Ecology and field biology of two dominant <i>Camponotus</i> ants (Hymenoptera: Formicidae) in the Brazilian savannah

<p><i>Camponotus renggeri</i> and <i>C. rufipes</i> are very abundant in Brazilian cerrado savannah, where they feed extensively on liquid rewards and commonly associate with plants bearing extrafloral nectaries and honeydew-producing insects. Here, we provide a qualitative and quantitative field account on the natural history and ecology of these two ant species. The study was carried out in a cerrado reserve in south-eastern Brazil across a rainy/hot season (summer) and a dry/cold season (winter). The ants were found in two vegetation physiognomies: all nests of <i>C. rufipes</i> were located in the cerrado <i>sensu stricto</i> (scrub of shrubs and trees, 3–8 m tall), whereas <i>C. renggeri</i> occurred mostly in the cerradão (forest with more or less merging canopy, 10–12 m tall). Both species nested in fallen or erect dead trunks, as well as underground. In addition, <i>C. rufipes</i> built nests using dead plant material arranged or not around shrub bases. Colonies of <i>C. rufipes</i> were generally more populous than those of <i>C. renggeri</i>, and both species had colonies with more than one dealated queen. Both species were active mainly at night and foraged for resources near their nests, mainly extrafloral nectar and hemipteran honeydew (aphids and mealybugs). The average size of the home ranges of <i>C. renggeri</i> in cerrado <i>sensu stricto</i> and cerradão varied from ≈ 2.8 to 4.0 m² and apparently were not affected by season. In <i>C. rufipes</i>, however, foraging grounds in cerrado <i>sensu stricto</i> showed a twofold increase from dry/cold (≈ 4.5 m²) to rainy/hot season (≈ 9.8 m²). Our study highlights the importance of natural history data to understand the foraging ecology and role of these ants in cerrado savannah.</p

Dynamics of foraging network use over the 8-month survey.

<p>(a) Fraction of foraging holes and (b) fraction of total length of active physical trails reused at each visit. For each graph the bold continuous line shows the predictions of a quasibinomial Generalized Additive Mixed Model with nest as random variable; the dashed lines show the predictions ± CI_0.95.</p

Assessment of foraging activity over the 8-month survey.

<p>(a) number of active foraging holes and (b) number of active physical trails observed at each visit. For each graph the bold continuous line shows the predictions of a quasipoisson Generalized Additive Mixed Model with nest entered as random variable; the dashed lines show the predictions ± CI_0.95.</p

Assessment of the excavation and trail construction effort over the 8-month survey.

<p>(a) Excavation effort: number of new foraging holes counted at each visit; (b) Physical trail construction effort: number of new physical trails observed at each visit. For each graph the bold continuous line shows the predictions of a quasipoisson Generalized Additive Mixed Model with nest as random variable; the dashed lines show the predictions ± CI_0.95.</p

Diagram showing how foraging, excavation, and physical trail construction could be related to rainfall.

<p>Rainfall data are from the Brazilian Institute of Meteorology meteorological station of the city of Juiz de Fora (about 12 Km from the study site).</p

Output of the multi-agent simulation implementing the individual level parameters observed experimentally.

<p>Each image is obtained by summing 300 snapshots of the simulation taken at equal intervals of 1 second of simulation time (corresponding to 5 minutes of simulation) in a similar way to what had been done for the experimental data.</p

Fit of eq. 4 parameters from individual replicates when assuming pheromone evaporation.

<p>The same as <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1002592#pcbi-1002592-t001" target="_blank">table 1</a>, but assuming pheromone evaporation with a half-life of 30 minutes ( in equation 9).</p

Evolution of the pattern formed by one colony (T09) over time.

<p>Each picture is obtained by summing all the ants detected from arena-level snapshots during 5 minutes (300 snapshots). The contrast and gamma are adjusted to make single ants visible in the images.</p

Correlation map between the observed turning angle and the angle predicted using pheromone information at positions and (equation 7).

<p>The colour associated with each point (, ) represents the value of the correlation coefficient between the observed turning angle and the turning angles predicted from equation 5 . The ant is situated in the centre of the map, facing upwards, and its approximate dimensions are given by the cyan rectangle. The scale for the figure is provided by+symbols, which are spaced 1 cm. apart. The map is for trial T09 and no pheromone evaporation. Similar maps are found in all the trials.</p

Simulation and analytical results implementing Weber's Law type response to pheromone in a binary bridge.

<p><b>A</b>. Illustrative drawing of the simulation domain; the blue dot near the top of maze represents the nest, while the large blue region at the bottom is the food source. <b>B</b>. Percentages of simulated ants on each branch of the maze at different times in one run of simulation (each point represent the average over three minutes of simulation). C. Schema providing an intuitive explanation of equation 8. The target direction of one ant depends linearly on . The probability for the ant to choose the left branch depends on the target direction and the directional noise. More precisely, if we assume that the branching point between left and right branch is at direction zero, the probability that the ant chooses the left branch is given by the integral of the curve in panel B from to 0. D. Bifurcation diagram for the density of ants on one branch of the bridge () as a function of the total flow of ants in the setup.</p