Effects of bird predation on canopy arthropods in wandoo Eucalyptus wandoo woodland

Abstract: As top predators, birds may have significant effects on arthropod abundances and affect the trophic structure of arthropod communities through predation of lower order predators (e.g. spiders) and by competition for prey. We investigated the effects of bird predation on canopy arthropods in south‐western Australia by using plastic bird mesh to exclude insectivorous birds from the foliage of wandoo Eucalyptus wandoo saplings. Exclosure resulted in an increase in the number of herbivorous and predatory arthropods. Total arthropods (with and without ants), spiders, adult Coleoptera, and larval Lepidoptera were significantly more abundant on meshed than unmeshed saplings. All size‐classes of arthropods, taxa grouped, were more abundant on meshed than unmeshed saplings, but with no evidence of a disproportionate increase of the largest arthropods on meshed saplings. All size‐classes of spiders increased in abundance on saplings from which birds were excluded. There were significant differences in the total abundance of arthropods (with and without ants), spiders (Araneae), sucking bugs (Homoptera), adult beetles (Coleoptera), larval moths (Lepidoptera), and wasps and ants (Hymenoptera) for both unmeshed and meshed saplings between sample periods. These seasonal patterns of abundance and differences between sample periods appeared to be determined by seasonal weather patterns, with the lowest numbers associated with drier and hotter conditions in summer and autumn than in winter and spring. The conclusion reached is that eucalypt forest birds have limited effects on temporal variation in canopy arthropod abundances, but depress abundances, and affect the size and trophic composition of the fauna. Given the cascading effects of birds as predators on arthropods, successful conservation management of eucalypt ecosystems, including plantations and revegetation, should be planned to maximize bird numbers and diversity.     

Contrasting cascades: insectivorous birds increase pine but not parasitic mistletoe growth

1. Intraguild predation occurs when top predators feed upon both intermediate predators and herbivores. Intraguild predators may thus have little net impact on herbivore abundance. Variation among communities in the strength of trophic cascades (the indirect effects of predators on plants) may be due to differing frequencies of intraguild predation. Less is known about the influence of variation within communities in predator-predator interactions upon trophic cascade strength. 2. We compared the effects of a single predator community between two sympatric plants and two herbivore guilds. We excluded insectivorous birds with cages from ponderosa pine Pinus ponderosa trees parasitized by dwarf mistletoe Arceuthobium vaginatum. For 3 years we monitored caged and control trees for predatory arthropods that moved between the two plants, foliage-feeding caterpillars and sap-feeding hemipterans that were host-specific, and plant damage and growth. 3. Excluding birds increased the abundance of ant-tended aphids on pine and resulted in an 11% reduction in pine woody growth. Mutualist ants protected pine-feeding aphids from predatory arthropods, allowing aphid populations to burgeon in cages even though predatory arthropods also increased in cages. By protecting pine-feeding aphids from predatory arthropods but not birds, mutualist ants created a three-tiered linear food chain where bird effects cascaded to pine growth via aphids. 4. In contrast to the results for tended aphids on pine, bird exclusion had no net effects on untended pine herbivores, the proportion of pine foliage damaged by pine-feeding caterpillars, or the proportion of mistletoe plants damaged by mistletoe-feeding caterpillars. These results suggest that arthropod predators, which were more abundant in cages as compared with control trees, compensated for bird predation of untended pine and mistletoe herbivores. 5. These contrasting effects of bird exclusion support food web theory: where birds were connected to pine by a linear food chain, a trophic cascade occurred. Where birds fed as intraguild predators, the reticulate food webs linking birds to pine and mistletoe resulted in no net effects on herbivores or plant biomass. Our study shows that this variation in food web structure occurred between sympatric plants and within plants between differing herbivore guilds.     

Eight years of ant‐exclusion from citrus canopies: effects on the arthropod assemblage and on fruit yield

• 1 Ants are important generalist predators in most terrestrial ecosystems. However, because many ant species are also hemipteran mutualists, their role in agriculture has generally been considered to be negative for plants.
• 2 In the present study, we report an experiment in ant‐exclusion from tree canopies in an organic citrus grove with two main objectives: (i) to examine whether the absence of ants increased the abundance of some beneficial arthropods and reduced the attack of some pests such as aphids and (ii) to examine whether ant‐exclusion increased the fruit yield of citrus trees.
• 3 The exclusion of ants from tree canopies had positive effects on the arthropod assemblage and on fruit yield. However, the 8‐year duration of the experiment can be divided into two periods with contrasting results. In the first period, the arthropod assemblage was only slightly affected, except for a greater density of aphids in ant‐excluded trees; in addition, fruit yield was higher in ant‐excluded trees than in the control ones. In the second period, ant‐exclusion increased the abundance of most arthropod groups, although the previous positive effect on fruit yield was no longer observed.
• 4 There are two main conclusions of the present study. First, from an applied perspective, ant‐exclusion from tree canopies is not a sound management alternative in citrus plantations in the Mediterranean. Second, the 8‐year duration of the experiment highlighted the importance of long‐term experiments in community ecology and biological control because the effects observed in the first 4 years of the experiment were very different from what occurred subsequently.

     

Negative effects of ant foraging on spiders in Douglas-fir canopies

 Spiders and ants are potential competitors and mutual predators. Indirect evidence from previous research has suggested that ant foraging may significantly lower the abundance of arboreal spiders in young Douglas-fir plantations in western Oregon. This study tested the effect of foraging by ants, dominated by Camponotus spp., on spider assemblages in Douglas-fir canopies in a 5-month ant-exclusion experiment. The biomass of potential prey organisms on foliage, dominated by Psocoptera, increased significantly by 1.9- to 2.4-fold following ant exclusion. The removal of ants did not affect the abundance of flying arthropods in the vicinity of tree canopies as indicated by sticky trap catches. The abundance of hunting spiders, the majority being Salticidae, increased significantly by 1.5- to 1.8-fold in trees without ants in the late summer; neither the abundance of web-building spiders nor the average body size of hunting and web-building spiders were significantly affected by ant removal. Spider diversity and community structure did not differ significantly between control and ant-removal trees. The majority of prey captured by ants were Aphidoidea (48.1%) and Psocoptera (12.5%); spiders represented only 1.4% of the ants’ diet. About 40% of observed ants were tending Cinara spp. aphids. Our observations suggest that the lower abundance of hunting spiders in control canopies with ants may be due to interference competition with ants resulting from ant foraging and aphid-tending activities. Direct predation of spiders by ants appeared to be of minor importance in this study system. This study did not provide sufficient evidence for exploitative competition for prey between ants and spiders. Received: 21 February 1996 / Accepted: 14 August 1996     

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.

     

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.     

Disruption of ant-aphid mutualism in canopy enhances the abundance of beetles on the forest floor

Ant-aphid mutualism is known to play a key role in the structure of the arthropod community in the tree canopy, but its possible ecological effects for the forest floor are unknown. We hypothesized that aphids in the canopy can increase the abundance of ants on the forest floor, thus intensifying the impacts of ants on other arthropods on the forest floor. We tested this hypothesis in a deciduous temperate forest in Beijing, China. We excluded the aphid-tending ants Lasius fuliginosus from the canopy using plots of varying sizes, and monitored the change in the abundance of ants and other arthropods on the forest floor in the treated and control plots. We also surveyed the abundance of ants and other arthropods on the forest floor to explore the relationships between ants and other arthropods in the field. Through a three-year experimental study, we found that the exclusion of ants from the canopy significantly decreased the abundance of ants on the forest floor, but increased the abundance of beetles, although the effect was only significant in the large ant-exclusion plot (80*60 m). The field survey showed that the abundance of both beetles and spiders was negatively related to the abundance of ants. These results suggest that aphids located in the tree canopy have indirect negative effects on beetles by enhancing the ant abundance on the forest floor. Considering that most of the beetles in our study are important predators, the ant-aphid mutualism can have further trophic cascading effects on the forest floor food web.     

Effects of ant competition and bird predation on the spider assemblage of a citrus grove

Characterizing intraguild interactions is key to improving understanding of food webs because they are major forces in the structuring of communities. Spiders are generalist predators with intermediate positions in the food web that establish intraguild interactions with ants and birds, which respectively compete with and prey on them. Research has also found interactions between birds and ants, potentially resulting in non-additive effects of both groups on arthropod assemblages, although studies of their combined impacts with tests for multiple-predator effects are scarce. We thus aimed to discern the relative effect of ants and birds on the spider assemblage of a citrus grove. We used a split-plot design to factorially exclude these groups over 2 years, preventing ants reaching the canopies by placing sticky bands around tree trunks, and birds by enclosing groups of trees in cages. We sampled spiders from the canopies (beating) and the ground (pitfalls) every 3 months, and we identified them to species. We found a strong influence of ants on the canopy spider assemblage, mainly through a negative effect on the families Araneidae and Theridiidae. Since spiders’ weights from ant-excluded and control trees were similar, these results suggest interference competition of ants on spiders rather than competitive exploitation. Bird exclusion did not affect the spider assemblage, contrasting with other studies reporting a marked predatory pressure of birds on spiders; nor were there any non-additive effects of ants and birds. Our findings show that spider assemblages are not uniformly affected by intraguild competitors.     

Maize‐field complexity and farming system influence insectivorous birds’ contribution to arthropod herbivore regulation

The contribution of insectivorous birds to reducing crop damage through suppression of herbivory remains underappreciated, despite their role as cropland arthropod predators. We examined the roles of farming system, crop cover pattern, and structural configuration in influencing assemblage composition of insectivorous birds and their herbivorous arthropod prey across maize fields, and determined how bird exclusion affects crop herbivory levels. To achieve these objectives, we collected data across a sample of organic and conventional small‐scale non‐Bt maize farms in western Kenya. Assessments of abundance, diversity, and richness of insectivorous birds and abundance of their arthropod prey were compared between organic and conventional small‐scale non‐Bt maize on monocultured and inter‐cropped farms. We also employed bird exclusion experiments to assess impacts of bird predation on herbivorous arthropod abundance. Results showed that higher structural heterogeneity supported higher insectivorous bird richness, particularly under organic systems, dense trees, large woodlots, and thick hedgerows. Bird abundance further increased with crop diversity but not in relation to cropping method, hedgerow type, or percent maize cover per se. Conversely, herbivorous arthropod abundance and richness increased on conventional farms and those with higher percent maize cover, but were unaffected by cropping methods, tree, or hedgerow characteristics. Birds’ arthropod prey was more abundant under completely closed experimental plots compared with open or semi‐closed plots, confirming a significant linkage between birds and herbivorous arthropod suppression. In this study, we demonstrate importance of structural heterogeneity in agricultural landscapes, including diverse croplands and on‐farm trees to maximize insectivorous birds’ contribution to reducing crop arthropod herbivory. Abstract in Swahili is available with online material.     

Plant-attracted ants affect arthropod community structure but not necessarily herbivory

Abstract.  1. The effectiveness of ants as plant defenders is equivocal for plants that attract ants via extrafloral nectaries (EFNs).
2. This study focused on the myrmecophilic savannah tree Pseudocedrela kotschyi that attracts ants to EFNs and on the arthropod fauna associated with P. kotschyi . Herbivory and arthropod community composition were compared between trees that were dominated by one of three congeneric ant species, Camponotus acvapimensis , C. rufoglaucus , and C. sericeus , and between trees where ants were experimentally excluded and untreated control trees.
3. Short-term ant-exclusion experiments failed to demonstrate a consistent effect of ants on herbivory.
4. Plants dominated by different ant species differed significantly in leaf damage caused by herbivorous insects. The relative ranking of herbivory levels of the trees dominated by different ant species was persistent in three consecutive years.
5. Ants significantly reduced the abundance of different arthropod groups (Araneae, Blattodea, Coleoptera, Homoptera, non-ant Hymenoptera). Other groups, including important herbivores, seemed not to be affected (Lepidoptera, Orthoptera, Thysanoptera, Heteroptera).
6. The study suggests that the presence of ants only benefits plants when specific ant species are attracted, and protection by these ants is not counterbalanced by their negative effect on other beneficial arthropods.     

Similar yet different: differential response of a praying mantis to ant‐mimicking spiders

Batesian mimics typically dupe visual predators by resembling noxious or deadly model species. Ants are unpalatable and dangerous to many arthropod taxa, and are popular invertebrate models in mimicry studies. Ant mimicry by spiders, especially jumping spiders, has been studied and researchers have examined whether visual predators can distinguish between the ant model, spider mimic and spider non‐mimics. Tropical habitats harbour a diverse community of ants, their mimics and predators. In one such tripartite mimicry system, we investigated the response of an invertebrate visual predator, the ant‐mimicking praying mantis (Euantissa pulchra), to two related ant‐mimicking spider prey of the genus Myrmarachne, each closely mimicking its model ant species. We found that weaver ants (Oecophylla smaragdina) were much more aggressive than carpenter ants (Camponotus sericeus) towards the mantis. Additionally, mantids exhibited the same aversive response towards ants and their mimics. More importantly, mantids approached carpenter ant‐mimicking spiders significantly more than often that they approached weaver ant‐mimicking spiders. Thus, in this study, we show that an invertebrate predator, the praying mantis, can indeed discriminate between two closely related mimetic prey. The exact mechanism of the discrimination remains to be tested, but it is likely to depend on the level of mimetic accuracy by the spiders and on the aggressiveness of the ant model organism.     

Top-down control of herbivory by birds and bats in the canopy of temperate broad-leaved oaks (Quercus robur)

The intensive foraging of insectivorous birds and bats is well known to reduce the density of arboreal herbivorous arthropods but quantification of collateral leaf damage remains limited for temperate forest canopies. We conducted exclusion experiments with nets in the crowns of young and mature oaks, Quercus robur, in south and central Germany to investigate the extent to which aerial vertebrates reduce herbivory through predation. We repeatedly estimated leaf damage throughout the vegetation period. Exclusion of birds and bats led to a distinct increase in arthropod herbivory, emphasizing the prominent role of vertebrate predators in controlling arthropods. Leaf damage (e.g., number of holes) differed strongly between sites and was 59% higher in south Germany, where species richness of vertebrate predators and relative oak density were lower compared with our other study site in central Germany. The effects of bird and bat exclusion on herbivory were 19% greater on young than on mature trees in south Germany. Our results support previous studies that have demonstrated clear effects of insectivorous vertebrates on leaf damage through the control of herbivorous arthropods. Moreover, our comparative approach on quantification of leaf damage highlights the importance of local attributes such as tree age, forest composition and species richness of vertebrate predators for control of arthropod herbivory.     

Lack of ant attendance may induce compensatory plant growth

Three levels in ant–plant protection systems need to be considered to fully understand how these symbiotic systems work. Here we present the effect of Oecophylla smaragdina ants on (1) the arthropod community, (2) herbivory, and (3) plant performance, within a studied mangrove ant–plant protection system. On Rhizophora mucronata trees in Thailand ants successfully colonised ant trees attached with a string to a natural ant tree, whereas they were unable to colonise control trees without this connection. Trees were monitored and arthropods (numbers and composition), leaf damage, leaf turnover and growth rates (stem diameter, tree height and total leaf area) were recorded in two surveys covering a period of 12 months. The number of herbivorous arthropods, but not the number of predators, was significantly lower on ant trees compared to control trees. Likewise, the amount of leaf damage inflicted by the four major groups of herbivores (Chrysomelidae, Tortricidae, Geometridae and Sesarminae) was significantly lower on ant trees compared to control trees and so was the leaf turnover rate. In spite of this, the released herbivore pressure on ant trees did not translate into higher growth rates. In contrast, all growth responses increased more on control trees compared to ant trees. Differences between the two groups were insignificant but leaf area increase was only marginally nonsignificant (P=0.062). The results show that ants remove herbivorous arthropods more efficiently than predators but ant-colonised mangroves do not necessarily benefit from this despite the resulting decrease in herbivory.     

Effects of ants on the foraging of birds in spruce trees

I experimentally excluded ants from randomly selected spruce trees Picea abies near colonies of the wood ant Formica aquilonia. Foraging activity of birds in these trees was then compared to the foraging activity of birds in neighboring spruce trees, where ants were allowed to continue foraging. Birds which foraged in the foliage showed the effects of competition with ants: they visited the trees without ants more frequently, and for longer periods. In addition, the insects and spiders that they utilized as food were more abundant in the foliage of trees without ants. Cone-foraging birds, however, which fed on seeds in cones at the tops of the trees, did not show a preference for trees without ants. The differences of tree usage between foliage-gleaning and coneforaging birds can be explained by alteration of the birds' food supply by wood ants: ants did not feed on seeds in cones, and so did not compete with cone-foraging birds. However, foraging wood ants did feed on arthropods living in the foliage, thus reducing the amount of food available to birds there.     

Argentine ants displace floral arthropods in a biodiversity hotspot

Argentine ant (Linepithema humile (Mayr)) invasions are often associated with the displacement of ground‐dwelling arthropods. Argentine ant invasions can also exert other effects on the community through interactions with plants and their associated arthropods. For example, carbohydrate resources (e.g. floral or extrafloral nectar) may influence foraging behaviour and interactions among ants and other arthropods. In South Africa's Cape Floristic Region, Argentine ants and some native ant species are attracted to the floral nectar of Leucospermum conocarpodendron Rourke (Proteaceae), a native tree that also has extrafloral nectaries (EFNs). Despite having relatively low abundance in pitfall traps, Argentine ants visited inflorescences more frequently and in higher abundance than the most frequently observed native ants, Camponotus spp., though neither native nor Argentine ant floral foraging was influenced by the EFNs. Non‐metric multidimensional scaling revealed significant dissimilarity in arthropod communities on inflorescences with Argentine ants compared to inflorescences with native or no ants, with Coleoptera, Diptera, Hymenoptera, Arachnida, Orthoptera, and Blattaria all being underrepresented in inflorescences with Argentine ants compared to ant‐excluded inflorescences. Native honeybees (Apis mellifera capensis Eschscholtz) spent 75% less time foraging on inflorescences with Argentine ants than on inflorescences without ants. Neither Argentine ant nor native ant visits to inflorescences had a detectable effect on seed set of Le. conocarpodendron. However, a pollen supplementation experiment revealed that like many other proteas, Le. conocarpodendron is not pollen‐limited. Flower predation was negatively associated with increased ant visit frequency to the inflorescences, but did not differ among inflorescences visited by native and Argentine ants. Displacement of arthropods appears to be a consistent consequence of Argentine ant invasions. The displacement of floral arthropods by Argentine ants may have far‐reaching consequences for this biodiversity hotspot and other regions that are rich in insect‐pollinated plants.     

Comparing four simple,inexpensive methods for sampling forest arthropod communities

Terrestrial arthropods are diverse, and quantifying their availability to consumers is important for understanding both consumer and insect distribution, abundance, and communities. However, characterizing arthropod communities in complex forest ecosystems is challenging. We compared arthropod communities in a wet‐limestone forest in Jamaica during the dry season sampled by four methods: branch clips, sweep netting, and sticky traps applied to tree trunks and hanging free of vegetation. We found no effect of relative height in the canopy for the two methods that could be used at different heights, i.e., hanging sticky traps and branch clips. In addition, the arthropod community sampled changed over time (season) for sweep nets and branch clips. We also found that branch clips and sweep nets sampled more arthropod taxa than the two sticky‐trap methods. In addition, branch clips and sweep nets sampled more ants and spiders than the two sticky‐trap methods, whereas collar sticky traps on tree trunks sampled more bark lice (Psocoptera), and hanging sticky traps more flies (Diptera) than the other methods. Percentages of flying insects and strong‐flying insects sampled did not differ between sweep netting and branch clipping, but a higher percentage of both groups were captured with collar and hanging sticky traps. Because we found that the different methods sampled different subsets of the arthropod community, both taxonomically and in terms of aerial versus non‐aerial taxa, investigators should choose the arthropod sampling methods that most closely align with their focal species and study questions. For example, investigators might use collar traps for studies of bark gleaners, hanging sticky traps for aerial foragers, and branch clips or sweep nets for foliage gleaners. Alternatively, if a focal species is known to prefer certain prey items, investigators may instead select a method that effectively samples those prey taxa. Finally, for some studies, using multiple sampling methods may be the best option.     

Effects of Shade‐Tree Species and Crop Structure on the Winter Arthropod and Bird Communities in a Jamaican Shade Coffee Plantation1

I examined the effects of two farm management variables, shade‐tree species and crop structure, on the winter (dry season) arthropod and bird communities in a Jamaican shade coffee plantation. Birds and canopy arthropods were more abundant in areas of the plantation shaded by the tree Inga vera than by Pseudalbizia berteroana. The abundance of arthropods (potential pests) on the coffee crop, however, was unaffected by shade‐tree species. Canopy arthropods, particularly psyllids (Homoptera), were especially abundant on Inga in late winter, when it was producing new leaves and nectar‐rich flowers. Insectivorous and nectarivorous birds showed the strongest response to Inga; thus the concentration of birds in Inga may be a response to abundant food. Coffee‐tree arthropod abundance was much lower than in the shade trees and was affected little by farm management variables, although arthropods tended to be more abundant in dense (unpruned) than open (recently pruned) areas of the plantation. Perhaps in response, leaf‐gleaning insectivorous birds were more abundant in dense areas. These results underscore that although some shade coffee plantations may provide habitat for arthropod and bird communities, differences in farm management practices can significantly affect their abundances. Furthermore, this study provides evidence suggesting that bird communities in coffee respond to spatial variation in arthropod availability. I conclude that /. vera is a better shade tree than P. berteroana, but a choice in crop structures is less clear due to changing effects of prune management over time.     

Does Argentine ant invasion affect prey availability for foliage-gleaning birds?

Food availability during the breeding season plays a critical role in reproductive success of insectivorous birds. Given that the invasive Argentine ant (Linepithema humile) is known to alter arthropod communities, we predicted that its invasion may affect the availability of food resources for coexisting foliage-gleaning birds. With this aim we studied, for 3 years, foliage arthropods occurring on cork oaks (Quercus suber) and tree heaths (Erica arborea) in invaded and non-invaded secondary forests of the northeastern Iberian Peninsula. Our results show that Argentine ants interact with arboreal foliage arthropods in a different manner than the native ants they displace do. The invasive ant impacted the arthropod community by reducing order diversity and ant species richness and by causing extirpation of most native ant species. Arthropod availability for foliage gleaners’ nestlings diminished in invaded cork oaks, mainly responding to the abundance and biomass depletion of caterpillars. Results suggest that the reproduction of canopy-foraging foliage-gleaning species that mostly rely on caterpillars to feed their young could be compromised by the Argentine ant invasion. Thus, the Argentine ant could be promoting bottom-up effects in the trophic web through its effects on the availability of arthropod preys for insectivorous birds.     

Ants and plant size shape the structure of the arthropod community of Hirtella myrmecophila, an Amazonian ant-plant

Abstract.  1. To investigate the influence of plant size and the presence of resident ants on the arthropod community associated with the ant-plant Hirtella myrmecophila , ants ( Allomerus octoarticulatus ) were experimentally removed from plants of various sizes, with a second group of similar-sized plants remaining as controls. The abundance and diversity of arthropods on these plants were determined at 45-day intervals for 7 months. Collected arthropods were assigned into one of three predetermined groups: herbivores, spiders (mostly web-building spiders), or 'tourists' (mostly non-resident ants, hemipterans, dipterans, or scarabeid beetles).
2. Ant removal had a positive influence on the abundance and diversity of herbivores, but no measurable effects on the abundance and diversity of 'tourists', while the effect on spider abundance was significant only when data from Dipoena sp. nov. were removed from the analysis. While A. octoarticulatus had a negative effect on most spiders, it favoured Dipoena sp. nov., which was found to be a specialist predator of A. octoarticulatus .
3. Plant size positively affected the abundance and diversity of 'tourists' in plants with and without ants, but for herbivores and spiders this effect was dependent on ant treatment. In ant-maintained plants the per-plant abundance of herbivores and spiders was independent of plant size, whereas in ant-removed plants it was not.
4. These results suggest that A. octoarticulatus affects all arthropods found on its host plant, except those presenting an occasional and temporary association with the plant, and that the magnitude of ant effects on the susceptible guilds increases as plant size increases.