Ant-dispersed Plants Research Articles

How urban riparian corridors affect the diversity of spontaneous herbaceous plants as pollination and dispersal routes - a case of the Wenyu River- North Canal in Beijing, China

The loss of biodiversity due to rapid urbanization can be mitigated by urban riparian corridors. As an important component of urban biodiversity, spontaneous herbaceous plants play an essential role in the ecological functions of urban river corridors. Currently, the influence of the landscape structure within corridors on plant diversity has been poorly understood. In this study, we investigated the species and functional diversity, especially the functional traits of origin, pollination, and dispersal, of spontaneous herbaceous plants in the Wenyu River-North Canal riparian corridor in Beijing. The results showed that urban riparian corridors have a positive effect on the spread of alien and invasive plants as well as increasing the native plant diversity. No significant differences in diversity indicators but significant differences in the composition of functional traits between habitat types. Plants with long pollination and dispersal distances tended to be more closely related to the landscape structure indices at larger scales. Invasive plants were more common in patches with significant connectivity, while native plants were positively correlated with water and road connectivity. Anemophilous and anemochores were more common in habitats with sinuous edges. Ant-dispersed plants were closely related to the water bodies. Autochores were positively correlated with the connectivity of habitat patches. Plants dispersed by birds and mammals were weakly correlated with landscape structure. Our study underlines that emphasis should be placed on the support for plant pollination and dispersal, together with the prevention and control of invasive plants in the construction and management of future urban ecological corridors.

Are seed-dispersing ants elaiosome-limited? An experimental test in a Connecticut forest dominated by myrmecochorous plants

Food-for-dispersal mutualisms are critical sources of energy flow in ecological networks. By providing a nutrient-rich reward in the form of a fruit or seed to an animal mutualist, plants gain directed dispersal. Myrmecochory is one form of animal-mediated seed dispersal in which ants are recruited to plant seeds by providing a nutrient rich appendage called an elaiosome. It is unclear to what impact nutrients provided by elaiosomes have on ants, and whether the mutualism can tolerate disruptions to this food source. In the Northeastern U.S. mixed deciduous forest ecoregion, a diverse assemblage of herbaceous plants are dispersed by Aphaenogaster ants. Since Aphaenogaster ants gain a significant nutrient subsidy from this mutualism, it is predicted that loss of these seeds could cause reductions in their population size. To test this hypothesis, I performed a long-term removal of elaiosome food sources for ants. All seeds were removed by hand from three 50m2 plots, each paired with control plots with no removal, and a supplementation plot from April to May, from 2010 to 2012. Five years following removal treatments, I collected data on coverage of ant-dispersed plants and the abundance of seed-dispersing Aphaenogaster ants. Removal of all sources of elaiosomes resulted in modest reductions in the proportional coverage of ant-dispersed plants relative to control plots. Ant forager abundance was not impacted by the treatments five years after the removal of elaiosomes. In sum, Aphaenogaster populations may not always be limited by the availability of elaiosomes or myrmecochorous plants produce can recover quickly (<5 years) to provide enough food for these ants. As long as surrounding populations of understory forest plants are maintained, it appears that both mutualistic ants may rebound from a short-term reduction in the production of elaiosomes.

Ant Guild Identity Determines Seed Fate at the Post-Removal Seed Dispersal Stages of a Desert Perennial.

Simple SummaryAnts play a dual role in their interaction with plant seeds. Many ant species, mainly harvester ants, consume plant seeds (granivory), whereas other ants, mainly scavengers, provide a beneficial seed dispersal service. Granivory by ants is frequently documented in deserts, but beneficial seed dispersal is rarely studied in such ecosystems. We followed the handling of seeds of Sternbergia clusiana, an ant-dispersed plant, by two guilds of desert ants. We focused on the treatment of seeds within the nest and on the redispersal of seeds after ejection from the nest. Scavenging ants rarely consumed the seed itself, they deposited most seeds away from the nest in apparently suitable microhabitats. In addition, we found that most of the seeds that were relocated by scavenging ants arrived at sites under the canopy of shrubs. Such sites might be beneficial for the establishment and success of plants in the arid environment. Indeed, we found that the subject plant was more likely to be found under shrubs than elsewhere, which suggests that it benefits from being placed there. Such documentation of seed dispersal activity by scavenging ants in arid ecosystems suggests they may be efficient seed dispersers in deserts, as they are in other ecosystems.Ants play a dual role in their interaction with plant seeds. In deserts, the consumption of seeds by granivorous ants is common, whereas mutualistic seed dispersal, often associated with scavenging ants, is rarely documented. We evaluated the contribution of both ant guilds to efficient seed dispersal of an ant-dispersed plant, Sternbergia clusiana, in a desert ecosystem. We presented seed to colonies of three species of desert ants from the Cataglyphis (scavengers) and Messor (granivorous) genera. We recorded seed consumption, ejection from the nest, and seed transportation to potentially beneficial microhabitats. We evaluated microhabitat quality by testing the association between habitat types and the plant at various life stages. As expected, granivores mainly consumed the seeds, whereas scavengers consumed the elaiosome (seed appendage serving as a reward), but left the seeds intact. Moreover, scavenging ants relocated the seeds much further than granivores, mainly to shrub patches. The disproportional distribution of the plant under shrubs at several life stages suggests that this microhabitat is beneficial for the plant. Overall, while granivores seem to mainly harm seed dispersal, we provide the first evidence for the beneficial contribution of scavenging ants in deserts, showing they exhibit the same suite of characteristics that render them efficient seed dispersers in other ecosystems.

How common and dispersal limited are ant-dispersed plants in eastern deciduous forests?

Most plant diversity in eastern deciduous forests occurs in the understory herbaceous layer. Ant-dispersed plants (myrmecochores) reside within that layer, and they often are reported to be a substantial part of understory plant abundance and diversity that is particularly threatened by global change because of their relatively short dispersal distances. Indeed, they are often, but not always, reported to be lacking or absent from young forests where they may fail to re-colonize after extirpation due to their dispersal limitations. Our objective was to characterize the woodland myrmecochorous plant communities across the northern- and southernmost reaches of eastern deciduous forests using vegetation from 2687 plots in 44 U.S. National Parks. We asked whether (a) myrmecochorous plants are a substantial portion of understory herbaceous communities in eastern North American deciduous forests, and (b) if they are particularly dispersal limited relative to other understory herbaceous dispersal guilds. If myrmecochores are notable in abundance and extent in understory herbaceous communities, we expected that they would comprise ~ 30% of the species and ~ 55–60% of the abundance, as reported in the literature. If myrmecochores, as a guild, are more dispersal limited than other dispersal modes (anemochory, autochory, zoochory), we also expected that myrmecochore species richness would be more limited by park age and area than other dispersal guilds because they would take longer to re-colonize. In contrast with the published literature on myrmecochores, our data suggest that myrmecochorous plants are much less common as reported in eastern deciduous understory herbaceous communities (~ 9% of herbaceous species; ~ 12% of herbaceous abundance), but twice as common as the global percentage of myrmecochorous plants (~ 4.5%). We also found that they are not particularly impacted by forest size and fragmentation. Ants appear to disperse myrmecochorous seeds at 1/20th the distance of wind-dispersed plants, but the dispersal distances for myrmecochores are about the same as other animal-dispersed plants and slightly less than gravity-dispersed plants in these same forests. Moreover, our data also suggest that myrmecochores, particularly large-seeded myrmecochores, may not occur in enough abundance to contribute meaningful biomass toward ant diets. Of course, species abundance does not equal species importance, and many keystone species impact ecosystems more than their abundance might suggest. Ant-mediated seed dispersal is a model system for understanding ecological and evolutionary dynamics, and certainly contributes toward understanding the threats of fragmentation and climate change in eastern deciduous forest systems, but they may not be as abundance or threatened as previously reported.

Interactions between seed-dispersing ant species affect plant community composition in field mesocosms.

In generalized mutualisms, species vary in the quality of services they provide to their partners directly via traits that affect partner fitness and indirectly via traits that influence interactions among mutualist species that play similar functional roles. Myrmecochory, or seed dispersal by ants, is a generalized mutualism with ant species varying in the quality of dispersal services they provide to their plant partners. Variation in ant species identity can directly impact seed dispersal patterns and plant community composition; however, we know less about how interactions among seed-dispersing ant species indirectly influence plant partners. The invasive ant Myrmica rubra, is a high-quality seed-disperser in its native range that interacts with myrmecochores (ant-dispersed plants) and the high-quality seed disperser Aphaenogaster sp. in its invaded range. We use this system to examine how interactions between two functionally similar mutualist ant species influence the recruitment and community composition of ant-dispersed plants. We performed a field mesocosm experiment and a laboratory behavioural experiment to compare discovery and dominance behaviours between ant species, and seed dispersal and seedling recruitment of four myrmecochore species among intraspecific interaction treatments of each ant species and an interspecific interaction treatment. We found that M. rubra was better at discovering and dispersing seeds, but Aphaenogaster sp. was dominantly aggressive over M. rubra. Interspecific interactions dampened seed dispersal relative to dispersal by the better disperser. Despite this dampening, we found no effect of interspecific interactions on seedling recruitment. However, community composition of seedlings in the interspecific interaction treatment was more similar to composition in the aggressively dominant ant (Aphaenogaster sp.) treatment than in the better discoverer ant M. rubra treatment. We show that interspecific interactions between mutualist species in the same functional guild affect the outcome of mutualistic interactions with partner species. Despite the native ant dispersing fewer seeds, its dominance over the subordinate (invasive) ant has the potential to allow for some level of biotic resistance against the effects of M. rubra on plant communities when these species coexist.

Investment in reward by ant-dispersed plants consistently selects for better partners along a geographic gradient.

Seed dispersal by ants (myrmecochory) is an asymmetric, presumably mutualistic interaction, where a few ant species benefit many plants. Myrmecochorous plants express specialized adaptations, most notably a large elaiosome, which promote interactions with efficient seed dispersers while decreasing interactions with poor dispersers, resulting in de facto partner choice. However, because variation in plants’ investment in reward and ant response to them may vary spatially and temporally, it is unclear whether such specialization is consistent along geographic gradients; especially towards myrmecochory’s range margin. To answer this question on context-dependent partner choice, we first estimated variation in reward investment by co-occurring myrmecochores along a steep environmental gradient in a Mediterranean region. Second, we tested whether variation in plant investment in reward was positively and consistently correlated with the quality of dispersal plant received along the same gradient. Using in situ cafeteria experiments, we simultaneously presented diaspores of locally co-occurring myrmecochorous species to ants of two guilds representing high- and low-quality dispersers. We then recorded ant-seed behaviour, seed preference and seed removal rates for each ant guild. We found both overall and within-site high variation among plant species in the total and relative investment in elaiosomes. Both ant guilds removed substantial proportion of the seeds. However, scavenging ants (high-quality dispersers) clearly preferred diaspores with larger elaiosomes, whereas granivorous ants (low-quality dispersers) exhibited no preference. Furthermore, both the variation in plant traits and the corresponding response of different ant guilds were consistent along the studied geographic gradient. This consistency holds even when granivores, which removed seeds in a non-selective fashion and provided apparently low-quality seed dispersal services, were, at least numerically, the dominant ant guild. This dominance and the consistency of the partner choice shed light on the functionality of elaiosomes at the margins of myrmecochory’s distribution.

Mutualism between co-introduced species facilitates invasion and alters plant community structure

Generalized mutualisms are often predicted to be resilient to changes in partner identity. Variation in mutualism-related traits between native and invasive species however, can exacerbate the spread of invasive species ('invasional meltdown') if invasive partners strongly interact. Here we show how invasion by a seed-dispersing ant (Myrmica rubra) promotes recruitment of a co-introduced invasive over native ant-dispersed (myrmecochorous) plants. We created experimental communities of invasive (M. rubra) or native ants (Aphaenogaster rudis) and invasive and native plants and measured seed dispersal and plant recruitment. In our mesocosms, and in laboratory and field trials, M. rubra acted as a superior seed disperser relative to the native ant. By contrast, previous studies have found that invasive ants are often poor seed dispersers compared with native ants. Despite belonging to the same behavioural guild, seed-dispersing ants were not functionally redundant. Instead, native and invasive ants had strongly divergent effects on plant communities: the invasive plant dominated in the presence of the invasive ant and the native plants dominated in the presence of the native ant. Community changes were not due to preferences for coevolved partners: variation in functional traits of linked partners drove differences. Here, we show that strongly interacting introduced mutualists can be major drivers of ecological change.

油质体在5种蚁播植物种子散布中的作用研究

PDF HTML阅读 XML下载 导出引用 引用提醒 油质体在5种蚁播植物种子散布中的作用 DOI: 10.5846/stxb201312172970 作者: 作者单位: 华中师范大学生命科学学院,华中师范大学生命科学学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目(31170310); 国家标本平台教学标本子平台项目(http://mnh.scu.edu.cn) The role of elaiosome in seed dispersal of five ant-dispersed herbaceous plants Author: Affiliation: College of Life Sciences,Central China Normal University,College of Life Sciences,Central China Normal University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:蚁播植物种子上常附着有蚂蚁喜食的油质体,该物体可吸引蚂蚁取食或为蚂蚁提供钳着位点从而影响种子散布。为进一步揭示油质体在种子散布中的作用,在野外研究了4属5种典型蚁播植物包括小花宽瓣黄堇(Corydalis giraldii Fedde)、假刻叶紫堇(C. pseudoincisa C. Y. Wu)、白屈菜(Chelidonium majus L.)、紫花堇菜(Viola grypoceras A. Gray)和柔毛淫羊藿(Epimedium pubescens Maxim.)其相应的搬运蚂蚁即玉米毛蚁(Lasius alienus (Foerster))和尼特纳大头蚁(Pheidole nietneri Emery)对植物完整种子(SE)、去除油质体的种子(S)和粘有人工模拟油质体的种子(S+H)的搬运行为和搬运效率。结果显示,蚂蚁对相同植物3类种子的触碰和检查次数均无显著差异。蚂蚁对种子的尝试搬运次数除玉米毛蚁对小花宽瓣黄堇、假刻叶紫堇和白屈菜去除油质体的种子(S)显著高于完整种子(SE)和粘有人工模拟油质体的种子(S+H)外,其它的均无显著差异。玉米毛蚁对小花宽瓣黄堇、假刻叶紫堇、白屈菜和紫花堇菜以及尼特纳大头蚁对小花宽瓣黄堇、假刻叶紫堇和紫花堇菜完整种子(SE)的搬运效率显著高于粘有人工模拟油质体的种子(S+H)和去除油质体的种子(S),此外,玉米毛蚁对小花宽瓣黄堇粘有人工模拟油质体的种子(S+H)的搬运效率显著高于去除油质体的种子(S)。这说明玉米毛蚁在搬运小花宽瓣黄堇种子过程中油质体不仅起到吸引作用,而且起到钳着位点作用;玉米毛蚁在搬运假刻叶紫堇、白屈菜和紫花堇菜以及尼特纳大头蚁搬运小花宽瓣黄堇、假刻叶紫堇和紫花堇菜种子过程中油质体仅起到吸引作用。研究表明油质体可通过对蚂蚁起吸引作用,或同时起吸引和钳着位点的双重作用等影响种子散布,油质体的影响作用不但取决于植物种类,也与搬运蚂蚁的种类有关。 Abstract:Ant-dispersed plants usually produce seeds with appendages (elaiosomes), which are beneficial to ants. It is generally accepted that seed dispersal by ants (myrmecochory) is mediated by the presence of elaiosome that lures ants to transport the diaspores. Several hypotheses have related removal of seeds to nutritional needs of ants, and others have argued the importance of possible handles (i.e. structures that ants can grasp) in transporting by ants. To clarify the functional role of the elaiosome, ant behavior and seed removal rate were assessed by presenting simultaneously three types of items including entire seeds with elaiosome (SE), seeds without elaiosome (S), and seeds with an artificial "handle" glued to seeds (S+H) from five myrmecochorous species from four genera, i.e. Corydalis giraldii Fedde, Corydalis pseudoincisa C. Y. Wu, Chelidonium majus L., Viola grypoceras A. Gray, and Epimedium pubescens Maxim. to their two corresponding dispersing ants including Lasius alienus (Foerster) and Pheidole nietneri Emery in the nest surroundings in the field. Among the five studied plants, we found that the seed size of E. pubescens was significantly larger than that of Corydalis giraldii (P < 0.05). Both the seed weight and elaiosome weight of E. pubescens was the largest, and the elaiosome/seed mass ratio of C. giraldii was the highest. In addition, we found that no significant differences existed in the ant ‘Antennate’, ‘Examine’, and ‘Pick-up attempt’ behaviors among the three types of seeds from each plant species, excluding L. alienus, in which ‘Pick-up attempt’ of the S by ants was greater than that of both SE and S+H in Corydalis giraldii, Corydalis pseudoincisa, and Chelidonium majus plants. For the three types of seeds from each plant species, the removal rate of SE was significantly greater than that of both S+H and S in Corydalis giraldii, Corydalis pseudoincisa, Chenopodium majus, and V. grypoceras by ant L. alienus and in Corydalis giraldii, Corydalis pseudoincisa and V. grypoceras by ant Ph. nietneri. In addition, the removal rate of S+H was significantly greater than that of S in Corydalis giraldii by ant L. alienus. The results indicated that the presence of elaiosomes on seeds might influence ant behavior and their seed removal rate either by serving as an attractant for ants or by both acting as a handle and serving as an attractant for ants. The results further showed that the role of elaiosomes strongly varied depending on the species of each partner in ant-mediated seed dispersal process. 参考文献 相似文献 引证文献

Species, Diaspore Volume and Body Mass Matter in Gastropod Seed Feeding Behavior

BackgroundSeed dispersal of ant-dispersed plants (myrmecochores) is a well studied ecosystem function. Recently, slugs have been found to act as seed dispersers of myrmecochores. The aim of our study was to (1) further generalize the finding that gastropods feed on seeds of myrmecochores and hence may act as seed dispersers, (2) to test whether gastropod body mass and the volume of diaspores have an influence on the seed dispersal potential.Methodology and Principal FindingsWe assessed the seed dispersal potential of four slug and snail species with a set of seven myrmecochorous plant species from seven different plant families common to Central European beech forests. Diaspores differed in shape and size. Gastropods differed in their readiness to feed on diaspores and in the proportion of seeds that were swallowed as a whole, and this readiness generally decreased with increasing diaspore size. Smaller Arionid slugs (58 mm body length; mean) mostly fed on the elaiosome but also swallowed small diaspores and therefore not only act as elaiosome consumers, a nutrient rich appendage on myrmecochorous diaspores, but may also disperse seeds. Large Arionid slugs (>100 mm body length) swallowed diaspores of all sizes. Diaspores swallowed by gastropods were defecated without damage. Within-species variability in body size also affect seed dispersal potential, as larger individuals of the red slug (Arion rufus) swallowed more diaspores of wood anemone (Anemone nemorosa) than smaller ones.Conclusions and SignificanceOur results help to generalize the finding that gastropods consume and potentially disperse seeds of myrmecochores. The dispersal potential of gastropods is strongly influenced by diaspore size in relation to gastropod size.

Spatial variation in the fatty acid composition of elaiosomes in an ant-dispersed plant: Differences within and between individuals and populations

Euphorbia characias is a common myrmecochorous plant of the western Mediterranean Basin whose seeds are dispersed by ants following fruit explosion. The variation in elaiosomes’ fatty acid composition of this species was studied at three hierarchical levels (sub-individual, individual and population) in four populations from the Iberian Peninsula. We found that differences in fruit location on the inflorescence do not seem to influence the fatty acid composition of elaiosomes, providing to each propagule an equal chance of being dispersed. However, significant differences in elaiosome fatty acid composition between individuals and populations were found for most of the compounds identified. The content of oleic acid, a key mediator in the ant–seed interaction, differed widely between populations, probably reflecting geographic variations in co-adaptation between plants and their dispersers. The finding that the fatty acid composition of E. characias elaiosomes is distinct from that of the seed itself, but very similar to that of elaiosomes from unrelated species, reinforces the idea of convergent evolution in the chemical composition of these structures.

Effects of seed passage through slugs on germination

Seed dispersal by invertebrates is mostly external (e.g. by ants). However, internal dispersal (endozoochory) seems to be uncommon due to size limitations. Slugs are generalist herbivores and increasing evidence suggests that they often disperse seeds. Nevertheless, we know very little on the consequences for plant recruitment. Here, we assess the effect of slug seed passage on germination and early seedling establishment of a set of nine common plant species with limited dispersal capabilities (unassisted or ant dispersed). Germination trials were performed under natural conditions (NW of Spain). Size was a clear limitation for seed ingestion: smaller seeds were eaten more readily, whereas only the largest slugs could swallow the largest seeds. All ingested seeds were voided undamaged. Only not-ingested seeds (the biggest) were damaged, with chewing marks in the surface and 0.8% (N = 250) were broken. In some cases, slugs ate the elaiosomes but discarded the seeds. Slug seed passage had an overall positive effect on total germination and sped it up in two species. Elaiosome removal by slugs had also a positive effect in Ulex europaeus seeds (+160%). However, slugs had no effect on early seedling survival and growth of the study species. Our results show that slugs are effective dispersers in terms of seed treatment in the digestive track. However, according to their reduced movement range (in the range of tens of metres; as shown by other studies), they can only provide rather limited dispersal as compared to vertebrate dispersers. This can be nonetheless significant for species with limited dispersal, e.g. unassisted and ant-dispersed plants, for which they act as non-standard dispersers.

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 estab- lishment. Ant communities are known to be highly hier- archical, 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 pen- cosensis. 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.

Disruption of ant-seed dispersal mutualisms by the invasive Asian needle ant (Pachycondyla chinensis)

By disrupting the structure of native ant assemblages, invasive ants can have effects across trophic levels. Most studies to date, however, have focused on the impacts just two species (Linepithema humile and Solenopsis invicta). The impacts of many other invasive ant species on ecological processes in their introduced range are unknown. In this study we tested the hypothesis that the invasive ant Pachy- condyla chinensis disrupts ant-seed dispersal mutu- alisms by displacing native ant species, especially the keystone mutualist Aphaenogaster rudis, while fail- ing to disperse seeds itself. In a paired design we measured the impact of P. chinensis on the native ant-plant seed dispersal mutualism. The number of A. rudis workers was 96% lower in invaded than in intact plots, and the number of seeds removed was 70% lower in these plots. Finally, in invaded plots the abundance of Hexastylis arifolia, a locally abundant myrmecochorous plant, was 50% lower than in plots where P. chinensis was absent. A parsimonious interpretation of our results is that P. chinensis causes precipitous declines in the abundance of A. rudis within invaded communities, thereby dis- rupting the ant-plant seed dispersal mutualisms and reducing abundances of ant-dispersed plants. In sum, the magnitude of the effects of P. chinensis on seed dispersal is quantitatively similar to that documented for the intensively studied invasive Argentine ant. We suggest that more studies on the impacts of less- studied invasive ant species on seed dispersal mutu- alisms may increase our knowledge of the effects of these invaders on ecosystem function.

Ecological differentiation among key plant mutualists from a cryptic ant guild

As key dispersers of herbaceous seeds, Aphaenogaster ants strongly influence the distribution of woodland plants in eastern North America. Ants within this genus are difficult to distinguish and often are identified by subgroup, but emerging research suggests they occupy species-specific ecological niches. As such, distinct climatic requirements among Aphaenogaster spp. might result in transient plant interactions with climate change. We examine whether there are ecological and distributional differences among Aphaenogaster species that coincide with current taxonomic differentiations. We use occurrence records for six Aphaenogaster spp. that occur in deciduous forests in eastern North America. We associate the geographic patterning of species occurrence with temperature and precipitation data, and we examine whether unique climatic niches characterize each species. We then predict habitat suitability throughout eastern North America using species distribution models. For verification, we test how well the predicted ranges fit observed occurrences using novel data sets for each species. We find that Aphaenogaster species within this cryptic genus demonstrate unique ecological and geographic signatures. Each species within the subgroup generally responds differently to temperature, and somewhat differently to precipitation and seasonal variance, suggesting unique ecological niches for each species. Our results indicate that each ant species may respond uniquely to changes in climate. Such shifts could disrupt current community associations and biotic interactions with ant-dispersed plants.

The direct and indirect effects of the red imported fire ant (Solenopsis invicta) on seed fate in the longleaf pine ecosystem

AbstractInvasion of non-native ants potentially disrupts natural relationships of native ants and ant-dispersed plants. These relationships may be affected directly through seed collection, or indirectly though impacts on the native ant community. Solenopsis invicta (the red imported fire ant), a widespread invasive of the southeastern United States, negatively impacts human health, agriculture, and wildlife. The impacts of S. invicta on native plant communities are less understood, partially because the invasions are usually coupled with human disturbance of soil or vegetation. The longleaf pine ecosystem is one of the few native communities successfully invaded by S. invicta. In a natural stand of longleaf pine with native groundcover we determined the fate of seeds collected by S. invicta, and the change in the ant community and seed removal due to disturbance by timber harvesting activities. We used cafeteria-selection trials with seeds of native plants to determine rates of seed removal. We presented S. invicta with dyed elaiosome-bearing seeds and recovered seed in middens above ground, and we sampled nests below ground with a wax cast. To examine changes in the ant community following disturbance, we sampled the ant community before and after timber harvest using pitfall traps and observing seed removal.We found that S. invicta preferentially collects myrmecochorous (elaiosome-bearing) seeds. We recovered approximately 30 percent of the dyed seed on the surface in midden piles of which only 17 percent had elaiosomes removed. However, this response varies seasonally. No seeds were recovered in the fall, suggesting that S. invicta is either consuming or storing more seeds prior to cold weather. We recovered few seeds in the nest castes. Initial ant community composition sampling resulted in 24 species. S. invicta was strongly dominant in most plots, and removed 83% of all seeds taken by ants.

Seed consumption and dispersal of ant-dispersed plants by slugs

In beech-dominated forests in Central Europe, many spring geophytes show adaptations to seed dispersal by ants (myrmecochory). Ants, however, can be rare in such moist forests. Motivated by observations of slug feeding on seeds we investigated the seed consumption of two plant species, Anemone nemorosa and Asarum europaeum, by slugs, in a series of experiments. In a seed predation experiment in a beech forest, we found that seed removal was strongly reduced when gastropods were excluded from the seed depots. The contribution of insects, including ants, and rodents to seed removal was relatively less but differed between May and July. In the laboratory, slug species, in particular Arion sp., consumed seeds of both plant species. Slugs either consumed the elaiosomes of seeds or swallowed seeds intact. Swallowed seeds were defecated undamaged and germinated as well as control seeds when buried overwinter, indicating the potential for seed dispersal by slugs. We also recovered seeds of myrmecochores in the faeces of several slugs caught in forests. In a slug release experiment in the forest, slugs moved up to 14.6 m (mean 4.4 m) in 15 h, which is the median gut passage time of seeds based on measurements made in the laboratory. We also found that when slug-defecated seeds were offered to rodents, these were less attractive than control seeds, suggesting that passage through the slug gut reduces seed predation risk. Our results demonstrate that slugs are significant consumers of elaiosomes or entire seeds of ant-dispersed plants and that they can function as seed dispersers of these plants.

Ants Sow the Seeds of Global Diversification in Flowering Plants

BackgroundThe extraordinary diversification of angiosperm plants in the Cretaceous and Tertiary periods has produced an estimated 250,000–300,000 living angiosperm species and has fundamentally altered terrestrial ecosystems. Interactions with animals as pollinators or seed dispersers have long been suspected as drivers of angiosperm diversification, yet empirical examples remain sparse or inconclusive. Seed dispersal by ants (myrmecochory) may drive diversification as it can reduce extinction by providing selective advantages to plants and can increase speciation by enhancing geographical isolation by extremely limited dispersal distances.Methodology/Principal FindingsUsing the most comprehensive sister-group comparison to date, we tested the hypothesis that myrmecochory leads to higher diversification rates in angiosperm plants. As predicted, diversification rates were substantially higher in ant-dispersed plants than in their non-myrmecochorous relatives. Data from 101 angiosperm lineages in 241 genera from all continents except Antarctica revealed that ant-dispersed lineages contained on average more than twice as many species as did their non-myrmecochorous sister groups. Contrasts in species diversity between sister groups demonstrated that diversification rates did not depend on seed dispersal mode in the sister group and were higher in myrmecochorous lineages in most biogeographic regions.Conclusions/SignificanceMyrmecochory, which has evolved independently at least 100 times in angiosperms and is estimated to be present in at least 77 families and 11 000 species, is a key evolutionary innovation and a globally important driver of plant diversity. Myrmecochory provides the best example to date for a consistent effect of any mutualism on large-scale diversification.

Influence of elaiosome on postdispersal dynamics of an ant-dispersed plant

Specialized myrmecochorous plants bear an elaiosome attached to the seed. Ants benefit from food provided by this appendage and plants get their seeds eventually dispersed. Aside from the benefits conferred by seed dispersal, we hypothesize that the influence of the elaiosome might extend to later life history stages such as emergence or survival, but few studies have examined rigorously such delayed effects on seed and seedling dynamics. This paper tests this hypothesis for the ant-dispersed herb Helleborus foetidus. Presence or lack of the elaiosome had some interesting delayed influences. Specifically, our results show that elaiosome removal not only enhanced seedling emergence, but also reduced cumulative long-term seed predation. The combination of these two effects, together with the inherent positive effect of the elaiosome on seed dispersal, highlights the ecological and evolutionary importance of myrmecochorous systems.

Forest edges and landscape history shape interactions between plants, seed-dispersing ants and seed predators

Ant-dispersed plants are often conspicuously rare in young forests and near forest edges. We monitored the distributions of five ant-dispersed plant taxa, the seed-collecting ant community, and variation in seed predation pressure by rodents in a 350-acre mesic forest in northern New York, USA to assess the incidence and effect of plant–animal interactions within the context of landscape history and proximity to forest edges. Sample plots were located in young and older forest stands (distinguished based on an 1880 map for forest cover) at varying distances from the forest edge. All five plant taxa were rarer in plots near forest edges, although diversity was more strongly influenced by landscape history. A sixth herbaceous species, one dispersed by vertebrates, was not influenced by forest edge proximity. The most effective seed-collecting ant, Aphaenogaster rudis, was less common in forest edge plots relative to interior plots, and predation pressure by small mammals was almost twice as great in plots near forest edges. Exclusion experiments demonstrated that ants (mutualists) and rodents (seed predators) compete for access to seeds, that ants can provide seeds some protection from mammal predation in most plots, and that the density of ant-dispersed plants is correlated with the proportion of rodent-accessible seeds that are collected by Aphaenogaster. Greater predation pressure and a paucity of ant mutualists may contribute to the rarity of ant-dispersed plants in edge habitats relative to forest interiors.

Chemical differences between seeds and elaiosomes indicate an adaptation to nutritional needs of ants

Ant-dispersed plants usually produce seeds with appendages (elaiosomes) as reward for ants. Plants that produce high-quality elaiosomes benefit because ants preferentially disperse their diaspores. We therefore hypothesized that seeds and elaiosomes differ in chemical composition in ways that make elaiosomes of high nutritional quality for ants, capable of providing essential dietary components that explain the increased fitness and higher gyne production documented for colonies with elaiosome consumption. To test the hypothesis we analysed the content and composition of lipids, amino acids, soluble carbohydrates, proteins and starch in seeds and elaiosomes of 15 central European ant-dispersed plants. After separating the different fractions, total lipids were determined gravimetrically, fatty acids and soluble carbohydrates were detected by gas chromatography (GC) and GC-mass spectrometry, free amino acids by an amino acid analyser while starch and protein were analysed photometrically. Seeds accumulated high molecular weight compounds such as proteins and starch, whereas elaiosomes accumulated more easily digestible low molecular weight compounds such as amino acids and monosaccharides. Analysis of similarities and similarity percentages analysis demonstrated that the composition of fatty acids, free amino acids and carbohydrates differed markedly between elaiosomes and seeds. The most important difference was in total amino acid content, which was on average 7.5 times higher in elaiosomes than in seeds. The difference was especially marked for the nitrogen-rich amino acid histidine. The availability of essential nutrients and, in some species, the higher nitrogen content in elaiosomes suggest that their nutritional value for larvae plays a key role in this interaction.