Abstract
Scavenging can have important consequences for food web dynamics, for example, it may support additional consumer species and affect predation on live prey. Still, few food web models include scavenging. We develop a dynamic model that includes two facultative scavenger species, which we refer to as the predator or scavenger species according to their natural scavenging propensity, as well as live prey, and a carrion pool to show ramifications of scavenging for predation in simple food webs. Our modeling suggests that the presence of scavengers can both increase and decrease predator kill rates and overall predation in model food webs and the impact varies (in magnitude and direction) with context. In particular, we explore the impact of the amount of dynamics (exploitative competition) allowed in the predator, scavenger, and prey populations as well as the direction and magnitude of interference competition between predators and scavengers. One fundamental prediction is that scavengers most likely increase predator kill rates, especially if there are exploitative feedback effects on the prey or carrion resources like is normally observed in natural systems. Scavengers only have minimal effects on predator kill rate when predator, scavenger, and prey abundances are kept constant by management. In such controlled systems, interference competition can greatly affect the interactions in contrast to more natural systems, with an increase in interference competition leading to a decrease in predator kill rate. Our study adds to studies that show that the presence of predators affects scavenger behavior, vital rates, and food web structure, by showing that scavengers impact predator kill rates through multiple mechanisms, and therefore indicating that scavenging and predation patterns are tightly intertwined. We provide a road map to the different theoretical outcomes and their support from different empirical studies on vertebrate guilds to provide guidance in wildlife management.
Highlights
Scavenging, or the use of carrion for energy gain, is an important energetic pathway in food webs
We focus on our central question of how predation is affected by the addition of a scavenger to the food web
In the systems we describe, the profitability of scavenging typically will be higher than predation given the high handling time associated with killing large prey
Summary
Scavenging, or the use of carrion for energy gain, is an important energetic pathway in food webs. The effect of increasing scavenger density on the kill rate of the predator in the No dynamics model depends on nP, the interference competition as manifested by the scavenger affecting the carrion handling time of the predator. Note: The interference competition specified by nP, the effect of scavenger on predator handling time, affects predation metrics and is why the predator kill rate for the No dynamics model has increases, 0, decreases for nP = − 1, nP = 0, nP = 1, respectively. In the lynx and wolverine interaction, lynx appears to quickly abandon a carcass when a wolverine is present, a negative nP effect of scavenger on handling time of the predator This can decrease the time until their kill, so there can be an increase in kill rate (aqua colored region) and exploitative competition can be high (López-Bao et al, 2016). These are all predictions of the net effects considering their hypothesized natural density regulation (management regime) that determines their placement in one of the three models arrayed along the vertical axis
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