Host specificity revisited: New data on Myrmica host ants of the lycaenid butterfly Maculinea rebeli

Larvae of Maculinea rebeli, one of the most endangered European butterflies, are obligatory social parasites of Myrmica ants. At present, this relationship is thought to be highly specific, with Myrmica schencki being regarded as the primary host. Here we present data on six populations from Poland and Austria, including the first record of Myrmica specioides as a host, together with published data from other central European countries, which severely questions the inference that M. schencki is the exclusive host of M. rebeli. Our results indicate that Myrmica sabuleti is the most frequently used host ant in central Europe, whereas M. scabrinodis, M. sulcinodis, M. specioides and M. schencki are used as secondary hosts. Possible explanations for this highly variable host use include (1) regional differences in semiochemicals, behaviour or social structure of the potential Myrmica host species and (2) the existence of different ecological subspecies or cryptic species of M. rebeli. Finally, we emphasize the importance of identifying local host ant species prior to further conservation strategies in order to avoid failure of management programs or even damage to populations on the edge of extinction.     

Effects of experimental and real land use on seedling recruitment of six fen species

Seedling emergence and early establishment of six fen species differing in seed mass and growth form were investigated under experimental land use with changed vegetation structure and under real land use in a calcareous fen. Seeds of all six species were sown in plots with different experimental land-use treatments: summer and autumn mowing with or without litter removal, trampling and abandonment. Additionally, emergence and survival of experimentally sown seeds was investigated under real land use on adjacent sites managed by mowing, grazing, intense trampling or abandonment.On abandoned plots and on plots without litter removal of the land-use experiment, emergence rates of all species were negatively affected either by high litter and moss cover or by tall canopy. No differences were found between autumn and summer mowing. Gap creation by experimental trampling did not increase germination rate. Under real land use, establishment of seedlings of most species was positively affected by litter cover and tall canopy. Trampling, in contrast, had a severe negative effect on seedling survival.The investigated species differed in their germination ability which was tested in the germination chamber and in their response to land use. Succisa pratensis with the highest seed mass germinated well in the chamber and in the field more or less regardless of land use. The low germination rate of Parnassia palustris in the germination chamber indicated a limitation of viable seeds. In the field, however, seedling emergence was additionally limited by microsite availability. Seeds of Serratula tinctoria and Primula farinosa germinated well in the germination chamber, but seedling recruitment in the field was hampered in the presence of a high litter or moss cover. Seeds of Tofieldia calyculata and Pinguicula vulgaris were strongly dependent on the availability of suitable microsites in the field. They hardly germinated under natural conditions, in spite of a high number of germinable seeds in the germination chamber.     

Determining the effectiveness of grazing and trampling by livestock in transmitting white clover mosaic and subterranean clover mottle viruses

Glasshouse and mini-sward experiments were done to determine the relative roles of grazing and trampling by livestock in transmitting white clover mosaic (WC1MV) and subterranean clover mottle (SCMoV) viruses between clover plants in pastures. Wounding due to grazing was simulated by repeatedly cutting plants with serrated scissors (glasshouse) or mowing (mini-swards), while wounding due to trampling was simulated by repeatedly bashing plants with the flat end of a wooden hammer handle (glasshouse) or rolling (mini-swards). In glasshouse experiments, cutting was more effective than bashing in transmitting WC1MV to white clover (Trifolium repens) plants but cutting and bashing transmitted it to subterranean clover (T. subterraneum) plants at similar rates. In an experiment with white clover mini-swards, mowing was more effective than rolling in transmitting WC1MV, and when both were combined, initially spread exceeded that obtained when the spread from mowing and rolling alone was added together. In glasshouse experiments, bashing was more effective than cutting in transmitting SCMoV to subterranean clover plants. In one experiment, neither mowing nor rolling spread SCMoV in mini-swards of subterranean clover. When transmission to subterranean clover cultivars which were ‘susceptible’ or ‘moderately susceptible’ to SCMoV was compared in glasshouse experiments, repeated bashing spread the virus more slowly to the ‘moderately susceptible’ cultivars. When mixed with ruminant saliva, infective sap containing WC1MV or SCMoV was still infective to clover plants after 4 wk storage at room temperature. When infective sap was allowed to dry naturally on a metal surface, SCMoV still infected clover plants when the dried sap was taken up in tap water after 4 but not 14 days, while WC1MV was infective after 24 h but not 4 days. These results suggest that grazing and mowing are more effective than trampling at transmitting WC1MV to white clover plants in pastures, while trampling is more effective at spreading SCMoV to subterranean clover. However, both transmitted WC1MV to subterranean clover at similar rates. Possible reasons for these differences are discussed in relation to differences in clover plant morphology and virus-specific factors.     

Multiple host-ant use by the predatory social parasite <Emphasis Type="Italic">Phengaris</Emphasis> (=<Emphasis Type="Italic">Maculinea</Emphasis>) <Emphasis Type="Italic">arion</Emphasis> (Lepidoptera,Lycaenidae)

Phengaris (=Maculinea) arion is an endangered social parasite of Myrmica ants, and for a very long time was considered as specific to Myrmica sabuleti. Previous studies carried out in Poland suggested some discrepancies within this assumption, and therefore a much more intensive survey was undertaken. The host ant use of P. arion was studied at five sites in different types of biotopes in Poland, i.e. xerothermal grasslands where Thymus pulegioides was used as a larval food plant by the butterfly, and more or less sandy biotopes with Thymus serpyllum. Altogether nine Myrmica species were recorded, and considerable variation in species composition and density of nests was recorded. At four localities M. sabuleti proved to be the most common ant. A total of 529 Myrmica nests were examined, and only 20 of them contained larvae and pupae of P. arion. Host ants belonged to five different species, i.e. M. sabuleti, Myrmica scabrinodis, Myrmica schencki, Myrmica lobicornis and Myrmica hellenica. Only at one site (NE Poland) was a significant heterogeneity in parasitation rates among Myrmica species detected. M. lobicornis was the most often infested ant there, which may suggest local specialisation of the butterfly. Overall low parasitism rates may explain the vulnerability of P. arion in Central Europe but further studies are also necessary.     

Typification of urban habitats,with ant assemblages of Moscow city taken as an example

A typification of Moscow city habitats is undertaken, based on their consideration as mosaic of patches and using such fundamental parameters as habitat origin (soil type), floristic composition, vegetation structure, and area of the biotopes. Altogether, 11 habitat types are distinguished: lawns, agrocenoses, xerophytic and mesophytic meadows, tall weeds, boulevards, small degenerative parks, small oppressed artificial parks, landscape parks, forest parks, and technocenoses. Such a classification is primarily useful for studying ants. The present paper describes the basic structure of ant assemblages in most types of urban biocenoses. The main pool of Moscow’s ant species ranked by their occurrence is as follows: Lasius niger (87%), Myrmica rugulosa (44%), Myrmica rubra (33%), Formica cunicularia (11%), Myrmica ruginodis (10%), etc. Leaf litter removal with a rake was shown to negatively affect the numbers, biomass, and species diversity of ant communities in urban areas with trees. The most stable two-species ant community revealed in Moscow City, termed an “elementary urban community,” consists of L. niger and M. rugulosa, with the former always outnumbering the latter.     

Less is more! Rapid increase in plant species richness after reduced mowing in urban grasslands

Urban lawns provide space for recreation in cities, and they are an important part of urban green infrastructures. However, most lawns are intensively managed. As only few plant species can survive frequent mowing, urban lawns typically harbor only a limited number of plant species. To improve the biodiversity of urban lawns, it is often suggested to reduce the mowing frequency. Here, we studied the plant diversity of urban grasslands that have recently undergone management changes from mowing every few weeks to mowing only once or twice per season and compared them to intensively managed lawns. Within six years after the management changes, the grasslands with reduced mowing frequency hosted 30% more plant species than intensively managed lawns, and they were more heterogeneous both within and between grasslands. Additionally, the species composition of less frequently mown grasslands shifted from common mowing-tolerant lawn species to typical meadow species. Our study thus shows that the reduction of mowing is a simple and effective tool for increasing the biodiversity in urban grasslands.     

Myrmica rubra microhabitat selection and putative ecological impact

1. Myrmica rubra (European fire ant) has invaded northern latitude coastal areas in North America. This macroscale distribution suggests that M. rubra is moisture‐ and temperature‐limited, but the distribution of the invaded range may reflect the legacy of original introduction locations preserved by limited dispersal. 2. This study examined a two‐decade population change in M. rubra (1994–2015) and the microscale abiotic (moisture and temperature), biotic (plants), anthropogenic (pesticide) and physiological (thermal tolerance) limits on the invasion at the Tifft Nature Preserve in Buffalo, NY (U.S.A.). Changes in the abundance of native ants and other invertebrates were also examined. 3. Despite localised declines with pesticide treatments, overall M. rubra forager abundance increased 27% between 1994 and 2015. Abundance increased the most in the warmest areas (native ants were unaffected by temperature), but M. rubra colony locations were strongly linked to higher soil moisture and lower soil temperature. Myrmica rubra ants also exhibited relatively low thermal tolerances consistent with high‐latitude and high‐elevation ants. 4. Where local M. rubra populations increased the most, native ant species decreased, and where local M. rubra populations declined, native ant species increased. Some arthropod species had lower abundance with M. rubra presence, but the impacts were less striking. 5. Myrmica rubra population growth was promoted at the microhabitat scale where relatively higher temperatures prompted foraging, and relatively lower temperatures and high moisture supported nesting. These results suggest that macroscale M. rubra invaded‐range distributions in northern climates near coastal areas are replicated at the microscale where the ant prefers cooler, moister microsites.     

Competition between a Lawn-Forming Cynodon dactylon and a Tufted Grass Species Hyparrhenia hirta on a South-African Dystrophic Savanna

South African savanna grasslands are often characterised by indigestible tufted grass species whereas lawn grasses are far more desirable in terms of herbivore sustenance. We aimed to investigate the role of nutrients and/or the disturbance (grazing, trampling) by herbivores on the formation of grazing lawns. We conducted a series of common garden experiments to test the effect of nutrients on interspecific competition between a typical lawn-forming grass species (Cynodon dactylon) and a species that is frequently found outside grazing lawns (Hyparrhenia hirta), and tested for the effect of herbivore disturbance in the form of trampling and clipping. We also performed a vegetation and herbivore survey to apply experimentally derived insights to field observations. Our results showed that interspecific competition was not affected by soil nutrient concentrations. C. dactylon did show much more resilience to disturbance than H. hirta, presumably due to the regenerative capacity of its rhizomes. Results from the field survey were in line with these findings, describing a correlation between herbivore pressure and C. dactylon abundance. We conclude that herbivore disturbance, and not soil nutrients, provide C. dactylon with a competitive advantage over H. hirta, due to vegetative regeneration from its rhizomes. This provides evidence for the importance of concentrated, high herbivore densities for the creation and maintenance of grazing lawns.     

Microsatellite loci for Myrmica kotokui and their application in some congeneric ant species distributed in northern Japan

We developed seven polymorphic microsatellite loci for Myrmica kotokui from RAPD (rapid analysis of polymorphic DNA) fragments. These loci showed two to six alleles with expected and observed heterozygosity of 0.13–0.73 and 0.14–0.78, respectively. These loci are transferable to the congeneric species as Myrmica rubra, Myrmica luteola and Myrmica taediosa from northern Japan. These loci will allow analyses of genetic structure of Myrmica species at both the colony level and population levels.     

Not only the butterflies: managing ants on road verges to benefit Phengaris (Maculinea) butterflies

Obligate myrmecophilic butterfly species, such as Phengaris (Maculinea) teleius and P. nausithous, have narrow habitat requirements. Living as a caterpillar in the nests of the ant species Myrmica scabrinodis and M. rubra, respectively, they can only survive on sites with both host ants and the host plant Great Burnet Sanguisorba officinalis. After having been reintroduced into a nature reserve in the Netherlands in 1990, both butterfly species expanded their distribution to linear landscape elements such as road verges and ditch edges outside this reserve. As additional habitat of both butterfly species, vegetation management of these landscape elements became important. Our results show that a management beneficial for Phengaris butterflies should aim to increase the nest density of Myrmica species, at the same time reducing the density of nests of the competitor Lasius niger or at least keeping them at a low density. Unfavourable grassland management under which L. niger thrives, includes not mowing or flail-cutting the grass, or depositing dredgings along the side of the ditch. Management favourable for the two Myrmica species differs, demanding some flexibility if both species are to benefit. M. scabrinodis is best supported with early mowing of the road verge vegetation or late mowing in the nature reserve, both of which result in an open vegetation and warm microclimate. In contrast, the nest sites of M. rubra should be left undisturbed during the summer, and mown in late autumn. Mowing of butterfly habitat should be avoided between mid-June and mid-September as this would remove the flowerheads of the Sanguisorba plants, on which the butterflies lay their eggs.     

Distribution,host specificity,and the potential for cryptic speciation in hoverfly Microdon myrmicae (Diptera: Syrphidae), a social parasite of Myrmica ants

1. In 2002 Microdon myrmicae, a social parasite of Myrmica ants, was taxonomically separated from Microdon mutabilis. The original study in the U.K. found Microdon myrmicae to be specific to one ant species, Myrmica scabrinodis, yet it became apparent that the range of Microdon myrmicae includes at least the western Palaearctic. 2. Current knowledge of the European distributions of both Microdon myrmicae and Microdon mutabilis in Europe is reviewed. Also, in detailed studies of two Polish populations, Microdon myrmicae was found to survive equally well with two Myrmica ant species. We examine, however, the possibility that this reflects the presence of two separate Microdon species, each connected to one species of Myrmica. 3. Forty populations of Microdon myrmicae and 37 populations of Microdon mutabilis are currently known in Europe. All the populations in central and southern Europe that were visited after the separation of the two species were identified as Microdon myrmicae, while Microdon mutabilis’ recognised range is now restricted to the British Isles and Scandinavia. Myrmica scabrinodis was found to host Microdon myrmicae in 26 out of 31 populations investigated. Four other Myrmica species were identified to the host Microdon myrmicae: Myrmica gallienii (eight populations), Myrmica rubra (four), Myrmica vandeli (one), and Myrmica sabuleti (one). Microdon myrmicae occurs in waterlogged grassland habitats, mainly of the ‘Molinietum’ type, resulting in a patchy distribution relative to its host ants. 4. In two populations Myrmica scabrinodis and Myrmica gallienii are both abundant and rear Microdon myrmicae in equal proportions. Microdon myrmicae pupae from Myrmica gallienii nests were heavier and the anterior respiratory organs were of significantly different shape. In contrast, the comparisons of Microdon myrmicae pupae among all other populations showed no significant differences, suggesting only one species throughout the European range.     

How ants find each other; temporal and spatial patterns in nuptial flights

Reproduction is a key factor in understanding population ecology and therefore species occurrence. However, patterns in reproductive behaviour for distinct ant species remain insufficiently known. In this paper strategies in mate finding are studied for six ant species (Lasius niger, Lasius umbratus, Temnothorax nylanderi, Myrmica rubra, Myrmica ruginodis, Stenamma debile) in a forest – forest edge – agricultural field gradient. Using window traps, we studied whether these species had a restricted nuptial flight season, displayed swarming behaviour, and whether the alates aggregated at the forest edge. The flight season was limited to one month or less for L. niger, T. nylanderi, M. rubra, M. ruginodis and S. debile. Swarming behaviour occurred in all but one (L. umbratus) species. Although none of the six species seemed to have highest nest density at the forest edge, three of them, M. rubra, M. ruginodis and S. debile, showed male aggregations there, indicating this to be the main reproduction site. This last finding could be due to a more suitable micro-climate, but most likely, edges are conspicuous land marks which are used by ants to meet mates. The behavioural patterns of ant sexuals at the forest edge can influence dispersal possibilities in fragmented landscapes, reproductive success and nest densities. Received 27 November 2007; revised 27 March; accepted 5 April 2008.     

刈割加遮荫对互花米草生长和存活的影响

该研究比较了在5月份实施刈割加不同程度遮荫处理后,互花米草地上部分和地下根茎6个月内的生长与死亡状况。结果表明:(1)单纯刈割处理在前2个月显著降低互花米草株高和生物量等生长指标(P0.05),随后地上部分生长和开花特征逐渐恢复并接近对照水平;而地下根茎存活率一直呈下降趋势;(2)刈割后加不同程度遮荫处理均可以有效抑制互花米草的生长并导致植株死亡,抑制效果显著高于单纯刈割的处理(P0.05),且遮荫程度越高抑制作用越明显。(3)刈割后加1层遮荫、2层遮荫和3层遮荫处理的平均透光率分别为15.27%、2.29%和0.31%,分别于11月份、7月份和7月份时导致互花米草地上部分全部死亡,至11月份时地下根茎存活率分别为3.68%、2.09%和1.70%,接近全部死亡。综合考虑治理费用、治理所需时间和治理效果,刈割后加1层遮荫是经济、有效的控制互花米草的方法。     

Some characteristics of the visual perception of the ant Myrmica sabuleti

Abstract. Using classical conditioning techniques, this study aims to determine what the ant Myrmica sabuleti can see and discriminate. It appears that workers see distinctly vertical as well as horizontal segments 1, 2, 3, 5, 10 and 15 mm wide and 1, 2, 3, 5, 10 and 15 cm long. They can also see distinctly horizontal segments (0.5 × 3 cm) located at 1, 2, 3, 5 and 10 cm height, but do not see such a segment situated at 15 cm height. This allowed the assessment of their maximum distance of vision. Myrmica sabuleti workers also see distinctly vertical segments (0.5 × 3 cm) sloping backwards towards the horizontal at different angles (90, 60, 45, 30, 15 and 0 °). Consequently, M. sabuleti workers see cues lying horizontally on the ground and have a stereovision of a portion of their environment. The species also see distinctly black circles of different sizes located horizontally above them. Thus, they are able to see distinctly slightly modified patterns located aside, below, above as well as before them, and have a small area of binocular vision that both eyes can look at. Myrmica sabuleti workers' maximum distance of vision is directly proportional to the square root of the surface of the object observed. Consequently, the smallest vision angular subtense of an object needed to elicit a reaction in M. sabuleti workers is evaluated as being approximately 5 angular degrees.     

Effects of human trampling and multispecies competition on early-phase development of a tread community

Effects of human trampling and multispecies competition on the development of a tread community in the first year were examined by comparing changes in the relative abundance of three main component species of tread communities,Plantago asiatica, Eragrostis ferruginea andEleusine indica, between monoculture and mixed culture along a trampling gradient. At low trampling levels in mixed culture,Ambrosia artemisiifolia var.elatior andDigitaria adscendens, which are common pioneer species of secondary succession, predominated and suppressed the tread community species. Severe trampling reduced markedly the predominance of the pioneer species, but not that of the tread community species. The maximum cover of the three tread commiunty species was lower in mixed culture than in monoculture. The trampling levels supporting the maximum cover were higher in mixed culture than in monoculture. The differences in these levels between monoculture and mixed culture varied among the three:P. asiatica< Eragrostis ferruginea<Eleusine indica. These results suggest that (1) the pioneer species interfere with the establishment of tread community species under lower trampling intensity, (2) heavier trampling reduces the competitive ability of pioneer species, while it favors the establishment of tread community species, (3), there are competitive interactions among the tread community species under higher trampling intensity, and (4) the species more susceptible to multispecies competition and tolerant to trampling are established in more heavily trampled habitats.     

Habitat requirements and niche selection of Maculinea nausithous and M. teleius (Lepidoptera: Lycaenidae) within a large sympatric metapopulation

Identifying the factors determining the distribution and abundance of species is a fundamental question in population ecology. Based on habitat characteristics, we sought to identify factors affecting the abundance of two vulnerable large blue butterflies, Maculinea teleius and Maculinea nausithous. Both species often occur in sympatry and thus seem to have very similar requirements with regard to their wetland habitats. Even though, M. nausithous is usually far more widespread and abundant than M. teleius in Central Europe. For understanding this difference despite a similar ecology, more data is needed on the niche selection of both species. We have recorded Maculinea numbers, vegetation structure, food-plant abundance and ant community for 120 patches within a large sympatric metapopulation of both species in the Westerwald area (Germany). Unexpectedly (based on previous data), both species were equally common in the study area, reaching high densities of up to 61 (M. teleius) and 58 (M. nausithous) individuals per 50 m2. In 116 out of 120 patches both species occurred sympatrically. The preferred habitat was extensively managed grassland, being mown or grazed twice a year. The abundance of both Maculinea species was positively related to vegetation height, food-plant and Myrmica rubra abundance. There was no association between M. teleius and its putative main host-ant Myrmica scabrinodis, indicating that M. rubra may serve as an important host in the Westerwald area. The positive effect of food-plant abundance was more pronounced for M. teleius, coinciding with a higher food-plant abundance at sites dominated by M. teleius compared to those dominated by M. nausithous. Thus, M. teleius seems to be slightly more demanding than M. nausithous in terms of food-plant availability.     

The impact of trampling by tourists on a high altitudinal grassland in the Tyrolean Alps,Austria

The long term effect of tourist trampling on a high altitudinal grassland (Caricion curvulae) in the Tyrolean Alps was investigated.Even under slight trampling the frequency of sensitive species decreases. The most sensitive species were found to be fruticose lichens, followed by mosses, some forbs and broadleaved grasses. Tolerant to trampling are the dominant species Carex curvula, and Ligusticum mutellina, which do not disappear completely even at a tourist frequency of 150 tourists per metre per day. Trampling increases soil bulk density moderately but has no marked effect on the soil water content.Comparison with high alpine sedge heath vegetation in North America shows a surprising uniformity of this vegetation type in response to trampling and also indicates that the common generalisation that alpine ecosystems are fragile and sensitive to disturbance does not hold true in this context. Furthermore these results represent evidence against the theory that ecosystems with low diversity are much more sensitive to arteficial impact than ecosystems with high diversity. However, if even the most resistant plants which are the dominant sedges are destroyed completely the rate of recovery is very low and may last for a long time. In the case of Carex curvula this is supported by the fact that it has very low seed production and grows mainly vegetatively. The rate of spread of the rhizome system of this species is 8 mm in 10 years. Similar figures may apply for the sedge species dominating in the alpine vegetation of North America. Thus fragility of this vegetation in regard to trampling does not mean low tolerance but low regeneration.Nomenclature of species follows Ehrendorfer (1973) for vascular plants and Poelt (1974) for lichens.The PCA calculations were done at the Computer laboratory of the University of Wales during a post doctoral stay at the School of Plant Biology in Bangor, U.K. I would like to record my thanks to Prof. Dr. P. Greig-Smith for fruitful discussions and reading the draft.     

Ant species distribution in a sandy coastal plain

Abstract.

• 1 Three species of ants, Lasius niger, Myrmica rubra and Myrmica scabrinodis, have been recorded in a 20-year-old coastal plain on the Dutch Wadden Zee island, Schiermonnikoog.
• 2 The habitats of these species appeared to be clearly segregated, both horizontally (different parts of the plain) and vertically (along dune slope gradients in the plain).
• 3 Lasius niger is distributed throughout the plain in sparsely vegetated sand-dunes and in mounds covered with turf of Festuca rubra ssp. litoralis, but always in areas that are only waterlogged or inundated in winter.
• 4 Myrmica rubra is limited to Festuca-turf, occurring in a distinct zone along the bases of small dunes and on isolated mounds.
• 5 Myrmica scabrinodis only occurs in mounds covered with Festuca-tutf and rarely in the small dunes.
• 6 Analysis of soil, vegetation, inundation and salinity of the ground-water demonstrated that Myrmica scabrinodis is dominant in areas with more silt and salt in the soil, characterized by a vegetation with more typical halophytes, whereas Myrmica rubra occurs most frequently in sandy habitats without much salt stress. The populations of both Myrmica species and Lasius niger do not seem to be affected by inundation during winter.
• 7 The distribution of the ant species is discussed in relation to data about ants in more stable habitats. In particular, attention is given to the absence, in this coastal plain, of Lasius flavus which is a dominant species in the sand-dunes and neighbouring parts of the salt-marsh on Schiermonnikoog.

     

How extreme summer weather may limit control of Festuca paniculata by mowing in subalpine grasslands

Background: The tussock grass Festuca paniculata can become strongly dominant in subalpine grasslands after cessation of mowing. The depletion of water-soluble carbohydrate (WSC) reserves has been suggested as a mechanism by which mowing can contain this species. By affecting plant physiology and especially by favouring WSC accumulation, extreme summer weather (i.e. exceptionally hot and dry) could however counterbalance the effects of mowing on WSC reserves in F. paniculata. The relevance of this hypothesis needs to be tested in the current context of climate and land-use changes.

Aims: We investigated (1) the physiological mechanisms that control the growth of F. paniculata, (2) how they are affected by mowing and (3) whether extreme summer heat and drought could influence physiological mechanisms and thereby the ecological response of F. paniculata to mowing.

Methods: In a field experiment we manipulated weather and mowing during two summers. For current summer weather (W0), ambient temperature was unchanged and precipitation was adjusted on the past 30-year average. Extreme summer weather (W+) corresponded to a seasonal change (+1 °C, –80% in precipitation compared to W0) and a three-week heatwave (+4.3 °C) in the first year. In addition, vegetation was either mown at 5 cm in late summer (M) or left unmown (U). Concentrations and absolute contents of WSC contained in tiller bases, leaf nitrogen concentration (LNC), vegetative multiplication, plant growth and leaf senescence were measured from one to four times, depending on the variable considered, throughout the summer of the second year of the experiment.

Results: As compared to the unmown treatment, late-summer mowing decreased tillering, tussock size and LNC, regardless of the summer weather treatment. However, it depleted WSC pools, including fructans, only under current summer weather (W0).

Conclusions: These results suggest that extreme summer heat and drought could alleviate the sensitivity of F. paniculata to mowing. They raise the question of the consequences of recurrent summer extremes for conservation management in subalpine grasslands.     

Specific patterns of excavation in isolated ants

Summary The tunnels dug by isolated worker ants [Myrmica ruginodis Nylander,M. scabrinodis Nylander,Formica lemani Bondroit,F. fusca L. andLasius niger (L.)] have been studied photographically. Although there was much variation within species, certain interspecific differences in tunnel shape appeared. The tunnels ofL. niger are more spreading, longer and more convoluted than those of the other species, and often branch beneath the surface. The tunnels ofM. scabrinodis show the same features to a smaller degree. The tunnels ofF. fusca andF. lemani are straight, unbranched and vertical.

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Résumé Nous avons étudié par un moyen photographique les tunnels que creusent les ouvrières isolées deMyrmica ruginodis Nyl.,M. scabrinodis Nyl.,Formica fusca L.,F. lemani Bondroit etLasius niger (L.). Quoiqu'il y ait une variation intraspécifique très importante, nous avons constaté plusieurs différences entre ces espèces. Les tunnels deL. niger sont plus longs, plus ramifiés et moins rectilignes que chez les autres espèces. Les tunnels deM. scabrinodis montrent les mêmes caractéristiques, mais d'une façon moins prononcée. Les tunnels deFormica fusca etF. lemani sont plus on moins verticaux et rectilignes et ne se divisent pas.