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Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Field studies of interspecific competition: Observations versus experiments
Auteurs :	Martin Fyhn Lykke Sorensen, Auteur
Type de document :	Article
Dans :	Dansk Ornitologisk Forenings Tidsskrift (92(3) 1998)
Article en page(s) :	268-274
Langues:	Anglais
Résumé :	Field studies of interspecific competition fall into two distinct groups: (1) observations of unmanipulated systems, and (2) experimental studies. Such studies are evaluated in this review, with the emphasis on competitive interactions in bird communities. Evidence from observational studies indicating that interspecific competition has occurred or is occurring is indirect. These indications are niche shifts, density compensation, character displacement, character release, and niche overlap. Experimental studies can be divided into two types, resource manipulation and density manipulation. Experiments only apply to ecological time, whereas observational studies also apply to evolutionary time. Examples of various investigations are presented and discussed. A major problem in observational studies is that the observed patterns may be attributed to an array of factors, ranging from weather to resource levels, differential predator or parasite densities on study sites, and disturbance in general. However, these factors are most often assumed to have a limited impact - the so-called ceteris paribus assumption. Still, it is always crucial to contemplate alternative hypotheses when assessing the effect of interspecific competition. Ceteris paribus assumptions are also made in experimental investigations. I do not question the significance of interspecific competition in most communities. It must be borne in mind, however, that studies "confirming" interspecific competition probably are over-represented in the scientific literature, because investigators as well as editors and referees (often mistakenly) tend to consider studies leading to "negative" results as failures. The ideal field study of interspecific competition, at least initially, seems to be observations, including natural experiments like mainland/island comparisons. Such observations can be followed up by experimental manipulations, with a sufficient number of experimental controls and replicas. Experiments should mainly aim at confirming or rejecting findings from prior observational studies.

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