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Intraguild predation is a very widespread and important interaction in many systems. It happens when two or more species that make use of similar resources (that is, a guild), making them competitors, also prey on each other. In the Coachella Valley, California intraguild predation occurs among four scorpion species. Polis & McCormick (1987) carried out a study on these species, and concluded that the most abudant scorpion species limited the growth of the others not through competition, but rather because of predation.

In this system, predation seems to be linked to a lack of other resources for the predator, mobility of the prey, and to disparate sizes (and often ages) of predator and prey. It is postulated that the intraguild predator may have a large impact on the characteristics of the other species.

Hadrurus arizonensis scorpion

Propose a mathematical model for the dynamics of these populations of scorpions. Your model should take into account the findings and hypotheses of Polis & McCormick (1987). Use this model to explore the consequences of this dynamics and advance hypotheses that can be tested in the field or in the laboratory.

• When is the predator-prey interaction, rather than competition, the decisive factor for which species is most abundant?
• Incorporate into your model and analyze the impact of one of the species traits over the persistence of different species. For instance, what is the relevance of age structure to the intraguild predation interaction affect the system? What about symmetry? Can this analysis offer further insight into the authors' hypotheses?

• Polis & McCormick (1987) Intraguild Predation and Competition Among Desert Scorpions Ecology 68(2), pp. 332-343 link