Impact of intraguild predation and stage structure on simple communities along a productivity gradient

Answers to the reading theory exercise

Make sure you have read your handout (or download the handout here) for the summary of this paper.

Question 1: In a linear food chain with a primary producer at one end, there is an expectation that the greater the primary productivity, the longer the chain that it can support, i.e. the more trophic levels can coexist. Is that expectation consistent with this study?

If the model were a simple linear food chain, high productivity should allow all 3 trophic levels to coexist. Since the authors found that high productivity leads to exclusion of intraguild prey C, this was an unexpected result.

Question 2: Intraguild predation is commonly observed in nature, but the model also assumes that the consumer is the better competitor for the shared resource. Does that seem realistic? Might this assumption matter for the result?

If both species were equally matched competitors, then the predator would be at an advantage because the predator would have an additional food source (the intraguild prey). So the prey must have some compensating advantage to persist, which in this model is being the superior competitor for the shared resource. Without that advantage, the predator would likely outcompete the consumer, and there would be no coexistence.

Question 3: Notice that the whole world for these species is C, R, and P alone. In a real food web with additional resources, prey, and predators, do you think these results would be likely to strengthen or weaken? Why?

Arguments could be made for strengthening the results or weakening the results. For example, if there were alternative prey species serving as resources for the predator, then the predator can switch to a different species if the shared prey species becomes uncommon. This might weaken the applicability of the results.