Amensalism in the Real World

European Mussel Beds

Dittman studied intertidal mussel beds in Europe. Mussel beds in general are known as rich habitats for a wide range of marine organisms but, given that the substrate (the mussels themselves) is also composed of living organisms, then the question of interactions between the mussels and the various infaunal species becomes of interest. Dittman showed that there was indeed an amensalistic interaction between those suspension feeders associated with the mussel beds and the mussels themselves. For other members of the mussel bed assemblage, she regarded the interaction more as one of amelioration in which the mussels provide suitable habitat for a range of predatory or other species at no real cost to themselves. In these terms, 'amelioration' may be regarded as a kind of commensalism.

Galapagos Boobies

In contrast to this essentially community-based study, Townsend and co-workers examined nesting populations of boobies in the Galapagos. They showed clearly that blue-footed boobies (Sula nabouxii) were displaced from preferred nesting sites by the aggressive interactions of Nazca boobies (S. granti), which in turn suffered no negative effects from the presence of the blue-foots. In this study, the actual issue was the various factors affecting the success or otherwise of the Sula species, and not the frequency or otherwise of amensalistic or any other kind of interaction.

This contrast is underlined by the fact that most authors who describe amensalistic interactions do so more or less by default after failing to identify strong competition. This is clear in wide-ranging studies on, for example, African ants, Japanese gall-forming aphids, even soil-dwelling bacteria and nematodes. The list of examples could be extended.

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