Behavioral interactions of the invasive Argentine ant with native ant species

Summary: The Argentine ant, Linepithema humile, has invaded many areas of the world, displacing native ants. Its behavior may contribute to its competitive success. Staged and natural encounters were observed at food resources in the field, between Argentine ants and eight ant species native to northern California. There was no relation between the frequency of aggression by any ant species and the outcome of encounters, though Argentine ants were more likely than ants of native species to behave aggressively. When an ant of one species initiated an encounter of any kind with an ant of another species, the ant that did not initiate was likely to retreat. This was true of all species studied. Most encounters between ants were initiated by Argentine ants. Thus the native species tended to retreat more frequently than Argentine ants. Interactions between Argentine ants and native species at food resources, causing ants of native species to retreat, may help Argentine ants to displace native species from invaded areas.     

Exploitation and interference competition between the invasive Argentine ant,Linepithema humile,and native ant species

Interactions between the invasive Argentine ant, Linepithema humile, and native ant species were studied in a 450-ha biological reserve in northern California. Along the edges of the invasion, the presence of Argentine ants significantly reduced the foraging success of native ant species, and vice versa. Argentine ants were consistently better than native ants at exploiting food sources: Argentine ants found and recruited to bait more consistently and in higher numbers than native ant species, and they foraged for longer periods throughout the day. Native ants and Argentine ants frequently fought when they recruited to the same bait, and native ant species were displaced from bait during 60% of these encounters. In introduction experiments, Argentine ants interfered with the foraging of native ant species, and prevented the establishment of new colonies of native ant species by preying upon winged native ant queens. The Argentine ants' range within the preserve expanded by 12 ha between May 1993 and May 1994, and 13 between September 1993 and September 1994, with a corresponding reduction of the range of native ant species. Although some native ants persist locally at the edges of the invasion of Argentine ants, most eventually disappear from invaded areas. Both interference and exploitation competition appear to be important in the displacement of native ant species from areas invaded by Argentine ants.     

Cryptic microsporidian parasites differentially affect invasive and native Artemia spp.

We investigated the host specificity of two cryptic microsporidian species (Anostracospora rigaudi and Enterocytospora artemiae) infecting invasive (Artemia franciscana) and native (Artemia parthenogenetica) hosts in sympatry. Anostracospora rigaudi was on average four times more prevalent in the native host, whereas E. artemiae was three times more prevalent in the invasive host. Infection with An. rigaudi strongly reduced female reproduction in both host species, whereas infection with E. artemiae had weaker effects on female reproduction. We contrasted microsporidian prevalence in native A. franciscana populations (New World) and in both invaded and non-invaded Artemia populations (Old World). At a community level, microsporidian prevalence was twice as high in native compared with invasive hosts, due to the contrasting host-specificity of An. rigaudi and E. artemiae. At a higher biogeographical level, microsporidian prevalence in A. franciscana did not differ between the invaded populations and the native populations used for the introduction. Although E. artemiae was the only species found both in New and Old World populations, no evidence of its co-introduction with the invasive host was found in our experimental and phylogeographic tests. These results suggest that the success of A. franciscana invasion is probably due to a lower susceptibility to virulent microsporidian parasites rather than to decreased microsporidian prevalence compared with A. parthenogenetica or to lower microsporidian virulence in introduced areas.     

Unadapted behaviour of native,dominant ant species during the colonization of an aggressive,invasive ant

Among the factors driving the invasive success of non-indigenous species, the “escape opportunity” or “enemy release” hypothesis argues that an invader’s success may result partly from less resistance from the new competitors found in its introduced range. In this study, we examined competitive interactions between the little fire ant Wasmannia auropunctata (Roger) and ant species of the genus Pheidole in places where both are native (French Guiana) and in places where only species of Pheidole are native (New Caledonia). The experimental introduction of W. auropunctata at food resources monopolized by the Pheidole species induced the recruitment of major workers only for the Guianian Pheidole species, which were very effective at killing Wasmannia competitors. In contrast, an overall decrease in the number of Pheidole workers and no recruitment of major workers were observed for the New Caledonian species, although the latter were the only ones able to kill the Wasmannia workers. These results emphasize the inappropriate response of native dominant New Caledonian species to W. auropunctata and, thus, the importance of enemy recognition and specification in the organization of ant communities. This factor could explain how invasive animal species, particularly ants, may be able to successfully invade species-rich communities.     

Invasive legume management strategies differentially impact mutualist abundance and benefit to native and invasive hosts

Determining the best management practices for plant invasions is a critical, but often elusive goal. Invasive removals frequently involve complex and poorly understood biotic interactions. For example, invasive species can leave potent legacies that influence the success of native species restoration efforts, and positive plant‐microbial feedbacks may promote continued reinvasion by an exotic species following restoration. Removal methods can vary in their effects on plant–soil feedbacks, with consequences for restoration of native species. We determined the effects of invasion by a leguminous shrub (French broom; Genista monspessulana) on the density and community composition of, and benefit conferred by, its microbial mutualists in its invading range. Densities of soil‐dwelling rhizobia were much higher in areas invaded by G. monspessulana relative to uninvaded areas, and this increased density of rhizobia fed back to increase seedling growth of both the invader and native legumes. We further compared how three techniques for removing G. monspessulana affected the densities of rhizobia relative to areas where G. monspessulana was still present. Removal by hand‐pulling reduced soil rhizobial densities, and reduced growth of one native legume, while having no effect on the growth of the invader. Overall, our results show that the consequences of restoration techniques, both above‐ and belowground, could be critical for the successful removal of an invasive legume and restoration of native species.     

土壤真菌差异影响入侵豚草与本地植物生长及互作

采用温室盆栽实验,研究了本地植物土壤与豚草入侵地土壤中真菌对外来植物豚草和2种本地植物生长及对豚草与本地植物互作的影响。结果表明:在本地植物土壤中,杀真菌剂处理下,豚草单独种植、与本地植物狗尾草混合种植或与紫花苜蓿混合种植时,其生物量分别比未采用杀真菌剂处理高46.7%、39.1%和90.5%,但杀真菌剂对狗尾草及紫花苜蓿的生物量却没有显著影响;在豚草入侵地土壤中,与未采用杀真菌剂的处理相比,杀真菌剂处理使单独种植的豚草的生物量降低了44.3%,同时杀真菌剂也降低了本地植物狗尾草和紫花苜蓿的生物量,但杀真菌剂的施用对与狗尾草或紫花苜蓿混合种植的豚草的生物量却没有显著影响;进一步比较了本地植物土壤和豚草入侵土壤中真菌对植物生长的反馈作用,结果显示,在本地植物土壤中,真菌对豚草生长呈现负反馈,但在豚草入侵地土壤中,真菌对单独种植的豚草表现出正反馈,而且与本地植物土壤比较,土壤真菌对与本地植物混合种植的豚草的负反馈作用明显变小了。本研究结果为深入研究豚草入侵的土壤微生物学机制提供了一定的实验证据。     

Modelling the potential geographic distribution of invasive ant species in New Zealand

Despite their economic and environmental impacts, there have been relatively few attempts to model the distribution of invasive ant species. In this study, the potential distribution of six invasive ant species in New Zealand are modelled using three fundamentally different methods (BIOCLIM, DOMAIN, MAXENT). Species records were obtained from museum collections in New Zealand. There was a significant relationship between the length of time an exotic species had been present in New Zealand and its geographic range. This is the first time such a time lag has been described for exotic ant species, and shows there is a considerable time lag in their spread. For example, it has taken many species several decades (40–60 years) to obtain a distribution of 17–25% of New Zealand regions. For all six species, BIOCLIM performed poorly compared to the other two modelling methods. BIOCLIM had lower AUC scores and higher omission error, suggesting BIOCLIM models under-predicted the potential distribution of each species. Omission error was significantly higher between models fitted with all 19 climate variables compared to those models with fewer climate variables for BIOCLIM, but not DOMAIN or MAXENT. Widespread species had a greater commission error. A number of regions in New Zealand are predicted to be climatically suitable for the six species modelled, particularly coastal and lowland areas of both the North and South Islands.     

Long-term dynamics of the distribution of the invasive Argentine ant, Linepithema humile, and native ant taxa in northern California

Invasive species, where successful, can devastate native communities. We studied the dynamics of the invasive Argentine ant, Linepithema humile, for 7 years in Jasper Ridge, a biological preserve in northern California. We monitored the distributions at the hectare scale of native ant taxa and L. humile in the spring and fall from 1993 to 1999. We also studied the invasion dynamics at a finer resolution by searching for ants in 1-m² plots. Our results are similar at both scales. The distributions of several native species are not random with regard to L. humile; the distributions of several epigeic species with similar habitat affinities overlap much less frequently than expected with the distribution of L. humile. We found that season had a significant influence on the distributions of L. humile and several native taxa. Over the 7-year period, L. humile has increased its range size in Jasper Ridge largely at the expense of native taxa, but there is seasonal and yearly variation in this rate of increase. Studies of invasions in progress which sample across seasons and years may help to predict the spread and effects of invasive species.     

Plant-based food resources,trophic interactions among alien species,and the abundance of an invasive ant

Recent research on invasive ants suggests that their success may be facilitated by increased resources at introduced locations stemming from the emergence of novel trophic interactions with abundant honeydew-producing Hemiptera. Moreover, those Hemiptera may themselves often be introduced or invasive. To test the importance of mutualisms for invasive species, we conducted a study in the southeastern United States of factors hypothesized to affect the abundance of an invasive ant native to South America, Solenopsis invicta. The study was conducted within grazing pastures, where S. invicta can be extremely abundant while also exhibiting substantial variability in abundance. A path analysis showed that the abundance of S. invicta was strongly and positively affected by the abundance of an invasive honeydew-producing mealybug native to Asia, Antonina graminis, and by the mealybugs’ host grasses because of their strong positive effect on mealybug abundance. Abundance of the mealybug was primarily attributable to an invasive host grass native to Africa, Cynodon dactylon. The abundance of S. invicta was also positively affected by the abundance of other arthropods that they are likely to consume, and those arthropods were positively affected by the abundance of both the A. graminis host grasses and other plants. Thus the study shows that the distribution and abundance of different plant species could have important effects on the abundance of S. invicta through their effect on the ants’ food resources. The results are also consistent with the hypothesis that the emergence of novel trophic interactions among invasive species can promote the abundance of invasive ants.     

Exploitative strategies of the invasive Argentine ant (Linepithema humile) and native ant species in a southern Spanish pine forest

The Argentine ant, Linepithema humile (Mayr, 1868), is displacing native ant species in Do?ana National Park (Spain). This paper discusses the results of experiments aimed at analyzing exploitation competition between the invading species and other ant species in a park community. The Argentine ant was found to implement several strategies favoring its success in exploitation competition: mass recruitment, use of various microhabitats (on the ground and in trees), and activity over a wide range of temperatures. Although these strategies were not exclusive to L. humile, their joint use, together with the large number of workers forming each "unicolony," conferred a clear advantage for resource exploitation. Some native species were more severely affected than others by the presence of L. humile in terms of both abundance and behavior. The worst affected species were those whose ecological characteristics were similar to those of the Argentine ant, e.g., Pheidole pallidula (Nylander, 1849); the species least affected was Cataglyphis floricola Tinaut, 1993, possibly because of its subordinate and thermophilous nature (little overlap of daily activity rhythms with the exotic species).     

Human land use promotes the abundance and diversity of exotic species on Caribbean islands

Human land use causes major changes in species abundance and composition, yet native and exotic species can exhibit different responses to land use change. Native populations generally decline in human‐impacted habitats while exotic species often benefit. In this study, we assessed the effects of human land use on exotic and native reptile diversity, including functional diversity, which relates to the range of habitat use strategies in biotic communities. We surveyed 114 reptile communities from localities that varied in habitat structure and human impact level on two Caribbean islands, and calculated species richness, overall abundance, and evenness for every plot. Functional diversity indices were calculated using published trait data, which enabled us to detect signs of trait filtering associated with impacted habitats. Our results show that environmental variation among sampling plots was explained by two Principal Component Analysis (PCA) ordination axes related to habitat structure (i.e., forest or nonforest) and human impact level (i.e., addition of man‐made constructions such as roads and buildings). Several diversity indices were significantly correlated with the two PCA axes, but exotic and native species showed opposing responses. Native species reached the highest abundance in forests, while exotic species were absent in this habitat. Human impact was associated with an increase in exotic abundance and species richness, while native species showed no significant associations. Functional diversity was highest in nonforested environments on both islands, and further increased on St. Martin with the establishment of functionally unique exotic species in nonforested habitat. Habitat structure, rather than human impact, proved to be an important agent for environmental filtering of traits, causing divergent functional trait values across forested and nonforested environments. Our results illustrate the importance of considering various elements of land use when studying its impact on species diversity and the establishment and spread of exotic species.     

Historic land use influences contemporary establishment of invasive plant species

The legacy of agricultural land use can have widespread and persistent effects on contemporary landscapes. Although agriculture can lead to persistent changes in soil characteristics and plant communities, it remains unclear whether historic agricultural land use can alter the likelihood of contemporary biological invasions. To understand how agricultural land-use history might interact with well-known drivers of invasion, we conducted factorial manipulations of soil disturbance and resource additions within non-agricultural remnant sites and post-agricultural sites invaded by two non-native Lespedeza species. Our results reveal that variation in invader success can depend on the interplay of historic land use and contemporary processes: for both Lespedeza species, establishment was greater in remnant sites, but soil disturbance enhanced establishment irrespective of land-use history, demonstrating that contemporary processes can help to overcome legacy constraints on invader success. In contrast, additions of resources known to facilitate seedling recruitment (N and water) reduced invader establishment in post-agricultural but not in remnant sites, providing evidence that interactions between historic and contemporary processes can also limit invader success. Our findings thus illustrate that a consideration of historic land use may help to clarify the often contingent responses of invasive plants to known determinants of invasibility. Moreover, in finding significantly greater soil compaction at post-agricultural sites, our study provides a putative mechanism for historic land-use effects on contemporary invasive plant establishment. Our work suggests that an understanding of invasion dynamics requires knowledge of anthropogenic events that often occur decades before the introduction of invasive propagules.     

The importance of factors controlling species abundance and distribution varies in native and non‐native ranges

How variation in factors controlling species abundance and distribution between native and non‐native ranges compares to that within ranges remains poorly understood. We used a globally distributed ruderal, Centaurea solstitialis (Centaurea), to explore the possibility that the importance of those factors exhibits great variation between and within ranges. To test our hypothesis, we established seed addition experiments with soil disturbance (turnover and control) and biocide (fungicides, insecticide, and control) treatments in two regions within native (the Caucasus and south‐western Turkey) and non‐native (the western United States – US – and central Argentina) distributions. Also, we estimated the rate of vegetation recovery after disturbance (resilience) and related it to Centaurea density in experimental plots. Disturbance strongly increased Centaurea density in all regions. Density was similar between the native Caucasus and non‐native Argentina and much greater in those regions than in the native Turkey and non‐native US in biocide‐free plots. Fungicides had positive effects on density in the US and negative ones in the Caucasus and Argentina, resulting in no differences between those three regions and greater density in the US than Turkey. Insecticide applications promoted Centaurea density in Turkey and Argentina, but inter‐regional comparisons of density in treated plots were comparable to those in biocide‐free plots. Overall, plants were smaller and less fecund in Turkey than the other regions, except the US. The greatest fungal attack was documented in Turkey, and herbivory was stronger there and in Argentina than in the Caucasus and US. The resilience of the local community explained a large proportion of variation in Centaurea density. These results support our hypothesis, and reveal that the speed at which competition is re‐gained after disturbance may influence global variation in Centaurea abundance. Because many ruderals exhibit native and non‐native distributions, our results are likely to be generalized to other systems.     

Local coexistence of native and invasive ant species is associated with micro-spatial shifts in foraging activity

Biological Invasions - Invasive species often displace native species by outcompeting them. Yet, some native species can persist even in heavily invaded areas. The mechanisms mediating this local...     

Quantifying uncertainty in the potential distribution of an invasive species: climate and the Argentine ant

Maps of a species' potential range make an important contribution to conservation and invasive species risk analysis. Spatial predictions, however, should be accompanied by an assessment of their uncertainty. Here, we use multimodel inference to generate confidence intervals that incorporate both the uncertainty involved in model selection as well as the error associated with model fitting. In the case of the invasive Argentine ant, we found that it was most likely to occur where the mean daily temperature in mid-winter was 7–14 °C and maximum daily temperatures during the hottest month averaged 19–30 °C. Uninvaded regions vulnerable to future establishment include: southern China, Taiwan, Zimbabwe, central Madagascar, Morocco, high-elevation Ethiopia, Yemen and a number of oceanic islands. Greatest uncertainty exists over predictions for China, north-east India, Angola, Bolivia, Lord Howe Island and New Caledonia. Quantifying the costs of different errors (false negatives vs. false positives) was considered central for connecting modelling to decision-making and management processes.     

Contrasting effects of an invasive ant on a native and an invasive plant

When invasive species establish in new environments, they may disrupt existing or create new interactions with resident species. Understanding of the functioning of invaded ecosystems will benefit from careful investigation of resulting species-level interactions. We manipulated ant visitation to compare how invasive ant mutualisms affect two common plants, one native and one invasive, on a sub-tropical Indian Ocean island. Technomyrmex albipes, an introduced species, was the most common and abundant ant visitor to the plants. T. albipes were attracted to extrafloral nectaries on the invasive tree (Leucaena leucocephala) and deterred the plant’s primary herbivore, the Leucaena psyllid (Heteropsylla cubana). Ant exclusion from L. leucocephala resulted in decreased plant growth and seed production by 22% and 35%, respectively. In contrast, on the native shrub (Scaevola taccada), T. albipes frequently tended sap-sucking hemipterans, and ant exclusion resulted in 30% and 23% increases in growth and fruit production, respectively. Stable isotope analysis confirmed the more predacious and herbivorous diets of T. albipes on the invasive and native plants, respectively. Thus the ants’ interactions protect the invasive plant from its main herbivore while also exacerbating the effects of herbivores on the native plant. Ultimately, the negative effects on the native plant and positive effects on the invasive plant may work in concert to facilitate invasion by the invasive plant. Our findings underscore the importance of investigating facilitative interactions in a community context and the multiple and diverse interactions shaping novel ecosystems.     

Changes in the photosynthetic characteristics of cotton leaves infested by invasive mealybugs tended by native ant species

Herbivore injury has a direct effect on the growth and performance of host plants through photosynthetic suppression. However, changes in plant photosynthesis affected by ant tending of hemipteran sap feeders remain poorly understood. We investigated the effects of an invasive mealybug (Phenacoccus solenopsis) tended by native ants (Paratrechina longicornis) on the chlorophyll content and chlorophyll fluorescence characteristics of cotton (Gossypium hirsutum) leaves under greenhouse conditions. The results showed that the relative chlorophyll content of the infested cotton leaves significantly decreased after 10 days, and the chlorophyll contents were reduced by 26.4 and 34.9 % after 20 days in the without and with ant treatments compared to the control, respectively. In addition, the light utilization efficiency and maximum relative electron transport rate were reduced by 53.0 and 51.3 % compared to the control, respectively. However, no significant differences in these factors were found between the without and with ant treatments. The light saturation coefficient, describing the capacity of a sample to resist glare, exhibited no significant difference among treatments. The number of tending P. longicornis ants increased with P. solenopsis numbers, and the P. solenopsis numbers decreased after 20 days compared to the without ant treatment. We suggest that the tending ants may enhance the feeding ability of individual mealybugs in spite of the decreased number of mealybugs in this situation. Additionally, P. longicornis decrease the relative chlorophyll content of infested cotton leaves and may accelerate the damage caused by P. solenopsis to plants over time.