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Abstract As sea‐level rise converts coastal forest to salt marsh, marsh arthropods may migrate inland; however, the resulting changes in arthropod communities, including the stage of forest retreat that first supports saltmarsh species, remain unknown. Furthermore, the ghost forest that forms in the wake of rapid forest retreat offers an unknown quality of habitat to marsh arthropods. In a migrating marsh in Virginia, USA, ground‐dwelling arthropod communities were assessed across the forest‐to‐marsh gradient, and functional use of ghost forest and high marsh habitats was evaluated to determine whether marsh arthropods utilized expanded marsh in the same way as existing marsh. Diet and body condition were compared for two marsh species found in both high marsh and ghost forest (the detritivore amphipod,Orchestia grillus, and the hunting spider,Pardosa littoralis). Community composition differed among zones along the gradient, driven largely by retreating forest taxa (e.g., Collembola), marsh taxa migrating into the forest (e.g.,O. grillus), and unique taxa (e.g., Hydrophilinae beetles) at the ecotone. The low forest was the most inland zone to accommodate the saltmarsh speciesO. grillus, suggesting that inland migration of certain saltmarsh arthropods may co‐occur with early saltmarsh plant migration and precede complete tree canopy die‐off. Functionally,O. grillusoccupied a larger trophic niche in the ghost forest than the high marsh, likely by consuming both marsh and terrestrial material. Despite this, both observed marsh species primarily consumed from the marsh grass food web in both habitats, and no lasting differences in body condition were observed. For the species and functional traits assessed, the ghost forest and high marsh did not show major differences at this site. Forest retreat and marsh migration may thus provide an important opportunity for generalist saltmarsh arthropods to maintain their habitat extent in the face of marsh loss due to sea‐level rise.
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Lizard and frog removal increases spider abundance but does not cascade to increase herbivory
Abstract Insectivorous vertebrates, especially on islands, can exert top‐down control on herbivorous prey, which can transfer through a food chain to reduce herbivory. However, in many systems insectivorous vertebrates feed on more than one trophic level, especially consuming arthropod predators, and this intraguild predation can diminish trophic cascades. Our goal was to determine, using an exclosure experiment, the relative importance of anole lizards and coqui frogs in controlling spider and arthropod abundances as well as herbivory rates in the understory of the Luquillo Experimental Forest, Puerto Rico. We found that exclosures removing both anoles and coquis doubled spider abundance compared to exclosures with anoles and coquis at natural densities. The effect of coquis on spiders was greater and occurred more quickly than that of anoles, potentially because of the higher natural densities of coquis and removal of both vertebrates produced no interactive effects. We found support for the idea that anoles, but not coquis, reduce foliar arthropod abundances on one of the two studied plant species. However, there was also evidence that anole removal decreased herbivory, the opposite of what we would expect if there was a trophic cascade. Potential explanations include that anoles reduced predatory arthropods on foliage more than they reduced herbivorous arthropods. Results highlight that the food web in tabonuco forest is not simple and that there are complex and dynamic relationships among vertebrate insectivores, predatory arthropods, and herbivorous arthropods that do not consistently result in a trophic cascade. Abstract in Spanish is available with online material
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- Award ID(s):
- 1831952
- PAR ID:
- 10449834
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Biotropica
- Volume:
- 53
- Issue:
- 2
- ISSN:
- 0006-3606
- Page Range / eLocation ID:
- p. 681-692
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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