Harvester Ant Mounds Research Articles

Lead bioaccumulation in Texas Harvester Ants (Pogonomyrmex barbatus) and toxicological implications for Texas Horned Lizard (Phrynosoma cornutum) populations of Bexar County, Texas.

Uptake of lead from soil was examined in order to establish a site-specific ecological protective concentration level for the Texas Horned Lizard (Phrynosoma cornutum) at the Former Humble Refinery in San Antonio, Texas. Soils, harvester ants, and rinse water from the ants were analyzed at 11 Texas Harvester Ant (Pogonomyrmex barbatus) mounds. Soil concentrations at the harvester ant mounds ranged from 13 to 7474mg/kg of lead dry weight. Ant tissue sample concentrations ranged from < 0.82 to 21.17mg/kg dry weight. Rinse water concentrations were below the reporting limit in the majority of samples. Two uptake models were developed for the ants. A bioaccumulation factor model did not fit the data, as there was a strong decay in the calculated value with rising soil concentrations. A univariate natural log-transformed regression model produced a significant regression (p < .0001) with a high coefficient of determination (0.82), indicating a good fit to the data. Other diagnostic regression statistics indicated that the regression model could be reliably used to predict concentrations of lead in harvester ants from soil concentrations. Estimates of protective levels for P. cornutum were developed using published sub-chronic toxicological findings for the Western Fence Lizard that were allometricly adapted and compared to the Doseoral equation, which estimated lead consumed through ants plus incidental soil ingestion. The no observed adverse effect level toxicological limit for P. cornutum was estimated to be 5500mg/kg.

AN INVERTEBRATE ECOSYSTEM ENGINEER UNDER THE UMBRELLA OF SAGE-GROUSE CONSERVATION.

Conservation practitioners often rely on areas designed to protect species of greatest conservation priority to also conserve co-occurring species (i.e., the umbrella species concept). The extent to which vertebrate species may serve as suitable umbrellas for invertebrate species, however, has rarely been explored. Sage-grouse (Centrocercus spp.) have high conservation priority throughout much of the rangelands of western North America and are considered an umbrella species through which the conservation of entire rangeland ecosystems can be accomplished. Harvester ants are ecosystem engineers and play important roles in the maintenance and function of rangeland ecosystems. We compared indices of the abundance of western harvester ants (Pogonomyrmex occidentalis) and Greater Sage-Grouse (Centrocercus urophasianus) at 72 sites in central Wyoming, USA in 2012. The abundance of harvester ant mounds was best predicted by a regression model that included a combination of local habitat characteristics and the abundance of sage-grouse. When controlling for habitat-related factors, areas with higher abundances of sage-grouse pellets (an index of sage-grouse abundance and/or habitat use) had higher abundances of ant mounds than areas with lower abundances of sage-grouse pellets. The causal mechanism underlying this positive relationship between sage-grouse and ant mound abundance at the fine scale could be indirect (e.g., both species prefer similar environmental conditions) or direct (e.g., sage-grouse prefer areas with a high abundance of ant mounds because ants are an important prey item during certain life stages). We observed no relationship between a broad-scale index of breeding sage-grouse density and the abundance of ant mounds. We suspect that consideration of the non-breeding habitat of sage-grouse and finer-scale measures of sage-grouse abundance are critical to the utility of sage-grouse as an umbrella species for the conservation of harvester ants and their important role in rangeland ecosystems.

An ecological engineer maintains consistent spatial patterning, with implications for community‐wide effects

In many ecosystems, foundational species create spatial patterns that structure a broader community. It is unclear, however, how robust these patterns are across large areas and strong environmental gradients, and how the landscape‐level consequences of these patterns may vary. We investigated the robustness of non‐random patterning in the dispersion of the western harvester ant (Pogonomyrmex occidentalis), a widely recognized ecosystem engineer of western North America. We used remote imagery to characterize the spatial structure and densities of western harvester ant mounds at sites spanning their range within the sagebrush steppe and short‐grass prairie areas of Wyoming (581 × 450 km area). We found that ant mound densities varied substantially across the study region, but that mounds were strongly and consistently overdispersed (regularly patterned) across both climatic gradients and mound densities. Precipitation was the only abiotic factor that significantly affected either density or pattern, with stronger patterning among mounds at drier sites. This robustness in ecological patterning is likely to have strong effects on community function; mound dispersion increased the fraction of the landscape within typical ant foraging distances up to 30% over what density alone would predict. We estimated how patterning can modify one key ant effect at a landscape level by combining mound dispersion data with information from a seed removal experiment. Randomization tests based on these results showed that in a representative area, overdispersion could increase the mean landscape‐wide seed removal rate by 16%, and decrease its spatial variance by 50%. Western harvester ants are known to affect multiple aspects of community function and structure at a relatively fine scale, and our results show that their spatial dispersion may therefore influence many features of interspecific interactions and community dynamics.

Does Prescribed Fire Facilitate Fire Ant Invasions in Coastal Prairies or Aid Management by Improving Mound Search Efforts?

Abstract We established a high-intensity prescribed-fire experiment in shrub-dominated coastal prairie to quantify (1) the proportion of Red Imported Fire Ant mounds that are likely to be missed by applicators of individual mound-based chemical treatments in prairie, based on the number of mounds found in unburned prairie compared to recently burned areas, and (2) to track changes in the densities of Red Imported Fire Ant and native Red Harvester Ant mounds in response to growing-season prescribed fires conducted during drought. First, our data suggest insecticide applicators are likely to miss 48% of Red Imported Fire Ant mounds when applying individual mound treatments in shrub-infested prairie. Second, fire treatments did not increase Red Imported Fire Ant or decrease Red Harvester Ant populations. Prescribed fire may therefore provide an advantageous management option for prairie managers that does not increase densities of Red Imported Fire Ants, and maintains mound densities of Red Harvester Ants, w...

Detecting red harvester ant mounds with panchromatic QuickBird imagery

Natural resource managers have an interest in locating red harvester ant (Pogonomyrex barbatus) mounds because of the negative impact that heavy infestations have on pastures and because of the importance of the ants to the survival of the threatened Texas horned lizard (Phrynosoma cornutum). We evaluated panchromatic QuickBird imagery (450-900 nm; 0.6 m spatial resolution) subjected to computer classification as a tool for detecting red harvester ant mounds. The study focused on two sites located at the Welder Wildlife Refuge (28° 07' 21 N, 97° 21' 51 W). User's accuracy and producer's accuracy of the thematic maps were greater than or equal to 94.0% for the ant mound class, indicating that it is possible to use thematic maps generated from panchromatic QuickBird imagery and computer classification to detect red harvester ant mounds. Natural resource managers can use this imagery to determine the severity of infestations, which should lead to better management decisions.

EFFECTS OF CONSERVATION RESERVE PROGRAM SEEDING REGIME ON HARVESTER ANTS (POGONOMYRMEX), WITH IMPLICATIONS FOR THE THREATENED TEXAS HORNED LIZARD (PHRYNOSOMA CORNUTUM)

I compared the presence and abundance of nest-sites made by harvester ants (Pogonomyrmex), the primary prey for the endangered Texas horned lizard (Phrynosoma cornutum), among restored grassland plots planted in different grass species and indigenous prairie. The restored plots had been seeded as part of the Conservation Reserve Program (CRP) as exotic monocultures of either Old World bluestem (Bothriochloa ischaemum) or weeping lovegrass (Eragrostis curvula), or as mixtures of native grasses (both with and without buffalograss, Buchloë dactyloides). On average, the fewest ant mounds were found on Old World bluestem plots, whereas the indigenous grassland had the highest density of harvester ant mounds. However, there were no significant differences between native and exotic CRP plantings. Results obtained from a simultaneous visual survey for Texas horned lizards corroborate these findings. Thus, there is no evidence that CRP plots planted in exotic grasses are significantly poorer habitat for Texas horned lizards in terms of ant abundance than native grass plantings.

Granivores, exclosures, and seed banks: harvester ants and rodents in sagebrush-steppe

Experiments were conducted to assess the influences of granivores on the seed bank in sagebrush-steppe. Rodent and/or ant exclosures were established at two distances from five harvester ant mounds. Monthly soil samples were collected from the exclosures, and from open access areas at two distances to ascertain changes in the seed bank. Seed dish experiments were conducted monthly to establish a maximum seed removal rate. Rodents were trapped monthly. More seeds were recovered from rodent exclosures than from ant exclosures. Seed banks changed temporally and spatially, with more seeds recovered in September and at 6 m from mounds. Rodents removed seeds more rapidly from seed dishes than did ants. Ants removed more seeds from dishes closest to the nests. Rodents may have a larger impact on the local seed bank than harvester ants. Ant activities, other than seed consumption, may have more influence on vegetation.

Effects of Habitat Manipulations on Texas Horned Lizards and Their Prey

The effects of habitat manipulations on Texas horned lizards (Phrynosoma cornutum) and their main prey, harvester ants (Pogonomyrmex spp.) were studied in South Texas. The relative abundance of lizards, their scat, and active harvester ant mounds was assessed on 1-ha plots that were manipulated with either prescribed burning, disking, burning and disking combination, grazing, or land in the Conservation Reserve Program (CRP). We determined differential habitat use or avoidance using Chi-square analysis and Bonferroni Z-statistics to control the experiment-wise error probability at 10%. Lizards used burned plots disproportionately more, were neutral in their use of the disked and grazed plots, and under-utilized the burned and disked combination and CRP plots. Analysis of scat led to similar conclusions in relation to burned, grazed, and CRP plots, but scats were distributed on combination plots pro rata to availability and were underrepresented on the disked plots. No difference was detected in the relative abundance of active ant mounds among the 5 land management practices. Even though Texas horned lizards preferentially used areas that were recently burned, the process of burning may harm them due to the shallow depths in which they hibernate.

Environmental Heterogeneity and Seedling Establishment: Ant-Plant-Microbe Interactions

1. Mounds produced by animals are important sources of disturbance in the sand shinnery oak community of western Texas. As a first step in the examination of the importance of animal-generated disturbances on the structure of the plant community we ask three questions in this study. (a) Are there differences in the abiotic or biotic characteristics of patch disturbances produced by three different species of ants? (b) Do seedling growth and survival vary when grown on soil from different species of ant mounds? (c) What is the influence of two components of the biotic environment, mycorrhizal fungi and non-mycorrhizal microbes, on seedling survival, growth rates, tissue nutrient content and patterns of biomass allocation? 2. Both the biotic and abiotic characteristics of ant mound soil differed from that of undisturbed soil and from each other. Mound soil typically had higher nutrient content than undisturbed soil and harvester ant mounds had higher nutrient content than the other species. Thus, ant mounds can generate environmental heterogeneity in this habitat. 3. Seedlings grown on unsterilized soil from harvester ant mounds were larger than seedlings grown on soil from the other two mounds, yet had lower tissue nutrient content and higher mortality rates. Seedlings grown in harvester ant soil were larger when the soil was sterilized suggesting that mycorrhizal fungi were a net energy drain in the higher nutrient content soil. Alternatively, seedlings grown without mycorrhizas in the other two mound soils were not different in size and had lower tissue nutrient concentrations than seedlings grown with mycorrhizas. 4. Thus, it appears that the fungi were beneficial in the lower nutrient content soil. In the more nutrient-rich harvester ant soil seedlings grown on sterilized soil with added non-mycorrhizal microbes were larger than seedlings grown in the absence of microbes.

The Interaction of Harvester Ants and Vesicular-Arbuscular Mycorrhizal Fungi in a Patchy Semi-Arid Environment: The Effects of Mound Structure on Fungal Dispersion and Establishment

Disc areas created by the western harvester ant, Pogonomyrmes occidentalis, around their mound nests can comprise over 10% of the land surface in semi-arid shrub steppes of the Great Basin, USA. The harvester ant mounds are abandoned after 12-20 years and the mycorrhizal fungal inoculum dispersion patterns within these patches may affect subsequent plant establishment. It was hypothesized that harvester ant activity reduces mycorrhizal inoculum levels within the disc, and that mycorrhizal fungi must re-establish in these patches from surface-deposited, immigrating inoculum. To test this, we first excavated two ant mounds, which revealed a chambered core consisting of a mat of densely packed, clipped roots with 2000-5000 times the vesicular-arbuscular mycorrhizal fungal spore density found in the surrou ding undisturbed vegetation (...)

Award Mound Treatments for Harvester Ant Control in Old-Field Pastures, Nm, 1992

Abstract Award 1% bait formulation was applied to harvester ant mounds in an open pasture near Estancia, NM. Treatments were randomized and replicated 6 times. Ant mounds were checked for activity, selected and marked, and counts made of active ants on and in the clear area of each mound and the number of active mound openings prior to treatment on 12 Jun. Treatments were made by sprinkling a measured amount of bait around each mound opening.

Prevalence of Oryzopsis Hymenoides near Harvester Ant Mounds: Indirect Facilitation by Ants

The distribution of plants in relation to harvester ant mounds was investigated at two study areas to examine associations between ants and plants in semiarid, sagebrush steppe vegetation. The bunchgrass Oryzopsis hymenoides usually was the closest plant to the center of Pogonomyrmex owyheei ant mounds and often was the only plant found within the disk-shaped areas around mounds that is cleared of vegetation by the ants. Although absolute numbers of 0. hymenoides seeds were greatest on mounds, proportions of its seeds in the total seedbank were not significantly different among the mound, cleared disk, and the native plant community. Mean size and density of 0. hymenoides plants near mounds were significantly greater than those of plants 15-20 m from mounds at an undisturbed study area. At the other study area, which three years before the study was burned, mean density and size of 0. hymenoides plants were not significantly different among plots located at 0, 1, 2, 3, 7, 15, and 20 m from the center of ant mounds. These measurements of the seedbank and plant density and size were used to differentiate among four mechanisms by which ants may influence plant distribution. The prevalence of 0. hymenoides near ant mounds was most likely an indirect effect of reduced plant competition caused by the severe defoliation of potential competitors by the ants. A second indirect mechanism, the abundance of 0. hymenoides near mounds resulted from reduced insect herbivory on 0. hymenoides because of ant predation on the herbivores, was specious. Two other mechanisms, a direct effect of seed harvesting activity by ants or an indirect effect of microsite modification were at best of minor importance.

The Effects of Disturbance Size and Frequency on a Shortgrass Plant Community

We examined the effects of small, patch—producing disturbances on a shortgrass plant community dominated by the perennial grass blue grama (Bouteloua gracilis [H.B.K.] Lag. ex Griffiths). Size distributions and rates of occurrence were determined from field data and from the literature for B. gracilis plants and for three disturbance types: cattle fecal pats, western harvester ant mounds, and small animal burrows. A Spatially explicit simulation model was then used to determine the effects of each disturbance. The average turnover rates (percent affected per year) of the basal cover and density of B. gracilis plants in the simulated plots were calculated for three topographic positions and three grazing intensities. Disturbance size relative to the size of B. gracilis plants distinguished two classes of disturbances. Ant mounds and animal burrows were significantly larger than B. gracilis plants, while fecal pats were comparable in size to B. gracilis plants. The frequency of occurrence of a disturbance was found to be a good predictor of the amount of basal cover and the number of pants killed each year by each disturbance type. The fastest turnover rates for basal cover were associated with the smallest and most frequent disturbance type (fecal pats). The effects of these disturbances were found to be dependent on topographic position and grazing intensity, especially the former. Slopes and lowlands had faster turnover rates than uplands. Our results suggest that the recovery of B. gracilis is dependent on the spatial scale of the disturbance.

The Use of Western Harvester Ant Mounds as Strutting Locations by Sage Grouse

Journal Article The Use of Western Harvester Ant Mounds as Strutting Locations by Sage Grouse Get access Keith I. Giezentanner, Keith I. Giezentanner Department of Game and Fish Santa Fe, New Mexico 87501 Search for other works by this author on: Oxford Academic Google Scholar William H. Clark William H. Clark Department of Biology 705 Smith St. Vale, Oregon 97918 Search for other works by this author on: Oxford Academic Google Scholar The Condor, Volume 76, Issue 2, 1 April 1974, Pages 218–219, https://doi.org/10.2307/1366739 Published: 01 April 1974 Article history Accepted: 15 February 1973 Published: 01 April 1974

Collecting Fossils from Harvester Ant Mounds

Fossilized remains of small vertebrates, seeds, and other items of paleontological or anthropological interest have been gathered for many years from mounds made by harvester ants. The methods of collecting these specimens have ranged from picking the individual specimens, one by one, from the surface of a mound to shoveling the complete mound, including the ants, into a container and subsequently separating the desired specimens from the collected mass of twigs, rocks, ants, silt, and other debris. Certain objections to these two extremes in collecting methods prompted me to devise a method that would recover most of the fossils from a mound with a minimum of time, labor, and expense, while preserving the ant colony as a source of future fossils. By collecting and keeping separate the component parts of several mounds, I learned that practically all of the fossilized material occurred in the one-halfto one-inch-thick outer layer of the mound' and in a surrounding zone where wind and rain leave bone fragments and silt eroded from the cone. Consequently, by using a small hand-scoop with a flat lip, it is possible to skim off the surface of the mound and the surrounding area and have most of the fossils concentrated in less than one-half cubic foot of silt and matrix.