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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. Exploitation of a marine subsidy by a terrestrial invader

   https://doi.org/10.1007/s10530-024-03500-5  

   Winters, Christopher; Jurgela, Grace; Holway, David (December 2024, Biological Invasions)

   Abstract Intertidal environments receive energy from marine ecosystems in the form of marine wrack, which makes up the base of a food web that includes both intertidal and terrestrial consumers. Consumption of wrack by terrestrial consumers can elevate their abundance and alter how they interact with organisms in adjacent terrestrial environments. Although rarely documented, terrestrial invaders may exploit marine wrack subsides and potentially disrupt intertidal and terrestrial food webs. Here, we examine consumption of marine wrack resources by the introduced Argentine ant (Linepithema humile), which occurs commonly on beaches in southern California. In controlled trials the Argentine ant readily scavenged arthropod detritivores (amphipods and flies) abundant in wrack. In spite of obvious risks (e.g., exposure to tides, desiccation, thermal stress) associated with intertidal foraging, Argentine ant activity on beaches was comparable to that in spatially-paired, scrub environments. Foraging on beaches allowed ants to access higher densities of arthropod prey and carrion compared to those found in scrub environments. Stable isotope analyses provide evidence for extensive assimilation of marine-derived resources. Values of δ¹⁵N and δ¹³C for the Argentine ant were higher at beach sites than at scrub sites, and Argentine ant δ¹⁵N values broadly overlapped those of intertidal consumers at beach sites. Although ants are known to forage in intertidal environments, this study provides a novel example of an introduced ant species exploiting a cross-boundary subsidy. 

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3. Direct evidence of native ant displacement by the Argentine ant in island ecosystems

   https://doi.org/10.1007/s10530-019-02121-7  

   Naughton, I. (November 2020, Biological invasions)

   null (Ed.)

   Ecological impacts associated with ant introductions have received considerable attention, but most studies that report on these impacts contrast species assemblages between invaded and uninvaded sites. Given the low inferential power of this type of space-for-time comparison, alternative approaches are needed to evaluate claims that ant invasions drive native species loss. Here, we use long-term data sets from two different Argentine ant eradication programs on the California Channel Islands to examine how the richness and composition of native ant assemblages change before and after invasion (but prior to the initiation of treatments). At four different sites on two different islands, pre-invasion native ant assemblages closely resembled those at uninvaded (control) sites in terms of species richness, species composition, and the presence of multiple indicator species. Invader arrival coincided with large (> 75%) and rapid (within 1 year) declines in species richness, shifts in species composition, and the loss of indicator species. These impacts will hopefully be reversed by the recolonization of formerly invaded areas by native ant species following Argentine ant treatment, and long-term studies of native ant recovery at these sites are ongoing. Unchecked spread of the Argentine ant on other islands in this archipelago, however, poses a grave threat to native ants, which include a number of endemic taxa. 

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4. 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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5. A Deep Learning Approach to the Automated Segmentation of Bird Vocalizations from Weakly Labeled Crowd-sourced Audio

   Ayers, Jacob; Perry, Sean; Prestrelski, Samantha; Zhang, Tianqi; von_Schoenfeldt, Ludwig; Blue, Mugen; Steinberg, Gabriel; Tobler, Mathias; Ingram, Ian; Schurgers, Curt; et al (December 2024, NeurIPS 2024 Workshop)

   Ecologists interested in monitoring the effects caused by climate change are increasingly turning to passive acoustic monitoring, the practice of placing autonomous audio recording units in ecosystems to monitor species richness and occupancy via species calls. However, identifying species calls in large datasets by hand is an expensive task, leading to a reliance on machine learning models. Due to a lack of annotated datasets of soundscape recordings, these models are often trained on large databases of community created focal recordings. A challenge of training on such data is that clips are given a "weak label," a single label that represents the whole clip. This includes segments that only have background noise but are labeled as calls in the training data, reducing model performance. Heuristic methods exist to convert clip-level labels to "strong" call-specific labels, where the label tightly bounds the temporal length of the call and better identifies bird vocalizations. Our work improves on the current weakly to strongly labeled method used on the training data for BirdNET, the current most popular model for audio species classification. We utilize an existing RNN-CNN hybrid, resulting in a precision improvement of 12% (going to 90% precision) against our new strongly hand-labeled dataset of Peruvian bird species.Jacob Ayers (Engineers for Exploration at UCSD); Sean Perry (University of California San Diego); Samantha Prestrelski (UC San Diego); Tianqi Zhang (Engineers for Exploration); Ludwig von Schoenfeldt (University of California San Diego); Mugen Blue (UC Merced); Gabriel Steinberg (Demining Research Community); Mathias Tobler (San Diego Zoo Wildlife Alliance); Ian Ingram (San Diego Zoo Wildlife Alliance); Curt Schurgers (UC San Diego); Ryan Kastner (University of California San Diego) 

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