Integrating quality and quantity of mutualistic service to contrast ant species protecting Ferocactus wislizeni

Generalized, facultative mutualisms are often characterized by great variation in the benefits provided by different partner species. This variation may be due to differences among species in the quality and quantity of their interactions, as well as their phenology. Many plant species produce extra...

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Bibliographic Details
Published in:Ecology (Durham) 2006-04, Vol.87 (4), p.912-921
Main Authors: Ness, J. H., Morris, W. F., Bronstein, J. L.
Format: Article
Language:English
Subjects:
Animal and plant ecology
Animal, plant and microbial ecology
Animals
ant
Ants
Ants - physiology
Biological and medical sciences
Cactaceae - parasitology
Cactaceae - physiology
Caterpillars
Desert insects
Ferocactus
Ferocactus wislizeni
Flowers & plants
Formicidae
Fundamental and applied biological sciences. Psychology
General aspects
Herbivores
Insect ecology
insect pests
Insect reproduction
Insects
Likelihood Functions
Manduca sexta
maximum likelihood
Michaelis-Menten
Mutualism
Phytophagous insects
plant defense
plant pests
plant protection
Plants
protection
Sonoran Desert
Species Specificity
Symbiosis
Worker insects
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Summary:Generalized, facultative mutualisms are often characterized by great variation in the benefits provided by different partner species. This variation may be due to differences among species in the quality and quantity of their interactions, as well as their phenology. Many plant species produce extrafloral nectar, a carbohydrate-rich resource, to attract ant species that can act as "bodyguards" against a plant's natural enemies. Here, we explore differences in the quality and quantity of protective service that ants can provide a plant by contrasting the four most common ant visitors to Ferocactus wislizeni, an extrafloral nectary-bearing cactus in southern Arizona. The four species differ in abundance when tending plants, and in the frequency at which they visit plants. By adding surrogate herbivores (Manduca sexta caterpillars) to plants, we demonstrate that all four species recruit to and attack potential herbivores. However, their per capita effectiveness in deterring herbivores (measured as the inverse of the number of workers needed to remove half of the experimentally added caterpillars) differs. Using these among-species differences in quality (per capita effectiveness) and quantity (number of workers that visit a plant and frequency of visitation), we accurately predicted the variation in fruit production among plants with different histories of ant tending. We found that plant benefits (herbivore removal and maturation of buds and fruits) typically saturated at high levels of ant protection, although plants could be "well defended" via different combinations of interaction frequency, numbers of ant workers per interaction, and per capita effects. Our study documents variation among prospective mutualists, distinguishes the components of this variation, and integrates these components into a predictive measure of protection benefit to the plant. The method we used to average saturating benefits over time could prove useful for quantifying overall service in other mutualisms.
ISSN:0012-9658
1939-9170
DOI:10.1890/0012-9658(2006)87[912:IQAQOM]2.0.CO;2