Interaction frequency as a surrogate for the total effect of animal mutualists on plants

Abstract

We evaluate whether species interaction frequency can be used as a surrogate for thetotal effect of a species on another. Because interaction frequency is easier to estimatethan per-interaction effect, using interaction frequency as a surrogate of total effect couldfacilitate the large-scale analysis of quantitative patterns of species-rich interactionnetworks. We show mathematically that the correlation between interaction frequency(I ) and total effect (T ) becomes more strongly positive the greater the variation of Irelative to the variation of per-interaction effect (P) and the greater the correlationbetween I and P. A meta-analysis using data on I, P and T for animal pollinators and seeddispersers visiting plants shows a generally strong, positive relationship between T and I,in spite of no general relationship between P and I. Thus, frequent animal mutualistsusually contribute the most to plant reproduction, regardless of their effectiveness on aper-interaction basis.