Effects of seed predation by ants on Mediterranean grassland related to seed size

Questions: 1. Do harvester ants (Messor barbarus) promote seed mortality in Mediterranean grassland?; 2. Is this effect greater in large‐seeded species? Location: Central Spain. Methods: We established an ant‐exclusion experiment of five circular (1.5 m diameter) plots from where ants were excluded during one year, along with ten control plots. We recorded the seed bank of all species in the plots both before and after the treatment. The effect of seed length and weight was analysed after transforming data into phylogenetically independent contrasts, and alternatively by dividing the species data set into morphological groups. Results: Longer and heavier seeded species significantly increased in the seed banks under the exclusion treatment, although ants did not significantly modify overall seed densities. Conclusions Although the ants do not collect large numbers of seeds, they differentially affect the composition of the seed banks by selecting the longest or heaviest seeds, or both. The persistence of this short‐term effect in the seed bank may result, over a number of years, in the system evolving towards a predominance of small‐seeded annuals, congruent with the species composition actually observed in Mediterranean grasslands.     

Functional extinction of a desert rodent: implications for seed fate and vegetation dynamics

Population declines of once‐abundant species have often preceded understanding of their roles within ecosystems. Consequently, important drivers of environmental change may remain undiagnosed because we simply do not know how species that are now rare or extinct shaped ecosystems in the past. Australia's desert rodents are thought to have little numerical impact on seed fate and vegetation recruitment when compared with ants or with desert rodents on other continents. However most research on granivory by Australian desert rodents has occurred in areas where rodents were rare or functionally extinct. Here we ask if the paradigm that rodents are relatively un‐important granivores in Australian deserts is an artefact of their historical decline. In the Strzelecki Desert, the endangered rodent, Notomys fuscus is rare where introduced mesopredators are abundant but common where dingoes (an apex predator) suppress mesopredator populations. We used foraging trays to compare rates of seed removal for a common shrub (Dodonaea viscosa angustissima hopbush) between areas where N. fuscus, hopbush shrubs and their seedlings were rare and common and found that seed removal was consistently higher where rodents were common and hopbush rare. By excluding ants and rodents from foraging trays we show that ants removed more seeds than rodents where rodents were rare but rodents removed far more seeds than ants where rodents were common. By manipulating rodents’ access to the soil seed‐bank we show that hopbush seeds persisted in greater numbers where rodents were excluded than where they had access. Our results support the hypothesis that granivory by rodents may once have been a far more important process influencing the fate of seeds and shaping plant communities in arid Australia and suggest that dingo extirpation has cascading effects on shrub seeds. Our study highlights that functional extinction of rodents may be an under‐appreciated driver of vegetation change.     

Meat ants as dominant members of Australian ant communities: an experimental test of their influence on the foraging success and forager abundance of other species

Meat ants (Iridomyrmex purpureus and allies) are perceived to be dominant members of Australian ant communities because of their great abundance, high rates of activity, and extreme aggressiveness. Here we describe the first experimental test of their influence on other ant species, and one of the first experimental studies of the influence of a dominant species on any diverse ant community. The study was conducted at a 0.4 ha savanna woodland site in the seasonal tropics of northern Australia, where the northern meat ant (I. sanguineus) represented 41% of pitfall catches and 73% of all ants at tuna baits, despite a total of 74 species being recorded. Meat ants were fenced out of experimental plots in order to test their influence on the foraging success of other species, as measured by access to tuna baits. The numbers of all other ants and ant species at baits in exclusion plots were approximately double those in controls (controlling for both the fences and for meat ant abundance), and returned rapidly to control levels when fences were removed after 7 weeks. Individual species differend markedly in their response to the fencing treatment, with species of Camponotus and Monomorium showing the strongest responses. Fencing had no effect on pitfall catches of species other than the meat ant, indicating that the effect of meat ants at baits was directly due to interference with foraging workers, and not regulation of general forager abundance. Such interference by meat ants has important implications for the sizes and densities of colonies of other ant species, and ultimately on overall ant community structure.     

The timing of seed dispersal in Viooa nuttallii: attraction of dispersers and avoidance of predators

Summary Elaiosomes attract rodent predators, as well as ant dispersers (Myrmica discontinua and Formica podzolica), to Viola nuttallii seeds. Seed removal by ants and rodents was studied over 24 h and over two separate 4-h periods. Experimental treatments included i) ants and rodents having access to seeds, ii) only ants having access, iii) only rodents having access, and iv) neither ants nor rodents having access. Seed dehiscence was monitored for 3 days. A simple model is used to determine the relative importance of ants and rodents in removing seeds, and these frequencies are related to the time when most seeds were released. The data show that most seeds are shed from capsules between 9 AM and 1 PM and are immediately removed by ants. Ants, on the average, remove 88% of the seeds. The timing of seed dehiscence increases the probability of seeds being dispersed by ants. The results are discussed with respect to the hypothesis that a sychrony of the time of seed dispersal and the period when most ants (mutualists) and least rodents (predators) are active would be advantageous to the plant species.     

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.     

Spatial organization of a desert rodent community: food addition and species removal

Summary From 1977 through 1983 we conducted experiments on a desert rodent community where supplemental seeds were added or certain rodent species and ants were removed from 0.25-ha fenced plots in a Chihuahuan Desert site in southeastern Arizona, USA. In this paper we examine the patterns of microhabitat use relative to vegetative cover by 11 rodent species. The results show that: i) removal of the largest seed-eating species, Dipodomys spectabilis, produced the most pervasive and dramatic shifts in microhabitat use by the remaining rodent species; ii) adding seeds or removing ants had little effect on the spatial use of microhabitats by rodents in this community; and iii) non-granivores were just as likely as granivores to shift microhabitat use when other granivores were removed. We believe these results indicate that both food and foraging microsites are limited but the relegation of subdominant species to lesspreferred microhabitats by the large Dipodomys spectabilis is the major factor underlying the spatial organization of this community. Results also demonstrate that strong interactions among species increase the probability that pathways of indirect interactions through intermediary species are important; these complex linkages may include species that overlap little in food preferences.     

Competition with insectivorous ants as a contributor to low songbird diversity at low elevations in the eastern Himalaya

Competitive interactions between distantly related clades could cause complementary diversity patterns of these clades over large spatial scales. One such example might be ants and birds in the eastern Himalaya; ants are very common at low elevations but almost absent at mid‐elevations where the abundance of other arthropods and insectivorous bird diversity peaks. Here, we ask if ants at low elevations could compete with birds for arthropod prey. Specifically, we studied the impact of the Asian weaver ant (Oecophylla smaragdina), a common aggressive ant at low elevations. Diet analysis using molecular methods demonstrate extensive diet overlap between weaver ants and songbirds at both low and mid‐elevations. Trees without weaver ants have greater non‐ant arthropod abundance and leaf damage. Experimental removal of weaver ants results in an increase in the abundance of non‐ant arthropods. Notably, numbers of Coleoptera and Lepidoptera were most affected by removal experiments and were prominent components of both bird and weaver ant diets. Our results suggest that songbirds and weaver ants might potentially compete with each other for arthropod prey at low elevations, thereby contributing to lower insectivorous bird diversity at low elevations in eastern Himalaya. Competition with ants may shape vertebrate diversity patterns across broad biodiversity gradients.     

The effects of ants on herbivory and herbivore numbers on foliage of the mallee eucalypt,Eucalyptus incrassata Labill.*

Although there has been much recent interest in ant-plant mutualisms, few data are available on the effects of foraging ants on herbivore numbers and levels of herbivory on plants that do not offer specific inducements to attract ant visitation. In forestry plantations and tropical crops, ants have erratic but sometimes dramatic effects on the numbers of insect herbivores but, in more natural habitats, their effects on levels of herbivory appear to be largely unknown. In Australia, where ants and Eucalyptus woodlands are ubiquitous and abundant and where considerable debate has occurred regarding levels of herbivory in Eucalyptus forests, very little work has been done to examine the effects of ants on densities of insect herbivores on eucalypts. In this study, ants were experimentally excluded from mature and immature foliage of saplings of the mallee Eucalyptus incrassata in South Australia, and herbivore numbers and levels of leaf herbivory were assessed during the next 6 months. No significant differences in herbivory were found between ant-access and ant-exclusion treatments. In spring and early summer, ants were found in associations with aggregations of eurymelid bugs on young foliage, and the effects of ants on bug densities were experimentally investigated. Bug densities decreased rapidly in ant-exclusion treatments compared with ant-access controls. Ants also quickly removed seeds of E. incrassata from experimental caches. The potential of ants to limit the numbers of insect herbivores on eucalypts seems limited given their tendency to form mutualistic associations with sap-feeding Homopterans and because of a lack of other herbivores that are particularly vulnerable to ant predation.     

Effect of three mound-building ant species on the formation of soil seed bank in mountain grassland

The effect of three ant species (Lasius flavus, Formica spp., Tetramorium caespitum) on soil seed bank formation was studied in temperate mountain grassland. Seed removal experiments, analysis of soil seed content and seed survival experiments were carried out to evaluate the influence of ground ants on the seed fate. In the seed removal experiment seeds of 16 species, including 5 species with elaiosome-bearing seeds (myrmecochores), were exposed and their removal followed for 39 h. On average, ants removed 63.8% of myrmecochorous seeds and 10.9% of seeds without adaptation to ant dispersal. Analysis of soil seed content revealed that myrmecochores, in spite of expectations that they would accumulate in nests of seed dispersing ants, were most abundant in the soil of control plots. Evidence on seed relocation to the ant nests was obtained from a comparison of mounds of seed dispersing and seed non-dispersing ant species, as more seeds were found in the mounds of Formica spp. and Tetramorium caespitum (seed dispersers) in comparison with the mounds of Lasius favus (non-disperser).The soil seed bank of the compared microhabitats (control plots and mounds of 3 ant species) differed in their species composition, seed abundance and vertical distribution. The most distinct qualitative differences were between seed flora of control plots and mounds of Tetramorium caespitum. Control plots had approximately 30,000 propagules per m², which was double the number of seeds found in the ant mounds. In control plots, abundance and diversity of seeds steeply declined with depth; this trend was not observed in the mounds probably due to bioturbation. In the seed survival experiment, more seeds (2 out of 3 species) survived in control plots, which may also contribute to the higher seed abundance in this microhabitat.This study showed that seed relocation by ants does not contribute significantly to seed bank build-up at this study site. Ants may, however, increase the regeneration success of myrmecochores, mainly by dispersal for distance and placement in a larger spectrum of microsites, in contrast to species not adapted for myrmecochory.     

大耳姬鼠对滇西北18种植物种子的捕食

2004年9月至10月在滇西北高海拔地区对18种植物种子进行了野外被捕食研究。选取高、低两种人为干扰程度的生境;高、低两种种子密度:3粒种子/塑料盘和15粒种子/塑料盘;3种试验设置:排除啮齿动物等大型捕食者、排除蚂蚁等小型捕食者,不作任何处理作为对照。其结果表明,种子捕食者主要为夜间活动的大耳姬鼠(Apodemus latronum)。种子在高人为干扰的生境中被捕食率要显著低于低人为干扰的生境(F1,430=7.78,P<0.01);种子在高密度状况下的被捕食率要显著高于低密度状况(F1,430=13.16,P<0.001)。大耳姬鼠对于不同种类植物种子也有很强的选择性(F17,414=106.69,P<0.001),如喜好取食华山松(Pinus armandi)、中甸乌头(Aconitum chungdianensis)、豆科一种(Leguminosae sp.)和大头续断(Dipsacusasper)的种子,而不喜好取食高山柏(Sabina squamata)、黄花木(Piptanthus concolor)、子(Cotoneaster sp.)和西南鸢尾(Iris bulleyana)的种子。18种植物中,种子大小与其被捕食率高低之间无显著相关性,不同硬度等级的种子与被捕食率也无显著差异(P>0.05)。     

Natural Control of Helicoverpa armigera in Sunflower: Assessment of the Role of Predation

In three field experiments in Kenya , the seasonal population trend of Helicoverpa armigera (Hubner) (= Heliothis armigera) in sunflower was followed in plots from which predators were excluded and in plots from which predators were not excluded . In experiment 1 , complete exclusion of crawling predators (predominantly Pheidole spp . of ants occurring at densities of 25 per plant) resulted in H. armigera densities 3 - 5 times higher than in plots where ants were not excluded . Pheidole sp . had more impact on young H. armigera larvae (instars 2 - 3) than on older larvae (instars 4 - 6) . The results of experiment 2 were less striking , because H. armigera infestation was low , and ant densities were moderate . Here , Myrmicaria spp . and Camponotus spp . were the predominant ants . Exclusion of ants resulted in a 1 . 8 - fold increase in densities of large H. armigera instars . In experiment 3 , the impact of predators on H. armigera was studied under three conditions: exclusion of crawling predators , exclusion of both crawling and flying predators , and the control where no predators were excluded . To evaluate the role of predation in total mortality , the recruitment of H. armigera larvae was determined with Southwood and Jepson ' s graphical method , and recruitment of newly laid eggs was directly measured on trap plants . Because it was difficult to detect older eggs due to colour change , the direct measurement of egg recruitment was superior to the graphical method . Ants and Anthocoridae were the dominant predators . M ortality from egg to older larvae (instars 4 - 6) was 73 - 78% . Exclusion of ants and anthocorids did not affect the densities of H. armigera larvae . Anthocorid predators increased only after the main oviposi tion peak of H. armigera and , therefore , their exclusion had little impact on the pest . Ant density was considerably lower than in experiment 1 , and did not significantly suppress H. armigera.     

Recolonization by ants of rehabilitated mineral sand mines on North Stradbroke Island,Queensland, with particular reference to seed removal

The ant fauna of 12 sand-mined plots representing a range of rehabilitation ages and three undisturbed vegetation controls was surveyed during 1982. Physical and botanical parameters were also measured in each plot. Sixty-four ant species were collected from the 15 study plots, of which 44 had colonized one or more of the mined plots. Ant recolonization proceeded rapidly in plots up to 6 years old and may have been influenced by the passage of time, plant cover, density and diversity variables, the amount of litter and by the paucity of logs. In terms of ant species composition, the mined plots were most different from the undisturbed areas. The older plots exhibited a lower ant species richness and this is believed to have resulted from interspecific competition with the tramp ant, Pheidole megacephala. Ant succession proceeded in a slower fashion in the plots dominated by P megacephala. The influence of ants on seeds applied during broadcast seeding of rehabilitated areas was also investigated. Seed removal by ants was greatest for the arillate seeds of Acacia concurrens but moderate quantities of Allocasuarina spp., Eucalyptus spp. Xanthorrhoea sp. and Banksia spp. were taken also. Seed removal by ants was low in the areas which had recently had topsoil applied except where ants foraged from adjacent rehabilitation areas; here they exerted their influence up to 50 m across the fresh topsoil. Seed removal rates in topsoil adjacent to forest were low. Removal rates in a revegetated area 2.5 years old approached those in forest. This indicates that the previous ant-seed relationship had been partially restored by this time, although the relative contribution of seed harvesters and elaiosome collectors still needs to be assessed.     

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

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

Response of the foraging behaviour of red wood ants (Formica rufa group) to exclusion from trees

Abstract 1 Because of the large numbers within a colony and their aggressive nature, red wood ants (Formica rufa group) have a potential to greatly influence the cold‐temperate forest ecosystem. Wood ants are omnivorous and hunt in trees as well as on the forest floor. 2 A field experiment in a mixed forest in central Sweden was carried out to examine (i) the foraging behaviour of wood ants on the forest floor and (ii) the impact of increased numbers of wood ants on the soil fauna. The foraging behaviour of wood ants was manipulated by excluding the ants from their food resources in the tree canopy, with the intention to increase ant activity on the forest floor. To estimate this activity, the number of trees with foraging ants, the numbers of ants going to and from their nests and the prey carried by home‐running wood ants were determined during the summer period. Pitfall traps were placed in the soil to determine effects on mobile soil invertebrates. 3 When excluded from local trees, wood ants searched other trees further away from the nests rather than searching more intensively for prey on the forest floor. By contrast to the initial hypothesis, more soil‐living prey were caught by ants in the control plots than in the plots where the local trees were not accessible to the wood ants. The proportion of soil‐living to tree‐living prey tended to be greater in the control plots. 4 In the treated plots (no access to the trees), wood ants had a negative effect on the activity of Linyphiidae spiders. There was little effect of wood ants on other soil invertebrates. 5 This study suggests that the role of wood ants as top predators in the forest soil food‐web in central Sweden is limited.     

Effect of neighboring seeds associated with habitats on the seed removal of two coexisting myrmecochorous plants in central China

Although neighboring plants can influence animal-seed dispersal interactions, little is known about the effect of neighboring seeds and the influence of habitat on seed dispersal by ants. Here we investigated the influence of neighboring seeds on seed removal in two coexisting myrmecochorous species (Epimedium pubescens and Helleborus thibetanus) from temperate deciduous forests of Qinling Mountains, central China, by examining (1) the potential role of ants and rodents and (2) whether the neighboring seed effect differed between forest edge and interior. We found that, presence of the higher-ESMR (elaiosome: seed mass ratio) E. pubescens did not significantly affect seed removal of the lower-ESMR H. thibetanus. By contrast, the presence of H. thibetanus decreased the seed removal rates of E. pubescens, with only a significant effect in rodent exclusion (ant alone) rather than in both ant exclusion (rodent alone) and full access (rodent + ant). Moreover, we found that those effects were not significantly different between the forest edge and the interior, which may be attributed to a similar pattern of overall seed-dispersing ant abundance in the two habitats. This suggested that neighboring seeds could influence seed removal of the focal plant depending on the absence of rodents; when rodents were present, the interaction of rodents and ants rendered no influence of neighboring seeds on seed removal. Our results show that the neighborhood effect was regulated by both dispersers and predators, and this effect was not context-dependent at a small spatial scale. This study highlights the importance to understand the effect of shared seed-removing animals and habitat context to assess the neighboring seed effect on plant-animal interactions.     

Are red imported fire ants facilitators of native seed dispersal?

Invasive ants threaten native communities, in part, through their potential to disrupt mutualisms, yet invasive species may also facilitate native species. The red imported fire ant (Solenopsis invicta) is one of the most conspicuous invasive ants in North America and its high densities, combined with its potential to displace native ants, have led to concerns that it may disrupt ant-plant seed dispersal mutualisms. We examined the potential of fire ants to disperse seeds in the longleaf pine ecosystem by comparing the removal of elaiosome-bearing seeds by fire ants versus native ants. A total of 14 ant species were observed removing seeds, with fire ants responsible for more than half of all removals. While fire ants were the dominant seed remover in this system, they did not remove significantly more seeds than would be expected based on their population density (46% of ground-dwelling ants). Moreover, red imported fire ants were similar to native ants with respect to distance of seed movement and frequency of moving seeds back to the nest. Areas of higher fire ant densities were found to have greater rates of seed removal by ants without a subsequent drop in seed dispersal by native ants, suggesting that fire ant-invaded areas may experience overall higher levels of seed dispersal. Thus, fire ants may actually facilitate dispersal of elaiosome-bearing plant species in the longleaf pine ecosystem.     

Ecosystem engineering and predation: the multi-trophic impact of two ant species

1. Ants are ubiquitous ecosystem engineers and generalist predators and are able to affect ecological communities via both pathways. They are likely to influence any other terrestrial arthropod group either directly or indirectly caused by their high abundance and territoriality. 2. We studied the impact of two ant species common in Central Europe, Myrmica rubra and Lasius niger, on an arthropod community. Colony presence and density of these two ant species were manipulated in a field experiment from the start of ant activity in spring to late summer. 3. The experiment revealed a positive influence of the presence of one ant colony on densities of decomposers, herbivores and parasitoids. However, in the case of herbivores and parasitoids, this effect was reversed in the presence of two colonies. 4. Generally, effects of the two ant species were similar with the exception of their effect on Braconidae parasitoid densities that responded positively to one colony of M. rubra but not of L. niger. 5. Spider density was not affected by ant colony manipulation, but species richness of spiders responded positively to ant presence. This effect was independent of ant colony density, but where two colonies were present, spider richness was significantly greater in plots with two M. rubra colonies than in plots with one colony of each ant species. 6. To test whether the positive ecosystem engineering effects were purely caused by modified properties of the soil, we added in an additional experiment (i) the soil from ant nests (without ants) or (ii) unmodified soil or (iii) ant nests (including ants) to experimental plots. Ant nest soil on its own did not have a significant impact on densities of decomposers, herbivores or predators, which were significantly, and positively, affected by the addition of an intact nest. 7. The results suggest an important role of both ant species in the grassland food web, strongly affecting the densities of decomposers, herbivores and higher trophic levels. We discuss how the relative impact via bottom-up and top-down effects of ants depends on nest density, with a relatively greater top-down predatory impact at higher densities.     

Influence of native ants on arthropod communities in a vineyard

• 1 Ants can have a range of effects on arthropods in crops, including suppressing herbivores such as caterpillars. However, ants can also increase hemipteran densities while reducing natural enemy numbers. In vineyard ecosystem, the effects of native ants and their interactions with other arthropods are poorly understood.
• 2 An ant‐exclusion experiment was designed to test the impact of native ants on both canopy and ground arthropods concurrently. The potential influence of ants on predation and parasitism of light brown apple moth (LBAM) eggs, a grape pest, was also examined. Adult grapevine scale insects and earwigs under bark were counted after a season of ant‐exclusion.
• 3 Among 23 ground ant species collected, six were found to forage in the canopy, with two Iridomyrmex species being the most commonly encountered.
• 4 There was no difference in the abundance of most arthropod orders and feeding groups between ant‐excluded and control vines, although ground spiders were more abundant under ant‐excluded vines, despite increased ground ant foraging pressure. LBAM egg parasitism and predation were low and probably affected by weather and other arthropods. Ant exclusion did not reduce survival of scale insects, although the distribution and abundance of scale insects were negatively associated with earwigs.
• 5 In conclusion, native ants did not consistently suppress arthropod assemblages, including natural enemies, and they did not promote the survival of scale insects. Interactions among native ant species within a vineyard might minimize their effects on other arthropods, although this needs further study.

     

中国东南部农区蚂蚁物种多样性研究

为探清我国东南部农区内蚂蚁物种多样性,本研究共设置86个采样单元格,每个单元格内选择农田、草地和人工林3种生境,每种生境设置3个重复样地,每个重复生境设置5个1 m2的重复采样样方,用吸虫器采集样方内的地表蚂蚁。结果表明：在我国东南部农区共采集鉴定地表蚂蚁30 077头,隶属于7亚科49属155种;长江中下游地区共采集蚂蚁5亚科34属93种,其中优势种3个,常见种9个,稀有种81个;华南地区采集蚂蚁7亚科42属124种,其中优势种2个,常见种11个,稀有种111个。红火蚁Solenopsis invicta Buren是华南地区个体数目最多的物种,占个体总数的39.40%;物种数目、个体密度、多样性指数和优势度指数均表现为华南地区＞长江中下游地区;不同生境内蚂蚁群落的物种数目、多样性指数和均匀度指数表现为人工林＞草地＞农田,个体密度和优势度指数人工林生境最低;两个地区3种生境蚂蚁群落间相似性系数0.2437~0.6581,处于极不相似至中等相似水平。结果表明,我国东南部农区蚂蚁种类丰富,在农区的生物多样性保护中具有重要价值;红火蚁在华南地区入侵扩散严重,亟需治理;农区内不同土地利用方式造成的生境差异影响蚂蚁群落的物种组成和多样性;不同区域、不同生境的蚂蚁群落间差异明显。     

Experimental evidence for weak effects of fire ants in a naturally invaded pine‐savanna ecosystem in north Florida

1. Fire ants naturally invade some undisturbed ecosystems of high conservation value and may negatively impact co‐occurring ants. 2. Over 3 years, fire ants were added and removed from a longleaf pine savanna ecosystem that naturally supports a low density of fire ants. Impacts on co‐occurring ants were monitored using pitfall traps. 3. Treatments resulted in significant differences in average fire ant abundance across all plots only in the first year of the experiment. Fire ants had little discernible impact. The abundance and species richness of co‐occurring ants in removal plots never differed from unmanipulated control plots. The abundance of co‐occurring ants was very slightly lower and ant species richness was slightly higher where Solenopsis invicta Buren colonies were added, but neither contrast was significant. 4. The poor conditions in this habitat for many native ants may explain this outcome. More broadly, the impact of fire ants on ant assemblages still appears to be secondary and largely a consequence of human impacts on the environment.