“Cannibalism and intraguild predation community dynamics: coexistence, competitive exclusion and the loss of alternative stable states”

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Benjamin J. Toscano, Vincent Hin, and Volker H. W. Rudolf

Cannibalism leads to predator population collapse within stage-structured intraguild predation systems

Cannibalism in predators drives dramatic changes in ecological communities, and can even lead to predator extinction

Example of a size-dependent predator (copepod) in which adult and juvenile predators engage in different species interactions (arrows indicate pathways of energy flow).
(Illustration credit: Volker H. W. Rudolf)

As predators grow in size, their role within ecological communities often changes. A common scenario is that while adult predators consume prey, juvenile predators engage in competition with prey for a shared food resource. In a new article in The American Naturalist, Benjamin Toscano, Vincent Hin, and Volker Rudolf provide evidence that such size-dependent predators are often preferentially cannibalistic, and further use theory to explore how such cannibalism alters the structure of ecological communities that predators inhabit. These authors, from the United States and the Netherlands, demonstrate that cannibalism causes the predator population to shift, counterintuitively, from a preponderance of adult predators to a preponderance of juvenile predators. This simple mechanism has cascading effects induced by a reduction in predation, a function unique to adult predators. For example, Toscano et al. show that cannibalism facilitates coexistence in the community, but can also drive predator extinction depending on system details. Considering the prevalence of size-dependent interactions in nature and that predators face a higher risk of extinction than other trophic levels, this work has broad implications for understanding the potential consequences of predator loss across the globe. Their work shows that even changes to the size structure of predator populations, for example due to fishing practices that target adults, have the capacity to dramatically shift the structure of entire ecological communities to new and potentially irreversible states. Read the Article