Coexistence of Predator and Prey in Intraguild Predation Systems with Ontogenetic Niche Shifts

Abstract

In basic intraguild predation (IGP) systems, predators and prey also compete for a shared resource. Theory predicts that persistence of these systems is possible when intraguild prey is superior in competition and productivity is not too high. IGP often results from ontogenetic niche shifts, in which the diet of intraguild predators changes as a result of growth in body size (life-history omnivory). As a juvenile, a life-history omnivore competes with the species that becomes its prey later in life. Competition can hence limit growth of young predators, while adult predators can suppress consumers and therewith neutralize negative effects of competition. We formulate and analyze a stage-structured model that captures both basic IGP and life-history omnivory. The model predicts increasing coexistence of predators and consumers when resource use of stage-structured predators becomes more stage specific. This coexistence depends on adult predators requiring consumer biomass for reproduction and is less likely when consumers outcompete juvenile predators, in contrast to basic IGP. Therefore, coexistence occurs when predation structures the community and competition is negligible. Consequently, equilibrium patterns over productivity resemble those of three-species food chains. Life-history omnivory thus provides a mechanism that allows intraguild predators and prey to coexist over a wide range of resource productivity.

Deadly competition and life-saving predation: the potential for alternative stable states in a stage-structured predator–prey system

“…This work thus provides novel empirical insights into the capacity of LHIGP to drive alternative stable states predicted by theory [4,14,17].…”

“…Theory suggests that the outcome of LHIGP and its effects on community dynamics are largely dependent on the balance of competition and predation [14,15]. In systems where predators exhibit a complete diet shift, no alternative stable states exist when the predator is competitively superior; dynamics are instead expected to follow a simple top-down food chain [14].…”

“…the cultivation effect: [9,14]). Thus competition-dominated versus predationdominated dynamics can lead to alternative stable states in LHIGP systems [4,8,11,14,15]. Alternative stable states are only possible in complete diet shift LHIGP systems when two specific conditions are met: (i) prey have to be able to competitively exclude juvenile predators through resource competition (i.e.…”

“…Alternative stable states are only possible in complete diet shift LHIGP systems when two specific conditions are met: (i) prey have to be able to competitively exclude juvenile predators through resource competition (i.e. prevent recruitment to the adult stage) and (ii) a relative increase in adult predator density has to reduce prey density and increase predator recruitment [14,17]. While studies of fish communities have supported the basic premise that competitively dominant prey can reduce growth rates of juvenile predators [10,18,19], empirical evidence demonstrating a prey's ability to eliminate predator recruitment through resource competition is scant (but see [11,12]).…”

“…Furthermore, the effects of changes in adult predator abundance, relative to the prey, in regulating juvenile competitive bottleneck dynamics (condition (ii)) have received little attention. This represents a major gap in our understanding of LHIGP systems, because theory posits that strong top-down control is necessary to drive an alternative stable state in which predators coexist with their prey [14].…”