Asymmetric specialization: a pervasive feature of plant-pollinator interactions.

VÁZQUEZ, D.P. Y M.A. AIZEN.

ECOLOGY

ECOLOGICAL SOC AMER

Año: 2004 vol. 85 p. 1251 - 1257

0012-9658

Although specialization in species interactions has usually been equated toreciprocal specialization, asymmetric specialization (i.e., a specialist interacting with ageneralist) is also likely. Recent studies have suggested that asymmetric specialization inspecies interactions could be more common than previously thought. We contrasted patternsof asymmetric specialization observed in 18 plant?pollinator interaction webs with predictionsbased on null models. We found that asymmetric specialization is common inplant?pollinator interactions, and that its occurrence is more frequent than expected undera simple null model that assumed random interactions among species; furthermore, largeassemblages with many pairs of interacting species tend to have more asymmetric interactionsthan smaller assemblages. A second null model, which incorporated a correlationbetween species frequency of interaction and degree of specialization observed in mostdata sets produced patterns that were generally closer to those present in the data. At leastthree kinds of explanations could account for the observed asymmetric specialization,including random interactions among individuals (rather than species), adaptive consequencesof specialization, and artifacts, such as data aggregation and sampling biases. Futurestudies should be aimed at understanding the relative importance of each of these alternativeexplanations in generating asymmetric specialization in species interactions.