Laraappleby

Phylogeny

The ant genus Pogonomyrmex consists of 16 species (salinus, owyheei, occidentalis, subnitidus, subdentatus, brevispinosus, maricopa, californicus, comanche, badius, apache, desertorum, rugosus, barbatus, anergismus, colei) subdivided into five species-complexes (occidentalis, subdentatus, californicus, desertorum, and barbatus) (Strehl thesis, Parker and Rissing 2002, Shattuck 1987).
Pogonomyrmex individuals are colloquially known as harvester ants.
Pogonomyrmex occidentalis individuals are colloquially known as western harvester ants.

Colonies

Mature colonies consist of up to 20,000 workers (Keeler 93). Mature colonies of the close relative P. owyheei contain up to 10,000 workers (Lavigne 1969).
Mature colonies contain one queen (Cole and Wiernasz '97 '99, Lavigne '69).
Queens can live up to 40 years, but live for an average of 20 years (Porter and Jorgenson '88, Keeler '82, 93)
1000 repros per year (Lavigne 1969)
Mature colonies of P. owyheei contain 1000-3000 brood items (Lavigne '69)
Mature P. occidentalis colonies that reproduce in a given year produce 180 alates (Cole and Wiernasz unpublished). Most mature colonies of P. owyheei produce 1000 reproductives each year (Lavigne '69).

Individual workers

Workers' bodies are usually dark red.
The average body length of a worker in a mature colony is 6 mm (Nagel and Rettenmeyer 1973)
This species has one worker caste, without subcastes.
A worker lives for an average of 6 months.
As a worker ages, it usually progresses through different roles within the colony. Workers forage towards the ends of their lives and then live for only an average of two more weeks (J. Fewell 1990).
In the field, workers are active when the temperature at the surface of the colony's mound is between 25oC and 53oC (Cole, et al. 2010).

Ecosystem

deserts and arid grasslands of the North American (Nearctic) west
This species is not usually found at altitudes above 6300 feet (Cole).
This species lives in dry environments (Cole).
This species lives in desert-shrub environments (Cole).
This species lives in salty/alkaline environments (Cole).
Workers groom sisters and the queen (personal observation).

Nest architecture

A colony inhabits a nest that is up to 5 meters deep (B. Cole, Insectes Sociaux 1994).
A colony's nest is topped by an irregularly conical nest mound (Cole) that can be more than 89 cm in diameter (Wiernasz & Cole 1995).
The mounds of most colonies are surrounded by an area devoid of vegetation (Cole).
The denuded areas do not burn during fires (Cole).
The queen stays at the bottom of the nest ().
The composition, shape, and size of the mound differ across plant environments (Cole).
The nest retains heat in the winter and resists it during the summer ().
Workers usually relocate within the nest, capturing safe levels of heat (Cole '94).
Workers move brood within the nest, capturing safe levels of heat (Cole 1932, Cole 1994).
The soil in the mound is drier than that in the surrounding denuded area ().
Bigger P. occidentalis colonies (in number of workers) have bigger mounds (Cole and Wiernasz '95). Bigger P. owyheei colonies (in number of workers) have bigger mounds (Lavigne '69).

Nutrition

Workers harvest seeds and pollen directly from plants and take fallen seeds.
Workers gather newly-dead insects.
Colony nests contain chambers filled with seeds that are depleted during winter.
Genetically diverse colonies forage for more hours daily (Cole et al. 2010).
Workers generally forage April-September (Cole et al. 2010).
Workers generally forage throughout the day during cooler months and only 5-11am and 3-9pm during summer (Cole et al. 2010).
Foraging times within a day and foraging temperature range vary consistently among colonies (Cole et al. 2010).
Given a choice, workers select seeds containing more energy (Fewell and Harrison '91).
Given a choice, workers select a diversity of seeds or seeds that are new to the colony (Fewell and Harrison '91).
Workers usually forage one kind of item each day, but change their specialty daily (Fewell and Harrison '91).
Workers usually forage in one direction over and over, even across days (Fewell '90).
Colonies recruit more workers (from the total worker pool) to forage at a good food source (Fewell '90).
Colonies lose foragers in encounters with neighboring colonies (DeVita '79).
Workers defend foraging territories against neighboring colonies (personal observation).
Different plant environments support different densities of colonies.
Foragers produce more period mRNA during the darkness, the timing of which varies seasonally (Ingram et al. 09).

Biomass/brood production

Different developmental stages of ants within a colony process different kinds of food; larvae ingest solids, while adults ingest liquids, including larval excretions (The Ants).
Immature individuals cannot pass from one larval stage to another or to adulthood without the help of adults; adults help immature individuals remove their old larval and/or pupal skins during molting/ecdysis.
As larvae are relatively immobile, they only interact with nutrients as adults bring the nutrients to the larvae or the larvae to the nutrients.
During a year in which a colony will reproduce, the colony first produces alates (gynes and males) and, later in the year, workers (Wiernasz & Cole personal observation).
Bigger colonies are more likely to reproduce, but there is not a simple size threshold for colony reproduction (Cole and Wiernasz).
Bigger colonies don't necessarily produce a greater total reproductive biomass (Cole and Wiernasz '00).
Colonies stop producing brood before they overwinter (Cole '34).

Mating

Colonies release alates synchronously (Wiernasz & Cole 1995, Cole & Wiernasz 2000).
Alates mate in hilltop leks (Nagel and Rettenmeyer '73, Wiernasz et al. '95, Abell et al. 99) in swarms (Mull and Crist '93, Wiernasz '95).
Major mating swarms are about 1400 meters apart (Billick et al. 04), and queens can fly 800 m max (Cole and Wiernasz 2002).
Mating swarms contain more males than females.
Gynes mate with 2-11 (an average of 6.3) genetically distinct males (Wiernasz et al. 2004). Females always mate multiply (Nagel and Rettenmeyer '73).
Queens that mate only a few times are less successful (Cole and Wiernasz 1999).
The colonies of queens that mate with more males grow faster (Wiernasz et al. 2004).
Males sometimes mate multiply (Nagel and Rettenmeyer '73).
Females mate nonrandomly (Wiernasz et al. '95).
Larger males are more successful at mating (i.e. they are overrepresented among collected maters), but small males can still mate (Abell et al. 1999, Wiernasz et al. 2001).
Certain shape characteristics improve male chances of mating success (Abell et al. 1999). but small males can still mate
P. occidentalis populations are effectively small and inbred (Cole and Wiernasz '97).

Colony founding

Most queens fly away from the mating swarm after mating ().
Queens pick bare and bright areas to land (Nagel and Rettenmeyer '73).
Queens dig where they land (Nagel and Rettenmeyer '73).
Individual queens found colonies on their own, without workers or other queens.
Survivorship of colonies in the first year is negatively correlated with increasing density of foundresses (Cole and Wiernasz '02)
Foraging workers kill queens that they encounter aboveground and occasionally excavate queens (Billick et al. 01).
Factors independent of colony density are responsible for >90% of foundress mortality (Billick et al. 01).
Queens in some populations found colonies claustrally (Nagel and Rettenmeyer '73) and in others, semi-claustrally (Wiernasz and Cole unpublished).
Many of the eggs laid in the first batch die or are unembryonated eggs (Nagel and Rettenmeyer '73).
During colony founding, larvae may eat eggs (Nagel and Rettenmeyer '73).
The first workers produced, nanitics, are 2 mm (33% shorter than typical worker) (Nagel and Rettenmeyer '73).
2/188 founding queens survived from July to March (Wiernasz and Cole '95)

Population ecology

Swarms that are consistently present and large determine much of the spatial variability in colony density and emerge over the long-term (Billick et al. 2004).
New colonies are founded in a clumped pattern, around the mating sites (Cole and Wiernasz '02, Wiernasz and Cole '95)
The population may self-thin through direct interference competition (Wiernasz and Cole 1995) resulting in a uniformly overdispersed distribution pattern (Wiernasz and Cole 1995).
Long-term colony survival is mediated by proximity to older colonies (Ryti and Case 88).
Smaller colonies have closer nearest neighbors (Wiernasz and Cole 1995).
Smaller nests are more likely to die (Wiernasz and Cole 1995).
The further a colony is from its nearest neighbor (especially for small colonies), the higher the colony's survival probability (Wiernasz and Cole 1995).
Colony age and size are correlated, especially in young colonies (Cole and Wiernasz '00).

References

Abell, A., Cole, B., Reyes, R., & Wiernasz, D. (1999). Sexual selection on body size and shape in the western harvester ant, Pogonomyrmex occidentalis Cresson. Evolution , 53 (2), 535-545.
Billick, I., Cole, B., & Wiernasz, D. (2004). Scale of recruitment limitation in the western harvester ant (Hymenoptera: Formicidae). Annals of the Entomological Society of America , 97 (4), 738-742.* *
Billick, I., Wiernasz, D., & Cole, B. (2001). Recruitment in the harvester ant, Pogonomyrmex occidentalis: effects of experimental removal. Oecologia , 129 (2), 228-233.
Cole Jr, A. (1932, Jan 1). The relation of the ant, Pogonomyrmex occidentalis Cr., to its habitat. Ohio Journal of Science .
Cole, A. (1932). The ant, Pogonomyrmex occidentalis, Cr., associated with plant communities. Ohio Journal of Science , 32, 10-20.
Cole, B. (1994). Nest architecture in the western harvester ant, Pogonomyrmex occidentalis (Cresson). Insectes Sociaux , 41 (4), 401-410.
Cole, B., & Wiernasz, D. (2000). Colony size and reproduction in the western harvester ant, Pogonomyrmex …. Insectes Sociaux .
Cole, B., & Wiernasz, D. (1997). Inbreeding in a lek-mating ant species, Pogonomyrmex occidentalis. Behavioral Ecology and Sociobiology , 40 (2), 79-86.
Cole, B., & Wiernasz, D. (2002). Recruitment limitation and population density in the harvester ant, Pogonomyrmex occidentalis. Ecology , 83 (5), 1433-1442.
Cole, B., Smith, A., Huber, Z., & Wiernasz, D. (2010). The structure of foraging activity in colonies of the harvester ant, Pogonomyrmex occidentalis. Behavioral Ecology , 21 (2), 337-342.
DeMers, M. (1993, Jan 1). … expansion of the western harvester ant (Pogonomyrmex occidentalis Cresson). Landscape Ecology .
Fewell, J. (1990, Jan 1). … as a foraging constraint in the western harvester ant, Pogonomyrmex occidentalis. Oecologia .
Fewell, J., & Harrison, J. (1991). Flexible seed selection by individual harvester ants, Pogonomyrmex occidentalis. Behavioral Ecology and Sociobiology , 28, 377-384.
Ingram, K., Krummey, S., & LeRoux, M. (2009, Jan 1). … with age-related polyethism in harvester ants, Pogonomyrmex occidentalis. BMC ecology .
Nagel, H., & Rettenmeyer, C. (1973). Nuptial flights, reproductive behavior and colony founding of the western harvester ant, Pogonomyrmex occidentalis (Hymenoptera: Formicidae). Journal of the Kansas Entomological Society , 46 (1), 82-101.
Rogers, L., Lavigne, R., & Miller, J. (1972). Bioenergetics of the western harvester ant in the shortgrass plains ecosystem. Environmental Entomology .
Shattuck, S. (1987). An analysis of geographic variation in the Pogonomyrmex occidentalis complex.(Hymenoptera: Formicidae). Psyche , 94 (1-2), 159-180.
Wiernasz, D., & Cole, B. (2010, Jul 27). Optimal offspring size and reproductive allocation in the western harvester ant, Pognomyrmex occidentalis. 1-50.
Wiernasz, D., & Cole, B. (1995, Jan 1). Spatial distribution of Pogonomyrmex occidentalis: recruitment, mortality and …. Journal of Animal Ecology .
Wiernasz, D., Perroni, C., & Cole, B. (2004). Polyandry and fitness in the western harvester ant, Pogonomyrmex occidentalis. Molecular Ecology , 13 (6), 1601-1606.
Wiernasz, D., Sater, A., Abell, A., & Cole, B. (2001, Jan 1). Male size, sperm transfer, and colony fitness in the western harvester ant, …. Evolution .

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