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When two prey (or resource) species share a common predator (consumer), they can be in apparent competition. An increase in one prey species can increase the common predator density, which negatively influences the other prey species.

A textbook (Molles, Seventh edition, ISBN-10: 0077837282) gives an example of apparent competition that confuses me. It gives another definition "one species facilitating populations of a predator or herbivore of the second species." Thus, one of the species does not have to be consumed by the predator/herbivore.

The specific example is that there are two plant species. Species A becomes the habitat for the herbivore (but is not consumed by the herbivore). Species B is consumed by the herbivore. Therefore, an increase in species A will increase the herbivore density and has negative effects on species B. I thought that to form an apparent competition relationship, it has to be mutually negative relationship (-,-). In this example, there is no mutually negative relationship. Furthermore, the plants do not share the common herbivore.

This is simply a definition question. Different sources have variable definitions, but is the example really considered an apparent competition?

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Competition-like interactions where only one species suffers ([0,-]) are usually labelled amensalism, so a suitable term for the situation you describe should be "apparent amensalism". I hadn't actually seen this term in use from before, but a quick Google search reveals that is in fact used. One example is in Jaworski et al. (2015):

Indirect interactions mediated by shared natural enemies are known as apparent competition, if negative interactions are reciprocal, or apparent amensalism, if one prey suffers from the presence of the other prey (Holt 1977; Holt and Lawton 1994).

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