Ness J. H., Morris W. F., Bronstein J. L., Integrating quality and quantity of mutualistic service to contrast ant species protecting Ferocactus wislizeni, Ecology, 2006, 87(4):912-921, doi: 10.1890/0012-9658(2006)87[912:IQAQOM]2.0.CO;2
This study compares four ant species visiting Ferocactus wislizeni. It connects visit frequency and worker number with protective effectiveness against potential herbivores. Separating the quantity and quality of mutualistic service helps explain differences among partners.