Veränderungen in einem natürlichen vorkommen hügelbauender waldameisen derFormica rufa-Gruppe (Hymenoptera: Formicidae) im verlauf von drei jahren

Zusammenfassung In zwei vollständigen Aufnahmen während der Jahre 1966 und 1969 wurde das natürliche Vorkommen hügelbauender Waldameisen derFormica rufa-Gruppe in einem 1639,5 ha grossen Waldgebiet der Vorbergzone des Schwarzwaldes nahe Freiburg/Br. festgestellt. 1966 wurden 260 bewohnte Ameisenhügel gefunden; dies entspricht einer Ameisendichte von 15,9 Nestern je 100 ha. Bei der zweiten Aufnahme 1969 wurden in demselben Gebiet nur noch 208 bewohnte Nesthügel vorgefunden. Dieser im Verlauf von drei Jahren eingetretene Rückgang der Nestzahl um 24,4% hat die einzelnen Arten in unterschieldlichem Ausmass betroffen.Durch zusätzliche Registrierung aller während des Untersuchungszeitraums neu entstandenen, aber bereits wieder verlassenen Nesthügel bei der Zweitaufnahme konnte gezeigt werden, dass die im Verlauf von drei Jahren eingetretenen Veränderungen des Bestandes an bewohnten Ameisenhaufen weit übertroffen werden durch die Zahl nicht dauerhafter Neuanlagen.

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Summary A total census was carried out near Freiburg/Br. (Black Forest) in a woodland of 1639.5 ha (=4098.8 acres) in the year 1966 and again in 1969 to evaluate the number of natural populations of ants of theFormica rufa-group. In 1966, 260 lived-in ant hills were found, this corresponds to 15.9 nests per 100 ha (=6.3/100 acres). In 1969, only 208 lived-in ant hills were found in the same area. The single species were differently affected by this reduction of 24.4% in three years.The amount of change in the natural populations of red wood ants in the area studied is in fact very much higher than indicated by the reduction in numbers of lived-in ant hills. This could be evaluated by an additional registration of all «dead» nests during the second survey; a comprehensive list of the shifting in nesting sites and populations during these three years is given.

     

Ant assemblages in the taiga biome: testing the role of territorial wood ants

Summary Ants were collected with sets of pitfall traps in four coniferous-forest habitats in southern Finland. A three-level competition hierarchy concept was used to generate predictions on ant community structure. The levels of the hierarchy, and the respective predictions, from top to bottom were: (1) The dominant territorial wood ants (Formica rufa-group species), expected to exclude each other. (2) The other aggressive species, likely to be excluded by the F. rufa-group. (3) The submissive species, non-aggressive and defending only their nest, and thus likely to coexist with the dominants but in reduced numbers. As expected, the species of the F. rufa-group excluded each other, and the species number of the other aggressive ants was significantly cut down in the presence of the F. rufa-group. The aggressive species F. sanguinea and Camponotus herculeanus showed complementary occurrences with the F. rufa-group, and Lasius niger reduced occurrences. The number of the submissive species was not significantly affected by the F. rufa-group. However, pairwise correlation coefficients were significantly more often negative than positive between presence of the F. rufa-group and average proportion of pitfalls per set with a submissive species, each analyzed in turn. The result indicates that the F. rufa-group also reduced the colony densities of the submissive species. We conclude that in the taiga biome territorial wood ants are, after adjusting for physical vicissitudes of the environment, the major structuring force of ant species assemblages.     

Impact of vegetation removal on the temperature and moisture content of red wood ant nests

We studied the influence of vegetation growing on red wood ant, Formica polyctena, hills and its removal, by cutting, on the temperature and moisture content of the nests. Vegetation was removed from half of nests (n = 10) in June and August. Generally, ant hills were small (0.1–1.1 m³) and their daily temperature fluctuations and moisture (16–38%) were low. The centre temperature of ant hills was positively correlated with ambient air temperature. Daily temperatures peaked at 13:00 and slowly decreased until 09:00 then increased again until 13:00. Nest moisture content was not related to nest volume. All the ant hills were covered with Reed Grass (Calamagrostis arundinacea) that grows through nests and reaches about 185–1085 g/dcm² of dry matter. Dry vegetation matter (g/dcm² of anthill surface) was the same on cut and uncut nests as well because all ant hills were under long-term management (vegetation removal) for at least 10 years. Although vegetation removal did not result in an immediate increase in the temperature of denuded ant hills removal did results in higher daily and night temperatures during the July-September period. The moisture content of nests with undisturbed and intact vegetation was the same. The dry matter content of vegetation strongly affected their moisture content. However, temperature at the inside centre of nests decreased as vegetation dry matter increased, i.e. there was a statistically negative correlation between temperature and moisture. The results support removing grass as a suitable management tool to facilitate the survival of wood ants. Received 30 December 2007; revised 22 April 2008; accepted 10 June 2008.     

Effect of host species,host nest density and nest size on the occurrence of the shining guest ant <Emphasis Type="Italic">Formicoxenus nitidulus</Emphasis> (Hymenoptera: Formicidae)

Understanding habitat requirements of species is important in conservation. As an obligate ant nest associate, the survival of the globally vulnerable shining guest ant, Formicoxenus nitidulus, is strictly tied to that of its hosts (mound building Formica ants). We investigated how host species, nest density, inter-nest distance and nest mound size relate to the occurrence of F. nitidulus. In total, 166 red wood ant nests were surveyed in SW Finland (120 Formica polyctena, 25 F. rufa, 14 F. aquilonia, 5 F. pratensis, and 2 F. lugubris). Overall, F. nitidulus was found in 60% of the nests. For the actual analysis, only F. polyctena and F. rufa nests were included due to the small number of other nests. F. nitidulus was more likely to be found among F. polyctena than F. rufa. Also, while inter-nest distance was not important, a high nest density, commonly found in polydomous (multi-nest) wood ant colonies, was beneficial for F. nitidulus. The guest ant was also more likely to be found in large host nests than small nests. Thus, our results show that the best habitat for the guest ant is a dense population of host nest mounds with a high proportion of large mounds. Conservation efforts should be directed at keeping the quality of the red wood ant habitats high to preserve their current populations and to increase colonization. This will not only benefit the guest ant, but also a plethora of other species, and help in maintaining the biodiversity of forests.     

The dynamics of vegetation on and around <Emphasis Type="Italic">Formica rufa</Emphasis> nests

The species composition and structure of plant communities related to the activity of Formica rufa ants were studied in green moss pine forests located in Nerusso-Desnyanskoe Polesye (Bryansk Province). Four types of microsites were established and examined: (1) the mound of an active ant nest, (2) the soil bank around an active ant nest, (3) the mound of an abandoned nest, and (4) the soil bank around an abandoned nest. The background plant community was considered as the fifth type. According to MRPP method, all pairs of microsites except (3–4) were different both in plant species composition and species abundance. The microsites created by Formica rufa increase the habitat capacity and β diversity of the plant communities due to the appearance of meadow species requiring richer soils.     

Immigration and formation of mixed colonies in red wood ants (Hymenoptera,Formicidae)

Long-term field studies of the composition and spatial structure of settlements of ants of the Formica rufa group were carried out in two regions of Russia (Moscow and Arkhangelsk provinces). Fragmentation of damaged nests followed by reintegration of the fragments is the main way of formation of mixed colonies of ants from different nests (including different species). The principal factor of nest fragmentation is their damage by wild boars, bears, and in some localities, by poachers. The formation of mixed nests and nest complexes with participation of different Formica species was observed. They are formed by joining the ants from several damaged nests or by a colony from a destroyed nest immigrating into an intact one. Regular damage of many nests leads to the formation of broad zones of mixed colonies. The mixed colonies including 2–3 species of wood ants have recently become common. The phenomenon of mixed colonies raises a question as to the relative importance of two basic principles (sociality and specific identity) in the life of ant societies and demonstrates the priority of the social principle.     

Wood ants prefer conifers to broadleaved trees in mixed temperate forests

1. Wood ants, species of the subgenus Formica s. str., are one of the most important groups of insects in forest ecosystems due to their high abundance and activity.
2. We assessed the foraging pressure of Formica polyctena and Formica rufa, two dominant wood ant species in the Białowieża Forest. In addition, we compared coniferous and mixed stands in these respects.
3. In mixed stands F. polyctena visited more trees per plot than F. rufa. F. polyctena might forage a larger area due to higher population sizes, which further confirms higher foraging pressure of F. polyctena in comparison with F. rufa.
4. In our study area, host trees of the ant–aphid mutualism were larger in diameter than nonhost trees. The ants also preferred trees situated closer to their nests. In both mixed and coniferous stands, the most visited tree species was Norway spruce. Thus, we can conclude that Norway spruce seems to be preferred by the ant. The decline of living spruce in the Białowieża Forest may endanger their food source and impact the vitality of ant colonies.

     

Nest architecture of the ant <Emphasis Type="Italic">Formica pallidefulva</Emphasis>: structure,costs and rules of excavation

Summary The architecture of underground ant nests was studied in the ant Formica pallidefulva. These ants build shallow (30–45 cm deep) nests, which consist of more or less vertical shafts that bear chambers. Shafts are modular units of nest growth; nests are enlarged by adding more shafts or extending previously existing ones. The nests are top-heavy, their volume declining exponentially with depth. The total volume of the nest is strongly correlated with the number of worker occupying the nest (R² = 0.87). Some of the rules and templates used by workers for nest construction were determined: (a) chambers are formed in the direction of the tunnels leading up to them, (b) the amount of soil excavated per unit time increases with soil temperature and moisture content. The amount of time and energy required to construct a typical nest were approximated using digging ability parameters determined in the lab. We estimate that if a colony was to move twice a year, it would expend around 20% of its energy intake and at least 6% of its worker time on nest excavation.Received 16 December 2002; revised 10 July 2003; accepted 23 July 2003.     

Nesting preferences of the threatened wood ant <Emphasis Type="Italic">Formica exsecta</Emphasis> (Hymenoptera: Formicidae); implications for conservation in Scotland

Wood ants are a dominant and ecologically important component of northern coniferous forests with interactions at many trophic levels. Each species exhibits specific habitat preferences which need to be understood if conservation measures are to be successful. In Britain, the rare narrow-headed ant Formica exsecta has disappeared from much of its former range and is now largely restricted to the highlands of Scotland where it is found in open canopy woodland and along forest edges. Nest locale of one small and vulnerable population at the edge of its current range, were compared with those of random locations within the same habitat and with actual nests within the stronghold of the Abernethy-Glenmore complex in Strathspey. After data exploration with Redundancy Analysis, stepwise multiple regression was used to create a model which best estimated the variance in nest location using a parsimonious selection of vegetation and environmental variables. The input variables included were light, soil moisture, altitude, tree stature and distribution, vegetation structure and composition, and ground characteristics. F. exsecta clearly exhibited preferences for the position of nest mounds in relation to light, vegetation and tree cover. Forest location was also important in determining which variables nests were affected by. This study highlights the importance of maintaining a dynamic mosaic of different-aged woodland enabling early successional species such as F. exsecta, with suitable areas to move to as conditions change and allowing the co-existence of all wood ant species.     

Pupation site choice of a North American lycaenid butterfly: the benefits of entering ant nests

Abstract.

• 1 Larvae of the North American lycaenid butterfly Hemiargus isola Reakirt tended by the ant Formica perpilosa Wheeler often enter nests of this ant species, and pupate in tunnels and chambers near the surface. Untended larvae and those tended by the ants Dorymyrmex Forel sp. (smithi complex), Forelius foetida (Buckley), and Myrmecocystus mimicus Wheeler pupate in crevices in the ground, under bark, and on leaves; but rarely inside ant nests.
• 2 The location and structure of F.perpilosa nests facilitates discovery by H.isola prepupae. At the southeast Arizona study site, F.perpilosa nests are located at the base of H.isola's host plant, whereas other species’nests are in open ground. Also, F.perpilosa nest openings are wide, whereas those of other species may be too narrow for prepupae to enter.
• 3 Prepupae associated with F.perpilosa spent 67% less time on the ground searching for pupation sites than prepupae associated with other ant species. Pupae in artificial chambers connected to F.perpilosa nests were 4–5 times less likely to disappear overnight, presumably due to predation, than those not connected to nests.
• 4 Formica perpilosa ants tend pupae inside nests. However, in the laboratory experiments tended pupae did not lose more weight prior to eclosion than untended ones, suggesting that chemicals or sounds produced by pupae as ant attractants are inexpensive, or are produced whether or not ants are present.
• 5 Newly-eclosed butterflies exited nests unmolested by ants in the field, but were attacked if confined with ants for several minutes after eclosion in the laboratory.

     

Colony success of the submissive ant Formica fusca within territories of the dominant Formica polyctena

Abstract. 1. Twenty-three nests of the submissive ant Formica fusca L. were sampled in two adjacent territories of the dominant wood ant Formica polyctena Först. The nests were dug up at different distances from the wood-ant mounds. Distance is assumed to be inversely related to the extent of disturbance of F. fusca by F. polyctena.
2. Colony success of F. fusca was assayed by counting the numbers of workers (colony size), and worker and sexual offspring in a nest. For individual size, the head width and dry weight of fifty workers per nest were measured.
3. Colony size correlated positively with the numbers of worker and sexual offspring in one territory, but only with worker offspring in the other.
4. Distance from the wood-ant mound correlated positively with colony size and numbers of worker and female offspring in one territory. In the other territory distance correlated positively with number of females, but negatively with number of worker offspring. No significant correlations between distance and the size measurements were obtained.
5. Because of its nonaggressive behaviour F. fusca may nest fairly close to a wood-ant mound but is likely to show reduced abundances in terms of nest density and forager number, and, ultimately, lowered fitness.     

Distribution of ant species and mounds (Formica) in different-aged managed spruce stands in eastern Finland

Mound‐building ants (Formica spp.), as key species, have large impacts on organisms and ecosystem functions in boreal Eurasian forests. The density, sizes and locations of ant mounds determine the magnitude and the spatial distribution of ant activities in forest ecosystems. Clear‐cutting can destroy wood ant colonies, and the species, abundance, dimensions and locations of ant mounds may change as forest stand structure changes with stand age. We compared ant species composition, ant mound numbers and dimensions, and the spatial distribution of mounds in Norway spruce [Picea abies (L.) Karst.] stands of different age (5, 30, 60 and 100 years) in eastern Finland. The mound density of Formica aquilonia Yarr. was greater in the two oldest stand age classes, while most mounds of Formica rufa L., Formica polyctena Först., Formica lugubris Zett., Formica exsecta Nyl. and Formica pressilabris Nyl. were found in the two youngest age classes. The mean volume, the volume per area and height/diameter ratio of F. aquilonia mounds increased with stand age. In the oldest stand age class, mounds were slightly smaller in well‐lit locations than in shade and near stand edges than further from the edges indicating that new mounds are established in well‐lit locations. Similarly, the longest slopes of the mounds faced south, indicating the importance of exposure to the sun. F. aquilonia mounds were concentrated near stand edges, and the spatial distribution of the mounds was aggregated in some stands. At the ecosystem level, the aggregation of ant mounds near stand edges may increase the edge productivity, as mounds concentrate resources to the edges and release nutrients after abandonment.     

Polydomy in red wood ants

Polydomy, a single colony spread between multiple nests, is a widespread life history strategy in ants. The mechanisms by which a polydomous colony functions, and the fitness benefits this nesting strategy provides, are poorly understood. Here we review what is known about polydomy in the well-studied and ecologically important Formica rufa group. We focus particularly on the ecological fitness benefits polydomy may provide to members of the F. rufa group. We discuss the well-documented association in this group between polygyny (multiple queens in a colony) and polydomy, and how this relationship may favour colony reproduction by budding. We argue that although polygyny and reproduction by budding may drive a colony to spread between multiple nests, the maintenance of prolonged communication between these nests needs further explanation in terms of fitness benefits. The potential benefits of polydomy in the F. rufa group are discussed, specifically how polydomy may help a colony: exploit resources, dominate spaces, or lower the cost of stochastic nest destruction. The potential consequences of polydomy for the social organisation of a colony are explored. We also highlight gaps in current knowledge, and suggest future research directions.     

A genetic model for disruptive selection on colony social organisation,reproduction, and ecotype distribution in wood ants inhabiting different woodland habitats

Summary Wood ants of theFormica rufa species complex are typically bound to woodland habitats and their eventual colonization of more open habitats depends on the presence of a sufficient number of woody plants. Computer simulations of the long-term development of large wood ant populations in woodland systems of differing structure were performed. A cellular, stochastic automation model simulated the alternatives of a compact, coherent woodland system and a fragmented, coarse-grained woodland system. The simulation of a compact woodland system gave evidence that disruptive selection alone may be sufficient to produce two distinct ectotypes, which are known asFormica rufa andFormica polyctena, even if there is a full fertility of the crosses. The simulation of a fragmented, coarse-grained woodland system has supported the view, that a high local frequency of nests with intermediate phenotypes might be explainable by a particular woodland pattern which favour mixed strategies. It was shown that queen dominance and intraspecific social parasitism are likely to be important factors in the dynamics of large wood ant populations.     

Sur la transmission d'isotopes radio-actifs entre deux fourmilières d'espèces différentes (Formica rufa etFormica polyctena)

Résumé LesFormica polyctena qui ont reçu un radio-isotope (or radio-actif) l'ingèrent rapidement et peuvent le transmettre aux fourmilières voisines deFormica rufa. La radio-activité se localise dans l'abdomen des Fourmis. Il est probable qu'il s'agit d'un échange par voie buccale. Les fourmilières présentent souvent,avant tout marquage, une certaine radio-activité très faible, et due sans doute d'après des recherches en cours, à la présence naturelle de potassium dont l'isotope 40 est naturellement radio-actif.

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Summary When a radioisotope is given toF. polyctena field nests the ants become active after a few hours; the activity is localized in abdomen only; it can be transmitted torufa nests in the neighbourhood. An oral exchange from polyctena to rufa is considered as a probable hypothesis. Ants nests show in many occasions,before radio-active tracer is given to, a small degree of activity, still unexplained.

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Zusammenfassung Die Ameisen (Formica polyctena) die man mit einem Radioisotop (Radio-Gold) gefüttert hat zeigen nach kurzer Zeit eine messbare Radioaktivität welche an Nachbar-Völker derFormica rufa Art übertragen wird. Die Radioaktivität liegt am Abdomen der Ameisen. Es handelt sich wahrscheinlich um einen Futteraustausch. Die Ameisenvölker zeigen oft, auch vor der Fütterung mit Radioisotopen, eine schwache natürliche Radioaktivität dessen Ursache noch ungeklärt bleibt.

     

Week-end bias at observatories

Capsule Although subject to human disturbance Turtle Doves do nest successfully in these olive and orange orchards.

Aim To investigate the breeding ecology of Turtle Doves in a man‐made agricultural habitat in central Morocco.

Methods Turtle Dove nests were monitored in orange and olive orchards over three years (2006, 2007 and 2008). Nest abundance, nest location, egg‐laying chronology, clutch size, nest survival rates and breeding success were determined and compared between orchard types.

Results The Moroccan population of Turtle Doves start breeding earlier than European populations. Clutch size, nest survival rates and breeding success were similar in orange and olive orchards. Nest location differed between orange and olive trees. Nest densities were 16 nests/ha in olive orchards and 45 nests/ha in orange orchards. Nest success rate averaged 48%. Daily nest survival rates did not vary according to orchard types, year and date. In the two orchards, no nest position variables were significant predictors of nesting success.

Conclusion Although highly frequented by people, fruit orchards seem to be suitable breeding habitats for Turtle Doves in this region.     

Nest structure and colony cycle of the Allegheny mound ant,Formica exsectoides Forel (Hymenoptera: Formicidae)

Summary The nest structure and colony cycle of a population of Allegheny mound ants,Formica exsectoides, were examined in central Michigan. The dispersion pattern of mounds was random. Nest structure and presence of brood were primarily determined by excavation of twenty-three nests over three intervals from June through September. Additional excavations of five nests in 1990 and ten nests in 1991 provided further details on nest structure and colony cycle. Most galleries occurred within the mound and upper 30 cm of soil, but some activity reached depths of 100 to 270 cm. Depth of nests showed little correlation with external measurements of height and diameter. Immature stages were recovered from two strata: the upper 20 cm of nest and mound and the lowest nest depths. Alate sexual forms were found in or near the mound in July, and numerous dealate queens were collected in September from peripheral galleries near the soil surface.     

Ecological aspects of development of testacean complexes in nests of Formica lugubris and Formica exsecta (Hymenoptera, Formicidae)

Testacean population in the nests of Formica lugubris and F. exsecta was studied in a spruce forest and in a mixed birch forest. Samples of the nest material (spruce litter and grass fragments) were taken from the surface layers, the inner parts of the nests, and from underlying soil. In all, 33 species of testaceans were identified. The highest species diversity and abundance were observed in the Formica lugubris nests, in the upper layer of the F. exsecta nest, and in the spruce litter. In all the samples, 10 widespread aerophilic and edaphic species (Centropyxis aerophila, C. sylvatica, C. orbicularis, Cyclopyxis kahli, Trinema lineare, and others) were the most common, resulting in a uniform species composition in all the habitats studied. In the presence of the relevant substrate, this group is supplemented by species of appropriate ecological groups (bryophilic, acidophilic, and inhabitants of coarse humus). In the inner part of the Formica lugubris nest, the testacean population is characterized by a very high abundance of Plagiopyxis penardi, whereas the surface layer of the F. exsecta nest is characterized by abundant Cyclopyxis eurystoma and very low species diversity in the inner layers. The initial composition and decree of decomposition of plant remains due to ant activity are considered as the main factors responsible for the testacean species diversity, as well as the availability of substrates suitable for the development of different ecological groups of testaceans.     

Nest relocation in the slavemaking ants Formica subintegra and Formica pergandei: a response to host nest availability that increases raiding success

Social insects typically occupy spatially fixed nests which may thus constrain their mobility. Nevertheless, colony movements are a frequent component of the life cycle of many social insects, particularly ants. Nest relocation in ants may be driven by a variety of factors, including nest deterioration, seasonality, disturbances, changes in microclimate, and local depletion of resources. The colony movements of slavemaking ants have been noted anecdotally, and in recent studies such relocations were primarily attributed to nest deterioration or shifts to overwintering locations. In this study we explore nest relocations in large colonies of formicine slavemakers which occupy stable and persistent earthen nest mounds. We investigate the hypothesis that colony relocations of these slavemakers are best explained by efforts to improve raiding success by seeking areas of higher host availability. Five summers of monitoring the raiding behavior of 11–14 colonies of the slavemakers Formica subintegra and Formica pergandei revealed relatively frequent nest relocations: of 14 colonies that have been tracked for at least three of 5 years, all but one moved at least once by invading existing host nests. Movements tended to occur in the middle of the raiding season and were typically followed by continued raiding of nearby host colonies. Spatial patterns of movements suggest that their purpose is to gain access to more host colonies to raid: the distance moved is typically farther than the mean raiding distance before the move, which may indicate an effort to escape their local neighborhood. Furthermore, the mean distance of raids after relocation is shorter than the distance before relocation. For many slavemaking ant colonies, particularly those on the verge of relocating, raiding distance increased as the raiding season progressed. In addition, movements tended to be toward areas of higher local host density. Nest relocation is likely an important component of the ecology of slavemaking ants that contributes to the dynamic nature of their interaction with the host ant population.     

Polygyny and Monoandry in the Ant Formica japonica (Hymenoptera: Formicidae)

Queen number, mating frequency and nest kin-structure of the ant Formica japonica were studied in the field and the laboratory. Nest excavation in the study site, the east slope of Mt. Fuji, Gotenba, Japan, revealed that F. japonica is weakly polygynous all year round and the queen number increases after the nuptial flight season, suggesting the adoption of newly mated queens by established nests. Dissection and laboratory rearing demonstrated that nearly all queens in polygynous nests had mated and were fertile with mature oocytes in their ovaries. Multilocus DNA fingerprinting was used to examine kin relationships among ants found in the same nests. The fingerprint band patterns were apparently governed by a simple genetic rule and suggested monoandry (single mating per queen). The mean band sharing score of DNA fingerprints among full sisters was 0.90, and the mean value between queens and their daughters was 0.75. Comparison of DNA fingerprints of adult and pupal workers with pupal gynes suggested that multiple queens in a nest may contribute unequally to gyne (new queen) production.