Intraguild predation (IGP), a system in which species compete for resources and prey upon each
other, is more common than existing theory predicts. In theory, an IG predator and its prey can
coexist if the IG predator is a weaker competitor for a shared resource and the predator directly
benefits from consuming the prey. However, many species that are IG predators also consume
members of their own species (cannibalism). Here we ask whether cannibalism can help resolve
the paradox of IGP systems. Our approach differs from previous work on IGP and cannibalism
by explicitly considering the size-dependence of predatory interactions and how the benefits of
predation are allocated to survival, growth, and fecundity of the predator or cannibal. Our results
show that cannibalism facilitates coexistence under conditions that are opposite of those
predicted by standard IGP theory: species can coexist when the cannibal is a better competitor on
the shared resources, directly benefits little from consuming conspecifics, and allocates resources
from predation more towards growth and fecundity over survival. Because the effects IGP and
cannibalism are opposite, when an IGP predator is also a cannibal, coexistence between the IGP
predator and its prey is not possible and instead depends on the operation of other coexistence
mechanisms (e.g. resource partitioning). These results point to the importance of understanding
the relative rates of IGP and cannibalism as well as the resource allocation strategy of the IG
predator in determining the likelihood of species coexistence