, a result we attribute to prey behavior and risk of predation. Mass gain and nitrogen intake in Pardosa were highly correlated with the biomass of prey consumed. However, after accounting for the biomass of prey consumed across all diet treatments, we found little evidence that either the nitrogen content or C:N stoichiometry of prey contributed to Pardosa's growth. Thus, there was little support for the hypothesis that the nitrogen stoichiometry of prey directly confers a performance advantage to Pardosa and in itself promotes intraguild predation. In this system, characteristics other than the nitrogen stoichiometry of prey play a significant role in prey capture and predator performance. Nonetheless, by supplementing their diet with readily captured intraguild prey, predators such as Pardosa can increase their nitrogen intake and performance.

Caught in the web: Spider web architecture affects prey specialization and spider–prey stoichiometric relationships

“…Consumer–resource nutrient ratios are typically used as indicators of the strength of consumer nutrient limitation (Filipiak & Weiner, 2017; Matsumura et al., 2004; Sterner & Elser, 2002). Here, we used the threshold elemental ratio (hereafter TER, Sterner & Elser, 2002; Urabe & Watanabe, 1992) to identify the point at which a consumer (i.e., spider) growth switches from limitation by one element to another.…”

“…(2004), for example, the C:N TER in a predator–prey interaction is given by: ${\text{TER}}_{\mathrm{C}:\mathrm{N}}=false(\text{C:N prey}false/\text{C:N predator}false)>{\mathrm{normal\alpha }}_{\mathrm{normalN}}/{\mathrm{normal\alpha }}_{\mathrm{normalC}}$where C:N prey and C:N predator are the C:N in prey and predator biomass, and α N is the maximum gross growth efficiency for N (i.e., fraction of ingested N that the predator converts into new biomass), α C is the maximum gross growth efficiency for C (i.e., fraction of ingested C that the predator converts into new biomass). To calculate the TER for each spider, we used a gross growth efficiency α C  = 0.65 C and α N  = 0.70 (Fagan & Denno, 2004; Fagan et al., 2002; Matsumura et al., 2004; Wiesenborn, 2013), and two values for α PL  = 0.6 (low maximum gross growth efficiency; Lehman, 1993) and α PH (high maximum gross growth efficiency; DeMott, Gulati, & Siewertsen, 1998; Frost et al., 2006). Values for α N /α C  = 1.077, α PL /α C  = 0.923, α PH /α C  = 1.333, and α PL /α N  = 0.857, and α PH /α N  = 1.143.…”

“…Recent findings suggest that predators may face elemental imbalances between their nutrient demands and the supply of those nutrients by their prey (Fagan & Denno, 2004; Matsumura et al., 2004; Okuyama, 2008). As insect prey species typically vary in their body elemental content (Fagan et al., 2002; González et al., 2011), specialization can increase the strength of trophic interactions, but may also impose constrains on the transfer of energy and matter (Sanders, Vogel, & Knop, 2015; Shurin, Gruner, & Hillebrand, 2006).…”

Importance of local vs. geographic variation in salt marsh plant quality for arthropod herbivore communities

“…7), they appear to have relatively inflexible diets that require them to also consume plant material (Jim enez et al 2012), and they may continue to eat high-quality plant tissue even when invertebrate prey are also available. Several studies have suggested (Denno & Fagan 2003;Matsumura et al 2004) that even a (2012) found that Orchelimum grew better on a mixed diet including both prey and plant material than on either single diet alone. We found that Orchelimum exhibited greater relative growth rates on plants with greater foliar nitrogen (Fig.…”

Trophic promiscuity, intraguild predation and the problem of omnivores

“…Omnivory is therefore favoured by the relative scarcity of food items that are good stoichiometric matches to the consumer. Of course, the evolution of omnivory is not just about stoichiometry ( Matsumura et al , 2004 ). Diet mixing in general can dilute toxins in food, reduce the risk of predation or parasitism, and increase resistance to natural enemies ( Singer & Bernays, 2003 ).…”