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Invasive species have had a profound impact on ecosystems all over the world. Their presence can lead to fundamental changes in the biodiversity of a given ecosystem as well as the extinction of native species. In particular, this work looks at the effect on the Gecarcoidea natalis (Red Crab) population on Christmas Island due to the presence of vast arrays of supercolonies containing Anoplolepis gracilipes (Yellow Crazy Ant). We primarily study the inter-species interaction occurring during the crab migration to the island coast. We propose a microscopic model for the dynamics of the crabs and ants with the goal of increasing crab survival. Through analysis of the model, we investigate a range of potential preventative measures that could be taken to preserve the native crab population dependent on their locations. The main result of this work is that by considering the locations of ant supercolonies incorporated into Monte Carlo simulations of the model, we can identify the order that the supercolonies need to be removed to provide the greatest chance at survival for the crabs per migration cycle., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Inc. All rights reserved.)

The entry of secondary invaders into, or their expansion within, native communities is contingent on the changes wrought by other (primary) invaders. When primary invaders have altered more than one property of the recipient community, standard descriptive and modeling approaches only provide a best guess of the mechanism permitting the secondary invasion. In rainforest on Christmas Island, we conducted a manipulative field experiment to determine the mechanism of invasion success for a community of land snails dominated by non-native species. The invasion of rainforest by the yellow crazy ant (Anoplolepis gracilipes) has facilitated these land snails, either by creating enemy-free space and/or increased habitat and resources (in the form of leaf litter) through the removal of the native omnivorous-detritivorous red land crab (Gecarcoidea natalis). We manipulated predator densities (high and low) and leaf litter (high and low) in replicated blocks of four treatment combinations at two sites. Over the course of one wet season (five months), we found that plots with high leaf litter biomass contained significantly more snails than those with low biomass, regardless of whether those plots had high or low predation pressure, at both the site where land crabs have always been abundant, and at the site where they have been absent for many years prior to the experiment. Each site was dominated by small snail species (<2 mm length), and through handling size and predation experiments we demonstrated that red crabs tend not to handle and eat snails of that size. These results suggest that secondary invasion by this community of non-native land snails is facilitated most strongly by habitat and resource augmentation, an indirect consequence of red land crab removal, and that the creation of enemy-free space is not important. By using a full-factorial experimental approach, we have confidently determined-rather than inferred-the mechanism by which primary invaders indirectly facilitate a community of secondary invaders., (© 2016 by the Ecological Society of America.)

Featured Application: This study offers fundamental insight for developing a model platform of artificial intelligence applicable for species distribution modeling, which has been currently emphasized for effective monitoring and control of invasive species. Recent advances in species distribution models (SDMs) associated with artificial intelligence (AI) and increased volumes of available data for model variables have allowed reliable evaluation of the potential distribution of any species. A reliable SDM requires suitable occurrence records and variables with optimal model structures. In this study, we developed three different machine learning-based SDMs [MaxEnt, random forest (RF), and multi-layer perceptron (MLP)] to predict the global potential distribution of two invasive ants under current and future climates. These SDMs showed that the potential distribution of Solenopsis invicta would be expanded by climatic change, whereas it would not significantly change for Anoplolepis gracilipes. The models were compared using model performance metrics, and the optimal model structure and spatial projection were selected. The MaxEnt exhibited high performance, while the MLP model exhibited low performance, with the largest variation by climate change. Random forest showed the smallest potential distribution area, but it was robust considering the number of occurrence records and changes in model variables. All the models showed reliable performance, but the difference in performance and projection size suggested that optimal model selection based on data availability, model variables, study objectives, or an ensemble approach was necessary to develop a comprehensive SDM to minimize modeling uncertainty. We expect that this study will help with the use of AI-based SDMs for the evaluation and risk assessment of invasive ant species. [ABSTRACT FROM AUTHOR]

Hawaii has a single group of native bees belonging to the genus Hylaeus (Hymenoptera: Colletidae) and known collectively as Hawaiian yellow-faced bees. The majority of the 63 species have experienced significant declines in range and population. In 2016, seven species received federal protection under the Endangered Species Act of 1973. Competitors and predators, such as invasive bees, wasps and ants, are thought to be important drivers of range reductions and population declines, especially at lower elevations where more non-native species occur. We evaluated the effects of invasive ants on nesting Hylaeus anthracinus using artificial nest blocks that allowed us to track nest construction and development. The blocks were placed in pairs at 22 points encompassing three sites on the north and east sides of Oahu. One block in each pair was treated with a sticky barrier to prevent access by ants, while the other block remained untreated. From December 2015 to December 2016, we monitored 961 individual nests in the blocks. Seventy percent of nests in control blocks were invaded by ants. Nests in treated blocks were more likely to produce at least one adult than nests in untreated blocks (38% vs. 14%, respectively). In untreated blocks, ants were the most common cause of nest mortality followed by lack of development, displacement (primarily by the competitor Pachodynerus nasidens) and presumed pathogens. The invasive ant, Ochetellus glaber was the only observed nest predator, although the big-headed ant, Pheidole megacephala was also present. Hylaeus anthracinus inhabits coastal strand habitat which occurs in a narrow band just above the high tide line. Nests at one site were destroyed due to a high wave event, highlighting this species' vulnerability to sea level rise. Additionally, no adult bees or nests were observed at the points where yellow crazy ants, Anoplolepis gracilipes were established. An increased understanding of the factors limiting Hawaii's yellow-faced bees will provide information for future conservation efforts that may include landscape-scale ant control, habitat restoration and translocations. [ABSTRACT FROM AUTHOR]

Ants are abundant in natural and managed tropical ecosystems and can have an impact on herbivorous arthropods, as well as plant pathogens. Although it has been shown for plants that the diversity of communities can result in improved ecosystem functioning, it remains uncertain how the species richness of ants affects multiple ecosystem services and disservices., In the present study, we used experimentally enhanced natural gradients in ant species richness on 100 cacao trees in a plantation aiming to analyze the effect of ant species identity and species richness on predation pressure and the incidence of cacao pod borer ( CPB), as well as the spread of black pod disease ( BPD)., Ant species richness did not significantly improve predation of experimentally exposed insects, and was not associated with a reduction in the incidence of CPB. However, the incidence of BPD was higher in ant species rich trees, presumably because more ant species were pathogen vectors. The identity of the dominant ant species affected the incidence of CPB and BPD, as well as predation pressure., Although both ant species richness and identity affected ecosystem services and disservices delivered by the ant community, the results of the present study suggest that the identity of dominant ants is the main driver for ecosystem services in these systems. [ABSTRACT FROM AUTHOR]

The lack of biological knowledge of many invasive species remains as one of the greatest impediments to their management. Here I detail targeted research into the biology of the yellow crazy ant Anoplolepis gracilipes within northern Australia and detail how such knowledge can be used to improve the management outcomes for this species. I quantified nest location and density in three habitats, worker activity over 24 h, infestation expansion rate, seasonal variation of worker abundance and the timing of production of sexuals. Nests were predominantly (up to 68%) located at the bases of large trees, indicating that search efforts should focus around tree bases. Nest density was one nest per 22, 7.1 and 6.3 m2 in the three habitats, respectively. These data form the baselines for quantifying treatment efficacy and set sampling densities for post-treatment assessments. Most (60%) nests were underground, predominantly (89%) occurring in an open area rather than underneath a rock or log. Some seasonality was evident for nests within leaf litter, with most (83%) occurring during the ‘wet season’ (October–March). Of the underground nests, most were shallow, with 44% being less than 10 cm deep, and 67% being less than 20 cm deep. Such nest location and density information serves many management purposes, for improving detection, mapping and post-treatment assessments, and also provided strong evidence that carbohydrate supply was a major driver of A. gracilipes populations. Just over half of the nests (56%) contained queens. Of the 62 underground nests containing queens, most queens (80%) were located at the deepest chamber. When queens were present, most often (38%) only one queen was present, the most being 16. Queen number per nest was the lowest in July and August just prior to the emergence of virgin queens in September, with queen numbers then remaining steadily high until April. Nothing is known for any ant species about how the queen number per nest/colony affects treatment efficacy, but further research would no doubt yield important breakthroughs for treating ants. Activity occurred predominantly nocturnally, ceasing during mid-day. These activity data determined the critical threshold above which work must be conducted to be considered reliable, and also suggests that treatments are best applied in the afternoon. Total brood production peaked in February and was the lowest around August and September. These abundance data form the baselines for quantifying treatment efficacy, and may have implications for treatment efficacy. Males were found every month, predominantly between August and November. Queen pupae were found in September. The reproductive timing of sexuals determines the treatment schedule. Targeted, site-specific research such as that described here should be an integral part of any eradication program for invasive species to design knowledge-based treatment protocols and determine assessment benchmarks. [ABSTRACT FROM PUBLISHER]

Lack of biological knowledge of invasive species is recognised as a major factor contributing to eradication failure. Management needs to be informed by a site-specific understanding of the invasion system. Here, we describe targeted research designed to inform the potential eradication of the invasive yellow crazy ant Anoplolepis gracilipes on Nu’utele island, Samoa. First, we assessed the ant’s impacts on invertebrate biodiversity by comparing invertebrate communities between infested and uninfested sites. Second, we investigated the timing of production of sexuals and seasonal variation of worker abundance and nest density. Third, we investigated whether an association existed between A. gracilipes and carbohydrate sources. Within the infested area there were few other ants larger than A. gracilipes, as well as fewer spiders and crabs, indicating that A. gracilipes is indeed a significant conservation concern. The timing of male reproduction appears to be consistent with places elsewhere in the world, but queen reproduction was outside of the known reproductive period for this species in the region, indicating that the timing of treatment regimes used elsewhere are not appropriate for Samoa. Worker abundance and nest density were among the highest recorded in the world, being greater in May than in October. These abundance and nest density data form baselines for quantifying treatment efficacy and set sampling densities for post-treatment assessments. The number of plants and insects capable of providing a carbohydrate supply to ants were greatest where A. gracilipes was present, but it is not clear if this association is causal. Regardless, indirectly controlling ant abundance by controlling carbohydrate supply appears to be promising avenue for research. The type of targeted, site-specific research such as that described here should be an integral part of any eradication program for invasive species to design knowledge-based treatment protocols and determine assessment benchmarks to achieve eradication. [ABSTRACT FROM AUTHOR]

Biotic interactions are often important in the establishment and spread of invasive species. In particular, competition between introduced and native species can strongly influence the distribution and spread of exotic species and in some cases competition among introduced species can be important. The Caribbean crazy ant, Nylanderia fulva, was recently introduced to the Gulf Coast of Texas, and appears to be spreading inland. It has been hypothesized that competition with the red imported fire ant, Solenopsis invicta, may be an important factor in the spread of crazy ants. We investigated the potential of interspecific competition among these two introduced ants by measuring interspecific aggression between Caribbean crazy ant workers and workers of Solenopsis invicta. Specifically, we examined the effect of body size and diet on individual-level aggressive interactions among crazy ant workers and fire ants. We found that differences in diet did not alter interactions between crazy ant workers from different nests, but carbohydrate level did play an important role in antagonistic interactions with fire ants: crazy ants on low sugar diets were more aggressive and less likely to be killed in aggressive encounters with fire ants. We found that large fire ants engaged in fewer fights with crazy ants than small fire ants, but fire ant size affected neither fire ant nor crazy ant mortality. Overall, crazy ants experienced higher mortality than fire ants after aggressive encounters. Our findings suggest that fire ant workers might outcompete crazy ant workers on an individual level, providing some biotic resistance to crazy ant range expansion. However, this resistance may be overcome by crazy ants that have a restricted sugar intake, which may occur when crazy ants are excluded from resources by fire ants. [ABSTRACT FROM AUTHOR]

Biotic interactions are often important in the establishment and spread of invasive species. In particular, competition between introduced and native species can strongly influence the distribution and spread of exotic species and in some cases competition among introduced species can be important. The Caribbean crazy ant, Nylanderia fulva, was recently introduced to the Gulf Coast of Texas, and appears to be spreading inland. It has been hypothesized that competition with the red imported fire ant, Solenopsis invicta, may be an important factor in the spread of crazy ants. We investigated the potential of interspecific competition among these two introduced ants by measuring interspecific aggression between Caribbean crazy ant workers and workers of Solenopsis invicta. Specifically, we examined the effect of body size and diet on individual-level aggressive interactions among crazy ant workers and fire ants. We found that differences in diet did not alter interactions between crazy ant workers from different nests, but carbohydrate level did play an important role in antagonistic interactions with fire ants: crazy ants on low sugar diets were more aggressive and less likely to be killed in aggressive encounters with fire ants. We found that large fire ants engaged in fewer fights with crazy ants than small fire ants, but fire ant size affected neither fire ant nor crazy ant mortality. Overall, crazy ants experienced higher mortality than fire ants after aggressive encounters. Our findings suggest that fire ant workers might outcompete crazy ant workers on an individual level, providing some biotic resistance to crazy ant range expansion. However, this resistance may be overcome by crazy ants that have a restricted sugar intake, which may occur when crazy ants are excluded from resources by fire ants. [ABSTRACT FROM AUTHOR]

Aim Invasive species frequently exhibit high temporal and spatial variation in abundance. Although ecological aspects undoubtedly affect this variation, genetic factors may also play a part. The invasive unicolonial yellow crazy ant Anoplolepis gracilipes exhibits considerable variation in abundance throughout its extensive distribution in Australia's Northern Territory, where it was first detected in the 1980s. First, we aimed to determine whether A. gracilipes variation in abundance was associated with behavioural and genetic differentiation of the population and to determine whether one or more introductions occurred. Second, we investigated whether the A. gracilipes population was genetically and behaviourally heterogeneous to determine whether population divergence has occurred since introduction. Location Tropical monsoonal savanna in Arnhem Land, Northern Territory, Australia. Methods Ant abundances were assessed at 13 sites throughout the study region. We used mitochondrial DNA sequences and microsatellite molecular markers to determine population genetic structure, which we correlated with abundance. Behavioural differentiation was assayed using aggression trials and analysed together with genetic data to investigate population divergence. Results Although we found considerable variation in abundance, we found no association between population structure and differences in abundance. Our analyses suggest that A. gracilipes ants in Arnhem Land resulted from a single introduction. The population is not homogeneous, however, as aggression scores varied over both genetic and geographic distance. We also found a positive relationship between genetic and geographic distance. Main conclusions The variation in abundance in the Arnhem Land population of A. gracilipes is clearly not owing to invasion by ants from different sources. The genetic and behavioural differentiation we observed is suggestive of incipient genetic and behavioural divergence, which may be expected over time when an invasive species enters in a new environment. [ABSTRACT FROM AUTHOR]

Benefits arising from facultative mutualisms between ants and plants vary with the identity of the ant partner. Invasive and native ants are both attracted to plants that offer extrafloral nectar, but few studies have compared their abilities to displace herbivores and benefit plants. Yellow crazy ants Anoplolepis gracilipes have invaded eucalypt woodlands of Arnhem Land, northern Australia, where they displace the native dominant weaver ant Oecophylla smaragdina. We compared the plant defense services provided by A. gracilipes and O. smaragdina ants on trees with ( Acacia lamprocarpa) and without ( Eucalyptus tetrodonta) extrafloral nectar rewards through surrogate herbivore (termite) addition experiments and surveys of herbivore damage. Anoplolepis gracilipes were more likely than O. smaragdina to discover termites on A. lamprocarpa, but the likelihood of termite discovery on E. tetrodonta did not vary with ant species. Anoplolepis gracilipes were also more thorough in their attacks of termites, recruited 3.4-4 times more workers to termites, and were 3.4 times quicker at discovering termites on A. lamprocarpa than were O. smaragdina. Discovery of termites by other predators did not vary significantly between trees in A. gracilipes and O. smaragdina sites. Herbivory scores did not reflect the foliage patrolling pattern by the ants. Old A. lamprocarpa leaves and both new and old leaves and branches on E. tetrodonta in A. gracilipes sites had higher chewing herbivory scores than their counterparts in O. smaragdina sites. Our results reveal that the more aggressive and efficient foliar patrolling by A. gracilipes does not translate to increased plant protection. Ant invasions can disrupt native ant-plant mutualisms despite invasive ants possessing many traits associated with effective plant guarding. [ABSTRACT FROM AUTHOR]

Changes to the Earth's climate may affect the distribution of countless species. Understanding the potential distribution of known invasive species under an altered climate is vital to predicting impacts and developing management policy. The present study employs ecological niche modeling to construct the global potential distribution range of the yellow crazy ant ( Anoplolepis gracilipes) using past, current and future climate scenarios. Three modeling algorithms, GARP, BioClim and Environmental Distance, were used in a comparative analysis. Output from the models suggest firstly that this insect originated from south Asia, expanded into Europe and then into Afrotropical regions, after which it formed its current distribution. Second, the invasive risk of A. gracilipes under future climatic change scenarios will become greater because of an extension of suitable environmental conditions in higher latitudes. Third, when compared to the GARP model, BioClim and Environmental Distance models were better at modeling a species' ancestral distribution. These findings are discussed in light of the predictive accuracy of these models. [ABSTRACT FROM AUTHOR]