Ant- and termite-eating in Australian mammals and lizards: a comparison

Abstract Relative abundance is one factor that influences selection of prey by insectivorous mammals and lizards. Ants and termites are extremely abundant over most of inland Australia. Their patterns of abundance are also broadly similar across climatic gradients, being most and least abundant in seasonally arid (tropic and sub-tropic) and temperate mesic regions, respectively. All else being equal (e. g. mechanisms of prey defence, palat-ability, availability), animals that eat many termites should also eat many (adult) ants. The present study asks three questions: (i) What is the diversity of specialized ant-eaters (>50% volume)?; (ii) Does specialization vary with climate?; and (iii) Are ants and termites eaten in broadly similar proportions (using an earlier study on termites). Of the mammals, only the echidna (Tachyglossus aculeatus) in mesic regions, and probably the marsupial mole (Notoryctes typhlops) in the arid zone and the striped possum (Dactylopsila trivirgata) in mesic regions are ant-specialized. Ant-specialization in mammals shows no pattern with regard to climate. Of the lizards, only four agamid lizards are ant-specialized: Moloch horridus (arid, semi-arid), Ctenophorus fordi (arid, semi-arid), Ctenophorus isolepis (arid) and Ctenophorus maculatus (arid). Specialization on ants by lizards is greatest in the arid zone (4 spp.); no lizard species were found to be ant-specialists in mesic regions. In the arid and semi-arid zone, two mammals each specialize on termites and one on ants; in mesic regions, two mammals specialize on ants and one on termites. Specialized insectivorous mammals thus demonstrate no marked preference for either termites or ants. Lizards, in contrast, are markedly termite-specialized (4 ant-specialist spp., 16 termite-specialist spp.), and specialization is greatest in the arid zone (16 spp.). Greater specialization on termites than on (adult) ants in lizards is explained with reference to differences in prey defence and palatability between ants and termites. Consumption of ant brood (eggs, larvae, pupae) appears to be associated with a fossorial foraging mode (the marsupial mole N. typhlops; spp. of Aprasia lizards; spp. of blindsnakes Ramphotyphlops).     

Community organization and species richness of ants (Hymenoptera/Formicidae) in Mongolia along an ecological gradient from steppe to Gobi desert

Aim Ants (Hymenoptera/Formicidae) have strong influences on ecosystems especially in arid regions. However, little is known about ants of the vast steppe and desert regions of Central Asia. Here we provide the first comprehensive study of ant communities in Mongolia, conducted along a north‐to‐south gradient in climate. We examined ants’ distribution patterns, assessed the impact of climatic parameters on community structure and species diversity and investigated the influence of the corresponding communities of plants. Location Mongolia (Central Asia). Methods We observed 31,956 ants at seed baits at 11 study sites along a transect from steppe to Gobi desert for which we attained meteorological data (mean yearly precipitation: 197 to 84 mm). Extra sampling was conducted at sugar and protein baits and by the inspection of different microhabitats. Vegetation patterns of each plot were recorded. Statistical evaluation comprised ordination and correlation. Results We observed 15 species of ants at seed baits. Three faunal complexes of ants could be distinguished by detrended correspondence analysis (DCA): (1) in steppe baits were dominated by Formica‐ and Myrmica‐species, (2) in semi desert we found mostly species of Tetramorium, Myrmica, Proformica, Plagiolepis, and Leptothorax, and (3) in desert Cataglyphis aenescens and Messor aciculatus dominated, and Lasius was exclusively found there. Another 11 rare ant species were sampled by hand and at sugar baits. Altogether five ant species were new to the Mongolian fauna: Cardiocondyla koshewnikovi, Myrmica koreana, Myrmica pisarskii, Polyergus nigerrimus, and Proformica kaszabi. Assignment of taxa to functional groups showed that in steppe cold climate specialists dominated, in semi desert we found mainly opportunists, and in desert hot climate specialists. Several functional groups know from arid zones in other parts of the world were missing. In desert certain species were highly dominant. First DCA scores of ant‐ and plant‐communities were highly correlated with each other and with climatic parameters. While plant species diversity was positively correlated with increasing northern latitude, ant diversity and ant species richness were not correlated with latitude and responded neither to precipitation, nor to any other climatic parameter. Semi desert was a transition zone between steppe and desert, with high species richness. Ant genus composition of the ecotone overlapped with both other regions. However, beta diversity between pairs of plots within this zone was low, indicating a small‐scale mosaic pattern. Main conclusions The ant communities in the Mongolian steppe and desert zones were strongly influenced by low temperatures and differed in many aspects from the ant fauna in other arid ecosystems, especially in terms of species richness, diversity of feeding guilds, and richness of functional groups.     

Responses of ants to disturbance in Australia,with particular reference to functional groups

Abstract Ants are widely used as bioindicators in environmental assessment in Australia, partly because the responses of ant communities to disturbance are relatively well understood. In particular, the use of functional groups has provided a predictive framework for analysing ant community responses to disturbance in the absence of reliable information on the responses of individual species. Here we review 45 studies of the responses of Australian ant communities to disturbance, in order to: (i) identify individual species or species‐groups that respond consistently to disturbance; and (ii) examine the usefulness of the functional group scheme as a framework for predicting ant community responses under different disturbance regimes in different biogeographical regions. The most common forms of disturbance in our studies were fire (17 studies), mining (12; mostly studies of minesite restoration) and grazing (7), with other disturbances including clearing, logging, flooding, recreation, urbanization and farming. Responses of individual species were inevitably variable because of differences in vegetation type, severity of disturbance and time since disturbance. However, we identified a range of widespread species that showed predictable responses, including species of the metallica group of Rhytidoponera in temperate Australia (‘increasers’ in relation to disturbance), species of the terebrans and denticulatus groups of Camponotus (increasers), the aeneovirens group of Melophorus (increasers) from the arid zone, and Iridomyrmex pallidus (increaser) from the monsoonal region. The functional group scheme assessed here was not designed specifically in the context of disturbance, but nevertheless in some situations provides a useful framework for analysing ant community responses. Three distinct syndromes of functional group responses can be recognized. First, Dominant Dolichoderinae and Hot Climate Specialists are groups that prefer open environments, and tend to be favoured by low levels of disturbance in well‐forested habitats. Second, Opportunists and often also Generalized Myrmicinae are broadly adapted taxa with wide habitat tolerances, but are particularly sensitive to competitive interactions such that their responses oppose those of Dominant Dolichoderinae. Finally, Cryptic Species and Specialist Predators have highly specialized requirements that make them especially sensitive to disturbance. Functional groups are of most use in situations where disturbance causes substantial change in habitat structure, particularly in the ground‐layer. Functional groups are of least use in very open habitats, where disturbance merely increases what is already extensive bare ground, and has relatively little impact on microclimate. The ant functional group scheme can play an important role in assessing disturbance in mesic Australia, but may be of more limited use for this in the arid zone.     

Response of an open‐forest ant community to invasion by the introduced ant,Pheidole megacephala

The introduced tramp ant, Pheidole megacephala, is a well‐known pest of urban areas and coastal dune ecosystems in eastern Australia. Until recently, establishment and spread of P. megacephala colonies has been regarded as likely only in disturbed areas. Here we describe the extent of an established colony of P. megacephala in a long undisturbed open forest near Maryborough in southeast Queensland and compare ant community structure with those of nearby uninfested sites. Tuna baiting revealed three distinct zones: (i) a zone totally dominated by P. megacephala (at least 10 ha) where few other ant ant species were detected; (ii) a zone where P. megacephala was absent and many other ant species were found; and (iii) a zone where opportunists (species of Ochetellus and Paratrechina) competed with P. megacephala at baits. Pitfall trapping over a 9‐month period resulted in 12 species being recorded at the infested site, compared with a mean of 25 species recorded at adjoining uninfested forest. Over 94% of ants recorded in pitfalls at the infested site were P. megacephala. Most notably, P. megacephala had completely displaced dominant Dolichoderines (species of Iridomyrmex), subordinate Camponotini (species of Camponotus, Opisthopsis and Polyrhachis) and other species of Pheidole which are common at forest sites.     

Strong influences of a dominant,ground‐nesting ant on recruitment,and establishment of ant colonies and communities

Many factors drive the organization of communities including environmental factors, dispersal abilities, and competition. In particular, ant communities have high levels of interspecific competition and dominance that may affect community assembly processes. We used a combination of surveys and nest supplementation experiments to examine effects of a dominant ground‐nesting ant (Pheidole synanthropica) on (1) arboreal twig‐nesting, (2) ground‐foraging, and (3) coffee‐foraging ant communities in coffee agroecosystems. We surveyed these communities in high‐ and low‐density areas of P. synanthropica over 2 years. To test for effects on twig ant recruitment, we placed artificial nesting resources on coffee plants in areas with and without P. synanthropica. The first sampling period revealed differences in ant species composition on the ground, in coffee plants, and artificial nests between high‐ and low‐density sites of P. synanthropica. High‐density sites also had significantly lower recruitment of twig ants and had species‐specific effects on twig ant species. Prior to the second survey period, abundance of P. synanthropica declined in the high‐density sites, such that P. synanthropica densities no longer differed. Subsequent sampling revealed no difference in total recruitment of twig ants to artificial nests between treatments. Likewise, surveys of ground and coffee ants no longer showed significant differences in community composition. The results from the first experimental period, followed by survey results after the decline in P. synanthropica densities suggest that dominant ants can drive community assembly via both recruitment and establishment of colonies within the community.     

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

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

Competitive dominance in the organisation of Mediterranean ant communities

1. Competition by dominant species is thought to be key to structuring ant communities. However, recent findings suggest that the effect of dominant species on communities is less pronounced than previously assumed. 2. The aim of the present study was to identify the role of dominant ants in the organisation of Mediterranean communities, particularly the role of competition in invaded and uninvaded communities. The effects on ant assemblages of two dominant ants, the invasive Argentine ant and the native ant, Tapinoma nigerrimum Nylander, were assessed. 3. The abundances of both dominant ants were significantly correlated with a decrease in native ant richness at traps. However, only the invasive ant was associated with a reduction in diversity and abundance of other ant species at site scale. In the presence of T. nigerrimum, species co‐occurrence patterns were segregated or random. Community structure in both the dominant‐free and the Argentine ant sites showed random patterns of species co‐occurrence. 4. The present findings indicate that dominant ants regulate small‐scale diversity by competition. However, at the broader scale of the assemblage, T. nigerrimum may only affect species distribution, having no apparent effect on community composition. Moreover, we find no evidence that inter‐specific competition shapes species distribution in coastal Mediterranean communities free of dominant ants. 5. These results show that dominant species may affect ant assemblages but that the nature and the intensity of such effects are species and scale dependent. This confirms the hypothesis that competitive dominance may be only one of a range of factors that structure ant communities.     

Ant Diversity and Abundance along an Elevational Gradient in the Philippines1

Ant communities were surveyed along an elevational gradient in the Philippines extending from lowland dipterocarp forest (250 m elevation) to mossy forest (1750 m). Standardized pitfall trapping in arboreal and terrestrial microhabitats at seven sites yielded 51 species. Collecting by hand at five of the sites yielded 48 species. The two methods produced substantially different assemblages, with only 22 species (29%) taken in common. Only a fraction of the total ant community appeared to be sampled at most of the sites. Measures of species richness and relative abundance peaked at mid-elevations and declined sharply with increasing elevation. Ants were extremely rare above 1500 m elevation. Arboreal ants were trapped much less frequently than terrestrial ants at all sites. Ant species that were abundant had broader elevational distributions than those that were less common, but most species were rare and occurred at only one or two sites. The elevational patterns for ants are largely the inverse of those documented for Philippine small mammals which reach their greatest diversity and abundance at high elevations where ants are rare. This suggests that the two groups may interact competitively. Some of the patterns observed or inferred from this study may apply to tropical ant communities in general, and are presented as series of testable hypotheses as a guide and stimulus for future research.     

Ant diversity in relation to time since fire in a mallee landscape of South-Eastern Australia

Fire is a dominant process shaping the Australian landscape and in many regions the frequency and severity of wildfires are predicted to increase under climate change. The primary impact of fire on fauna is typically indirect through habitat change. In particular, in mesic forests different animal species are favoured at different times since fire as habitat complexity increases with vegetation recovery. However, this will not necessarily be the case in habitats with low complexity such as many of those occurring in arid and semi-arid regions. Here, we investigate the relationship between fire history and ant diversity and composition in semi-arid mallee of south-eastern Australia. We surveyed ants at 11 sites in the Little Desert National Park and nearby private land that last burnt 0.5, 6 or 40 years ago. We found no relationship between time since fire and either ant diversity or composition, and this can be explained by a lack of relationship between time since fire and vegetation cover. Our findings contrast with those for mallee bird species, which show clear successional patterns following fire, but are likely to be typical of ground-foraging fauna that lack specialized habitat requirements.     

Impacts of the invasive Argentine ant on native ants and other invertebrates in coastal scrub in south‐eastern Australia

Invasive ants threaten native biodiversity and ecosystem function worldwide. Although their principal direct impact is usually the displacement of native ants, they may also affect other invertebrates. The Argentine ant, Linepithema humile (Dolichoderinae), one of the most widespread invasive ant species, has invaded native habitat where it abuts peri‐urban development in coastal Victoria in south‐eastern Australia. Here we infer impacts of the Argentine ant on native ants and other litter and ground‐dwelling invertebrates by comparing their abundance and taxonomic composition in coastal scrub forest either invaded or uninvaded by the Argentine ant. Species composition of native ants at bait stations and extracted from litter differed significantly between Argentine ant‐invaded and uninvaded sites and this was consistent across years. Argentine ants had a strong effect on epigeic ants, which were either displaced or reduced in abundance. The native ant Rhytidoponera victoriae (Ponerinae), numerically dominant at uninvaded sites, was completely absent from sites invaded by the Argentine ant. However, small hypogeic ants, including Solenopsis sp. (Myrmicinae) and Heteroponera imbellis (Heteroponerinae), were little affected. Linepithema humile had no detectable effect upon the abundance and richness of other litter invertebrates. However, invertebrate group composition differed significantly between invaded and uninvaded sites, owing to the varied response of several influential groups (e.g. Collembola and Acarina). Floristics, habitat structure and measured environmental factors did not differ significantly between sites either invaded or uninvaded by Argentine ants, supporting the contention that differences in native ant abundance and species composition are related to invasion. Changes in the native ant community wrought by Argentine ant invasion have important implications for invertebrate communities in southern Australia and may affect key processes, including seed dispersal.     

Introduced ants reduce interaction diversity in a multi‐species,ant–aphid mutualism

Mutualisms contribute in fundamental ways to the origin, maintenance and organization of biological diversity. Introduced species commonly participate in mutualisms, but how this phenomenon affects patterns of interactions among native mutualists remains incompletely understood. Here we examine how networks of interactions among aphid‐tending ants, ant‐tended aphids, and aphid‐attacking parasitoid wasps differ between 12 spatially paired riparian study sites with and without the introduced Argentine ant Linepithema humile in southern California. To resolve challenges in species identification, we used DNA barcoding to identify aphids and screen for parasitoid wasps (developing inside their aphid hosts) from 170 aphid aggregations sampled on arroyo willow Salix lasiolepis. Compared to uninvaded sites, invaded sites supported significantly fewer species of aphid‐tending ants and ant‐tended aphids. At invaded sites, for example, we found only two species of ant‐tended aphids, which were exclusively tended by L. humile, whereas at uninvaded sites we found 20 unique ant–aphid interactions involving eight species of ant‐tended aphids and nine species of aphid‐tending ants. Ant–aphid linkage density was thus significantly lower at invaded sites compared to uninvaded sites. We detected aphid parasitoids in 14% (28/198) of all aphid aggregations. Although the level of parasitism did not differ between invaded and uninvaded sites, more species of wasps were detected within uninvaded sites compared to invaded sites. These results provide a striking example of how the assimilation of introduced species into multi‐species mutualisms can reduce interaction diversity with potential consequences for species persistence.     

Reduced dispersal at nonexpanding range margins: A matter of disperser identity

The evolution of dispersal at range margins received much attention recently, especially in the context of dynamic range shifts, such as those following climate change. However, much less attention has been devoted to study variation in and selection on dispersal at nonexpanding range margins, where populations are often small and isolated, and empirical test is dearly missing. To fill this gap, we tested whether dispersal of an ant‐dispersed perennial plant (Sternbergia clusiana) is quantitatively and/or qualitatively reduced toward a nonexpanding range margin. We evaluated plant investment in dispersal structures (elaiosome), seed removal rates, and the relative abundance, activity, and behavior of low‐ and high‐quality seed‐dispersing ants in six sites ranging from mesic Mediterranean site to arid site (>600 to <100 mm of annual rainfall, respectively), which marks the southern range margin of the species. In a set of cafeteria and baiting experiments, we found that overall seed removal rates, the contribution of high‐quality dispersers, maximum dispersal distance and dispersal‐conducive ant behavior decreased toward range margins. These findings agree with a lower investment in reward by range margin plant populations, as reflected by lower elaiosome/seed ratio, but not by variation in the reward chemistry. More than variation in traits controlled by the plants, the variation in ant–seed interactions could be attributed to reduced presence and activity of the more efficient seed‐dispersing ants in the marginal populations. Specifically, we found a mismatch between local distribution of potentially effective seed dispersers and that of the plant, even though those dispersers were observed in the study site. Interestingly, although the observed variation in the outcome of ant–seed interactions supported the prediction of reduced dispersal at nonexpanding range margins with small and isolated populations, the underlying mechanism seems to be incidental difference in the seed‐dispersing ant community rather than a plant‐mediated response to selection.     

Twig-Nesting Ants: The Hidden Predators of the Coffee Berry Borer in Chiapas,Mexico

Coffee is a globally important crop that is subject to numerous pest problems, many of which are partially controlled by predatory ants. Yet several studies have proposed that these ecosystem services may be reduced where agricultural systems are more intensively managed. Here we investigate the predatory ability of twig-nesting ants on the main pest of coffee, the coffee berry borer (Hypothenemus hampei) under different management systems in southwest Chiapas, Mexico. We conducted both laboratory and field experiments to examine which twig-nesting ant species, if any, can prey on free-living borers or can remove borers embedded in coffee fruits and whether the effects of the twig-nesting ant community differ with habitat type. Results indicate that several species of twig-nesting ants are effective predators of both free-living borers and those embedded in coffee fruits. In the lab, Pseudomyrmex ejectus, Pseudomyrmex simplex, and Pseudomyrmex PSW-53 effectively removed free-living and embedded borers. In the field, abundance, but not diversity, of twig-nesting ant colonies was influenced by shade management techniques, with the highest colony abundance present in the sites where shade trees were recently pruned. However, borer removal rates in the field were significant only in the shadiest site, but not in more intensively managed sites. This study provides evidence that twig-nesting ants can act as predators of the coffee berry borer and that the presence of twig-nesting ants may not be strongly linked to shade management intensity, as has been suggested for other arthropod predators of the borer.     

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.     

Ant community structure on a small Pacific island: only one native species living with the invaders

In most studies about ant communities, species are grouped into competitive hierarchies where top dominants drive the majority of other species away from resources. Nevertheless, in some ecosystems high ground temperatures may disrupt this hierarchical organization. Other changes in community structure are caused by the arrival of invasive ant species, which rapidly disassemble local communities. We studied the effects of competition and temperature on ant community organization on Surprise Island (New Caledonia). Four different habitats were distinguished: a central plain, a sea shore Argusia shrubland, a dense Scaveola shrub, and an arboreal Pisonia strata. Eight ant species were identified from pitfall traps (seven introduced and only one native species, Pheidole oceanica). Ant assemblages in each habitat had a different ecologically dominant species, and a dominant species in one habitat could be non-dominant and less abundant in another. From interactions at baits, we built a competitive hierarchy where the top dominant species was the native Ph. oceanica. Daily foraging activity rhythms of the different species mostly overlapped. The relationship between bait occupation and ground temperature followed a negative linear pattern at all sites and for most species, except for the relatively thermophilous Monomorium floricola. Indices of co-occurrence in pitfall traps indicated that species co-occurred randomly with respect to one another. Conversely, species appeared to be segregated when we examined co-occurrence at baits at the sites where Ph. oceanica was abundant. Oceanic islands are very susceptible to alien species, but on Surprise Island it seems that the sole native species dominates in some habitats when confronted by invasive species.     

Invasion of Argentine ants (Hymenoptera: Formicidae) in South Australia: Impacts on community composition and abundance of invertebrates in urban parklands

Abstract The Argentine ant (Linepithema humile Mayr) is a worldwide invasive pest species that has been associated with losses of native ant and non‐ant invertebrates in its introduced range. To date, few studies have investigated the effects of Argentine ants on native invertebrates in Australia. This study assessed the effects of Argentine ants on community composition of invertebrates, with particular focus on resident ant communities and functional groups. In this study, the author compared the composition and abundances of invertebrates between invaded and uninvaded locations at four paired sites in Adelaide, South Australia. The results showed that there were significantly fewer non‐Argentine ants at invaded sites than at uninvaded sites. In particular, ants from the two common and widespread genera Iridomyrmex and Camponotus showed decreased abundances at the invaded sites. Multidimensional scaling analyses revealed differences in the composition of ant communities at the invaded and uninvaded sites, with uninvaded sites characterized by a similar native ant species composition, while communities at the invaded sites displayed much greater variability in species composition. These results suggest that the presence of Argentine ants may have a negative effect on particular ant genera and functional groups, with likely disruptions to ecosystem processes.     

The ant community response to the arrival of Monomorium sydneyense forel (Hymenoptera: Formicidae) at sulphur point,Tauranga, New Zealand

Abstract

Impacts of highly invasive ants in new ecosystems are well documented, but many more ant species are establishing in new ranges for which there is little or no information. We studied the effects of the recently discovered Australian ant, Monomorium sydneyense Forel, on the ant community of Sulphur Point in Tauranga, New Zealand. At the community scale, the species composition in invaded areas was significantly different from that in areas free of M. sydneyense. However, no single ant species was significantly more or less abundant in the presence of M. sydneyense. Some resident ant species categorised in the same functional group as the invader appeared to be scarcer when sympatric with M. sydneyense, but the local abundances of these species were always spatially variable, so the effects were not statistically significant Patchy distribution of M. sydneyense, and other aspects of its behaviour, such as poor foraging abilities and a lack of unicoloniality (where there is little or no aggression between conspecific ants from spatially separate nests), appear to allow resident ant species to coexist with M. sydneyense at Sulphur Point.     

A canopy dominant ant affects twig‐nesting ant assembly in coffee agroecosystems

One commonly studied driver of community assembly is the effect of dominant species on subordinate species. Dominant species may impact community assembly during competitive sorting, or recruitment. For ants, important and abundant species in the tropics, several factors may drive community assembly including competition, dispersal, priority effects, and environmental conditions. Although competition is a hallmark of ant ecology, few have examined the influence of patchily distributed dominant ants on other ant species and diversity, especially at the recruitment stage. Here, I consider the impacts of a canopy dominant ant species, Azteca instabilis, and changes in vegetation on twig‐nesting ant colony founding and ant community assembly in a coffee agroecosystem. I added artificial nests to coffee plants in areas with and without A. instabilis four times over a year, and then examined the occupation rate and identity of species colonizing nests. I also examined vegetation characteristics of sites where nests were added. The presence of A. instabilis on coffee plants drastically lowered colonization rates, but nest occupation increased with tree density, and with decreasing proportion of Inga spp. trees in the canopy. The presence of A. instabilis limited the number of nests occupied by six of the ten most common species; most rare species, however, were not affected by A. instabilis presence. Richness of colonizing ants in areas with A. instabilis was lower, but these effects did not significantly affect richness across broader scales. Despite large effects on individual species, species composition did not differ greatly in areas with and without A. instabilis, but some vegetation characteristics (basal area and tree richness) were predictive of ant composition. These results suggest that A. instabilis strongly affects founding events especially for common twig‐nesting species and that both vegetation and influences from this dominant species affect community assembly of twig‐nesting ants at the local scale.     

Invasive species and climate change: <Emphasis Type="Italic">Conyza canadensis</Emphasis> (L.) Cronquist as a tool for assessing the invasibility of natural plant communities along an aridity gradient

The predicted reduction in precipitation in the eastern Mediterranean due to climate change may expose the natural plant communities to invasive species. We assessed whether natural plant communities along an aridity gradient in Israel were resistant to invasion by considering differences in abiotic conditions and community characteristics in these regions. We considered Conyza canadensis as a model plant as it is a common invader in the region. We examined the mechanisms and functional traits of both the plant communities and C. canadensis that promote or discourage invasion. Study sites represented a rainfall gradient with four ecosystem types: mesic Mediterranean, Mediterranean, semiarid and arid. Our results showed that the mechanisms of community invasion resistance varied along the aridity gradient. At the arid and semiarid sites, water deficiency impaired the establishment of C. canadensis. At the mesic Mediterranean site, plant competition had a negative effect on C. canadensis performance, thus greatly reducing the likelihood of its establishment. We conclude that a decrease in regional precipitation due to climate change may not affect intrinsic resistance characteristics of natural plant communities to invasion in the area.     

Myrmecochory in some plants (F. chenopodiaceae) of the Australian arid zone

Summary Several common plants (Chenopodiaceae) of the Australian arid zone produce diaspores that bear small and inconspicuous food bodies and are adapted for dispersal by ants. For these species, myrmecochory probably represents an adaptation for highly directional dispersal of diaspores to favorable microsites where nutrients are concentrated and possibly more accessible. Dispersal of diaspores by ants can have a pronounced effect on plant dispersion. In habitats characterized by red, crusty alluvial loam soils, myrmecochorous species grow almost exclusively on ant mounds; these same species grow in relatively continuous stands in sandy soil habitats. The flora of the Australia arid zone may contain many plant species that are adapted to use ants as dispersal agents. We consider several factors that may have promoted or facilitated the evolution of myrmecochory in arid zone plants.