Ant Nest Mounds Research Articles

The negative effect of wood ants (Formica rufa) on microarthropod density and soil biological quality in a semi-arid pine forest

Wood ants (Formica rufa group) are widely distributed in the northern hemisphere and have an important effect on ecosystem processes. The objectives of this study were to evaluate the relationship between F. rufa and the soil biological quality and microarthropod diversity in a semi-arid black pine forest. Microarthropod sampling was conducted for 2 years, from October 2014 to September 2016, at four ant nest mounds of similar size. A total of 288 soil cores were sampled bimonthly, near the nests (designated as the adjacent zone) and at a distance of 10 m away from the nests (designated as the distant zone) during the study period. The results were evaluated by the mean density, QBS-ar index, and Shannon diversity index scores. The mean density of the microarthropods in the adjacent zone (32,797 ind m–2) was lower than the mean density observed in the distant zone (44,462 ind m–2). The Shannon diversity index values were insensitive to differences in microarthropod density, as affected by wood ants, between the adjacent and distant zones, but the QBS-ar values were significantly different between the zones. This suggested that the QBS-ar index may be advantageous in monitoring the impact of wood ants on soil microarthropods in a semi-arid pine forest. Overall, this study reveals that F. rufa may have a significant impact on soil microarthropods in semi-arid forest ecosystems.

The impacts of forest clear felling on the oribatid mite fauna inhabiting Formica aquilonia nest mounds

The ubiquitous soil-dwelling oribatid mites have long been investigated as potential bioindicator agents for environmental changes, such as those resulting from forest management. However, the oribatid community composition often lacks detectable changes, mainly due to the difficulties of finding homogenous microhabitats from the landscape for investigation purposes. Red wood ant nest mounds in boreal forests, however, form uniform, moisture, and temperature regulated, microhabitats of which are also inhabited by a rather characteristic oribatid fauna. With this standardized microhabitat—the red wood ant Formica aquilonia nest mounds in Finland—we studied the impacts of forest clear felling on the oribatid mites inhabiting those nests. We compared the oribatid assemblages of altogether 41 ant mounds, located in three separate clear fell areas and in adjacent mature coniferous forest. A total of 16,499 specimens, representing 67 oribatid species, were observed. The ten most abundant species represented 90.9% of the total abundance. The oribatid species richness was significantly lower in clear fell mounds and was positively related to the surface moisture content of the mounds. Oribatid abundance or community composition did not markedly differ between clear fell and forest mounds. Despite the attempt to standardize the microhabitat of oribatid fauna, the use of oribatid mites as biological indicators of harvesting disturbance was limited with this study design due the lack of changes in community composition. Then again, the oribatid species richness of this characteristic microhabitat may provide useable quality measures about the harms of forest clear felling.

Chronosequences of ant nest mounds from glacier forelands of Jostedalsbreen, southern Norway: Insights into the distribution, succession and geo-ecology of red wood ants (Formica lugubrisandF. aquilonia)

Red wood ant nest mounds were investigated on terrain deglaciated since the mid-18th century at three outlet glaciers of the Jostedalsbreen ice cap in southern Norway. Chronosequence methodology was combined with a geo-ecological approach in the context of autecology. Size and composition of 168 mounds, most of which belonged to Formica lugubris, were related to terrain age, vegetation characteristics and physical habitat types using non-metric multidimensional scaling (NMDS) linked to segmented bubble plots and inferential statistical techniques. Substantive insights include (1) colonisation occurs 50–80 years after deglaciation; (2) mounds up to 100 cm high occupy the glacier forelands with a density of 2.5–4.6 mounds/hectare; (3) the positive correlation between mound size and terrain age is weakened by the presence of numerous small mounds attributed to the expansion of polydomous colonies by budding; (4) although mounds are mostly composed of plant remains (litter), they contain up to 17% mineral material (mostly gravel) on relatively young terrain; (5) mound size and composition are related to the number of trees ( Betula pubescens) occurring within 5 m of each mound, which reflects the availability of biological resources for mound thatch and ant food, the latter being primarily honeydew from aphids; (6) where aphids are present on trees, the mounds tend to be relatively large, reflecting the presence of ant–aphid mutualism; (7) mounds are larger on moraines and till plains than on outwash deposits, probably reflecting the enhancement of tree growth because of greater moisture availability and soil fertility in the former habitat types; (8) a strong southerly preferred aspect in mound orientation indicates the importance of direct solar radiation in maintaining internal mound temperatures and (9) glacier-foreland landscapes are not simply time-dependent chronosequences reflecting succession but the product of spatio-temporal dynamics involving biotic and abiotic interactions, which we summarise in a conceptual geo-ecological model. The main methodological implications are that chronosequences can be used to investigate the autecology of keystone species using a geo-ecological approach and multivariate analysis.

Distribution of oribatid mites is moisture-related within red wood ant Formica polyctena nest mounds

Abundant and species rich oribatid mite faunas live as ant associates in red wood ant nest mounds. Distribution of oribatids (as of many other groups) within mounds is unknown, yet there is an indication that many oribatid species favor moist microclimates. The ant mounds typically have a relatively dry core covered by a moister surface layer, but the moisture variance of mound parts has rarely been verified by measurements. We measured the moisture variance of nine Formica polyctena mounds (surface, rim, core) located in three different forest types in Finland. The moisture may affect the mounds’ temperature maintenance, and we further investigated this relationship. We also hypothesised that the abundance, species richness and community composition of oribatids may be related to the moisture, and investigated these differences between the mound parts and forest types. The moisture varied significantly between the mound parts; moisture was highest in surface followed by rim and core. The surface moisture had a positive relationship with nest core temperature. A total of 18,614 oribatid mites belonging to 93 species and one higher taxon were recorded. The oribatids occurred predominantly on the surface (77.9%), followed by the rim (16.6%) and the core (5.5%) of the ant nest mounds. The abundance and species richness of oribatids was positively related to moisture and differed significantly between the mound parts and forest types. The mound volume had no effect on moisture, temperature or mite community composition. The results indicate that the moisture harbored in the surface layer of ant nest mounds is a vital factor for maintaining rich oribatid mite communities within mounds.

Vegetation heterogeneity caused by an ecosystem engineer drives oviposition-site selection of a threatened grassland insect

Soil-disturbing ecosystem engineers play an important role in plant-species diversity in grasslands as they increase vegetation heterogeneity by creating gaps due to burrowing or mound-building activities. However, knowledge of the ecological importance of these microsites for arthropods is still rare. In this study, we analyse the role of ant-nest mounds of the yellow meadow ant (Lasius flavus) for oviposition-site selection of the silver-spotted skipper (Hesperia comma). Ant mounds were searched for H. comma eggs. Microclimatic and vegetation parameters were ascertained at occupied sites and control sites within the matrix vegetation. Furthermore, we analysed the habitat requirements of L. flavus by means of nest counting and the sampling of environmental parameters within different sites. L. flavus occurred most frequently in abandoned and less steep sites with deeper soils. Mean egg occupancy rates of H. comma on ant hills were 32 %, nearly twice as high as at control sites (18 %). In contrast to the surrounding vegetation, nest mounds were characterized by a lower vegetation cover and litter and a higher proportion of bare ground. Furthermore, they had a higher cover of host plants compared with control samples. These microhabitats offered the following essential key factors for the larval development of H. comma: (1) a suitable microclimate due to open vegetation and (2) a high amount of host plants. This study highlights the importance of L. flavus as an ecosystem engineer within central European grasslands because this species increases vegetation heterogeneity.

Seasonal changes in methane and carbon dioxide flux in wood ant (Formica aquilonia) nests and the surrounding forest soil

Abstract We investigated the seasonal fluxes of CH 4 and CO 2 in wood ant ( Formica aquilonia ) nest mounds and in the surrounding temperate forest soil because temperate forest soils are important sinks of CH 4 and sources of CO 2 . Gas fluxes were measured eight times (at 1- to 2-month intervals) from July 2013 to May 2014 using a static chamber method in a spruce forest in the Czech Republic. Nest and air temperatures were recorded using dataloggers. Averaged across the 11-month sampling period, CH 4 flux was less negative in ant nest mounds (−16 ± 19 μg CH 4 m −2 h −1 ) than in the forest soil (−44 ± 18 μg CH 4 m −2 h −1 ). CH 4 flux did not show a strong seasonal pattern and was negative in ant nest mounds and forest soil, even in winter when the surfaces of ant nest mounds and forest soil were frozen. The only exception occurred in ant nest mounds in summer, when CH 4 fluxes tended to be less negative. Averaged across the 11-month sampling period, CO 2 flux was higher in ant nest mounds (189 ± 204 μg CO 2 m −2 h −1 ) than in the forest soil (105 ± 80 μg CO 2 m −2 h −1 ). The biggest difference in CO 2 flux occurred in July when it was almost six times higher in the ant nest mounds than in the forest soil. CO 2 flux was greater in summer than in winter in both ant nest mounds and the forest soil. In conclusion, ant nest mounds oxidize less CH 4 and produce more CO 2 than the surrounding forest soil.

Different microhabitats affect soil macroinvertebrate assemblages in a Mediterranean arid ecosystem

Spatio-temporal variability is a key factor in conservation, management and restoration of ecosystems. Spatial heterogeneity is caused in many cases by organisms that are able to modify their environments. This is especially relevant in arid systems, where organisms such as shrubs and ants create patches of high nutrient availability (fertile islands) surrounded by a low-nutrient matrix. Although variations in structure and physiology among shrubs provoke differences in their effects as fertile islands, whether different microhabitats vary in their influence on animal communities is poorly known. The principal aim of our study is to analyse the effects of different shrub species and Messor harvester ant-nest mounds on the structure of soil macroarthropod assemblages in a strongly seasonal desert location of SE Spain. Shrub microhabitats and ant-nest mounds maintained higher species density, abundance and biomass of soil macroinvertebrates than the surrounding soil matrix. The different microhabitats differed in taxonomic and trophic composition, abundance, and biomass of soil macroinvertebrates, at both litter and belowground levels. Also, variations of invertebrate abundance among microhabitats changed throughout sampling periods. Thus the spatio-temporal heterogeneity of the study site affected the distribution and dynamics of the macroinvertebrate community. The above results indicate that the spatio-temporal mosaic created by microhabitat and seasonal variations on macroinvertebrate assemblages is a relevant issue to be considered in conservation, sustainable management and environmental restoration in heterogeneous arid systems to preserve their biodiversity and ecosystem functioning.

Vertical distribution of soil macrofauna in an arid ecosystem: Are litter and belowground compartmentalized habitats?

The vertical distribution of soil macroarthropods has been poorly studied despite their importance in understanding the interrelationship between the surface litter and deeper soil layers. Analyzing macrofaunal assemblages in litter and mineral soil layers is especially relevant in soils of arid and semiarid areas, where the litter usually forms a discrete layer that remains separated from the mineral soil and supports a markedly different fauna. In order to analyze the degree of compartmentalization among litter and mineral soil communities, we studied the vertical distribution of macroinvertebrates in an arid area of Southeastern Spain. During 2 years, macroinvertebrates were sampled in the litter and mineral soil beneath shrubs, ant nest mounds and bare soil using cores to a depth of 50 cm. Results showed that macroinvertebrate richness, abundance and biomass decreased gradually with soil depth with small differences between microhabitats. Assemblage composition also varied with depth; an overall vertical stratification was observed, although effects of sampling period, especially in the winter, and microhabitats with higher litter accumulations on the similarity among assemblages were observed. Although the faunal assemblages of the litter and mineral soil habitats displayed some important differences in taxonomic and trophic composition, there were taxa inhabiting both habitats, acting as connectors between litter and the mineral soil. In addition, seasonal differences in the vertical distribution of detritivorous tenebrionid larvae indicate that this connection varies in time, emphasizing the importance of temporal variability in the connection between the surface layer and the below-ground soil.

Native harvester ants threatened with widespread displacement exert localized effects on serpentine grassland plant community composition

Seed‐harvesting ants can influence the abundance and distribution of plant species through both the selective harvesting of seeds and the construction of nutrient‐rich nest mounds, but the relative contributions of these two mechanisms have not been addressed by previous studies. Furthermore, the impact of ant seed harvesting in California serpentine grasslands remains unresolved because of divergent results from several previous experiments. This study investigates the influence of harvester ants on serpentine grassland plant species composition by examining two potential signatures of seed harvesting ants on plant community composition: species composition on versus off ant nest mounds, and species abundance as a function of distance from nest mounds. Of the 28 plant species identified in this study, 22 exhibited spatial patterns consistent with effects of seed harvesting, nest construction, or both. Although most species showed significant gradients in abundance with distance from a nest, there were no clear relationships between plant species distributions and previously reported harvester ant seed foraging patterns. Harvester ant nest mounds supported plant communities that were distinct from the surrounding serpentine grassland, with notably higher densities of legumes and invasive annual grasses. Comparison of our results with those of previous studies indicates that the patterns we observed are generally consistent over time, but affect more species and a larger fraction of the grassland than previously reported. Unaffected areas of the grassland seem likely to serve as important refuges for some plant species.

Composition and Trophic Structure of Detrital Food Web in Ant Nest Mounds of Formica aquilonia and in the Surrounding Forest Soil

Community composition and food web structure of soil decomposer biota in relation to various habitat properties were compared between upper parts of red wood ant (Formica aquilonia) nest mounds and the adjacent forest soil. For a description of trophic structure of the decomposer community in the two habitats, soil decomposers were classified into 14 trophic groups. Classification of the taxa into three habitat preference categories resulted in a clear division of the fauna into either soil or nest specialists, relatively few taxa falling between these two groups. A large majority of the nest specialists belonged to a non-myrmecophilous soil decomposer fauna so far largely overlooked in studies on ant-invertebrate associations. Trophic organisation of the nest mound community differed clearly from that in the soil by having considerably larger biomass at the base of the food web, and less large predators -other than ants - at the top of the web. Contrary to forest soils. the clear dominance of bacterial feeding microfauna over the fungal feeding microfauna in the nest mounds suggests that most of the energy passing through the food web is channelled through a bacterial-based food-web compartment in the nest mounds. Relatively constant temperature and moisture in the nest surface, continuous energy input by the ants to the nests, and ant-induced reduction in predation pressure on macropredators are suggested to be responsible for the development of the typical decomposer community structure in the nest mounds. Thus, the food-web dynamics in ant nest mounds represent an interesting case in which the behaviour of an invertebrate species (i.e. the ant) has a potential to control the development of a system-level organisation. The high biomass of microbi-detritivorous animals, especially earthworms, in the nest mounds suggests that the activities of the decomposer fauna may feed back to the structure of nest mound and indirectly alter the performance of the ant colony.

Nest mounds of red wood ants (Formicaaquilonia): hot spots for litter-dwelling earthworms.

A previously undocumented association between earthworms and red wood ants (Formicaaquilonia Yarr.) was found during an investigation of the influence of wood ants on the distribution and abundance of soil animals in boreal forest soil. Ant nest mounds and the surrounding soil of the ant territories were sampled. The ant nest mound surface (the uppermost 5-cm layer) harboured a much more abundant earthworm community than the surrounding soil; the biomass of the earthworms was about 7 times higher in the nests than in the soil. Dendrodrilusrubidus dominated the earthworm community in the nests, while in soils Dendrobaenaoctaedra was more abundant. Favorable temperature, moisture and pH (Ca content), together with abundant food supply (microbes and decomposing litter) are likely to make a nest mound a preferred habitat for earthworms, provided that they are not preyed upon by the ants. We also conducted laboratory experiments to study antipredation mechanisms of earthworms against ants. The experiments showed that earthworms do not escape predation by avoiding contact with ants in their nests. The earthworm mucus repelled the ants, suggesting a chemical defence against predation. Earthworms probably prevent the nest mounds from becoming overgrown by moulds and fungi, indicating possible mutualistic relationships between the earthworms and the ants.

The role of ant nest-mounds in maintaining small-scale patchiness in dry grasslands in Central Germany

Nest-mounds of Lasius flavus, Lasius alienus and Formica rufibarbis are mainly on north-facing slopes with a markedly patchy distribution at Gimritz, northwest of Halle (Saale). Nest-mound soils had higher sodium and potassium levels but lower phosphorus and nitrogen levels than soils away from mounds. Moisture content was lower but soil pH was significantly higher in nest-mound soils. However, there was no difference in the relative abundance of plants of alkaline or acid soils growing on mounds compared to plants off mounds and no significant difference between the numbers of nitrophilous plants on and off mounds. Fewer plant species (35 spp.) in total occurred on mounds than off mounds (42 spp.). Plant species richness and total plant cover was significantly less on the nest-mounds than off the mounds. Similarly, the mean number of grass (1.39 spp dm−2) and forb species (1.13 spp dm−2) on mounds was lower than the mean number of grass (1.99 spp dm−2) and forb species (1.91 spp dm−2) off mounds. Some shrubs and forbs had higher occurrence and cover on the mounds, although only in Calluna vulgaris, Thymus serpyllum and Cerastium arvense was this difference particularly marked. Ant nest-mounds may favour plant species that cannot compete with tall grasses on unmanaged, set-aside meadows.

The effects of harvester ant Messor capensis nest-mounds on the physical and chemical properties of soils in the southern Karoo, South Africa

Soils of Messor capensis nest-mounds had a higher infiltrability, but were drier than inter-mound soils after a rain event of 26 mm at the end of the hot, dry summer and after 59·5 mm of frontal rains in winter. Soils of M. capensis nest-mounds contain significantly more organic matter, phosphorus, potassium and nitrogen than soils of inter-mound spaces. Plants growing on mounds generally contained more leaf nitrogen than plants in inter-mound spaces. A bioassay, using radishes grown in soils from ant nest-mounds showed fewer symptoms of nutrient deficiencies, grew faster, had lower root:shoot ratios and were significantly heavier at harvest than those grown in inter-mound soils.

The influence of harvester and Messor capensis nest-mounds on the productivity and distribution of some plant species in the southern Karoo, South Africa

Nest-mounds of the harvester ant Messor capensis occur on and around nutrient-rich patches, along minor drainage lines in nutrient-rich soils, and on the plains, generally in nutrient-poor soils. Nest-site selection is related to the presence of suitable deep soils, the presence of stones and the distance from the nearest neighbouring nest. Two plant species, Galenia fruticosa and Pteronia pallens, were significantly associated with Messor capensis nest-mounds, both in numbers of mounds occupied and in numbers of individuals. A third species, Drosanthemum montaguense, was also more common in numbers of individuals, while a fourth species, Rhinephyllum macradenium was negatively associated with these mounds. The analysis of species guilds by soil type shows that significantly more species of nutrient-rich soils are present on M. capensis nest-mounds. Also, significantly more taller, woody species occurred on nest-mounds than in inter-mound spaces. Two species, Pteronia pallens and Osteospermum sinuatum, growing on ant nest-mounds had significantly longer inter-nodes than the same species growing off mounds. However, two other species, Pteronia cf. empetrifolia and Galenia fruticosa showed no difference in inter-node lengths between plants growing on and off mounds. Six of the nine species of plants sampled on ant nest-mounds had significantly higher seed production than plants of the same species growing in inter-mound spaces. The other three species showed a tendency towards more seeds per plant on ant nest-mounds. The proportions of live and dead plants on mounds differed between species. Only Ruschia spinosa showed a significant difference between the numbers of dead plants in the population on and off mounds, with more dead plants occurring on mounds. Significantly more seeds set on individuals of Pteronia pallens growing on ant nest-mounds than those growing off nest-mounds, but no such difference occurred in P. cf. empetrifolia. There was no significant difference in the proportion of seeds parasitized by the tephritid fly Desmella anceps for individuals of P. pallens and P. cf. empetrifolia growing on and off mounds.