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1. Historical resurveys provide support for abiotic limits to Argentine ant invasion in southern California

   https://doi.org/10.1007/s10530-025-03583-8  

   Hathaway, Shane; Menke, Sean_B; Holway, David_A (April 2025, Biological Invasions)

   Abstract Predicting where introduced species will establish and spread remains a central goal of invasion biology. While climate data are often used to forecast potential occurrence at regional scales, environmental filtering can limit susceptibility to invasion at finer scales. Factors underlying such filtering are important to identify, especially when they influence spread into protected areas set aside for conservation. Useful information about factors limiting invasion can be obtained from historical resurveys. Between 2022 and 2024, we used pitfall traps and visual surveys to resurvey 111 sampling points in two protected areas in coastal San Diego County, California (Torrey Pines State Reserve and the Point Loma Ecological Conservation Area) that were originally surveyed for the non-native Argentine ant between 1995 and 1997. The multi-decade time span between the surveys coupled with the observed distributional limits, which have either contracted (Torrey Pines) or appear static (Point Loma), indicate that the Argentine ant has reached the limits of its ability to invade these sites. At Torrey Pines the soil types with the lowest water retention values were the least invaded in the original survey and were overrepresented among retractions observed in the resurvey. These findings are consistent with experimental work demonstrating the central role of soil moisture in limiting Argentine ant spread in seasonally dry areas. Variation in precipitation combined with changes in human water use will likely continue to influence the distribution of the Argentine ant in semiarid regions. These results generally illustrate the value of historical resurveys in clarifying limits to invasion. 

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2. Plant invasion impacts on fungal community structure and function depend on soil warming and nitrogen enrichment

   https://doi.org/10.1007/s00442-020-04797-4  

   Anthony, M. A.; Stinson, K. A.; Moore, J. A.; Frey, S. D. (December 2020, Oecologia)

   null (Ed.)

   Abstract The impacts of invasive species on biodiversity may be mitigated or exacerbated by abiotic environmental changes. Invasive plants can restructure soil fungal communities with important implications for native biodiversity and nutrient cycling, yet fungal responses to invasion may depend on numerous anthropogenic stressors. In this study, we experimentally invaded a long-term soil warming and simulated nitrogen deposition experiment with the widespread invasive plant Alliaria petiolata (garlic mustard) and tested the responses of soil fungal communities to invasion, abiotic factors, and their interaction. We focused on the phytotoxic garlic mustard because it suppresses native mycorrhizae across forests of North America. We found that invasion in combination with warming, but not under ambient conditions or elevated nitrogen, significantly reduced soil fungal biomass and ectomycorrhizal relative abundances and increased relative abundances of general soil saprotrophs and fungal genes encoding for hydrolytic enzymes. These results suggest that warming potentially exacerbates fungal responses to plant invasion. Soils collected from uninvaded and invaded plots across eight forests spanning a 4 °C temperature gradient further demonstrated that the magnitude of fungal responses to invasion was positively correlated with mean annual temperature. Our study is one of the first empirical tests to show that the impacts of invasion on fungal communities depends on additional anthropogenic pressures and were greater in concert with warming than under elevated nitrogen or ambient conditions. 

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3. A soil‐nesting invasive ant disrupts carbon dynamics in saplings of a foundational ant–plant

   https://doi.org/10.1111/1365-2745.13803  

   Milligan, Patrick D.; Martin, Timothy A.; Pringle, Elizabeth G.; Riginos, Corinna; Mizell, Gabriella M.; Palmer, Todd M. (November 2021, Journal of Ecology)

   Abstract Nearly every terrestrial ecosystem hosts invasive ant species, and many of those ant species construct underground nests near roots and/or tend phloem‐feeding hemipterans on plants. We have a limited understanding of how these invasive ant behaviours change photosynthesis, carbohydrate availability and growth of woody plants.We measured photosynthesis, water relations, carbohydrate concentrations and growth for screenhouse‐rearedAcacia drepanolobiumsaplings on which we had manipulated invasivePheidole megacephalaants and nativeCeroplastessp. hemipterans to determine whether and how soil nesting and hemipteran tending by ants affect plant carbon dynamics. In a field study, we also compared leaf counts of vertebrate herbivore‐excluded and ‐exposed saplings in invaded and non‐invaded savannas to examine how ant invasion and vertebrate herbivory are associated with differences in sapling photosynthetic crown size.Though hemipteran infestations are often linked to declines in plant performance, our screenhouse experiment did not find an association between hemipteran presence and differences in plant physiology. However, we did find that soil nesting byP. megacephalaaround screenhouse plants was associated with >58% lower whole‐crown photosynthesis, >31% lower pre‐dawn leaf water potential, >29% lower sucrose concentrations in woody tissues and >29% smaller leaf areas. In the field, sapling crowns were 29% smaller in invaded savannas than in non‐invaded savannas, mimicking screenhouse results.Synthesis. We demonstrate that soil nesting near roots, a common behaviour byPheidole megacephalaand other invasive ants, can directly reduce carbon fixation and storage ofAcacia drepanolobiumsaplings. This mechanism is distinct from the disruption of a native ant mutualism byP. megacephala, which causes similar large declines in carbon fixation for matureA. drepanolobiumtrees.Acacia drepanolobiumalready has extremely low natural rates of recruitment from the sapling to mature stage, and we infer that these negative effects of invasion on saplings potentially curtail recruitment and reduce population growth in invaded areas. Our results suggest that direct interactions between invasive ants and plant roots in other ecosystems may strongly influence plant carbon fixation and storage. 

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4. Contrasting invasion histories and effects of three non-native fishes observed with long-term monitoring data

   https://doi.org/10.1007/s10530-023-03146-9  

   Pintar, Matthew R.; Dorn, Nathan J.; Kline, Jeffrey L.; Trexler, Joel C. (August 2023, Biological Invasions)

   Boom-bust population dynamics are long-recognized phenomena during species invasions, but few studies documented impacts of these dynamic changes. The Florida Everglades is the largest wetland in the United States, is undergoing a multi-decade hydro-restoration effort, and has been invaded by several tropical freshwater fishes. We used a 26-year dataset of small native marsh fishes and decapods to assess potential effects of African Jewelfish (Hemichromis letourneuxi) invasion and compared their effects to those of a more recently invading species, Asian Swamp Eels (Monopterus albus/javanensis), and a long-established non-native species, Mayan Cichlids (Mayaheros urophthalmus). Unlike boom-bust dynamics of jewelfish, swamp eel abundance increased and stabilized over the course of this study. After accounting for effects of hydrologic variation, the densities of several native species were more reduced by either jewelfish or swamp eels than by native fish predators, while effects of Mayan Cichlids were similar to those of native fish predators. Impacts of the jewelfish boom in Shark River Slough were smaller (density reductions ≤ 50%) and more temporally limited than those of swamp eels, which produced near-complete loss of four species in Taylor Slough. Following the jewelfish bust, the density of affected species approximated pre-invasion predictions based on hydrology, but their recovery is now threatened by the subsequent invasion of swamp eels in Shark River Slough. Long-term monitoring data provide opportunities to probe for population-level effects at field scales, and indicate that impacts of non-native species can be context-dependent and vary across ecosystems and temporal scales. 

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5. Experimental warming weakens positive plant diversity effects on pitfall trap sampled ant diversity.

   Clark, A. (April 2022, Soil organisms)

   Abstract Ants are important components of many terrestrial ecosystems because of their high abundance, their central position in food webs, and because they can strongly influence ecosystem properties such as soil aeration, nutrient cycling, and plant community composition. Moreover, ants are also known to respond strongly to changes in environmental and biological conditions. In particular, two major anthropogenic environmental impacts – climate change and the loss of primary producers – may have interactive effects on ant communities. To examine this potential interaction, we quantified pitfall trap sampled ant diversity and activity across a fully factorial experiment manipulating temperature and grassland plant species richness at the Cedar Creek Ecosystem Science Reserve in Minnesota, USA. Consistent with previous arthropod studies, we found a significant increase in sampled ant diversity in plots with higher sown plant species richness, such that plots with the largest number of plant species also had the highest sampled ant diversity. However, the strength of this relationship declined significantly in experimentally warmed subplots, especially when considered for higher aggregated spatial scales of samples. Taken together, these results suggest that the positive effects of plant diversity on sampled ant diversity may be partially undermined under warmer conditions. 

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