Invasive Ants Disrupt Gecko Pollination and Seed Dispersal of the Endangered Plant Roussea simplex in Mauritius

In Mauritius, the endemic blue-tailed day-gecko Phelsuma cepediana is currently the sole pollinator and seed disperser of the critically endangered endemic plant Roussea simplex (Rousseaceae). The flowers and fruits are often visited by the invasive ant Technomyrmex albipes , which forages on the nectar and fruit pulp, and tends honeydew-producing mealybugs on the fruits. Here, we experimentally explore how the presence of this alien ant species influences geckos foraging at flowers and fruits of R. simplex by removing and excluding ants from flowers and fruits. Gecko visitation rates to ant-free control flowers and fruits, and flowers and fruits where ants had been removed and excluded, were higher than those to ant-infested flowers and fruits. The resulting seed set of ant-infested flowers was greatly reduced, compared to ant-free control flowers. Similarly, for fruits with ants, very few seeds were likely to be ingested and dispersed by the geckos. Thus, T. albipes monopolizes flowers and fruits of R. simplex , and prevents access of pollinating and seed-dispersing P. cepediana geckos by aggressive interference competition. For a critically endangered plant like R. simplex , this double-disruption of two vital mutualistic interactions is of urgent conservation concern.     

蚁对植物种子的传播作用

许多种子植物依靠动物传播种子 ,称为动物传播。根据动物类群的不同 ,可分为哺乳类传播 ,鸟传播 ,鱼传播 ,蚁传播等。鸟传播和蚁传播的研究近年取得了很大的进展 ,但国内在这方面研究较缺乏 ,作者已就鸟传播作了综述报道 ,现将蚁传播的研究综述报道如下。1　蚁与植物的相互关系蚁类属膜翅目 (Ｈｙｍｅｎｏｐｔｅｒａ) ,蚁科 (Ｆｏｒｍｉｃｉ ｄａｅ) ,典型的社会性昆虫。多数蚁类是肉食性的 ,以小动物或更小的蚁类为食 ,但也有很多蚁类是植物食性的。在大多数生态系统中均有蚁类分布 ,而且蚁类数量众多 ,在森林生态系统中每 1ｈａ可达 6～10…     

The Morphometry of Solenopsis Fire Ants

Size-related changes of body shape were explored in 15 polymorphic species of Solenopsis fire ants by analyzing body weight along with linear measurements of 24 body parts. Log regression slopes were used to detect changes of shape with increasing size. Within species, the largest workers weighed from about 5 to 30-fold as much as the smallest. The range of within-species body lengths varied from 1.6 mm to 4 mm. As worker size increased, the gaster tended to make up a larger proportion of body length, usually at the cost of the petiole, and rarely at the cost of head length or mesosoma length. In most, the relative volume of the gaster increased and that of the head and mesosoma decreased. Most also showed an increasingly “humped” mesosoma. For all species, head shape changed from barrel-shaped to heart-shaped as worker size increased. Antennae became relatively shorter as the relative size of the club decreased. Shape changes of the legs were more variable. S. geminata was exceptional in the extreme nature of its head shape change, and was the only species in which relative head volume increased and gaster volume decreased with increasing body size. With the exception of S. geminata, the allometric rules governing shape are remarkably similar across species, suggesting a genus-level developmental scheme that is not easily modified by evolution. It also suggests that the evolution of shape is highly constrained by these conserved growth rules, and that it acts primarily (perhaps only) through allometric growth. The results are discussed in light of the growth of imaginal discs in a resource-limited body (the pupa). The substantial variation of allometries within species and across localities is also discussed in relation to using allometric patterns to identify species or to construct phylogenies.     

Steep Decline and Cessation in Seed Dispersal by Myrmica rubra Ants

Myrmecochorous diaspores bear a nutrient-rich appendage, the elaiosome, attractive to ant workers that retrieve them into the nest, detach the elaiosome and reject the seed intact. While this interaction is beneficial for the plant partner by ensuring its seed dispersal, elaiosome consumption has various effects −positive, negative or none − on ants’ demography and survival, depending on both the ant/plant species involved. In this context, the contribution of ants to seed dispersal strongly varies according to the ant/plant pairs considered. In this paper, we investigate whether the dynamics of myrmecochory also vary on a temporal scale, for a given pair of partners: Myrmica rubra ants and Viola odorata seeds. During their first encounter with seeds, ants collect all the diaspores and eat the majority of elaiosomes. Both the harvesting effort and the elaiosome consumption decline when seeds are offered on the next week and completely cease for the following weeks. This is related to a decrease in the number of foragers reaching the food source, as well as to a reduced probability for an ant contacting a seed to retrieve it. Seed retrieval is not reactivated after seven weeks without any encounter with V. odorata seeds. By contrast, naive ant colonies only fed with fruit flies do not show a decline of prey harvesting of which the speed of retrieval even increases over the successive weeks. Myrmecochory may thus be labile at the scale of a fruiting season due to the ability of ants to steeply tune and cease for several months the harvesting of these seemingly poorly rewarding items and to maintain cessation of seed exploitation. The present study emphasizes the importance of a long-lasting follow up of the myrmecochory process, to assess the stability of this ant-plant partnership and to identify mechanisms of adaptive harvesting in ants.     

Avian Seed Dispersal of an Invasive Shrub

The incorporation of an animal-dispersed exotic plant species into the diet of native frugivores can be an important step to that species becoming invasive. We investigated bird dispersal of Lonicera maackii, an Asian shrub invasive in eastern North America. We (i) determined which species of birds disperse viable L. maackii seeds, (ii) tested the effect of gut passage on L. maackii seeds, and (iii) projected the seed shadow based on habitat use by a major disperser. We found that four native and one exotic bird species dispersed viable L. maackii seeds. Gut passage through American robins did not inhibit germination, but gut passage through cedar waxwings did. American robins moved mostly along woodlot edges and fencerows, leading us to project that most viable seeds would be defecated in such habitats, which are very suitable for L. maackii. We conclude that L. maackii has been successfully incorporated into the diets of native and exotic birds and that American robins preferentially disperse seeds to suitable habitat.     

The Effects of Invasive Ants on Prospective Ant Mutualists

Ants are recognized for their abilities both to engage in mutualistic interactions with diverse taxa, and to invade and dominate habitats outside their native geographic range. Here, we review the effects of invasive ants on three guilds of mutualists: ant-dispersed plants, ant-tended arthropods, and ant-tended plants. We contrast how those three guilds are affected by invasions, how invasive ants differ from native ants in their interactions with those guilds, and how the seven most invasive ant species differ amongst themselves in those interactions. Ant-dispersed plants typically suffer from interactions with invasive ants, a result we attribute to the small size of those ants relative to native seed-dispersing ants. Effects on the ant-tended arthropods and plants were more frequently positive or non-significant, although it is unclear how often these interactions are reciprocally beneficial. For example, invasive ants frequently attack the natural enemies of these prospective mutualists even in the absence of rewards, and may attack those prospective mutualists. Many studies address whether invasive ants provide some benefit to the partner, but few have asked how invasives rank within a hierarchy of prospective mutualists that includes other ant species. Because ant invasions typically result in the extirpation of native ants, this distinction is highly relevant to predicting and managing the effects of such invasions. Interspecific comparisons suggest that invasive ants are poorer partners of ant-dispersed plants than are most other ants, equally effective partners of ant-tended arthropods, and perhaps better partners of ant-tended plants. Last, we note that the invasive ant taxa differ amongst themselves in how they affect these three mutualist guilds, and in how frequently their interactions with prospective mutualists have been studied. The red imported fire ant, Solenopsis invicta, appears particularly likely to disrupt all three mutualistic interactions, relative to the other six invasive species included in this review.     

Host Location Behavior in a Parasitoid of Imported Fire Ants

Female parasitoids use a hierarchy of cues to locate suitable hosts. We conducted a series of field observations and experiments to examine host location behavior in Pseudacteon tricuspis Borgmeier, a phorid parasitoid of Solenopsis invicta Buren worker ants. The parasitoids were frequently attracted to host workers at disturbed colonies, but were almost never attracted to host workers foraging at baits. When conspecific nonnestmate workers were introduced to baits, resulting in aggressive interactions, parasitoids appeared at the majority of baits. Moreover, larger numbers of parasitoids appeared at baits to which greater numbers of nonnestmate workers had been added. Addition of nonnestmate workers to disturbed colonies resulted in increased numbers of parasitoids attracted. Pseudacteon tricuspis did not display a pattern of uniform distribution at disturbed colonies but often was very abundant at some colony locations while absent or rare at nearby colony locations. Solenopsis invicta workers release alarm pheromones in aggressive interactions with nonnestmates, and this substance is likely an important chemical cue that attracts P. tricuspis flies to host workers from a distance.     

Selection against Aerial Dispersal in Ants: Two Non-Flying Queen Phenotypes in Pogonomyrmex laticeps

The South American seed-harvester ant Pogonomyrmex laticeps has dimorphic queens: ergatoid (permanently wingless) and brachypterous (short, non-functional wings). Surveys in western Argentina indicated that colonies near Chilecito, La Rioja Province, produced only ergatoid queens, while those near Punta Balasto, Catamarca Province (263 km away), produced only brachypterous queens. Brachypterous queens were significantly larger than ergatoid queens for 10 of 11 external characters, but both phenotypes had comparable reproductive potential, i.e., a spermatheca and a similar number of ovarioles. Using normal winged queens of the closely related P. uruguayensis for comparison, we determined that both queen phenotypes in P. laticeps had a full set of dorsal thoracic sclerites, albeit each sclerite was much reduced, whereas workers had a thorax without distinct dorsal sclerites. Sclerites were fused and immobile in ergatoid queens, while they were separable and fully articulated in brachypterous queens. Both phenotypes lacked the big indirect flight muscles, but brachypterous queens retained the tiny direct flight muscles. Overall, this dimorphism across populations indicates that there are alternative solutions to selective pressures against flying queens. We lack field data about colony founding strategy (independent or dependent) for either queen phenotype, but colonies at both sites produced numerous gynes, and we infer that all foundresses initiate colonies independently and are obligate foragers.     

Long-distance Dispersal of Invasive Grasses by Logging Vehicles in a Tropical Dry Forest

Predicting responses of vegetation to environmental factors in human-altered tropical ecosystems requires an understanding of the controls on plant population expansion across landscapes (i.e., long-distance dispersal) as well as of factors affecting recruitment at local scales (i.e., microsite conditions). We studied the roles of light availability, habitat type, soil disturbance, and seed dispersal in a selectively logged forest in lowland Bolivia where the exotic forage grass Urochloa (Panicum) maxima is abundant on roads and log landings but does not invade felling gaps or unlogged forest. Shade-house trials and seed addition experiments with U. maxima revealed that this C₄ grass thrives in high light but also grows in partial shade (10% full sun, but not 1% full sun), and that felling gaps, but not undisturbed forest, are suitable for grass establishment. To determine if seed dispersal by logging vehicles explains the discrepancy between actual and potential grass recruitment sites, we collected grass seeds that fell from trucks onto log landings located long distances (>500 m) from established grass populations. Trucks dispersed an estimated 1800 alien grass seeds per log landing during the early dry season; automobiles also transported seeds of grass (135 seeds/vehicle). The seeds collected (and relative abundances) were the exotics U. (Panicum) maxima (97%) and Urochloa (Brachiaria) brizantha (2%), and the pan-tropical weeds Sorghum halapense (1%) and Rottboellia cochinchinensis (0.2%). Grasses invade this forest where disturbance coincides with seed dispersal by motor vehicles, while dispersal limitation apparently prevents invasion of many sites otherwise suitable for grass recruitment (i.e., felling and natural gaps).     

Red Imported Fire Ants: A threat to eastern Australia's wildlife?

The discovery of the Red Imported Fire ants (Solenopsis invicta) in Brisbane on 22 February 2001 sent shock waves through urban and rural communities alike. This article is an attempt to address the often repeated question ‘What will become of Australia's unique fauna if they spread along Australia's eastern seaboard?     

Multilocus Evolution in Fire Ants: Effects of Selection, Gene Flow and Recombination

The reproductive success of individual fire ant queens (Solenopsis invicta) previously has been shown to be strongly influenced by their genotype at a single enzyme-encoding gene, designated Pgm-3. This paper presents evidence that a second, tightly linked gene, designated Gp-9, is under similarly strong selection in these ants. Selection appears to act independently on the two genes and is detectable in only one of the two social forms of this species (the ``polygyne' social form, in which nests contain multiple fertile queens). Strong directional selection on Pgm-3 in this form involves worker destruction of all queens with genotype Pgm-3(AA) before they reproduce. Selection on Gp-9 is more complex, involving both lethality of all Gp-9(bb) females and a strong or even complete survival advantage to reproductive queens with the heterozygous genotype Gp-9(Bb). Pgm-3 and Gp-9 are tightly linked (r(f) = 0.0016) and exhibit strong gametic phase disequilibrium in introduced populations in the U.S. This disequilibrium seems not to have stemmed from the founder event associated with the introduction, because the same associations of alleles found in the U.S. apparently occur also in two native populations in Argentina. Rather, selection acting independently on Pgm-3 and Gp-9, in conjunction with gene flow from the alternate, ``monogyne' social form (in which nests contain a single fertile queen), may explain the origin of disequilibrium between the two loci in polygyne fire ants.     

火与外来植物相互关系的研究进展

入侵种对本地的生态系统和生物多样性均有不良的影响,严重的会造成物种的灭绝和生态系统的崩溃,这已在全球范围引起广泛关注.在植物外来种与火生态因子的作用研究中发现,火与外来种的关系随物种生物学特性、火作用的时间、频度、强度不同而不同,火有时会有效地抑制外来种的生长和入侵,有时会促进一些外来种的生长和入侵.反之,一些外来种会对火的产生起到积极的作用,一些外来种又会抑制火的发生.火作为控制入侵种的一种方法,经科学地运用,可对某些入侵种起到有效的控制作用.     

Colony Wide Behavioral Contexts of Stridulation in Imported Fire Ants (Solenopsis invicta Buren)

Red imported fire ants, Solenopsis invicta, possess stridulatory organs and stridulate in a variety of contexts. We used a stethoscope mounted microphone to study stridulation at the colony level in the context of emigration, disturbance, and excavation. In conjunction with preliminary observations of nest and foraging activities, our results suggest stridulation serves multiple functions in S. invicta. Stridulation was not significantly increased in colonies during responses to disturbance, and only marginally during colony emigration. Colonies involved in excavation, however, exhibited a significant increase in stridulatory activity. Four possible explanations for the function of stridulation in this context are discussed in relation to the stridulatory behavior of individuals, solitary wasps, and published literature on formicid stridulation.     

Disturbance, Herbivory, and Propagule Dispersal Control Dominance of an Invasive Grass

Despite the dramatic changes invasive plants cause to ecosystems and communities, factors that control dominance of invasive species after establishment in a community are poorly understood. Most active management relies on catastrophic disturbances of invasive-dominated communities to increase richness and diversity of plant communities. This study examines the importance of propagule dispersal and deer herbivory on continued dominance of Phalaris arundinacea after a non-catastrophic, short-term disturbance to monotypic stands of this invasive grass. The disturbance caused no change in P. arundinacea cover among treatments during any year of the study and, thus, simulates disturbance intensity more likely to be encountered in unmanaged settings. Despite the small disturbance, the combinations of disturbance + seeding and disturbance + seeding + deer exclusion caused greater species richness than controls even three years after disturbance. Increased invasion of P. arundinacea stands caused few effects on the dominant, as P. arundinacea biomass was unaffected after the first year. Selective herbivory by deer of species other than P. arundinacea increased the effects of disturbance and seeding, and aided in continued dominance of the grass. The tolerance of P. arundinacea for direct anthropogenic effects, including poor water quality and hydroperiod fluctuations, and indirect effects, such as increased herbivory by historically high deer populations, indicates the complexity of determining persistence of invasive species.     

The Ants of the Juan Fernández Islands: Genesis of an Invasive Fauna

A first study of the ants on the three main islands of the Juan Fernández Archipelago (Chile) has revealed the presence of just three species, Hypoponera confinis, Linepithema humile, and Tetramorium bicarinatum, all widely distributed invasive species. Most notable among them is the Argentine ant, L. humile, an ecologically destructive species that has established several populations and appears to be expanding.     

The Effects of Habitat on Dispersal Patterns of an Invasive Thistle, Cynara Cardunculus

Dispersal of offspring is a critical step in the spread of invasive species, yet dispersal patterns are seldom well studied, inhibiting effective management and ecological understanding of invasions. Dispersal patterns can be affected by characteristics of the parent plant and by climatic or site characteristics, including community vegetation structure, but these factors have not been studied in the context of plant invasion processes. Cynara cardunculus (L.) is a polycarpic perennial thistle invasive in coastal grasslands in California that produces large numbers of wind-dispersed seeds. This study quantified and compared C. cardunculus dispersal patterns in an exotic grassland (vegetated site) and an agricultural field (non-vegetated site). Seed size variation in C. cardunculus was also quantified within inflorescences, between inflorescences, and between years of production, and compared across dispersal distances. Results indicate that dispersal distance increased dramatically from less than 20 m in the vegetated site to more than 40 m in the non-vegetated site. Plants producing fewer seeds produced heavier seeds and dispersal distance decreased over time, but seed size was not related to dispersal distance, which may serve to spread the risk to seeds or seedlings across the environment. C. cardunculus has great potential for dispersal in open areas such as agricultural fields or disturbed sites, but may be limited in highly structured natural communities. Management of C. cardunculus and other wind-dispersed plant invasions may be improved by prioritizing populations with open or disturbed areas downwind and minimizing the removal of vegetation during dispersal.     

Impact of the Little Fire Ant,Wasmannia auropunctata,on Native Forest Ants in Gabon1

The Neotropical little fire ant, Wasmannia auropunctata, is notorious for its negative impacts on the native biota of tropical islands, such as the Galapagos and New Caledonia, where it has been introduced. Here, I evaluate the impact of exotic W. auropunctata populations on continental Africa. I surveyed ants at nine sites in Lopé National Park in Gabon, Central Africa, and found a highly significant correlation between ant diversity and length of infestation by W. auropunctata. I found many more native ant species present in areas not infested with W. auropunctata (39.0 ± 4.6) compared with areas infested by W. auropunctata for approximately 5–10 yr (7.0 ± 6.2 and 1.7 ± 1.2, respectively). In infested areas, W. auropunctata made up the bulk of specimens collected in every plot. This study demonstrates that the threat posed by W. auropunctata to biodiversity is as serious in continental ecosystems as it is in the more fragile island ecosystems of previous studies. Introductions near waterways are particularly devastating: in Lopé, the infested territory is most extensive along waterways and occurs in a pattern that strongly suggests moving water facilitates colonization.     

Post-Release Host-Specificity Testing of Pseudacteon tricuspis, a Phorid Parasitoid of Solenopsis Invicta Fire Ants

Inherent in any biological control program is the risk of nontarget effects. Pseudacteon tricuspisBorgmeier, a parasitoid phorid fly, has been introduced to the United States from South America as a potential biocontrol agent of the red imported fire ant, Solenopsis invictaBuren. We conducted tests of host specificity on introduced populations of P. tricuspis, which are attracted to alarm pheromones released by their hosts during events such as mound disturbances and interspecific interactions. We monitored disturbed mounds of S. invicta and its close congener, S. geminata(F.), during the expansion of P. tricuspis across north Florida and after populations had been established for ~3 years. We also tested host acceptance in established populations of P. tricuspis by offering trays containing S. invicta, S. geminata, and 14 additional ant species representing 12 different non-Solenopsis genera. Although P. tricuspiswas commonly observed to hover over and attempt to oviposit on S. invicta, we never observed any parasitization attempts on any other ant species. As predicted by laboratory tests, released populations of P. tricuspis appear to be highly host specific and pose no obvious threat to nontarget species.