The possible advantage of myrmecochory in diplochorous species: A test on two Mediterranean Euphorbia species

Myrmecochory commonly complements the advantages of ballistic dispersal in diplochorous species. We studied the role of the elaiosome in two populations of the two diplochorous Mediterranean spurges Euphorbia boetica and E. nicaeensis, which share an efficient ballistic dispersal mechanism followed by secondary removal by ants. They differ in elaiosome persistence, as most E. boetica seeds lose the elaiosome during explosive dispersal. Self-assessed dietary preferences with seeds with and without elaiosomes of each species showed differences in behaviour among and within ant species. In general, the absence of elaiosome entailed a decrease in the number of disperser ant species interacting with the seeds, whereas the number of predatory ants remains invariable. However, in one population of E. nicaeensis, experimental elimination of the elaiosome did not affect seed removal by mutualistic ants. On the other hand, analysis of refuse piles of the granivorous Messor marocanus and M. bouvieri suggests that they act as seed predators in E. boetica, whereas unintentional dispersal can be important in E. nicaeensis. We suggest, therefore, that the presence of the elaiosome in the seeds of the studied spurges increases the interaction with disperser ant species, but the possible dispersal advantage is not apparent and is spatially variable.     

Ant-seed interactions: combined effects of ant and plant species on seed removal patterns

Seed dispersal by ants (i.e. myrmecochory) is usually considered as a mutualism: ants feed on nutritive bodies, called elaiosomes, before rejecting and dispersing seeds in their nest surroundings. While mechanisms of plant dispersal in the field are well documented, the behaviour of the ant partner was rarely investigated in details. Here, we compared in laboratory conditions the foraging behaviour of two ant species, the omnivorous Lasius niger and the insectivorous Myrmica rubra to which seeds of two European myrmecochorous plants (Chelidonium majus and Viola odorata) were given. Ant colonies were simultaneously presented three types of items: entire seeds with elaiosome (SE), seeds without elaiosome (S) and detached elaiosomes (E). The presence of elaiosomes on seeds did not attract workers from a distance since ants first contact equally each type of items. Although ants are mass-recruiting species, we never observed any recruitment nor trail-laying behaviour towards seeds. For ants having contacted seed items, their antennation, manipulation and seed retrieval behaviour strongly varied depending on the species of each partner. Antennation behaviour, followed by a loss of contact, was the most frequent ant-seed interaction and can be considered as a “hesitation” clue. For both plant species, insectivorous Myrmica ants removed items in larger number and at higher speed than Lasius. This fits with the hypothesis of a convergence between odours of elaiosomes and insect preys. For both ant species, the small Chelidonium seeds were retrieved in higher proportion than Viola ones, confirming the hypothesis that ants prefer the higher elaiosome/diaspore-ratio. Thus, in these crossed experiments, the ant-plant pair Myrmica/Chelidonium was the most effective as ants removed quickly almost all items after a few antennations. The presence of an elaiosome body increased the seed removal by ants excepting for Myrmica which retrieved all Chelidonium seeds, even those deprived of their elaiosome. After 24 h, all the retrieved seeds were rejected out of the nest to the refuse piles. In at least half of these rejected items, the elaiosome was discarded by ants. Species-specific patterns and behavioural differences in the dynamics of myrmecochory are discussed at the light of ant ecology. Received 10 September 2007; revised 5 February 2008; accepted 5 March 2008.     

New mutualism for old: indirect disruption and direct facilitation of seed dispersal following Argentine ant invasion

The indirect effects of biological invasions on native communities are poorly understood. Disruption of native ant communities following invasion by the Argentine ant (Linepithema humile) is widely reported to lead indirectly to the near complete collapse of seed dispersal services. In coastal scrub in southeastern Australia, we examined seed dispersal and handling of two native and two invasive alien plant species at Argentine ant-invaded or -uninvaded sites. The Argentine ant virtually eliminates the native keystone disperser Rhytidoponera victoriae, but seed dispersal did not collapse following invasion. Indeed, Argentine ants directly accounted for 92% of all ant-seed interactions and sustained overall seed dispersal rates. Nevertheless, dispersal quantity and quality among seed species differed between Argentine ant-invaded and -uninvaded sites. Argentine ants removed significantly fewer native Acacia retinodes seeds, but significantly more small seeds of invasive Polygala myrtifolia than did native ants at uninvaded sites. They also handled significantly more large seeds of A. sophorae, but rarely moved them >5 cm, instead recruiting en masse, consuming elaiosomes piecemeal and burying seeds in situ. In contrast, Argentine ants transported and interred P. myrtifolia seeds in their shallow nests. Experiments with artificial diaspores that varied in diaspore and elaiosome masses, but kept seed morphology and elaiosome quality constant, showed that removal by L. humile depended on the interaction of seed size and percentage elaiosome reward. Small diaspores were frequently taken, independent of high or low elaiosome reward, but large artificial diaspores with high reward instead elicited mass recruitment by Argentine ants and were rarely moved. Thus, Argentine ants appear to favour some diaspore types and reject others based largely on diaspore size and percentage reward. Such variability in response indirectly reduces native seed dispersal and can directly facilitate the spread of an invasive alien shrub.     

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.     

SEED DISPERSAL IN VIOLA (VIOLACEAE): ADAPTATIONS AND STRATEGIES

Surveys of Viola dispersal mechanisms result in the distinction of two major adaptive syndromes: one purely myrmecochorous for the exploitation of seed-transporting ants, the other partially myrmecochorous (= diplochorous) for the explosive ejection of seeds followed by ant exploitation. Diplochory is exhibited by the majority of Viola species, but myrmecochory is exhibited only by eleven species with limited Eurasian distribution. Morphological and experimental evidence suggests the hypothesis that Viola is basically myrmecochorous but that different selective pressures, especially seed predation, have produced a clear divergence in dispersal systems. The majority of species, the diplochores, have evolved a system which combines ballistic and ant seed dispersal with predator avoidance. Diplochory itself may be a response to predation pressure. The minority of species are purely myrmecochorous, possibly highly coevolved with specific ant species, thus limiting the distribution of the Viola species concerned.     

Ant benefits in a seed dispersal mutualism

Myrmecochorous plant seeds have nutrient rich appendages, elaiosomes, which induce some ant species to carry the seeds back to their nest where the elaiosome is consumed and the seed is discarded unharmed. The benefits to plants of dispersal of their seeds in this way have been well documented, but the benefits to the ants from consuming the elaiosomes have rarely been measured and are less clear. Ant benefits from myrmecochory were investigated in a laboratory experiment using the ant Myrmica ruginodis and seeds of Ulex species. To separate the effects of elaiosome consumption on the development of newly produced larvae versus existing larvae, ten ‘Queenright’ colonies containing a queen were compared to ten ‘Queenless’ colonies. Six measures of colony fitness over a complete annual cycle were taken: sexual production, larval weight and number, pupal weight and number, and worker survival. Queenless colonies fed with elaiosomes produced 100.0±29.3 (mean ± SE) of larvae compared to non-elaiosome fed colonies which produced 49.6±19.0; an increase of 102%. Larval weight increased in both Queenright and Queenless colonies. In colonies fed with elaiosomes, larvae weighed 1.02±0.1 mg, but in non-elaiosome fed colonies larvae weighed 0.69±0.1 mg; an increase of 48%. The food supplement provided by Ulex elaiosomes was trivial in energetic terms, under the conditions of an ample diet, suggesting that these effects might be due to the presence of essential nutrients. Chemical analysis of Ulex elaiosomes showed the presence of four essential fatty acids and four essential sterols for ants.     

The role of ants and mammals in dispersal and post-dispersal seed predation of the shrubs Grevillea (Proteaceae)

The role seed predators play in influencing the dynamics of plant populations has been little studied in Australia. The interaction of ant dispersal and seed predation on the soil seedbank in six shrubby species of Grevillea from the Sydney region of southeastern Australia was examined in selective exclusion experiments, seed array trials and placement of single seeds on the ground.Two distinct seed types in Grevillea were examined and different seed dispersal and post-dispersal seed predation patterns were associated with each: (a) seeds lacking an elaiosome were not attractive to ants and annual seed losses of between 82 and 95% were found in vegetation unburnt for greater than 8 years. Native rodents, Rattus fuscipes, and macropods, Wallabia bicolor, were responsible for these seed losses; (b) seeds with an elaiosome were rapidly handled by ants. Two functional types of ants were recognised. Most encounters were by ants that were small (Local) relative to seed size and these ants simply removed the elaiosome in situ or moved seeds only small distances (<20 cm). Some 0–24% of ant/seed encounters were by large (Removalist) ant species that were capable of moving seeds back to nests. In addition, Rattus fuscipes and Wallabia bicolor consumed at least 32–68% of seeds of Grevillea species with an elaiosome.Ants may reduce the overall levels of seed predation where seeds moved by Removalist ant species escape predation and are deposited in safe sites, hence allowing more seeds to reach the persistent soil seedbank. Mammals do not consume all seeds when ants are excluded, allowing for the potential for some seed escape from predation after seeds are discarded by Local ant species.     

Pogonomyrmexcunicularius as the keystone disperser of elaiosome‐bearing Jatropha excisa seeds in semi‐arid Argentina

Myrmecochory or seed dispersal by ants is often described as a diffuse mutualism, because many of the ant species that function as partners are considered to be similar in terms of the frequency and consequences of their interactions. In this work, we test this assumption by conducting ant community surveys and seed removal experiments in six study sites located within a semi‐arid region of northwest Argentina. At each site, we characterized the ant assemblage that interacted with the seeds of Jatropha excisa Griseb. (Euphorbiaceae), an ant‐dispersed native shrub. Our results demonstrate that seed removal was dominated by one species, Pogonomyrmex cunicularius Mayr (Hymenoptera: Formicidae: Myrmicinae), which was responsible of 84% of the observed seed removal events. Although several ant species were attracted to the elaiosome‐bearing seeds of J. excisa, seed removal did not depend on ant community composition (species richness and ant activity) but was significantly influenced by the abundance of P. cunicularius. Its physical, behavioral, and ecological attributes are common with other ant species that have been characterized as keystone seed dispersers in other regions of the world. Nest feeding with marked seeds revealed that once P. cunicularius ants consume the elaiosomes, seeds are left inside the nests undamaged and at an appropriate depth for emergence. Our results support the hypothesis that myrmecochory is often an unevenly diffuse mutualism (i.e., one partner species is particularly important) and that at a local scale P. cunicularius is the keystone seed disperser of J. excisa.     

其它可利用食物对小花宽瓣黄堇(Corydalis giraldii Fedde)种子散布的影响

作为蚁播植物种子的重要传播者,蚂蚁不但取食种子上附着的油质体,也喜食其它富含蛋白质、脂类、糖和维生素等的食物,因此环境中其它可利用食物的存在可能会影响蚂蚁对种子的搬运进而影响种子散布,但目前对于这种影响是如何发生的仍不清楚。在野外研究了蚂蚁对小花宽瓣黄堇(Corydalis giraldii Fedde)种子、肉、蜂蜜、苹果、馒头等食物的趋性和偏好程度,以及添加食物后蚂蚁对种子的拜访频率和搬运效率,以揭示其它可利用食物如何影响蚂蚁觅食和取食偏好,进而影响小花宽瓣黄堇种子散布。结果显示,在所诱捕的8种蚂蚁中,玉米毛蚁(Lasius alienus(Foerster))和丝光蚁(Formica fusca Linnaeus)是小花宽瓣黄堇种子的主要搬运者,不同食物诱捕的玉米毛蚁数量无显著性差异(P0.05),但蜂蜜和苹果诱捕的丝光蚁数量均显著大于种子(P0.05)。玉米毛蚁和丝光蚁均为杂食性,在觅食中分别行使群体募集和简单协作性募集。在仅有种子的对照处理中,玉米毛蚁和丝光蚁对种子的拜访频率分别为(38.73±4.57)头和(30.8±2.87)头(40min,n=15),两种蚂蚁对种子的拜访频率差异不显著(P0.05);玉米毛蚁和丝光蚁搬运种子的效率分别为(33.87±4.22)粒和(16.27±3.35)粒(40min,n=15),玉米毛蚁的搬运效率显著高于丝光蚁(P0.05)。与对照相比,添加馒头、苹果和蜂蜜后丝光蚁对种子的拜访频率显著降低(P0.05),分别为(15.6±3.61)头、(9.07±1.4)头和(7.67±1.58)头(40min,n=15);添加苹果和蜂蜜后丝光蚁对种子的搬运效率显著降低(P0.05),分别为(3.47±1.17)粒和(2.87±0.9)粒(40min,n=15);添加不同食物后玉米毛蚁对种子的拜访频率和搬运效率均无显著变化(P0.05)。研究结果表明行使群体募集的玉米毛蚁比行使简单协作募集的丝光蚁有更高的种子搬运效率,添加食物后影响丝光蚁对种子的拜访频率和搬运效率,这说明其它可利用食物对小花宽瓣黄堇种子散布的影响与搬运蚂蚁的种类及其觅食的募集方式有关。研究结果可为进一步研究蚂蚁与植物(种子)间的互利共生关系及其影响因素提供资料。     

Seed dispersal by ants in the semi-arid Caatinga of North-East Brazil

BACKGROUND AND AIMS: Myrmecochory is a conspicuous feature of several sclerophyll ecosystems around the world but it has received little attention in the semi-arid areas of South America. This study addresses the importance of seed dispersal by ants in a 2500-km(2) area of the Caatinga ecosystem (north-east Brazil) and investigates ant-derived benefits to the plant through myrmecochory. METHODS: Seed manipulation and dispersal by ants was investigated during a 3-year period in the Xingó region. Both plant and ant assemblages involved in seed dispersal were described and ant behaviour was characterized. True myrmecochorous seeds of seven Euphorbiaceae species (i.e. elaiosome-bearing seeds) were used in experiments designed to: (1) quantify the rates of seed cleaning/removal and the influence of both seed size and elaiosome presence on seed removal; (2) identify the fate of seeds dispersed by ants; and (3) document the benefits of seed dispersal by ants in terms of seed germination and seedling growth. KEY RESULTS: Seed dispersal by ants involved one-quarter of the woody flora inhabiting the Xingó region, but true myrmecochory was restricted to 12.8 % of the woody plant species. Myrmecochorous seeds manipulated by ants faced high levels of seed removal (38-84 %) and 83 % of removed seeds were discarded on ant nests. Moreover, seed removal positively correlated with the presence of elaiosome, and elaiosome removal increased germination success by at least 30 %. Finally, some Euphorbiaceae species presented both increased germination and seedling growth on ant-nest soils. CONCLUSIONS: Myrmecochory is a relevant seed dispersal mode in the Caatinga ecosystem, and is particularly frequent among Euphorbiaceae trees and shrubs. The fact that seeds reach micro-sites suitable for establishment (ant nests) supports the directed dispersal hypothesis as a possible force favouring myrmecochory in this ecosystem. Ecosystems with a high frequency of myrmecochorous plants appear not to be restricted to regions of nutrient-impoverished soil or to fire-prone regions.     

Removal of seeds from frugivore defecations by ants in a Costa Rican rain forest

At our Costa Rican field site, seeds defecated by frugivorous birds usually do not remain where they have been deposited. Many species of ants are attracted to frugivore defecations and remove seeds and/or pulp. Pheidole species selectively remove seeds, fungus-growing species (tribe Attini) remove both pulp and seeds. Seeds of many Melastomataceae have an appendage, which we hypothesized is an elaiosome. Indeed, preference trials demonstrated that two species of Pheidole selected seeds with the appendage over seeds of the same species in which the appendage had been removed. However, we found that these ants did not take the appendage when it was offered by itself. We conclude that the appendage is not an elaiosome. In further trials, different ant species preferentially selected different seed species. These ants consumed some seeds and deposited others unharmed in refuse piles. We conclude that because the composition of leaf-litter ant communities is highly variable between neighboring square meter plots, and the probability of seed predation depends upon the species of ant, the over-all effect of ants on seed shadows and seed banks is spatially unpredictable. Addendum: The names of the two Pheidole emphasized in this study. P. nebulosa and P. nigricula, are unpublished names from a generic revision being prepared by E. O. Wilson and W. L. Brown. Their use here is not intended to constitute taxonomic publication but is solely for more precise indentification in future ecological research of similar nature     

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.     

Dispersal mechanisms of the narrow endemic <Emphasis Type="Italic">Polygala vayredae</Emphasis>: dispersal syndromes and spatio-temporal variations in ant dispersal assemblages

This study assesses the dispersal mechanisms of the narrow endemic Polygala vayredae, analysing the functioning of its dispersal syndromes (anemochory and myrmecochory), the spatio-temporal variability of the disperser assemblage, foraging behaviour and dispersal ability, and the role of the elaiosome in ant attraction and seed germination. The dispersion of diaspores begins when either (1) capsules or seeds fall beneath the mother plant (barochory) or (2) the seeds are directly collected in the suspended capsules by ants (myrmecochory). As capsules frequently open and expose/disseminate seeds before leaving the mother plant, the adaptation for anemochory appears to be reduced and rarely functional, possibly with only occasional events of long-distance dispersal (e.g. under extreme weather conditions). P. vayredae is essentially myrmecochorous and a diverse array of ant species are involved in seed manipulation, with the elaiosome playing a major role in ant attraction. From the plant’s perspective for dispersal, the majority of ant species had a positive interaction with the seeds, but negative and potential neutral interactions were also observed. Overall, dispersal distances were limited and were mainly determined by ant body size. The frequency of interactions and the ant assemblage varied significantly both spatially and temporally, and these factors may have an effect on directing or disrupting the selection of plant traits. Low seed predation and similar germination rates of intact seeds compared with seeds without elaiosome indicate that seed predator avoidance and seed germination improvement after ant manipulation are not among the selective advantages of myrmecochory operating at present. Dispersal mechanisms that enhance seed dispersal within the population and only occasionally lead to long-distance dispersal events, along with the rarity and patchiness of suitable habitats, may be the main factors explaining the actual density and narrow distribution of this species.     

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

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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.     

Indirect effects of alternative food resources in an ant–plant interaction

The seeds of many plant species present a food body that is consumed by animal dispersers. In theory, if the animals are polyphagous, the availability of alternative food resource other than the diaspore itself may influence its dispersal and survival. We used the myrmecochore Helleborus foetidus L. (Ranunculaceae), the seeds of which are attached to a lipid-rich elaiosome that is attractive to ants, as a model system to investigate (1) whether alternative foods that are present along with the plant affect ant foraging behavior and diaspore removal and (2) whether food availability in an ant nest affects seed predation and germination. In a field experiment, artificial diaspore depots were offered together with either sugar, insect corpses, seed, or no food (control). Contrary to the prediction that ants would rather concentrate their foraging effort on the highly rewarding alternative foods only, many workers, attracted by the sugar, switched to the hellebore diaspores, which significantly enhanced removal rate. Results obtained in the laboratory further indicated that the larvae of Aphaenogaster iberica (a major seed disperser) predated more on the H. foetidus embryos when no alternative food was available. This, in turn, slightly reduced seed germination. Overall, these results shed light, for the first time, on the potential indirect effects of alternative resources on the fate of diaspores adapted for ant dispersal.     

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.     

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.     

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.     

Interactions between ants and seeds of two myrmecochorous plant species in recently burnt and long‐unburnt forest sites

Myrmecochory (seed dispersal by ants) is a common seed dispersal strategy of plants in fire‐prone sclerophyll vegetation of Australia, yet there is little understanding of how fire history may influence this seed dispersal mutualism. We investigated the initial fate of seeds of two myrmecochorous plant species, the small‐seeded Pultenaea daphnoides J.C. Wendl. and the large‐seeded Acacia pycnantha Benth., in replicated burnt (3.25 years since fire) and unburnt (53 years since fire) forest plots in the Mount Lofty Ranges, South Australia. Specifically we measured (i) seed removal rates; (ii) the frequency of three ant–seed interactions (seed removal, elaiosome robbery and seed ignoring); (iii) the relative contribution of different ant species to ant–seed interactions; and (iv) the abundance of common interacting ant species. Rates of seed removal from depots and the proportion of seeds removed were higher in recently burnt vegetation and the magnitude of these effects was greater for the smaller‐seeded P. daphnoides. The overall proportion of elaiosomes robbed was higher in unburnt vegetation; however, the decrease in elaiosome robbery in burnt vegetation was greater for P. daphnoides than for A. pycnantha. Ants ignored seeds more frequently in burnt vegetation and at similar rates for both seed species. In total, 20 ant species were observed interacting with seeds; however, three common ant species accounted for 66.3% of ant–seed interactions. Monomorium sydneyense almost exclusively robbed elaiosomes, Rhytidoponera metallica typically removed seeds and Anonychomyrma nr. nitidiceps showed a mix of the three behaviours towards seeds. Differences in the proportions of seeds removed, elaiosomes robbed and seeds ignored appeared to be largely driven by an increase in abundance of A. nr. nitidiceps and a decrease in abundance of M. sydneyense in burnt vegetation. Understanding how these fire‐driven changes in the initial fate of myrmecochorous seeds affect plant fitness requires further investigation.