Can indigenous carabid beetles confer biotic resistance to invasion of native grassland remnants by alien slugs?
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2025
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Kapuscinski, N.K.
Nash, M.A.
Morgan, J.W.
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Biological Invasions, 2025; 27(1):56-1-56-13
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NK Kapuscinski, Michael A. Nash, John W. Morgan
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Invasive alien slugs alter plant community assemblages via selective herbivory, yet evidence of their impacts on indigenous plant species in threatened Australian native grasslands are scarce. Carabid beetles have been explored as biocontrol agents of pest slugs in agriculture, with native grassland habitat adjoining agricultural fields thought to be a potential source of beneficial carabid predators. The association between indigenous carabid beetles and invasive alien slugs within remnant native grassland vegetation patches, however, is unquantified. Studies were conducted to identify (i) The extent and determinants of slug invasion into remnant native grassland, and (ii) Whether carabid beetles can confer biotic resistance to native plant species in remnant grasslands. The interaction between alien slugs, carabid beetles and a rare grassland forb was explored in microcosm experiments to test the hypothesis that carabid beetles, by regulating slug herbivory, influence plant survival and growth. Slugs were found at 90% of the remnant native grasslands surveyed; carabid beetles were infrequent and their active abundance was low. There was little evidence that landscape or site-level parameters influence slug density, although species-specific patterns were apparent for the two most abundant slug species. This may reflect the importance of propagule pressure from source populations (the agricultural matrix) affecting slug invasion success, suggesting that native grassland habitat features are of secondary importance. The microcosm experiments provided evidence that slug herbivory may significantly impact the survival of a native forb at the seedling stage, but less so at a mature plant stage. We found that carabid beetles can markedly reduce the impact of alien slugs on plants, provided that encounters between the two taxa occurs. Interactions in the field are likely to be density-dependent such that beneficial impacts of carabid beetles are only apparent when their abundance is high. The high abundance of alien slugs in remnant grasslands, and lack of evidence for biotic resistance via carabid beetle predation, indicates that grassland conservation management may need to include slug baiting to mitigate the potential for negative impacts of slugs on seedling recruitment of threatened native plant species.
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© The Author(s) 2025. This is an open access article