The effect of ants on the seed dispersal cycle of the typical myrmecochorous <Emphasis Type="Italic">Ricinus communis</Emphasis>

The directed dispersal hypothesis has two components: (1) non-random seed deposition by a predicted vector, which removes greater amounts of seeds to specific sites, and (2) higher seed survival and seedling establishment in these specific sites. Several studies suggest that ants perform both tasks. This study was designed to cover the processes from post-dispersed seeds to established juvenile plants of a typical ant-dispersed species. Our main objective was to determine whether Ricinus communis benefits from directed dispersal by ants to maintain its populations in previously colonized habitats. We examined whether there were differences between ant nest pile mounds and their vicinities in the: (1) densities of seeds with and without elaiosome, seedlings and juveniles; (2) performance of post-dispersed seeds (without elaiosome), which may be affected by seed density, a key feature attracting seed predators; (3) nutrient quantities; (4) number of germinated seeds and juvenile biomass measurements; and (5) ant protection of seedlings from herbivores. There were more seeds without elaiosome, seedlings and juveniles in pile mounds, and seeds with elaiosome were equally distributed. There was no difference in the number of non-removed seeds in pile mounds and in their vicinities, and there was no tendency for this difference to increase or decrease with time or with initial seed density. Apparently, there was no difference in nutrient contents in soils of pile mounds and their vicinities. Likewise, there was no difference in the number of seeds germinated and in the biomass measurements of juveniles in both soils. Ants did not provide differential protection for seedlings in pile mounds against potential herbivores. The dispersal of Ricinus seeds by ants had a marked effect on the distribution pattern of the seeds, seedlings and juveniles of this species. However, there were no additional advantages for the seeds, seedlings and juveniles in pile mounds and, therefore, Ricinus does not benefit from directed dispersal by ants to maintain its populations in the study sites.     

Testing the directed dispersal hypothesis: are native ant mounds (Formica sp.) favorable microhabitats for an invasive plant?

Ant-mediated seed dispersal may be a form of directed dispersal if collected seeds are placed in a favorable microhabitat (e.g., in or near an ant nest) that increases plant establishment, growth, and/or reproduction relative to random locations. We investigated whether the native ant community interacts with invasive leafy spurge (Euphorbia esula) in a manner consistent with predictions of the directed dispersal hypothesis. Resident ants quickly located and dispersed 60% of experimentally offered E. esula seeds. Additionally, 40% of seeds whose final deposition site was observed were either brought inside or placed on top of an ant nest. Seed removal was 100% when seeds were placed experimentally on foraging trails of mound-building Formica obscuripes, although the deposition site of these seeds is unknown. Natural density and above-ground biomass of E. esula were greater on Formica mound edges compared to random locations. However, seedling recruitment and establishment from experimentally planted E. esula seeds was not greater on mound edges than random locations 3 m from the mound. Soil from Formica mound edges was greater in available nitrogen and available phosphorus relative to random soil locations 3 m from the mound. These results suggest Formica ant mounds are favorable microhabitats for E. esula growth following seedling establishment, a likely consequence of nutrient limitation during plant growth. The results also indicate positive species interactions may play an important role in biological invasions.     

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.     

Impact of Formica exsecta Nyl. on seed bank and vegetation patterns in a subalpine grassland ecosystem

The mound building ant Formica exsecta Nyl. is widely distributed in grassland ecosystems of the Central European Alps. We studied the impact of these ants on seed bank and vegetation patterns in a 11 ha subalpine grassland, where we counted over 700 active ant mounds. The mounds showed a distinct spatial distribution with most of them being located in tall‐grass, which was rarely visited by ungulates (red deer; Cervus elaphus L.). Heavily grazed short‐grass, in contrast, seemed to be completely avoided by ants as only few mounds were found in this vegetation type. The species composition of the ant mound and grassland seed banks was quite similar, i.e. from 15 common plant species 12 were found in both seed bank types. We found the same proportions of myrmecochorous seeds in ant mound and grassland soil samples. In contrast, the number of seeds was 15 times higher in mound compared with the grassland soil samples. Also, the vegetation growing on ant mounds significantly differed from the vegetation outside the mounds: graminoids dominated on ant mounds, herbaceous and myrmecochorous species in the grassland vegetation. We found significant continuous changes in vegetation composition on gradients from the ant mound centre to 1 m away from the mound edge. Overall, F. exsecta was found to have a considerable impact on seed bank and vegetation patterns in the grassland ecosystem studied. These insects not only altered grassland characteristics in the close surrounding of their mounds, but also seem to affect the entire ecosystem including, for example, the spatial use of the grassland by red deer.     

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.     

Indirect effects of granivory by harvester ants: plant species composition and reproductive increase near ant nests

Summary Of 36 plant species surveyed, 6 were significantly associated with nests of the desert seed-harvester ant Veromessor pergandei or Pogonomyrmex rugosus; two other plant species were significantly absent from ant nests. Seeds of two common desert annuals, Schismus arabicus and Plantago insularis, realize a 15.6 and 6.5 fold increase (respectively) in number of fruits or seeds produced per plant growing in ant nest refuse piles compared to nearby controls. Mass of individual S. arabicus seed produced by plants growing in refuse piles also increased significantly. Schismus arabicus, P. insularis and other plants associated with ant nests do not have seeds with obvious appendages attractive to ants. Dispersal and reproductive increase of such seeds may represent a relatively primitive form of ant-plant dispersal devoid of seed morphological specializations. Alternatively, evolution of specialized seed structures for dispersal may be precluded by the assemblage of North American seed-harvester ants whose workers are significantly larger than those ants normally associated with elaiosome-attached seed dispersal. Large worker size may permit consumption of elaiosome and seed.     

Vegetation of ant-hills in a mountain grassland:effects of mound history and of dominant ant species

Vegetation in grasslands with well-developed long-lastingant-hills in the Slovenské Rudohorie Mts., Slovakia, was studiedin relation to (i) position on the mound, (ii) ant speciesforming the mound, and (iii) history of the mound. Permanent plotrecordings of mound size and dominant ant species started fifteen years priorthe study began provided information on the history of individual mounds.The mound vegetation bears a striking similarity to vegetation insimilar habitats across a large part of Europe due to presence of species suchas Agrostis capillaris, Dianthusdeltoides, Polytrichum commune agg.,Thymus pulegioides, and Veronicaofficinalis. Out of the three major ant species-groups presentat the site (Lasius flavus, Tetramoriumcaespitum and Formica spp.), L.flavus had the most pronounced and the most lasting effect on themound vegetation. The dominance of the plant species listed above increased withthe time span over which the mound was inhabited by L.flavus. The effects of other species on vegetation composition,though discernible from short-term observation, disappeared over severalyears. The mounds proper did not differ from the undisturbed grassland in theproportion of myrmecochorous plants or plants with specific seed size ordormancy type. However, there was a highly significant concentration ofmyrmecochorous plants in the grassland patches immediately neighbouring themounds; this is likely to be due to seeds deposited there by the workers fromthe nest after the elaiosomes had been consumed. The mound vegetation wascomposed mainly of species with long stolons or rhizomes; however, there was nosignificant difference in formation type or length of stolons/rhizomesbetween mounds and the rest of the grassland or among mounds formed by differentant species.     

The effects of the red imported fire ant on seed fate in the longleaf pine ecosystem

The natural patterns of myrmecochory are disrupted by the dominance of red imported fire ants (Solenopsis invicta) in the southeastern United States. This leads to questions about the role of fire ants as seed dispersers. We examined the fate of ant-dispersed seed in the longleaf pine ecosystem. First, we determined removal rates for a suite of common ground cover species. Then, we verified the final location of removed seeds by using a wax cast to examine nest contents, and locating dyed seeds deposited in trash piles on the ground surface. Finally, we determined if the germination rate of seeds deposited by fire ants was affected by ant dispersion. Fire ants were most attracted to elaiosome-bearing seed and collected nonelaiosome-bearing seed at a much lower rate. No seeds were found in the contents of wax castings of fire ant nest chambers, suggesting that seed is not stored within the nest. Of the dyed seeds that we presented to fire ants, 30–40 % were recollected in surface trash piles in the mound vicinity within 1 week following removal. Undiscovered seeds were considered destroyed or buried in foraging tunnels. A small percentage of the deposited seeds were able to germinate, but there was no difference in the percent germination between seeds manipulated by fire ants and the control. Low germination was likely due to a high percentage of immature seeds used in the study. Our findings support a growing body of evidence that fire ants facilitate the movement of seeds in the longleaf pine ecosystem.     

Secondary seed dispersal by ants in Neotropical cerrado savanna: species‐specific effects on seeds and seedlings of Siparuna guianensis (Siparunaceae)

1. Most woody plant species in tropical habitats are primarily vertebrate‐dispersed, but interactions between ants and fallen seeds and fruits are frequent. This study assesses the species‐specific services provided by ants to fallen arillate seeds of Siparuna guianensis, a primarily bird‐dispersed tree in cerrado savanna. The questions of which species interact with fallen seeds, their relative contribution (versus vertebrates) to seed removal, and the potential effects on seedling establishment are investigated. 2. Seeds are removed in similar quantities in caged and control treatments, suggesting that ants are the main dispersers on the ground. Five ant species attended seeds. Pheidole megacephala (≈0.4 cm) cooperatively transported seeds, whereas the smaller Pheidole sp. removed the seed aril on spot. Large (> 1.0 cm) Odontomachus chelifer, Pachycondyla striata, and Ectatomma edentatum individually carried seeds up to 4 m. Bits of aril are fed to larvae and intact seeds are discarded near the nest entrance. 3. Overall, greater numbers of seedlings were recorded near ant nests than in control plots without nests. This effect, however, was only detected near P. megacephala and P. striata nests, where soil penetrability was greater compared with controls. Soil nutrients did not differ between paired plots. 4. This study confirms the prevalence of ant–seed interactions in cerrado and shows that ant‐derived benefits are species‐specific. Ant services range from seed cleaning on the spot to seed displacement promoting non‐random spatial seedling recruitment. Although seed dispersal distances by ants are likely to be shorter than those by birds, our study of S. guianensis shows that fine‐scale ant‐induced seed movements may ultimately enhance plant regeneration in cerrado.     

Seedling recruitment in a semi‐arid Patagonian steppe: Facilitative effects of refuse dumps of leaf‐cutting ants

Question: What is the influence of refuse dumps of leaf‐cutting ants on seedling recruitment under contrasting moisture conditions in a semi‐arid steppe? Location: Northwestern Patagonia, Argentina. Methods: In a greenhouse experiment, we monitored seedling recruitment in soil samples from refuse dumps of nests of the leaf‐cutting ant Acromyrmex lobicornis and non‐nest sites, under contrasting moisture conditions simulating wet and dry growing seasons. Results: The mean number of seedling species and individuals were higher in wet than in dry plots, and higher in refuse dump plots than in non‐nest soil plots. The positive effect of refuse dumps on seedling recruitment was greater under low moisture conditions. Both the accumulation of discarded seeds by leaf‐cutting ants and the passive trapping of blowing‐seeds seems not explain the increased number of seeds in refuse dumps. Conversely, refuse dumps have higher water retention capacity and nutrient content than adjacent non‐nest soils, allowing the recruitment of a greater number of species and individual seedlings. Conclusions: Nests of A. lobicornis may play an important role in plant recruitment in the study area, allowing a greater number of seedlings and species to be present, hence resulting in a more diverse community. Moreover, leaf‐cutting ant nests may function as nurse elements, generating safe sites that enhance the performance of neighbouring seedlings mainly during the driest, stressful periods.     

Positive interactions between desert granivores: localized facilitation of harvester ants by kangaroo rats

Facilitation, when one species enhances the environment or performance of another species, can be highly localized in space. While facilitation in plant communities has been intensely studied, the role of facilitation in shaping animal communities is less well understood. In the Chihuahuan Desert, both kangaroo rats and harvester ants depend on the abundant seeds of annual plants. Kangaroo rats, however, are hypothesized to facilitate harvester ants through soil disturbance and selective seed predation rather than competing with them. I used a spatially explicit approach to examine whether a positive or negative interaction exists between banner-tailed kangaroo rat (Dipodomys spectabilis) mounds and rough harvester ant (Pogonomyrmex rugosus) colonies. The presence of a scale-dependent interaction between mounds and colonies was tested by comparing fitted spatial point process models with and without interspecific effects. Also, the effect of proximity to a mound on colony mortality and spatial patterns of surviving colonies was examined. The spatial pattern of kangaroo rat mounds and harvester ant colonies was consistent with a positive interspecific interaction at small scales (<10 m). Mortality risk of vulnerable, recently founded harvester ant colonies was lower when located close to a kangaroo rat mound and proximity to a mound partly predicted the spatial pattern of surviving colonies. My findings support localized facilitation of harvester ants by kangaroo rats, likely mediated through ecosystem engineering and foraging effects on plant cover and composition. The scale-dependent effect of kangaroo rats on abiotic and biotic factors appears to result in greater founding and survivorship of young colonies near mounds. These results suggest that soil disturbance and foraging by rodents can have subtle impacts on the distribution and demography of other species.     

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. Received: 21 November 1996 / Accepted: 3 April 1997     

Seed handling behaviours of native and invasive seed‐dispersing ants differentially influence seedling emergence in an introduced plant

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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.     

SEED DISPERSAL OF TRILLIUM OVATUM (LILIACEAE) IN SECOND-GROWTH REDWOOD FORESTS

Trillium ovatum (Liliaceae) is myrmecochorous: its seeds bear large elaiosomes that are attractive to ants. Nevertheless, in coastal second-growth redwood forests of northern California, most seedlings occur in mixed-age clusters close to potential parents, suggesting that seed dispersal is limited. Ants were absent or rare at two relatively cool, moist study sites. At these sites, most seeds either eventually fell passively from fruits or were knocked to the ground by banana slugs that foraged on the elaiosomes. At two warmer, drier sites, a single species of ant, Lasius pallitarsis, dispersed the seeds but tended to remove the elaiosomes before returning to the nest. Thus at all sites a large number of seeds remained close to adults, accounting for the observed pattern of seedling distribution. The dispersal adaptations of T. ovatum and other redwood forest myrmecochores probably evolved in forests where seed-carrying ants were more common.     

Effects of harvester ants on plant species distribution and abundance in a serpentine grassland

Seed harvesting ants can have important effects on the composition and structure of plant communities. We investigated two effects of Messor andrei, the black seed-harvesting ant, on a serpentine grassland plant community in northern California. First, to determine if selective seed predation by ants affects plant community composition, we excluded harvester ants from 1-mediameter circular plots of grassland. Abundances of all species on these plots and on control plots were measured before and after exclosure. Second, to determine if M. andrei nest mounds affect plant community composition, we compared plant species abundances on and off nest mounds. M. andrei deposit large amounts of organic matter on their nest mounds over a foraging season, so mounds may alter the edaphic environment. The exclusion of seed-harvesting activity did not cause changes in the plant community. Nest mounds had a strong effect on plant communities: there were many more grasses and fewer forbs on ant mounds, although at least one forb, Lepidium nitidum, produced twice as many seeds when it grew on nest mounds. We found that nest mounds formed islands of higher-temperature soil in the serpentine grassland. Received: 31 March 1997 / Accepted: 6 May 1997     

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.     

Thermoregulatory brood transport in the fire ant, <Emphasis Type="Italic">Solenopsis invicta</Emphasis>

Nest structure in ants is often designed to optimize the colony’s ability to thermoregulate, and this specialization is most highly developed in mound-building ant species. Solenopsis invicta invest a large amount of energy in building mounds and transporting their brood up and down in their nests as a means of thermoregulation. Because few ant species build true mounds, we wanted to determine the effectiveness of these mounds in harvesting solar heat as well as to distinguish what factors (temperature vs. circadian rhythm) govern where fire ants place their brood in the mound and when they place it. We measured temperature patterns in the mound over several days at different depths and under different conditions (under direct sunlight or shade), and then conducted a series of field experiments to manipulate the orientation and time of heating. On cool mornings in spring or fall, surface temperatures of the mound rise at the fastest rate on the side receiving the most direct sunlight (usually the south side). This heating causes a temperature gradient through different depths in the mound, and shows little difference from outside ground temperature at a depth greater than ~40 cm inside the nest. In the morning, fire ants move their brood up into the mound on the side most directly heated, and when temperatures exceed optimal (~32°C) they move their brood down the temperature gradient to lower depths in the nest. In addition to this, mound temperature does not only increase due to direct sunlight, but temperature also increases higher than ground temperatures when the mound is in the shade due to its low specific heat. Experiments in which sunlight was mirrored to the normally shaded side of the mound, or when mounds were heated at night, revealed that S. invicta primarily track temperature patterns and do not rely on behavioral habits or circadian rhythms for the thermoregulatory transport of their brood. When mounds were shaded, S. invicta brood was evenly distributed directly under the surface of the mound rather than aggregating towards a specific side. The fire ant mound is important for thermoregulation because, compared to moundless subterranean nests, it absorbs heat more rapidly both in direct sunlight and shady conditions. Temperature tracking within the nest is key to understanding thermoregulatory placement of fire ant brood, as well as insight into the production of sexual brood and reproduction. Received 9 August 2007; revised 31 January 2008; accepted 7 February 2008.     

Ants accelerate succession from mountain grassland towards spruce forest

Question: What is the role of mound‐building ants (Lasius flavus) in successional changes of a grassland ecosystem towards a spruce forest? Location: Slovenské Rudohorie Mountains, Slovakia; ca. 950 m a.s.l. near the Obrubovanec point (1020 m a.s.l.; 48°41′N, 19°39′E). Methods: Both chronosequence data along a successional gradient and temporal data from long‐term permanent plots were collected on ants, spruce establishment, and vegetation structure, together with additional data on spruce growth. Results: There are more spruce seedlings on ant mounds (4.72 m^?2) than in the surrounding vegetation (0.81 m^?2). Spruce seedlings grow faster on these mounds compared to surrounding areas. The first colonization wave of seedlings was rapid and probably occurred when grazing prevailed over mowing. Ant colony presence, mound volume, and plant species composition change along the successional gradient. Mounds become bigger when partly shaded but shrink in closed forest, when ant colonies disappear. Shade‐tolerant acidophylic species replace grassland plants both on the mounds and in surrounding areas. Conclusions: The massive occurrence of Lasius flavus anthills contributes to a runaway feedback process that accelerates succession towards forest. The effect of ants as ecosystem engineers is scale‐dependent: although they stabilize the system at the scale of an individual mound, they may destabilize the whole grassland system over a longer time scale if combined with changes in mowing regime.     

Myrmecochory in Polygala vulgaris L., Luzula campestris (L.) DC. and Viola curtisii Forster in a Dutch dune area

Summary Seed dispersal by ants in Polygala vulgaris, Luzula campestris and Viola curtisii was studied in a primary dune valley on the island of Terschelling, The Netherlands. Normally developed seeds of all three species are taken by the ants into their nests. The ants show a distinct preference for the seeds of the specialized myrmecochore Polygala vulgaris, as compared with the two diplochorous species. It could be demonstrated that the elaiosome is the attractive part of the seed. Mapping studies demonstrate that the dispersal of the seeds by ants has a marked effect on the distribution pattern of the standing population of Polygala and Viola. Adult plants are often found on or close to the active nest mounds of all ant species present, while the growing sites of juvenile individuals and seedlings are practically restricted to the nest environment. The nests of two of the seed-dispersing ant species, viz., those of Lasius niger and Tetramorium caespitum, show differences in soil chemistry with the surroundings. The ant nests are significantly richer in some essential plant macronutrients, such as phosphate, potassium and nitrate. The advantage of myrmecochory in the dune area of Terschelling is discussed.