Ontogenetic diet shifts often lead to life-history intraguild predation (LHIGP), an interaction where juvenile predators compete with the prey of adults. Predator persistence in LHIGP is only possible when adult predators outnumber juveniles, regulating prey to avoid competitive exclusion. Thus LHIGP systems are highly sensitive to changes in predator size/stage structure. Cannibalism, a common interaction in natural LHIGP systems, is known to alter predator population structure, yet its effects on LHIGP are understudied. Here, we examine the effects of cannibalism on LHIGP systems characterized by food-dependent maturation and reproduction.
Results/Conclusions
We show that in the absence of cannibalism, reproduction is the limiting process in the life-history of the predator driving a predator stage distribution dominated by adults. Cannibalism enhances reproduction, shifting predator stage distribution to a preponderance of juveniles. This shift in turn eliminates or destabilizes the predator-present state because predators can no longer control the population growth of competitively-dominant consumers. Furthermore, this effect occurs at a low cannibalistic voracity (~25 % conspecific vs. heterospecific consumption) relative to lab and field estimates, and is consistent across systems in which the predator undergoes a complete diet shift or diet broadening over ontogeny. Thus our results demonstrate that even weak cannibalism can inhibit predator persistence in two main LHIGP system variants, prompting the exploration of mechanisms that reconcile theory with the common occurrence of such interactions in nature.