Interactions with Plants
From seed foraging to plant removal. Pogos
interacting with the plant life around them, in North America.
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Pogonomyrmex salinus
● Wanapum Rec. Area [Kittitas Co], WA USA [el. 190 m / 623 ft] view location in Google Maps » ● 5/17/09 10:35AM sunny, air temp: 20°C / 68°F
This was a particularly difficult image to capture, as the grass stem and ant were bobbing up and down wildly! A determined Pogonomyrmex salinus worker using her mandibles to cut away a dried cheatgrass (Bromus tectorum) spikelet. Keeping her head perpendicular to the stem, she rotated from side to side, cutting a deep groove. 23 seconds later, the spikelet detached and fell, sending the ant catapulting backward - then falling to the ground. She ran off in the direction of the nest. Presumably the spikelet was eventually picked up by one of the many other workers in the immediate vicinity. [scroll down for additional notes/references]
ADDITIONAL NOTES/REFERENCES:
The introduced (and invasive) grass Bromus tectorum (cheatgrass), is common in many of the areas inhabited by Pogonomyrmex ants, and is often a target of their foraging activities.
One study in central Oregon found cheat grass (Bromus tectorum), to be one of the 5 most frequently collected seeds by P. salinus. The others were: Phacelia linearis, Hordeum jubatum, Descurainia pinnata, and Sisymbrium altissimum.
Pogonomyrmex occidentalis (a member of the same complex as P. salinus) has long been known to have an association with Bromus tectorum, though there are indications that this ant prefers other species when they are available. In the Twin Falls, Idaho area, Cole found the seeds of B. tectorum to be harvested in great quantities "...primarily due to the predominance of Bromus tectorum in the semi-desert areas." He also notes that "the seed chambers of mounds in dense bromegrass areas often contain a greater quantity of other seeds and only a few colonies were located which seemed to harvest bromegrass seeds exclusively."
This seems to be in keeping with the preliminary findings of a study of P. occidentalis in Colorado, by D. Wiernasz, where it was found that "Bromus tectorum was strongly avoided, and never exceeded 3% of seeds collected by foragers, even in high density areas."
·Cole, A.C. 1932a. The Relation of the Ant, Pogonomyrmex occidentalis CR., to its Habitat. Ohio Journal of Science, 32:133-46, Ohio State University
·Wiernasz, D. 2005. Granivore Activity on the Invasive Grass Bromus tectorum: a Factor in Establishment or Exclusion? University of Huston
·Willard, J.R. & H.H. Crowell. 1965. Biological Activities of the Harvester Ant, Pogonomyrmex owyheei, in Central Oregon. Journal of Economic Entomology Vol.58, No.3
pogopogonomyrmexpogonomyrmex salinusants interacting with plantsmacroharvester ants
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