Ant Nest Soil Research Articles

A Review of Ant Nests and Their Implications for Architecture

This paper discusses the latest progress in research on ant nests and explores innovative scientific concepts associated with underground ant nests from the perspective of bionics. The methods used by scholars to study the structure of ant nests and the interaction between the structure itself and the individual ants are investigated. The structural characteristics of the ant nest, its internal environment and ventilation characteristics are discussed in detail. In addition, this paper presents an innovative project in which the effect of underground ant nests on soil geotechnical properties and the effect of calcined ant nest soil powder, from the perspective of civil engineering, are addressed. Practical examples of the application of the structural and inter-relational aspects of subterranean ant nests in the field of architectural bionics are also provided, from the perspectives of construction, morphology, function and material. This review attempts to integrate civil engineering, architecture and biology, enlighten architects and biologists on converging their thinking, provide new ideas regarding underground ant colony nests, and provide references for long-term human habitation.

Lycaenid-tending ants can contribute to fitness gain of the infested host plants by providing nutrients

Ground-nesting ant species are known to promote plant growth by soil nutrient enhancement. Camponotus compressus ants regularly visit the extrafloral nectary-bearing, lycaenid-infested cowpea, Vigna unguiculata plants and construct a shelter for the lycaenid caterpillars at the plant base. The present study shows that ants may influence the overall fitness of the infested cowpea plants by providing nutrients via soil and foliar pathways. Total carbon, nitrogen and phosphorous content of ant constructed shelter (ACS) soil of the lycaenid-harbouring plants were assessed, microbes from the ACS soil were isolated and their plant growth promotion ability was evaluated. Nitrate content of the ant faecal matter was estimated and overall plant fitness was assessed in terms of its growth and yield. The results revealed higher content of total C, N and P in the debris and chamber soil of ACS as compared to the control soil from the base of ant-excluded plants. The microbes isolated from the ACS and ant nest soil were found to possess plant growth promotion abilities. Ant faecal matter was found to contain substantial amount of nitrate. The ant-included, lycaenid-infested plants as well as those lacking the caterpillars demonstrated significantly higher number of pods, number of seeds per pod, root length, shoot length, plant height, number of leaves, plant fresh and dry weight as compared to the control plants. Lycaenid caterpillar tending ant species with a high propensity for visiting plants thus have the potential to increase plant fitness by increasing nutrient availability via multiple pathways.

Paenibacillus aurantiacus sp. nov., isolated from ant nest soil.

A Gram-stain-positive, rod-shaped and endospore-forming bacterium, strain RC11T, isolated from ant nest soil collected from Udon Thani Province, Thailand was characterized in a taxonomic study based on a polyphasic approach. On the basis of 16S rRNA gene sequence analysis, strain RC11T was affiliated to the genus Paenibacillus and was closely related to Paenibacillus phyllosphaerae LMG 22192T with 98.1 % sequence similarity. Strain RC11T contained meso-diaminopimelic in the cell-wall peptidoglycan. The major menaquinone was MK-7. Anteiso-C15 : 0, iso-C16 : 0, anteiso-C17 : 0 and C16 : 0 were the predominant cellular fatty acids. Diphosphatidylglycerol, phosphatidylethanolamine and phosphatidylglycerol were the major polar lipids. The DNA G+C content was 57.9 mol%. In addition, strain RC11T and P. phyllosphaerae LMG 22192T showed a low level of DNA-DNA relatedness (15.6-33.2 %). Therefore, strain RC11T represents a novel species of the genus Paenibacillus, for which the name Paenibacillus aurantiacus sp. nov. is proposed. The type strain is RC11T (=KCTC 33816T=LMG 29659T=TISTR 2452T).

The effects of ant nests on soil fertility and plant performance: a meta‐analysis

Ants are recognized as one of the major sources of soil disturbance world-wide. However, this view is largely based on isolated studies and qualitative reviews. Here, for the first time, we quantitatively determined whether ant nests affect soil fertility and plant performance, and identified the possible sources of variation of these effects. Using Bayesian mixed-models meta-analysis, we tested the hypotheses that ant effects on soil fertility and plant performance depend on the substrate sampled, ant feeding type, latitude, habitat and the plant response variable measured. Ant nests showed higher nutrient and cation content than adjacent non-nest soil samples, but similar pH. Nutrient content was higher in ant refuse materials than in nest soils. The fertilizer effect of ant nests was also higher in dry habitats than in grasslands or savannas. Cation content was higher in nests of plant-feeding ants than in nests of omnivorous species, and lower in nests from agro-ecosystems than in nests from any other habitat. Plants showed higher green/root biomass and fitness on ant nests soils than in adjacent, non-nest sites; but plant density and diversity were unaffected by the presence of ant nests. Root growth was particularly higher in refuse materials than in ant nest soils, in leaf-cutting ant nests and in deserts habitats. Our results confirm the major role of ant nests in influencing soil fertility and vegetation patterns and provide information about the factors that mediate these effects. First, ant nests improve soil fertility mainly through the accumulation of refuse materials. Thus, different refuse dump locations (external or in underground nest chambers) could benefit different vegetation life-forms. Second, ant nests could increase plant diversity at larger spatial scales only if the identity of favoured plants changes along environmental gradients (i.e. enhancing β-diversity). Third, ant species that feed on plants play a relevant role fertilizing soils, which may balance their known influence as primary consumers. Fourth, the effects of ant nests as fertility islands are larger in arid lands, possibly because fertility is intrinsically lower in these habitats. Overall, this study provide novel and quantitative evidence confirming that ant nests are key soil modifiers, emphasizing their role as ecological engineers.

Detection ofSolenopsis invicta(Hymenoptera: Formicidae) Nests using Spectral Data

Rapid detection of red imported fire ant (Solenopsis invicta Buren; Hymenoptera: Formicidae) nests is important in assessing the control efforts and for monitoring dispersal of this pest. In this study, spectroscopic techniques were employed to characterize the reflectance spectra of fire ant nest soil and the areas surrounding the nests. The results showed significant differences between nest soil, grass, and bare soil not disturbed by fire ant at the 680 nm wavelength of the electromagnetic spectrum. The reflectance of nest soil was 10% to 15% lower than that of the surrounding non-nest bare soil at wavelengths of 780 to 1000 nm. Furthermore, the reflectance of nest soil was significantly correlated with soil water content (R2 = 0.962).

Interactions between Ants and Non‐myrmecochorous Fruits in Miconia (Melastomataceae) in a Neotropical Savanna

AbstractThe aim of this study was to evaluate the role of ants as secondary seed dispersers of six primarily bird‐dispersed Miconia species in the cerrados of southeastern Brazil. Vertebrate exclosure and seed germination experiments were performed for M. albicans, M. alborufescens, M. corallina, M. ferruginata, M. ibaguensis, and M. irwinii. Excluding vertebrates did not significantly alter fruit removal rate for any of the Miconia species relative to open controls. Fruits on stalks and fallen fruits were removed and transported to nests mainly by species of Atta, Acromyrmex, and Ectatomma (dispersal distance ranging from 0.1 to 45.2 m), while Camponotus ants tended to be observed removing the fruit pulp (seed cleaning) where the fruits were found. Seed manipulation by Atta decreased germination of M. irwinii, but not M. ferruginata. Germination did not occur in intact fruits, and thus seed cleaning was an important service provided by the ants. Ant nest soils did not inhibit germination of any of the Miconia species, suggesting they are a good substrate for long‐lived Miconia seeds. We conclude that ant activity could have important effects on the fate of Miconia seeds adapted for bird dispersal.

Geographical and interspecific variation and the nutrient‐enrichment hypothesis as an adaptive advantage of myrmecochory

In myrmecochory, the relocation of diaspores to ant nests may lead to the enhancement of plant fitness because ant nests and their middens are often richer in essential nutrients than surrounding areas. This idea is the basis of the nutrient‐enrichment hypothesis (NEH), which suggests that nutrient enrichment may be a major selective influence in the evolution of myrmecochory. However, there is little evidence regarding whether the greater plant performance and fitness enhancement in ant nests is due to nutrient enrichment or other benefits of directed dispersal. Here, we present the results of a large‐scale seed‐sowing experiment that tests the NEH in the ant‐dispersed perennial herb Helleborus foetidus, exploring geographical and inter‐ant taxa variation. Experiments were conducted in three well‐separated regions of the Iberian Peninsula, targeting the nests of major and minor local ant dispersers (nine ant species in total) and the soil beneath maternal plants as seed destinations. Seedling emergence, survival and early establishment rates, as well as variation in soil characteristics, were obtained for each seed destination at each region. Our results do not fully support the NEH in our study system. Instead, we found that the advantage of ant nest soil for establishment in H. foetidus was conditional. Differences in soil fertility and concomitant differences in seedling establishment between ant nests and beneath the canopy of maternal plants were observed in some regions and for some ant species, but not in others. Thus, the conditional outcomes arise from inconsistencies among regions, between stages of seedling regeneration and among ant species in the advantages of being dispersed to nests. Because variation in the guilds of ant dispersers of myrmecochore plants across their ranges is common, this study illustrates the need to consider geographic and inter‐ant taxa variation for a complete evaluation of the NEH.

Unique soil microbial assemblages associated with grassland ant species with different nesting and foraging strategies

Ants are important ecosystem engineers and can be abundant in extensively managed grassland ecosystems. Different ant species create nests varying in structure and size, and tend to have a variety of feeding strategies. Differences in food imported to the nest and contrasting nesting behaviour may control soil microbial community structure in nest soil, with cascading effects on nutrient cycling, but this has not been tested in grassland ants. Soil and ants were sampled from nests of three ant species: two formicines; Lasius flavus (aphid farmer/scavenger, mound builder) and Formica lemani (scavenger/hunter, non-mound builder), and a myrmicine; Myrmica sabuleti (hunter/scavenger, non-mound builder), in an extensively grazed temperate grassland and compared to similar soils without ants. Microbial assemblages were determined using molecular approaches (terminal restriction length polymorphism and automated ribosomal intergenic spacer analysis). Both aboveground (vegetation diversity) and belowground (soil physico-chemical properties) components were measured to assess the potential of the different ant species to modify the environment. Stable isotope ratios (δ13C and δ15N) of ant tissues and nest soil organic matter confirmed differences in trophic distances. Significant changes in soil pH, moisture content, total C and total N, and in vegetation composition, demonstrated ant ecosystem engineering effects. In turn, nests of L. flavus, M. sabuleti and F. lemani had different microbial activities and harboured significantly different microbial assemblages (total bacteria, total fungi, ammonia-oxidising bacteria and nitrogen-fixing bacteria), but the diversity was similar. These findings suggest that grassland ants can control microbial assemblages via changes in physical and biological soil characteristics in their nests, and as such, different ant species harbour unique microbial assemblages in nests.

Ecosystem engineering and predation: the multi-trophic impact of two ant species

1. Ants are ubiquitous ecosystem engineers and generalist predators and are able to affect ecological communities via both pathways. They are likely to influence any other terrestrial arthropod group either directly or indirectly caused by their high abundance and territoriality. 2. We studied the impact of two ant species common in Central Europe, Myrmica rubra and Lasius niger, on an arthropod community. Colony presence and density of these two ant species were manipulated in a field experiment from the start of ant activity in spring to late summer. 3. The experiment revealed a positive influence of the presence of one ant colony on densities of decomposers, herbivores and parasitoids. However, in the case of herbivores and parasitoids, this effect was reversed in the presence of two colonies. 4. Generally, effects of the two ant species were similar with the exception of their effect on Braconidae parasitoid densities that responded positively to one colony of M. rubra but not of L. niger. 5. Spider density was not affected by ant colony manipulation, but species richness of spiders responded positively to ant presence. This effect was independent of ant colony density, but where two colonies were present, spider richness was significantly greater in plots with two M. rubra colonies than in plots with one colony of each ant species. 6. To test whether the positive ecosystem engineering effects were purely caused by modified properties of the soil, we added in an additional experiment (i) the soil from ant nests (without ants) or (ii) unmodified soil or (iii) ant nests (including ants) to experimental plots. Ant nest soil on its own did not have a significant impact on densities of decomposers, herbivores or predators, which were significantly, and positively, affected by the addition of an intact nest. 7. The results suggest an important role of both ant species in the grassland food web, strongly affecting the densities of decomposers, herbivores and higher trophic levels. We discuss how the relative impact via bottom-up and top-down effects of ants depends on nest density, with a relatively greater top-down predatory impact at higher densities.

Faunalpedturbation effects on soil microarthropods in the Negev Desert

Soil microarthropod communities in seed-harvester ant-nest ( Messor spp.) soils and pits excavated by porcupines ( Hystrix indica) were examined on a hill-slope catena in the Negev Desert to test the hypothesis that animal-produced soil disturbances increase abundance and diversity of soil biota. There were significantly fewer arthropods and lower taxonomic diversity of soil microarthropods at the top and mid-slope locations, with no consistent patterns of abundance between cool-wet and hot-dry seasons. Some prostigmatids, cryptostigmatids, and other arthropods in ant-nest, porcupine-pit, and undisturbed soils were more abundant in wet than dry seasons at some locations but more abundant in the hot-dry season at other locations and sample sites. Seven prostigmatid mite families that were relatively abundant in undisturbed soils were absent or of low abundance in ant-nest modified and porcupine-pit soils at mid- and low-slope catena locations. The data result in rejection of the hypothesis. However, the significant effects of topographic position on the catena on soil microarthropod communities emphasize the importance of examining broad spatial patterns and temporal variation before making generalizations about the effects of ecological engineers on arid ecosystem structure and function.

Ant nests and soil nutrient availability: the negative impact of fire

Abstract:High-nutrient patches are important for regulating the structure and physiognomy of dystrophic habitats. Leaf-cutting ants create these rich patches in many neotropical habitats. Burning, however, could diminish or even annul the effects of ant nests on soil properties. To test this hypothesis, we compared the nutrient concentrations at various depths in soil samples near three nests of the leaf-cutting ant Atta laevigata and three non-nest soils, located in 10-ha plots subjected to burning or with fire-protection within a Brazilian cerrado. Root density in ant-nest soil was greater than in non-nest soil in both unburned and burned plots. Besides, the concentration of Ca, Mg, K and P increased 2–50-fold in ant nests from the unburned area compared to non-nest soils. In contrast, nutrient concentrations and pH in burned ant nests were similar to or lower than non-nest soils, but the nests maintained higher values of organic matter and cation exchange capacity. The positive effect of leaf-cutting ant nests as high-nutrient patches may be strongly reduced in habitats with frequent burning. In this case, the negative effects of leaf-cutter herbivory on a plant community could surpass the benefits of local nutrient enrichment by their nests.Resumo: Sauveiros modificam as propriedades físicas e químicas do solo, alterando a estrutura e fisionomia local. Entretanto, queimadas podem reduzir os efeitos dos formigueiros nesses ambientes como, por exemplo, pela diminuição do forrageamento das formigas e, conseqüentemente, pela baixa incorporação de material orgânico ao solo. Este estudo testou o efeito do fogo sobre a concentração de nutrientes no solo de colônias de Atta laevigata em área de cerrado. A densidade de raízes foi maior nas colônias do que áreas controle, independentemente da presença do fogo. Na ausência de queimadas, as concentrações de nutrientes foram até 50 vezes superiores nos sauveiros. Contudo, queimadas reduzem a concentração de nutrientes e pH nas colônias. Possivelmente, essa baixa concentração seja atribuída à maior demanda pela vegetação remanescente, em resposta à perturbação provocada pelo fogo. Nesse caso, os efeitos negativos da herbivoria podem superar os benefícios causados por meio da disponibilização de nutrientes pelos sauveiros.

Landscape position moderates how ant nests affect hydrology and soil chemistry across a Chihuahuan Desert watershed

Ants moderate the supply of critical resources such as water and nutrients in desert environments by changing the physical arrangement of soils during nest construction. We measured water infiltration and soil physical and chemical properties on and off the nests of two ant species (Pogonomyrmex rugosus, Aphaenogaster cockerelli) across five sites at differing landscape positions within a Chihuahuan Desert watershed. Our aim was to test whether the effects of these long-lived ant nests on water infiltration and soil chemistry varied between ant species or across sites within a watershed. Water flow was generally slowest at the site with the highest silt and clay contents, and fastest at the site with sandy soils. Flow was generally greater through ant nest soils than adjacent non-nest soils, and we attribute this to increases in macropores in the nests. However, the effects of both ant nests and species varied among sites. Despite wide variation in soil chemical properties across all sites, ant nests had a consistent effect on soil chemical properties, with higher levels of carbon, nitrogen, sulphur, phosphorus and electrical conductivity on nests compared with non-nest soils. Our results demonstrate that while we can generalise about the effects of ant nests on water flow and nutrient levels, differences in soil type, nest density and ant species across sites are likely to moderate these effects.

Effects of harvester ant (Messor spp.) activity on soil properties and microbial communities in a Negev Desert ecosystem

Harvester ants (Messor spp.) function as an essential link between aboveground resources and below-ground biota such as the microbial community. We examined changes in soil microbial biomass and functional diversity resulting from harvester ant (Messor spp.) activity in the Negev Desert, Israel. Abiotic and biotic soil parameters were recorded during two seasons—wet and dry—also representing food availability periods for the ants (low and high seed availability, respectively). Soil samples were collected monthly from the 0- to 10- and 10- to 20-cm soil layers: (1) near the nest entrance, (2) under chaff piles, and (3) at a 2-m radius from the nest entrance (control). Harvester ant activity increased the percentage of organic matter, total soluble nitrogen, and microbial activity in nest-modified soils in comparison to the control soils. Higher CO2 evolution was recorded in the low-seed season in ant nest soils than in the control soils. During the high-seed season, higher carbon dioxide evolution was recorded only at the nest entrance locations. There were no differences in microbial biomass between the low- and high-seed seasons, but highest microbial biomass was found under chaff in low-seed season and in nest soils in high-seed season. Microbial functional diversity was higher in nest-modified soils than in the control soils. This study suggests that the effect of harvester ant nests on soil fertility is due to increased microbial biomass and microbial activity in ant nest-modified soils.

Imported Fire Ant (Hymenoptera: Formicidae) Bioturbation and Its Influences on Soils and Turfgrass in a Sod Production Agroecosystem

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Cite Icon Cite Search Site Citation Sherri L. DeFauw, James T. Vogt, Debbie L. Boykin; Imported Fire Ant (Hymenoptera: Formicidae) Bioturbation and Its Influences on Soils and Turfgrass in a Sod Production Agroecosystem. Journal of Entomological Science 1 January 2008; 43 (1): 121–127. doi: https://doi.org/10.18474/0749-8004-43.1.121 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search nav search search input Search input auto suggest Search

MICROHABITAT-SPECIFIC CONTROLS ON SOIL RESPIRATION AND DENITRIFICATION IN THE MOJAVE DESERT: THE ROLE OF HARVESTER ANT NESTS AND VEGETATION

Seed harvesting ants (Pogonomyrmex rugosus) concentrate organic matter and nutrients near their nests and create biogeochemical hotspots in desert soil. We examined factors regulating denitrification and soil respiration in a Mojave Desert ecosystem to determine the role harvester ant colonies play in nitrogen loss and carbon mineralization. Organic matter and nutrient storage were significantly greater in colonies than under the dominant vegetation (i.e., Pleuraphis rigida, a bunch grass) and in bare soil, with standing stocks of inorganic nitrogen in colonies nearly 4-fold greater than in the other microhabitats. Soil respiration, measured with laboratory incubations, was below detection limits under ambient soil conditions. Respiration rate in soil from bare patches and under grass was limited by water and labile organic carbon, with secondary nitrate limitation evident only once carbon limitation was alleviated. Soil respiration in ant nest soil was limited by water and labile organic carbon only. Denitrification, measured by the acetylene block technique, was elevated in bare soil and under grass with the addition of nitrate. Ant nest soil also responded to a nitrate addition; however, denitrification rate was greatest with addition of glucose. Ordinarily desert soil has low rates of respiration and denitrification due to dry ambient conditions. However, ant colonies likely function as important sites for nitrogen loss and carbon mineralization following rain storms, especially if storms coincide with seed set and the temporally pulsed input of organic matter into colonies.

The impact of harvester ants on decomposition, N mineralization, litter quality, and the availability of N to plants in the Mojave Desert

In arid areas of North America, nests of the seed-harvesting ant Pogonomyrmex rugosus tend to be elevated in mineral nitrogen and other soil nutrients relative to other microhabitats. We investigated the roles of decomposition, N mineralization, and plant nutrient uptake in maintaining high standing stocks of nutrients in P. rugosus ant nests. Decomposition rates of standard cellulose substrates placed on the surface of ant nests and other desert microhabitats suggest that conditions found in ant nests and bare areas are conducive to higher rates of decomposition than conditions under shrubs. In laboratory incubations of moist soil, net N mineralization rates were significantly higher in soil from ant nests than from bare areas and under two of three plant species. Net N mineralization rates measured in situ were much lower than those measured in laboratory incubations, but ant nest soil still exhibited higher rates at one of two sites. Litter collected from ant mounds, composed chiefly of seed chaff, was similar in N content to litter collected from underneath the dominant plant species, but had a significantly higher mean δ 15N. Using this distinctive isotope signature as a tracer, we found no evidence that large perennial shrubs tap ant nests as a source of N. An invasive, annual grass species was significantly enriched in 15N, had higher leaf %N, and produced more seeds when growing on the mound than when growing several meters away; however P. rugosus nest surfaces are typically free of such annuals. We conclude that both high rates of nutrient cycling relative to other Mojave Desert microhabitats and low N utilization by the surrounding vegetation contribute to high standing stocks of mineral N in P. rugosus nests.

Soil fertility and plant growth in soils from pine forests and plantations: Effect of invasive red imported fire ants Solenopsis invicta (Buren)

Summary Through nest building and foraging activities, ants alter physical properties and nutritional status of soils through structural modifications and nutrient accumulation. In turn, these alterations may enhance soil quality for plant growth. This study examined the effect of the invasive red imported fire ant, Solenopsis invicta Buren, on soil properties and plant growth. In our greenhouse study, ant activity decreased soil pH and increased phosphorus (P + ) and potassium (K + ) in the soil. We collected soil from within and adjacent to randomly selected nests in two common habitats of Louisiana – longleaf-pine ( Pinus palustris ) forests and longleaf-pine plantations. After physical and chemical properties were measured, Gardenia japonicus seedlings were planted in the soil to determine growth rate. In comparison to adjacent soil, ant nest soils from both habitats were lower in moisture content and bulk density and higher in NH 4 + . Ant nest soils were also higher in Ca 2+ , Mg 2+ , K + and Na + than in adjacent soils in longleaf-pine forests. G. japonicus seedlings grown in nest soil from pine forests were an average of three times taller than those grown in adjacent soil, and those from pine plantations were twice as tall as those grown in adjacent soils. These results suggest that invasive fire ants alter the physical and chemical properties of the soil. These soil modifications enhance plant growth since NH 4 + , a nutrient that limits growth, has been increased.

The Contribution of Harvester Ant Nests,Pogonomyrmex rugosus(Hymenoptera, Formicidae), to Soil Nutrient Stocks and Microbial Biomass in the Mojave Desert

The distribution of soil nutrients in deserts is heterogeneous, with high concentrations of organic and inorganic nutrients occurring under shrubs and near animal dwellings. Attention has focused on shrubs in creating “fertile islands.” In this study, we compare the effects of the harvester ant Pogonomyrmex rugosus Emery (Hymenoptera: Formicidae) and shrubs on soil composition in the Mojave Desert. Soil organic matter, total N, mineral N, and available P were significantly more concentrated in the nests of P. rugosus than under the dominant vegetation and in sparsely vegetated interspaces between shrubs and ant nests. Ant nests also contained high concentrations of total C, organic C, and soluble organic C and N relative to other microhabitat types. On an areal basis, ant nests stored 3% of mineral N and 0.7–1.6% of organic matter, total N, and available P on the landscape while covering 0.5% of the surface. At field moisture, microbial biomass C and N were significantly more concentrated in ant nests at one of two study sites. When moistened, ant nest soils had a higher capacity for microbial growth than soils from other microhabitats. As a result of ant activities, ant nests accumulated surface materials at an average rate 3.5 mm/yr faster than the surrounding soil. We conclude that P. rugosus nests impact arid ecosystems by creating highly concentrated patches of soil nutrients and microflora on the landscape that could affect biogeochemical cycling rates and plant community dynamics.

Harvester ant nests, soil biota and soil chemistry.

Many ant species accumulate organic debris in the vicinity of their nests. These organic materials should provide a rich resource base for the soil biota. We examined the effect of harvester ant nests (Pogonomyrmex barbatus) on the soil community and soil chemistry. Ant nest soils supported 30-fold higher densities of microarthropods and 5-fold higher densities of protozoa than surrounding, control soils. The relative abundances of the major groups of protozoa differed as well: amoebae and ciliates were relatively overrepresented, and flagellates underrepresented, in ant nest versus control soils. Densities of bacteria and fungi were similar in the two soil types. Concentrations of nitrate, ammonium, phosphorus, and potassium were significantly higher in ant nest soils, while concentrations of magnesium, calcium, and water were similar in nest and control soils. Ant nest soils were marginally more acidic than controls. The results demonstrate that P. barbatus nests constitute a significant source of spatial heterogeneity in soil biota and soil chemistry in arid grasslands.

The Influence of Ant Nests on Acacia Seed Production, Herbivory and Soil Nutrients

1 The ant Formica perpilosa nests underneath the shrub Acacia constricta in arid regions of south-western United States. The influence of ant nests on seed production, soil nutrient availability and herbivore protection was evaluated. 2 Plants with basal ant nests were found to produce 1.9 times as many seeds on average than plants of similar size and location without ant nests. Seeds from plants with and without ant nests were equal in fresh mass and were equally likely to germinate. 3 Soil from beneath plants with ant nests contained significantly higher concentrations of nitrate, ammonium, phosphorus, and water than soil from beneath plants without nests. Soil from ant nests also had significantly higher nitrogen mineralization rates. Seed production was not, however, significantly correlated with the concentration of any single soil nutrient measured. Nutrients may interact in ways that benefit plant reproduction. In addition, the microenvironment of ant nest soils may lead to the proliferation of soil organisms beneficial to the plant. 4 Because A. constricta is capable of forming symbioses with nitrogen fixing bacteria, it was predicted that plants with ant nests, exposed to greater concentrations and fluxes of available nitrogen, would utilize more soil nitrogen and less atmospheric nitrogen than plants without basal nests. Nitrogen isotopic analysis of seed tissue revealed that plants with and without ant nests obtained nitrogen from the same source or combination of sources, suggesting that nitrogen may not have limited A. constricta reproduction. Additional interpretations are also discussed. 5 Ants were much more abundant on plants with ant nests at the base than on those without ant nests, but there was little evidence that proximity to ant nests increased protection against herbivory. Plants with and without basal ant nests sustained similar levels of damage to leaves and seeds. 6 If seed production is correlated with reproductive success, then selection may favour A. constricta plants which harbour Formica perpilosa nests at the base. Enhancement of soil nutrient concentrations may be of general importance in understanding how plants benefit from interaction with ants, especially if ants are more likely to nest near plants bearing extrafloral nectaries.