Multiple predator effects result in risk reduction for prey across multiple prey densities

Abstract

Investigating how prey density influences a prey's combined predation risk from multiple predator species is critical for understanding the widespread importance of multiple predator effects. We conducted experiments that crossed six treatments consisting of zero, one, or two predator species (hellgrammites, greenside darters, and creek chubs) with three treatments in which we varied the density of mayfly prey. None of the multiple predator effects in our system were independent, and instead, the presence of multiple predator species resulted in risk reduction for the prey across both multiple predator combinations and all three levels of prey density. Risk reduction is likely to have population-level consequences for the prey, resulting in larger prey populations than would be predicted if the effects of multiple predator species were independent. For one of the two multiple predator combinations, the magnitude of risk reduction marginally increased with prey density. As a result, models predicting the combined risk from multiple predator species in this system will sometimes need to account for prey density as a factor influencing per-capita prey death rates.

Interactions of multiple predators with different foraging modes in an aquatic food web

“…In contrast, the strength of trophic cascades is weakened by intraguild predation of multiple predators in a terrestrial food web (Finke and Denno 2004). Thus, direct and indirect behavioral interactions can overwhelm trophic effects generating dynamics different from what is expected by following energy flow (Soluk and Richardson 1997;Luttbeg et al 2003;Vance-Chalcraft and Soluk 2005).…”

“…Substitution designs are limited in that variation in intra-and interspecific interactions are confounded with predator treatments (Inouye 2001;Griffen 2006). Few studies have simultaneously used both additive and substitution designs in multiple predator studies (e.g., Vance-Chalcraft et al 2004;Vance-Chalcraft and Soluk 2005); however, both experimental designs in combination are necessary to determine the influence of multiple predators on food webs (Relyea 2003;Griffen 2006;Schmitz 2007).…”

“…When a prey species is able to compensate for different predator species a neutral interaction will result . Prey species experience a risk reduction if predator species interfere with each other or if a prey response to one predator reduces the risk to another predator species (Griswold and Lounibos 2006;Crowder et al 1997;Vance-Chalcraft and Soluk 2005). Multiple predators that impose conflicting demands on the anti-predator defenses of their shared prey create an effect that is risk enhanced (Soluk and Richardson 1997).…”

Non-interactive multiple predator effects on tadpole survival

“…This approach asks whether the two predators have equivalent impacts on prey, essentially calibrating the effects of one species against the other. Rather few studies of multiple predator systems have deployed both designs, although both in combination are needed to evaluate the impacts of both species composition and density of predators (Vance-Chalcraft and Soluk 2005;Griffen 2006;Carey and Wahl 2010).…”

Expanding the Propagule Pressure Concept to Understand the Impact of Biological Invasions

“…An increase in propagule richness provides more opportunities for the introduction of natural enemies of a previously established or future invader, which can constrain the invader ' s spread and population growth (and hence its impact); but they might instead facilitate the invader if they harm resident species in the invaded range (Colautti et al 2004 ). Multiple invaders can interfere with each other in such a way as to attenuate their impacts (Vance -Chalcraft & Soluk 2005 ;Griffen et al 2008 ). Conversely, through a variety of positive interactions, multiple invaders can produce synergistic effects (Simberloff & Von Holle 1999 ;Richardson et al 2000 ;Ricciardi 2005 ).…”