Rhytidoponera violacea

Rhytidoponera violacea is a keystone seed disperser in many Western Australia habitats.

Distribution
Occurs in the western half of Australia.

This taxon was described from Australia.

Biology
In areas where R. violacea is found, it appears to be the dominant ant responsible for seed dispersal (Majer 1984; Gove et al. 2007; McCoy 2008).

Lubertazzi et al. (2010) studied the biology of this species in two multi-hectare plots located just north of Eneabba and on opposite sides of the Brand Highway (29° 37'33" S, 115° 12' 59" E). Both areas contained native Kwongan Heathland. Findings from this study include:

Foraging/Diet
The average number of successful foragers returning to the nest over a 30-minute period was 5 ± 0.5 (range = 1 - 14, n = 36). There there were typically between 10 to 15 return trips to the nest during 30 minutes of sampling, suggesting that approximately 30 – 50% of foraging bouts are successful. The majority of items captured (65%) were insects (either whole individuals or insect parts). Plant parts were more commonly collected (17%) than seeds (5%). In a few cases, foragers were observed subduing live insect prey that was then brought back to the nest. In addition, some insects (e.g., non-conspecific ants, small beetles, and termites) were often found to be alive when they were collected from the foragers.

The average foraging distance from the nest was 3.5 ± 2.2 m, with a maximum distance of 10.4 m. These distances are similar to those previously observed in the same study region for R. violacea carrying seeds back to the nest (Gove et al. 2007; McCoy 2008).

Colony Attributes
The average number of workers in a colony was 190 ± 23.5 (range = 47 - 474, n = 22). All of the colonies excavated contained pupae (mean = 83 ± 13.4, range = 2 - 293) and many contained larvae (mean = 22 ± 3.8, range = 0 - 85). Small larvae (< 3 mm) and eggs were either uncommon or entirely absent. A total of seven males were collected from two colonies.

Nesting Biology
All the excavated nests were located under plants. The nests were either supported in part by a large mass of roots from a plant or, less commonly, incorporated a larger root of a shrub into their structure. The mean (n = 14) size of the nest entrance was 4.0 ± 0.58 cm (longest axis) by 2.1 ± 0.29 cm (perpendicular to widest axis). The number of nest openings varied (9 nests with 1 opening, 3 nests with 2 openings, 1 nest with 3 openings, and 1 nest with 4 openings). When present, multiple nest openings were located within a few centimeters of one another and coalesced into a single chamber or tunnel 1 - 2 cm below ground. A mound of nest spoil was found around most, but not all, nest entrances.

Mounds were typically oval in shape, approximately centered on the nest opening, and often obscured by the stems and shoots of the vegetation of the overlaying plant. The average longest axis width of a mound was 21.0 ± 1 cm, the width perpendicular to the longest axis averaged 15.7 ± 1.4 cm, and the average mound height was 5.4 ± 0.7 cm.

Nests were centered under nest entrances and had an average depth of 23.0 ± 1.6 cm (N = 19 nests). The upper portion of the nest (the first 4 to 5 cm below ground) was a collection of small chambers, side by side, that were often supported by many fine roots. These chambers were between 1 and 2 cm deep and collectively filled an area from 5 to 10 cm in diameter.

A number of distinctive chambers were located below this area and were found at depths ranging from 8 - 43 cm. The sides of these chambers had an average width of 4.3 ± 0.6 cm, an average height of 1.6 ± 0.2 cm, and were roughly ovoid in shape. These were connected to the central shaft at one side of their longest axis, but were not directly connected to any other chambers. Each chamber was offset in a vertical plane from any chambers that were directly above or below.

Nomenclature

 * gemma. Ectatomma (Rhytidoponera) convexum var. gemma Forel, 1907h: 269 (w.m.) AUSTRALIA. Combination in Rhytidoponera: Emery, 1911d: 37. Junior synonym of violacea: Clark, 1936: 87.
 *  violacea. Ectatomma (Rhytidoponera) convexum subsp. violaceum Forel, 1907h: 269 (w.m.) AUSTRALIA. Combination in Rhytidoponera: Emery, 1911d: 38. Raised to species: Brown, 1958g: 205. Senior synonym of gemma: Clark, 1936: 87; of opacior: Brown, 1958g: 205.
 * opacior. Rhytidoponera convexa subsp. opacior Clark, 1936: 86 (w.) AUSTRALIA. [First available use of Rhytidoponera convexa subsp. violacea var. opacior Crawley, 1925b: 583; unavailable name (Taylor, 1986: 34).] Junior synonym of violacea: Brown, 1958g: 205.

Additional References

 * [[Media:Crawley 1925b.pdf|Crawley, W. C. 1925b. New ants from Australia. - II. Ann. Mag. Nat. Hist. 9(16): 577-598 PDF]]
 * Gove AD, Majer JD, Dunn RR. 2007. A keystone ant species promotes seed dispersal in a “diffuse” mutualism. Oecologia 153: 687-697.
 * Lubertazzi D, Lubertazzi MAA, McCoy N, Gove AD, Majer JD, Dunn RR. 2010. The ecology of a keystone seed disperser, the ant Rhytidoponera violace. Journal of Insect Science 10:158
 * Majer, J., A. Gove, S. Sochacki, P. Searle, and C. Portlock. 2011. A comparison of the autecology of two seed-taking ant genera, Rhytidoponera and Melophorus. Insectes Sociaux. 58:115-125.