The allometric ant foraging data was collected to test the allometric ant foraging model proposed by Jun et al. (2003). Key variables are the number of foragers in the colony, the time of an average foraging trip for the colony and the average distance a forager travels to collect a seed. Data on Pogonomyrmex rugosus and Pogonomyrmex maricopa were collected at the Sevilleta.
This study was designed to test the predictions of the Jun et al (Evolutionary Ecology Research, 2003) Allometric Ant Foraging Model which predicts longer foraging times in colonies with large population sizes. The primary prediction of the model is that the average time of a foraging trip (Tf) is proportional to the average distance a forager travels (dt), and both of these increase with forager population size (F) by Tf = F^1/3 and dt = F^1/3. Standard regression was then used to determine whether the predicted exponent of 1/3 was rejected when comparing empirical values of Tf , dt and F. The predictions are based on the assumptions that forager travel speed, the density of foragers searching in the landscape and the time spent actively searching (as opposed to travelling) are invariant across colony sizes. These variables were measured to test for statistical differences across colony sizes. Measurements made at the Sevilleta were part of a larger study. Similar data were collected in Portal, AZ, including data on another species, Pogonomyrmex barbatus.
For each colony in the study, I followed individual foraging ants as they left the nest. Ants initially exhibit 'travel' behavior in which they move relatively directly and quickly away from the nest. When they began the slower, meandering 'search' behavior, I noted the time, and marked the location with a flag. Searching continued until a seed was located, at which point I noted the time, marked the location with a flag, and then noted the time that the ant returned to the nest. Temperature, total distance travelled, travel time and search time were recorded. Data are reported from following 61 foragers in 6 colonies on 11 days. On approximately 6 days, foraging was almost non-existant due to extremely hot and dry conditions, and no data are reported from those days. As a result, the study was continued in July and August 2003 in Portal, AZ where climate conditions were slightly better for Pogonomyrmex. Data on colony size was estimated by multiplying the 'flux' of ants leaving the nest by the average search time of foragers. The flux rate was measured by counting the number of foragers leaving the nest in one minute, then the number returning in the next minute, repeated 3 times for a total of 6 minutes of observations, approximately once per hour during the foraging period.
Plot size is 50 x50 m.
Additional Study Area Information
Study Area Name: McKenzie FlatsStudy Area Location: The northeast section of the Sevilleta, stretching from Black Butte south to the canyon and east to the Los Pinos. McKenzie Flats, between black Butte, 5 Points, Palo Duro Canyon, and the old McKenzie headquarters ranch building site.Elevation: 1615 mVegetation: The terrain was generally mixed-species desert grassland, dominated by black grama (Bouteloua eriopoda), blue grama grass (B. gracilis), sand muhly (Muhlenbergia arenicola), various drop seeds and sacatons (Sporobolus spp.), purple three-awn (Aristida purpurea), and burrow grass (Scleropogon brevifolia). Shrubs were common in Five Points area; these were creosote bush (Larrea tridentata) and snakeweed (Gutierrezia sarothrae).
Soils: Turney Series: fine-loamy, mixed, thermic Typic Calciorthids. Berino Series: fine-loamy, mixed, thermic Typic Haplargids.
Hydrology: Surface water only during rain events, no arroyos. Run on plain for Los Pinos Mountains.
Landform: McKenzie Flats is a broad, nearly flat grassland plain between the Los Pinos Mountains and the breaks on the east side of the Rio Grande.
Geology: Deep (20,000 ft) alluvial and eolian deposits.
Climate: Long-term mean annual precipitation is 243 mm, about 60% of which occurs during the summer. Long-term mean monthly temperatures for January and July are 1.5°C and 25.1°C, respectively.
Site history: McKenzie Flats encompasses an area of approximately 50 square miles. McKenzie Flats was one of the primary livestock grazing areas of the Sevilleta NWR. Cattle have been excluded from the site since 1974-76.North Coordinate:34.3592South Coordinate:34.3592East Coordinate:-106.691West Coordinate:-106.691
Data are reported from 11 collection dates, primarily in June 2003. A number of incomplete foraging trips are not reported. Many of the data here were taken on days in which foraging activity appeared subdued, probably due to hot and dry conditions. Additional data of a similar nature were collected in Portal AZ in July and August 2003, and are available upon request from email@example.com.
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