Mechanisms and Density Dependence of Benefit in an Ant–membracid Mutualism

Abstract

I examined mechanisms and patterns of benefit for the membracid (treehopper) Publilia concava tended by the ant Formica obscuriventris to test two hypotheses: that treehoppers benefit from ant attendance only by protection from predators, and that density‐dependent benefit depends on the presence of predators. I used a factorial design, manipulating ants and predators in 1996, and ants and removal of uncollected honeydew in 1997. Results showed that treehoppers benefit from ant attendance by protection from predators. Additionally, results suggested that treehoppers benefit from ant attendance in ways other than protection from predators; tended treehoppers outperform untended treehoppers even with predators excluded. There was no support for the hypothesis that a proximate benefit of ant‐tending includes removal of uncollected honeydew. A possible benefit (untested) of ant‐tending is increased feeding rates. Treehoppers in small aggregations benefited more than treehoppers in large aggregations, indicating a density‐dependent benefit in this mutualism, independent of predator level. Correspondingly, the number of ants per treehopper was highest for small aggregations. This study suggests that individuals can benefit from mutualisms in complex ways. Additionally, it adds to a growing number of studies that support the hypotheses that mutualisms may be stabilized by density‐dependent benefit and that density‐dependent benefit may be driven by the recruitment patterns of mutualists.

Multitrophic relationships, conditional mutualisms, and the study of interaction biodiversity in tropical savannas

“…Treehoppers occur on D. vinosum throughout the year, and levels of infestation on a plant range from one female with her egg mass to around 200 individuals in a single aggregation (mean ± SD = 18.8 ± 23.6; n = 222). Summarizing the main results (Del-Claro & Oliveira 1993, 1996, 1999, 2000, we observed that 21 different ant species are associated to the membracid and that daily turnover of ant species at a given treehopper aggregation frequently occurs (Del-Claro & Oliveira 1999). The number of individuals and species of ants collecting honeydew (membracid exsudate -its faeces rich in water, sugar, amino acids and other compounds), vary not only through the day, but also through the months of the year.…”

Allee dynamics generated by protection mutualisms can drive oscillations in trophic cascades

“…Although relatively little is known about the benefits and dynamics of the participants in many of these interactions (Bronstein and Barbosa 2002), ant-herbivore protection mutualisms are a particularly well-studied category of protection mutualism, so we use a plant-herbivorepredator-ant system to motivate our model. Ant-tended herbivores are insects (e.g., aphids and caterpillars) that excrete or secrete sugar rewards in return for protection from predators (Buckley 1987;Cushman and Whitham 1989;Morales 2000b;Pierce and Easteal 1986). Often the rewards are metabolic byproducts that involve little or no cost to produce.…”

Trophobiosis Between Formicidae and Hemiptera (Sternorrhyncha and Auchenorrhyncha): an Overview

“…The survival rate of 'Homoptera' also depends on the aggressiveness of its protective ant or whether the attendant ant is dominant (Nixon 1951, Wood 1982, Buckley & Gullan 1991, Campbell 1994, Gullan 1997. The survival rate does not depend of the number of trophobionts living in the aggregation (Flatt & Weisser 2000, Morales 2000. In some cases, trophobionts are marked by an ant colonyspecific odor that they can discriminate from conspecifics attended by another ant colony (Schütze & Maschwitz 1992).…”