How Ant Nests Increase Soil Biota Richness and Abundance: A Field Experiment

Although many studies have shown that ant nests tend to increase soil nutrient concentrations, only a few have examined ant impact on soil biota. To date, no one has examined the mechanism behind this complex ‘ant effect.’ In this study, we employed a 2 × 2 complete factorial design (water × food) in the field to mimic the effects of harvester ant nests (Messor andrei) on soil. We hypothesized that, in the absence of ants, addition of moisture and food (seeds and insects) would interact to produce conditions found in ant nests. Our results indicated that the addition of food to the soil (regardless of water addition) best mimicked the conditions found inside M. andrei nests. Both food-treated and ant-nest soils supported higher numbers of bacteria, nematodes, miscellaneous eukaryotes, and microarthropods compared to the other soil treatments. Microbial richness was also highest in ant and food-treated samples. Moreover, the ant effect in our experiment occurred in just two months. Because ants are a widespread, abundant group with many long-lived species, they could substantially influence soil properties and belowground food webs and may have important restoration/conservation implications for terrestrial communities.     

Influence of the wood ant, Formica polyctena, on soil nutrient and the spruce tree growth

The effect of Formica polyctena ant nests on the distribution of soil nutrients, soil pH and the growth of Norway spruce trees was studied in the southern part of the Czech Republic. Soil nutrient content (exchangeable P, N, K and pH) and growth of mature spruce trees were measured at four distances from the nearest ant hill (0–1, 3–5, 10–50 and >200 m). Trees at all distances were visited by ants, except for those >200 m from the nearest nest. Soil pH and of P, K and NO₃ concentrations were higher near ant nests (<1 m), and pH and K at distances of 3–5 m, when compared with distances of 10–50 and >200 m from the nests, where no significant differences in these variables were detected. In contrast, tree ring analyses (1974–2004) showed that trees >200 m from the ant nests grew significantly faster than trees at other distances, followed by trees within 1 m of the nests. No growth differences were found between the growth of trees at 3–5 and 10–50 m from ant nests. We postulate that nutrient and carbohydrate removal of honeydew collected by ant‐tended aphids are slowing growth of tree. However, trees may partly compensate for this depletion by having access to a larger supply of soil nutrients near ant nests.     

The relationship between soil variables and leafcutter ant (Atta sexdens) nest distribution in the Colombian Amazon

We determined the relationships between several soil variables and the distribution of leafcutter ant (Atta sexdens) nests on the Colombian shore of the Amazon River. Seven habitats were identified in which nests were consistently present or absent. Soil samples for physiochemical analysis were taken near nest sites in three habitats where nests were present and from randomly selected sites in four other habitats where nests were absent. Percent canopy cover and soil resistance were also measured for each site. Almost all of the 20 identified soil variables were significantly different between habitats with and without A. sexdens nests, and the values of all variables were heterogeneous between the seven habitats. The most important variables correlated with leafcutter ant nest presence were percent canopy cover (positively), percent silt, soil resistance at 0–20 cm, and pH (all negatively). We deduced a binomial and a multinomial logistic regression which showed how each of these variables was related to nest presence and habitat, respectively. We describe how each variable may affect leafcutter ant nest development, especially in its earliest stages, and therefore influences nest distribution. We propose a suitable-soil hypothesis which, complementary to the palatable forage hypothesis, aims to explain patterns in leafcutter ant nest demography based on soil conditions.     

Essential but invisible: non-apparent but widespread ant nests favour soil nutrients and plant growth in semi-arid areas

1. Ants provide multiple ecosystem services, including nutrient cycling. Although most studies on nests effects on soil fertility and plant performance include species with large nests, species with less apparent nests may have a relevant effect, especially if they are widespread, abundant, and/or inhabit nutrient-poor soils. 2. We studied the effects of nests of three abundant and widespread ant species in the Patagonian steppe (the generalist Dorymyrmex tener, and the seed harvesters Pogonomyrmex carbonarius and Pheidole spininodis) on soil properties, plant growth of two native species, and seedling recruitment. Our main hypothesis was that, despite their non-apparent nests, these species have a positive effect on soils and enhance plant growth. 3. Nest soils showed higher soil conductivity, %K and %Mg than non-nest soils. In a greenhouse experiment, individuals of the biennial forb Oenothera odorata grew bigger in nest soils of P. carbonarius and D. tener than in non-nest soils. Individuals of the perennial tussock grass Pappostipa speciosa grew taller and had more tillers in nest versus non-nest soils. Seedling abundance and richness were the highest in P. carbonarius nest soils and the general trends were similar to those observed in the plant growth experiment. 4. Our results show that ant species with non-apparent nests in an arid area enhance soil properties, favouring plant growth (nests of P. carbonarius and D. tener) and seedling abundance (nests of P. carbonarius). Due to their high abundance and widespread distribution, these two species could have a relevant role in ecosystem recovery after disturbance.     

Seed dispersal by ants in the semi-arid Caatinga of North-East Brazil

BACKGROUND AND AIMS: Myrmecochory is a conspicuous feature of several sclerophyll ecosystems around the world but it has received little attention in the semi-arid areas of South America. This study addresses the importance of seed dispersal by ants in a 2500-km(2) area of the Caatinga ecosystem (north-east Brazil) and investigates ant-derived benefits to the plant through myrmecochory. METHODS: Seed manipulation and dispersal by ants was investigated during a 3-year period in the Xingó region. Both plant and ant assemblages involved in seed dispersal were described and ant behaviour was characterized. True myrmecochorous seeds of seven Euphorbiaceae species (i.e. elaiosome-bearing seeds) were used in experiments designed to: (1) quantify the rates of seed cleaning/removal and the influence of both seed size and elaiosome presence on seed removal; (2) identify the fate of seeds dispersed by ants; and (3) document the benefits of seed dispersal by ants in terms of seed germination and seedling growth. KEY RESULTS: Seed dispersal by ants involved one-quarter of the woody flora inhabiting the Xingó region, but true myrmecochory was restricted to 12.8 % of the woody plant species. Myrmecochorous seeds manipulated by ants faced high levels of seed removal (38-84 %) and 83 % of removed seeds were discarded on ant nests. Moreover, seed removal positively correlated with the presence of elaiosome, and elaiosome removal increased germination success by at least 30 %. Finally, some Euphorbiaceae species presented both increased germination and seedling growth on ant-nest soils. CONCLUSIONS: Myrmecochory is a relevant seed dispersal mode in the Caatinga ecosystem, and is particularly frequent among Euphorbiaceae trees and shrubs. The fact that seeds reach micro-sites suitable for establishment (ant nests) supports the directed dispersal hypothesis as a possible force favouring myrmecochory in this ecosystem. Ecosystems with a high frequency of myrmecochorous plants appear not to be restricted to regions of nutrient-impoverished soil or to fire-prone regions.     

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.     

The effects of two abundant ant species on soil nutrients and seedling recruitment in Brazilian Atlantic Forest

Ants can influence soil fertility and the spatial distribution of seeds, with possible effects on seedling recruitment. The ant species Pachycondyla striata Fr. Smith, 1858 and Odontomachus chelifer (Latreille, 1802) co-occur in many forest areas in the Neotropics. We assessed soil fertility and seed bank structure in soil samples close and distant (control) from ant nests in forest fragments. We also assessed the richness and abundance of seedlings on nests and control sites. In soil samples from ant nests, the concentration of phosphorus and potassium were respectively 55.6% and 36% higher than in control sites. Aluminium was 11–15% lower in soil samples from ant nests. In the greenhouse, soils from ant nests had higher plant abundance and species richness, but the same species composition in comparison with control sites. Although more plants emerged from soil samples of O. chelifer nests, in the field, the density and richness of seedlings were similar for the two ant species studied. Seedlings in the nest sites were, on average, 1.8 times more abundant and 1.6 times richer in species than in control sites. Our results showed that ant species can play a key role in seedling recruitment in forest fragments, where other animals with equivalent and positive effects, such as mammals, are missing.     

Switching roles from antagonist to mutualist: a harvester ant as a key seed disperser of a myrmecochorous plant

1. Harvester ants are major seed predators in arid environments. However, given that many harvester ants are partly omnivorous and therefore potentially attracted to the elaiosomes of myrmecochorous seeds, it is unclear if these ants act as predators or dispersers when removing myrmecochorous seeds. 2. We describe the outcomes of interactions between the harvester ant, Pogonomyrmex naegelii, and myrmecochorous plant, Microstachys serrulata, in a Brazilian savanna. We: (i) evaluated the role of elaiosome in seed removal by P. naegelii; (ii) investigated the fate and viability of removed seeds; (iii) tested if soils associated with P. naegelii nests are nutrient-enriched; (iv) compared seedling survival; and (v) the density of seedling and adult M. serrulata nearby to P. naegelii nests compared with those away from these nests (i.e. controls). 3. Rates of removal of M. serrulata seeds were two-fold higher with elaiosomes than without. The ant attractant oleic acid was the dominant fatty acid in elaiosomes, but it was absent from seeds. Removed seeds are taken into nests, and Tetrazolium tests indicated that 95% of seeds remain viable. Soils associated with P. naegelii nests were not nutrient-enriched, and seedling survival was similar nearby to P. naegelii nests compared with control areas. However, densities of both seedling and adult M. serrulata were higher nearby to P. naegelii nests than in control areas. 4. Our findings show that P. naegelii switches its role from seed predator for most plant species to be the dominant seed disperser for M. serrulata, playing a key role in the distribution of adult plants.     

Utilization of harvester ant nest sites by Persian goitered gazelle in steppes of central Iran

Ants are among the most important elements in many ecosystems and known as famous ecosystem engineers. By changing physical and chemical properties of soil, ants may provide suitable habitats for other species. Based on previous observations, we hypothesized that Persian goitered gazelles (Gazella subgutturosa subgutturosa) exhibit a preference for utilizing sites close to seed harvester ant (Messor spp.) nests. We tested our hypothesis by (1) mapping the occurrence of harvester ant nests and aggregated gazelle pellet groups along 31 strip transects, (2) monitoring pellet group accumulation bimonthly at 56 pairs of permanent plots established on ant nests and at adjacent control sites for a complete year, and (3) comparing vegetation and soil parameters between ant nest sites used by gazelles and paired control plots without ant nests. Although the area of Messor spp. nest sites covered only about 0.29% of the sampled transects, 84% of the gazelle pellet group aggregation sites were positioned upon ant nests, suggesting that gazelles actively selected Messor spp. nest sites. Pair-wise comparisons between ant nest plots and paired control plots also confirmed higher use of ant nest sites by gazelles compared to sites without ant nests in all time periods. Percent soil organic matter, percent cover of gravel, and annual herb vegetation significantly differed between ant nest and paired control plots in all the vegetation communities. We suggest that the alterations brought about by harvester ants on soil and vegetation make these sites attractive to gazelles. Gazelle territoriality behaviour and use of ant nests as bedding sites may be the reasons for selection of ant nest sites by gazelles.     

THE FATE OF VIOLA SEEDS DISPERSED BY ANTS

Experimental plantings of the seeds of the two species Viola odorata and V. hirta were carried out to determine relative importance of three effects of myrmecochory: 1) clumping of seeds, 2) scarification of the testa and elaiosome removal, and 3) relocation into ant nests. The study site was a beech-larch wood in southern England. Data show that clumping slightly reduces seedling emergence, scarification and elaiosome removal slightly enhances it, while the nest environment significantly increases the rate of seedling emergence. Only the last effect is statistically significant. Seedlings from nests have larger first adult leaves. The possible impact of ant manipulation of seeds on seedling recruitment into myrmecochorous populations is discussed.     

Soil of the nest-mound of the seed-dispersing ant,Aphaenogaster longiceps,enhances seedling growth

Although a major benefit of myrmecochory in the Australian environment is believed to be the targeting of seeds to nutrient-enriched ant nests, there is very little direct evidence for this. Here I report that, compared to control soil, soil from nest mounds of Aphaenogaster longiceps enhances the growth of seedling roots and shoots by about 50% in glasshouse trials. This benefit of nutrient-enrichment, however, probably only occurs when seeds are dispersed by ants that construct large, long-lived, nest mounds. This is very often not the case, and there is now increasing evidence that distance dispersal is often the major benefit of myrmecochory in Australia.     

Positive ecosystem engineering effects of the ant Atta vollenweideri on the shrub Grabowskia duplicata

Question: How does the ant Atta vollenweideri indirectly affect the shrub Grabowskia duplicata? Does environmental modification induced by nest building affect the life history and population structure of this dominant shrub? Location: Halophytic savanna of western Uruguay, South America. Methods: We compared the density of three shrub size classes, seedlings, saplings and adults, among patches created by ant nest building and in non‐modified areas. We studied key soil properties for plant growth in both live nests and non‐modified areas. We performed a greenhouse experiment to study the effects of soils (live nest versus non‐modified area) on shrub germination probability. We also assessed vegetative propagation by measuring the incidence of root suckers and clonal offshoots in live nests and non‐modified areas through a field survey. Results: Seedling‐size class was more abundant on live nests than in non‐modified areas, suggesting that environmental conditions of this type of habitat (i.e. increased sodium and moisture content of soil, and decreased soil compaction) could facilitate shrub recruitment. We did not find any effects of soil type (live nests versus non‐modified areas) on shrub germination probability. However, the vegetative propagation incidence was higher in the environment with live nests. Conclusions: We found a strong indirect relationship between the ant A. vollenweideri and the shrub G. duplicata. This relationship seems to be mediated by an allogenic engineering process, i.e. soil bioturbation caused by nest building. The environmental conditions of live nests seem to facilitate shrub recruitment, mainly by increasing vegetative propagation.     

A stochastic model of seed dispersal pattern to assess seed predation by ants in annual dry grasslands

A combined field experiment and modelling approach has been used to provide evidence that ants may be responsible for an observed lower patchiness and higher plant diversity in the neighbourhood of ant nests, within Mediterranean dry grasslands belonging to the phytosociological class Tuberarietea guttatae. The hypothesis was that seeds occurring in clumps may have a higher probability to be harvested than seeds having a scattered distribution. In order to test this hypothesis, four analysis steps were performed. First, pattern of seed production and dispersal of four species was recorded; two of them were more abundant next to ant nests (Tuberaria guttata, Euphorbia exigua), whereas the other two were more abundant away from ant nests (Bromus scoparius and Plantago bellardi). Second, a stochastic model was developed to simulate the observed dispersal patterns of each studied species. Third, 10 seed spatial arrangements in accordance to the distribution patterns created by the model were offered to ants and the location of predated seeds was recorded. Finally, the observed pattern of seed predation was matched to models performed by different distributions of probability. Results showed that the probability of being predated decreased as distance among seeds increased. This preference of ants for high concentration of food items holds down the dominant species sufficiently to allow the subordinates to survive, thus increasing diversity near nests. The observed higher frequency of small-seeded, small-sized, or creeping therophytes close to the ant nests can be therefore seen as an example of indirect myrmecophily.     

Ecology of spiders inhabiting abandoned mammal burrows in South African savanna

Summary We marked the sites chosen by 338 foundress queens of two desert ant species (Veromessor pergandei and Myrmecocystus flaviceps) and monitored changes in the spacing of both species and the foraging activity at V. pergandei young nests. Although the long established colonies of both species tend intraspecifically toward regular dispersion, queens of both species were intraspecifically clumped. After 3 months, when the first workers emerged, the young colonies (reduced to a total of 42 colonies) were randomly spaced intraspecifically. We also followed the spatial patter of queens with respect to established colonies of both species. Queens founded nests away from the nests of all established colonies on the site. After three months, the young colonies were dispersed away from conspecifics only. During June through August 1986, we censused the number of foragers at the surviving V. pergandei nests. Young colonies that were more active also tended to be far from established conspecifics in July and August. There was no correlation of forating activity with distance to heterospecific established colonies in any month. These results indicate that established conspecifics may reduce the survivorship of young ant colonies.     

Soil temperature, digging behaviour, and the adaptive value of nest depth in South American species of Acromyrmex leaf-cutting ants

In leaf-cutting ants, workers are expected to excavate the nest at a soil depth that provides suitable temperatures, since the symbiotic fungus cultivated inside nest chambers is highly dependent on temperature for proper growth. We hypothesize that the different nesting habits observed in Acromyrmex leaf-cutting ants in the South American continent, i.e. superficial and subterranean nests, depend on the occurrence, across the soil profile, of the temperature range preferred by workers for digging. To test this hypothesis, we first explored whether the nesting habits in the genus Acromyrmex are correlated with the prevailing soil temperature regimes at the reported nest locations. Second, we experimentally investigated whether Acromyrmex workers engaged in digging use soil temperature as a cue to decide where to excavate the nest. A bibliographic survey of nesting habits of 21 South American Acromyrmex species indicated that nesting habits are correlated with the soil temperature regimes: the warmer the soil at the nesting site, the higher the number of species inhabiting subterranean nests, as compared to superficial nests. For those species showing nesting plasticity, subterranean nests occurred in hot soils, and superficial nests in cold ones. Experimental results indicated that Acromyrmex lundi workers use soil temperature as an orientation cue to decide where to start digging, and respond to rising and falling soil temperatures by moving to alternative digging places, or by stopping digging, respectively. The soil temperature range preferred for digging, between 20°C and maximally 30.6°C, matched the range at which colony growth would be maximized. It is suggested that temperature-sensitive digging guides digging workers towards their preferred range of soil temperature. Workers’ thermopreferences lead to a concentration of digging activity at the soil layers where the preferred range occurs, and therefore, to the construction of superficial nests in cold soils, and subterranean ones in hot soils. The adaptive value of the temperature-related nesting habits, and the temperature-sensitive digging, is further discussed.     

Multivariate analyses of the factors affecting the distribution,abundance and social form of Louisiana fire ants, <Emphasis Type="Italic">Solenopsis invicta</Emphasis>

We surveyed 165 sites to determine the ecological factors influencing the distribution, abundance, and occurrence of polygyny in the red imported fire ant (Solenopsis invicta) in Louisiana. On average, sites had 220 nests/ha, 14% of mounds were polygyne, and 22% of sites had ≥ one polygyne mound. The density of nests and ants per site both increased with the proportion of mounds that were polygyne and the organic and phosphorous content of the soil but decreased with longitude, latitude, and the silt: clay, calcium and sodium content of the soil. Ant density also declined with ambient relative humidity. These multivariate models explained ~25% of the variation in nest and ant density per site. Mean mound size per site increased with the phosphorous content of the soil and the number of nests at the site suggesting that prospective queens may select sites that are conducive to produce large mounds. Mean nest size, however, decreased with the proportion of nests that were polygyne and soil potassium while mounds in forests were typically larger than those in residential areas. Overall, this model accounted for 29% of the variation in mean nest size per site. Polygyne sites were patchily distributed across Louisiana. The probability of a site being polygyne declined with mean monthly temperature for 1999 – 2003 and distance to the nearest commercial waterway suggesting that shipping activities may have played a role in the introduction of polygyne colonists to an area. Forested sites were also less likely to be polygyne than those in residential areas. Finally, the density of polygyne nests and ants increased with latitude whereas that of the monogyne form generally declined with latitude. The abundance of both social forms was also greater when they occurred alone. These data are consistent with the hypothesis that monogyne and polygyne S. invicta compete with one another. Received 28 July 2006; revised 2 March 2007; accepted 29 May 2007.     

Interaction between the non-myrmecochorous herb Galium aparine and the ant Formica polyctena

Non-myrmecochorous plant species are able to colonize Formica polyctena mounds. Galium aparine has been chosen as a model to study this kind of ant-plant association. In order to understand benefits to ants and plants, we have studied removal rates of fruits by ant workers, and compared soil seed material, seedling pattern and development of plants of the nest versus forest.Ant workers remove fruits at very low rates; removal time for half of the sample of 10 seeds was on average 5 h. Removed fruits were usually lost within 20–30 cm distance of the ant route. The soil samples from the nests contained a higher number of fruits, than those from randomly chosen sites in the forest. Seeds start to germinate in late August; on the F. polyctena mounds significantly earlier than at surrounding places. The seedling density was higher within experimental quadrats located on mound sites especially in late September–early October. The highest density of seedlings was on the slope of the mound. Plants from mounds are significantly longer, have a higher number of nodes during all stages of development and a higher mortality rate than that at surrounding places.The interactions between G. aparine and F. polyctena ants are asymmetrical. In spite of higher mortality rate of seedlings on mounds, ants provide some benefits to the plant. Firstly, workers are additional dispersal agents for G. aparine fruits. Furthermore, the soil peculiarities of ant mounds are beneficial for seed germination and seedling growth. G. aparine does not provide ants with energetically valuable food like plants with elaiosome-bearing seeds. Moreover, the high density of seedlings and plants on the mounds shades the nest.     

Effect of three mound-building ant species on the formation of soil seed bank in mountain grassland

The effect of three ant species (Lasius flavus, Formica spp., Tetramorium caespitum) on soil seed bank formation was studied in temperate mountain grassland. Seed removal experiments, analysis of soil seed content and seed survival experiments were carried out to evaluate the influence of ground ants on the seed fate. In the seed removal experiment seeds of 16 species, including 5 species with elaiosome-bearing seeds (myrmecochores), were exposed and their removal followed for 39 h. On average, ants removed 63.8% of myrmecochorous seeds and 10.9% of seeds without adaptation to ant dispersal. Analysis of soil seed content revealed that myrmecochores, in spite of expectations that they would accumulate in nests of seed dispersing ants, were most abundant in the soil of control plots. Evidence on seed relocation to the ant nests was obtained from a comparison of mounds of seed dispersing and seed non-dispersing ant species, as more seeds were found in the mounds of Formica spp. and Tetramorium caespitum (seed dispersers) in comparison with the mounds of Lasius favus (non-disperser).The soil seed bank of the compared microhabitats (control plots and mounds of 3 ant species) differed in their species composition, seed abundance and vertical distribution. The most distinct qualitative differences were between seed flora of control plots and mounds of Tetramorium caespitum. Control plots had approximately 30,000 propagules per m², which was double the number of seeds found in the ant mounds. In control plots, abundance and diversity of seeds steeply declined with depth; this trend was not observed in the mounds probably due to bioturbation. In the seed survival experiment, more seeds (2 out of 3 species) survived in control plots, which may also contribute to the higher seed abundance in this microhabitat.This study showed that seed relocation by ants does not contribute significantly to seed bank build-up at this study site. Ants may, however, increase the regeneration success of myrmecochores, mainly by dispersal for distance and placement in a larger spectrum of microsites, in contrast to species not adapted for myrmecochory.     

Geophagy in masked titi monkeys (Callicebus personatus melanochir) in sBrazil

Geophagy was observed 14 times during an 11-month field study on the ecology and behavior of masked titi monkeys (Callicebus personatus melanochir). Geophagy took place in 12 cases on the surface of a leaf-cutting ant mound (Atta spec.). Analysis of chemical composition and natural features of the soils consumed by the monkeys showed elevated concentrations of several elements. In contrast, a lower concentration of carbohydrates was found in the ant mound sample compared to random non-ant mound soil samples. No difference in the concentration of clay elements, pH-value or percentage of organic matter was found between ant mound samples and randomly collected soil samples. Comparison of used versus not used samples failed to reveal significant clues about function of geophagy. However, chemical and physical properties of soils ingested support previous hypothesis that this behavior may aid in the adsorbtion of plant toxins.     

Organic mound-building ants: their impact on soil properties in temperate and boreal forests

Ants are important components of most soil invertebrate communities, and can affect the flow of energy, nutrients and water through many terrestrial ecosystems. The vast majority of ant species build nests in the mineral soil, but a small group of ants in temperate and boreal forests of Eurasia and North America build large parts of their nests above‐ground using organic materials collected from the surrounding soil. Many studies have shown that ants nesting in mineral soil can affect water infiltration rates, soil organic matter (OM) content, and nutrient cycling, but much less is known on how mound‐building ants influence soil physical and chemical properties. In this paper we summarize what is known on the soil impacts of organic mound‐building ants in temperate and boreal forests, and how these ants could be affected by ecosystem disturbance and future climate change. Much of this information comes from studies on Formica rufa group ants in Europe, which showed that CO₂ emissions and concentrations of C, N, and P are usually higher in ant mounds than in the surrounding forest soil. However, ant mounds are a minor component of total soil C and nutrient pools, but they do increase spatial heterogeneity of soil water and available nutrients. Mound‐building ants can also impact tree growth, which could change the quantity and quality of OM added to soil. Forest management, fire, and projected climate change, especially in boreal forests, could affect mound‐building ant population dynamics, and indirectly, soil properties.