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.     

Opening myrmecochory’s black box: what happens inside the ant nest?

In the process of seed dispersal by ants (myrmecochory), foragers bring diaspores back to their nest, then eat the elaiosome and usually reject viable seeds outside the nest. Here, we investigate what happens inside the nest, a barely known stage of the myrmecochory process, for two seed species (Viola odorata, Chelidonium majus) dispersed either by the insectivorous ant Myrmica rubra or by the aphid-tending ant Lasius niger. Globally, elaiosome detachment decreased ants’ interest towards seeds and increased their probability of rejecting them. However, we found marked differences in seed management by ants inside the nest. The dynamics of elaiosome detachment were ant- and plant-specific whereas the dynamic of seed rejection were mainly ant-specific. Seeds remained for a shorter period of time inside the nest of the carnivorous ant Myrmica rubra than in Lasius niger nest. Thus, elaiosome detachment and seed rejection were two competing dynamics whose relative efficiency leads to variable outcomes in terms of types of dispersed items and of nutrient benefit to the ants. This is why some seeds remained inside the nest even without an elaiosome, and conversely, some seeds were rejected with an elaiosome still attached. Fresh seeds may be deposited directly in contact with the larvae. However, the dynamics of larvae-seeds contacts were also highly variable among species. This study illustrates the complexity and variability of the ecological network of ant–seed interactions.     

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.     

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.     

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     

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

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Dispersal distance as a benefit of myrmecochory

Summary Nutrient-enrichment and predator avoidance are generally considered the major benefits of myrmecochory, but this is apparently not so in Australia where some of the greatest known concentrations of myrmecochorus plants occur. Here I demonstrate that distance dispersal is a potential benefit of myrmecochory in the Australian environment. Although mean dispersal distance at a site in southeastern Australia was only 2.1 m, the dispersal curve was characterised by a narrow peak and long tail. A dispersal curve of this shape has been shown by Green (1983) to be optimal when safe sites for seedling establishment are rare, as is typically the case for Australian myrmecochores in the absence of fire. Both mean disperal distance and shape of the dispersal curve are influenced strongly by nest density and dispersion, population size, and territoriality of seed-dispersing ants. I argue that distance dispersal is likely to be a benefit of myrmecochory throughout Australia, independent of any targeting of seeds to ant nests.     

Geographical and interspecific variation and the nutrient‐enrichment hypothesis as an adaptive advantage of myrmecochory

In myrmecochory, the relocation of diaspores to ant nests may lead to the enhancement of plant fitness because ant nests and their middens are often richer in essential nutrients than surrounding areas. This idea is the basis of the nutrient‐enrichment hypothesis (NEH), which suggests that nutrient enrichment may be a major selective influence in the evolution of myrmecochory. However, there is little evidence regarding whether the greater plant performance and fitness enhancement in ant nests is due to nutrient enrichment or other benefits of directed dispersal. Here, we present the results of a large‐scale seed‐sowing experiment that tests the NEH in the ant‐dispersed perennial herb Helleborus foetidus, exploring geographical and inter‐ant taxa variation. Experiments were conducted in three well‐separated regions of the Iberian Peninsula, targeting the nests of major and minor local ant dispersers (nine ant species in total) and the soil beneath maternal plants as seed destinations. Seedling emergence, survival and early establishment rates, as well as variation in soil characteristics, were obtained for each seed destination at each region. Our results do not fully support the NEH in our study system. Instead, we found that the advantage of ant nest soil for establishment in H. foetidus was conditional. Differences in soil fertility and concomitant differences in seedling establishment between ant nests and beneath the canopy of maternal plants were observed in some regions and for some ant species, but not in others. Thus, the conditional outcomes arise from inconsistencies among regions, between stages of seedling regeneration and among ant species in the advantages of being dispersed to nests. Because variation in the guilds of ant dispersers of myrmecochore plants across their ranges is common, this study illustrates the need to consider geographic and inter‐ant taxa variation for a complete evaluation of the NEH.     

The effects of 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.     

Why do more plant species use ants for dispersal on infertile compared with fertile soils?*

Myrmecochores are plant species that bear seeds with food-bodies adapting them for dispersal by ants. Within Australia and South Africa, myrmecochores account for a large percentage of the flora in sclerophyll vegetation on very infertile soils. On fertile soils, there are few myrmecochores and more species with fleshy fruits adapted for dispersal by vertebrates. This effect of very infertile soils may also account for the high incidence of myrmecochores in the floras of Australia and South Africa compared with other continents. The taxonomic distribution of myrmecochory shows it has evolved many times within the Australian flora. Evidence has been collected in relation to eight hypotheses that might account for the prevalence of myrmecochory on very infertile soils: (1) Myrmecochore seeds do not appear to be relocated to nutrient-enriched microsites. Seed-removing ant species relocate their nest entrances frequently; active ant nests are not nutrient-enriched; and seedlings emerging after fire are not located in nutrient-enriched soil. (2) Traffic of seed-removing ants is not greater on infertile than on fertile soils. (3) Burial to avoid predation by small mammals is not a significant factor for seeds in Australian vegetation. (4) Experiments in which diaspore traits are manipulated support the idea that a larger food body increases the likelihood that a diaspore will be taken by a seed-disperser ant species that will not eat the embryo, rather than by a seed-predator ant. However, evidence so far does not support the hypothesis that, on very infertile soils, seed-disperser ants are consistently more available than seed-predator ants. (5) Removal rates of fruits adapted for dispersal by vertebrates were, on average, two and a half times greater in vegetation on fertile soils. Birds were the main removers. Our current opinion is that the fruit-removing bird assemblage is more likely to be a consequence of the high incidence of species with vertebrate-adapted fruits, rather than the reverse. (6) Fleshy fruits are more expensive in potassium than food bodies for ants, but not in nitrogen or phosphorus. This might be a reason why fleshy fruits are uneconomic on very infertile soils. (7) Species with smaller embryo-plus-endosperm weight are relatively more likely to be adapted for dispersal by ants rather than vertebrates. However, differences in the frequency distribution of embryo-plus-endosperm weights between infertile and fertile soils are moderate in the Sydney area. An indirect association between soil fertility and dispersal mode via embryo-plus-endosperm weight cannot account for much of the difference in dispersal spectrum. (8) Species growing to less than 2 m tall are relatively more likely to be adapted for dispersal by ants rather than vertebrates, and also account for more of the flora on infertile than on fertile soils. This indirect correlation is capable of accounting for as much as 80% of the higher incidence of myrmecochory on infertile soils.     

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

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

Does the morphology of animal foraging pits influence secondary seed dispersal by ants?

Secondary seed dispersal by ants (myrmecochory) is an important process in semi‐arid environments where seeds are transported from the soil surface to an ant nest. Microsites from which ants often remove seeds are the small pits and depressions made by native and exotic animals that forage in the soil. Previous studies have demonstrated greater seed retention in the pits of native than exotic animals, but little is known about how biotic factors such as secondary seed dispersal by ants affect seed removal and therefore retention in these foraging pits. We used an experimental approach to examine how the morphology of burrowing bettong (Bettongia lesueur), greater bilby (Macrotis lagotis), short‐beaked echidna (Tachyglossus aculeatus) and European rabbit (Oryctolagus cuniculus) foraging pits and ant body size influenced ant locomotion and seed removal from pits along an aridity gradient. Ants took 3.7‐times longer to emerge from echidna pits (19.6 s) and six‐times longer to emerge from bettong pits (30.5 s) than from rabbit pits (5.2 s), resulting in lower seed removal from bettong pits than other pit types. Fewer seeds were removed from pits when cages were used to exclude large body‐sized (>2 mm) ants. Few seeds were removed from the pits or surface up to aridity values of 0.5 (humid and dry sub‐humid), but removal increased rapidly in semi‐arid and arid zones. Our study demonstrates that mammal foraging pit morphology significantly affects ant locomotion, the ability of ants to retrieve seeds, and therefore the likelihood that seeds will be retained within foraging pits.     

Ant behaviour and seed morphology: a missing link of myrmecochory

Seed dispersal by ants (myrmecochory) is mediated by the presence of a lipid-rich appendage (elaiosome) on the seed that induces a variety of ants to collect the diaspores. When seeds mature or fall onto the ground, these ant species transport them to their nest. After eating the elaiosome, the seed is discarded in nest galleries or outside, in the midden or farther away, where seeds can potentially germinate. The final location of seeds with their elaiosomes removed was evaluated to assess the importance of possible handles (structures that ants can grasp to carry) in transporting ants during re-dispersal experiments of seeds from nests of six species of ants. The results indicate that seeds remained within the nest because the ants were not able to transport them out of the nest. As a consequence of the elaiosome being removed, small ant species could not take Euphorbia characias seeds out of their nests. Only large ant species could remove E. characias seeds from their nests. Attaching an artificial handle to E. characias seeds allowed small ant species to redistribute the seeds from their nests. On the other hand, Rhamnus alaternus seeds that have a natural handle after the elaiosome removal were removed from the nests by both groups of ant species. If a seed has an element that acts as a handle, it will eventually get taken out of the nest. The ants’ size and their mandible gap can determine the outcome of the interaction (i.e. the pattern of the final seed shadow) and as a consequence, could influence the events that take place after the dispersal process.     

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

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

Impact of seed abundance on seed processing and dispersal by the red ant Myrmica rubra

1. Myrmecochory sensu stricto is an ant–plant mutualism in which non‐granivorous ants disperse plant diaspores after feeding on their nutrient‐rich seed appendage, the elaiosome. Phenological traits associated with the diaspore can influence the behaviour of ants and thus their ultimate efficiency as seed dispersers. 2. This study investigated how a contrasting availability of seeds (20 vs. 200 seeds) from the diplochorous Chelidonium majus (Papaveraceae, Linnaeus) plant species influences the behaviour of Myrmica rubra (Formicidae, Linnaeus) ants, from the retrieval of seeds until their dispersal outside the ant nest. 3. Regardless of seed abundance, the ants collected the first diaspores at similar rates. Then, seed retrieval sped up over time for large seed sources until satiation took place with only one‐third of the tested colonies wholly depleting abundant seed sources. 4. No active recruitment by trail‐laying ants was triggered, even to an abundant seed source 5. In both conditions of seed abundance, the majority of the diaspores retrieved inside the nest were discarded with the elaiosome removed and were dispersed at similar distances from the nest. 6. The paper concludes with a discussion of how the quantity of seeds released by a plant with a dual mode of dispersal can potentially influence the behaviour of ant dispersers and hence the dispersal efficiency derived from myrmecochory.     

Invasive cutleaf coneflower seeds cached in nest boxes: possibility of dispersal by a native rodent

Invasive species present serious problems for ecosystems and economies. One such species, the invasive cutleaf coneflower (Rudbeckia laciniata L.), has several modes of seed dispersal, namely autochory, anemochory, epizoochory, myrmecochory and anthropochory. Because we found caches of this invasive plant's seeds in two nest boxes, suggesting the possibility of synzoochory, we report here the details of the caches. In one of the boxes, many of the seeds were cached in autumn and eaten during the winter. Automatic sensor cameras directed at the boxes revealed that three rodent species and two avian species visited the boxes. The characteristics of the caches and the nest‐box visitors suggested that the small Japanese field mouse (Apodemus argenteus Temm.) was the animal most likely to have cached the seeds in the boxes.     

Testing myrmecochory from the ant’s perspective: The effects of Datura wrightii and D. discolor on queen survival and brood production in Pogonomyrmex californicus

Interspecific interactions are often assumed to be mutualistic if one species appears to benefit. However, most studies do not test whether both participants benefit. Myrmecochory, or seed dispersal by ants, is characterized by a lipid-rich appendage, or elaiosome, on a seed. Typically, ants gather the diaspores (i.e., seeds with elaiosomes), carry them to the nest, consume the elaiosome, and discard the seed unharmed either inside the nest or on a refuse pile. The benefit to the ants is presumably the nutritional content of the elaiosome, whereas benefits to the plant include dispersal from the parent plant, protection from predators, reduced seedling competition, protection from fire, or transportation to nutrient-rich microsites. Most studies of myrmecochory focus on potential benefits to the plants and simply assume that ants receive a benefit from consuming elaiosomes. I tested whether Pogonomyrmex californicus benefits from consuming Datura wrightii and D. discolor elaiosomes by raising newly-mated queens (i.e., foundresses) on different diets and measuring their survival and brood production. Foundresses reared solely on D. wrightii or D. discolor had similar probabilities of surviving and producing brood as foundresses fed a standard diet, but the number and developmental stage of the brood produced was severely reduced. Because the initial number of brood produced is critical for successful colony establishment, the future fitness of foundresses consuming only Datura is likely reduced. In addition, adding Datura to a standard diet did not increase queen survival or brood production. Although it is possible that Datura may help sustain a colony through periods of scarcity, P. californicus do not appear to receive nutritional benefits from myrmecochorous interactions with Datura in the northern Sonoran Desert. Received 4 July 2005; revised 17 April 2006; accepted 9 May 2006.     

Are subordinate ants the best seed dispersers? Linking dominance hierarchies and seed dispersal ability in myrmecochory interactions

True myrmecochory involves the dispersal of elaiosome-bearing seeds by ants. Between the guild of ants that are attracted to these seeds, only a few of them will act as effective dispersers, that is, transporting the seeds to suitable sites (the nests) for germination and plant establishment. Ant communities are known to be highly hierarchical, and subordinate ants quickly deliver resources to their nest rather than consuming it on-site, thereby avoiding encounters with more dominant species. As a result of a series of studies that were carried out during summer in semi-arid Northwest Argentina, we have found that the most important seed disperser of the myrmecochorous plant Jatropha excisa Griseb. (Euphorbiaceae), the ant Pogonomyrmex cunicularius pencosensis Forel, was the most subordinate species during interspecific interactions. The daily timing of release of the J. excisa seeds through ballistic dispersal increased their probability of being removed by the highly thermophilic P. cunicularius pencosensis. Foraging during the warmest hours of the day allowed P. cunicularius pencosensis ants to avoid the risk of interference competition with dominant species, which also behaved as elaiosome predators. As a conclusion, subordinance behaviour appears to be integral to successful myrmecochory, and also the timing of seed release plays a key role in shaping the dynamics of myrmecochorous interactions. Therefore, ant-dispersed plants should not only favour their discovery by subordinate ants, but also should present their seeds at those times of the day when the behaviourally dominant ants are less active.     

Seasonally different modes of seed dispersal in the prostrate annual, <Emphasis Type="Italic">Chamaesyce maculata</Emphasis> (L.) Small (Euphorbiaceae), with multiple overlapping generations

The modes of seed dispersal in the prostrate annual, Chamaesyce maculata, with multiple overlapping generations were investigated. We found that C. maculata has two modes of seed dispersal; autochory in the summer and myrmecochory in the autumn. Seasonally different modes of seed dispersal have not been known in other plant species. The large proportion of seeds produced in the summer was positioned further than the expanse of the parent plants by automatic mechanical seed dispersal. Therefore, autochory would be effective for avoiding competition between parent and offspring plants. No autochory occurred in the seeds produced in the autumn. The seeds of C. maculata without an elaiosome were dispersed by seed-collecting ants in the autumn. Although 18 ant species in total visited the plants of C. maculata at the 50 sites investigated, only two ant species, Tetramorium tsushimae and Pheidole noda frequently carried the seeds of C. maculata. The low frequency of seeds carried out of the nest by P. noda suggests that the workers of P. noda carry the seeds as food into their nest. So, P. noda might be a less effective seed disperser for C. maculata, corresponding to the effectiveness of seed dispersal by harvester ants. However, T. tsushimae ants frequently carried the seeds into and out of their nest, suggesting that T. tsushimae do not regard the seeds of C. maculata as a food resource. Thus, T. tsushimae may be an effective seed disperser for C. maculata.     

Heuweltjies (earth mounds) in the Clanwilliam district,Cape Province,South Africa: 4000-year-old termite nests

Summary Examination of eroded and intact earth mounds in the Clanwilliam district, South Africa, indicates that they are well-established active termitaria of the harvester termite Microhodotermes viator. Unoccupied lower portions of the mounds contain ubiquitous trace-fossil evidence of earlier inhabitation by the same species. Previous studies indicating that fossorial molerats played a major role in the formation of the mounds are not supported by the observations presented here. Calcretization of the basal parts of the earth mounds has been caused by groundwater interaction with the more alkaline mound soil. ¹⁴C dating of this calcrete indicates that the earth mounds have been in existence for at least 4000 years, an order of magnitude greater than any previously recorded longevity for termitarium inhabitation.