Arthropod Food Web Restoration Following Removal Of An Invasive Wetland Plant

University of Wisconsin-Madison, Department of Entomology, 444 Russell Laboratories, 1630 Linden Drive, Madison, Wisconsin 53706, USA.
Ecological Applications (Impact Factor: 4.09). 05/2006; 16(2):622-31. DOI: 10.1890/1051-0761(2006)016[0622:AFWRFR]2.0.CO;2
Source: PubMed


Restoration of habitats impacted by invasive plants is becoming an increasingly important tool in the management of native biodiversity, though most studies do not go beyond monitoring the abundance of particular taxonomic groups, such as the return of native vegetation. Yet, the reestablishment of trophic interactions among organisms in restored habitats is equally important if we are to monitor and understand how ecosystems recover. This study examined whether food web interactions among arthropods (as inferred by abundance of naturally occurring stable isotopes of C [delta13C] and N [delta15N]) were reestablished in the restoration of a coastal Spartina alterniflora salt marsh that had been invaded by Phragmites australis. From patterns of C and N stable isotopes we infer that trophic interactions among arthropods in the native salt marsh habitats are characterized by reliance on the dominant marsh plant Spartina as a basal resource. Herbivores such as delphacid planthoppers and mirid bugs have isotope signatures characteristic of Spartina, and predatory arthropods such as dolicopodid flies and spiders likewise have delta13C and delta15N signatures typical of Spartina-derived resources (approximately -13 per thousand and 10 per thousand, respectively). Stable isotope patterns also suggest that the invasion of Phragmites into salt marshes and displacement of Spartina significantly alter arthropod food web interactions. Arthropods in Phragmites-dominated sites have delta13C isotope values between -18 per thousand and -20 per thousand, suggesting reliance on detritus and/or benthic microalgae as basal resources and not on Phragmites, which has a delta13C approximately -26 per thousand. Since most Phragmites herbivores are either feeding internally or are rare transients from nearby Spartina, these resources do not provide significant prey resources for other arthropod consumers. Rather, predator isotope signatures in the invaded habitats indicate dependence on detritus/algae as basal resources instead of the dominant vegetation. The reestablishment of Spartina after removal of Phragmites, however, not only returned species assemblages typical of reference (uninvaded) Spartina, but stable isotope signatures suggest that the trophic interactions among the arthropods were also similar in reestablished habitats. Specifically, both herbivores and predators showed characteristic Spartina signatures, suggesting the return of the original grazer-based food web structure in the restored habitats.

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    • "5 m , as well as live Spartina plants ( , 20 cm height , clipped at base ) from the adjacent marsh . Sediment values only indirectly represent the isotopic ratios of potential trophic resources available on the mudflat surface ( Gratton and Denno 2006 ) , because benthic microalgae , bacteria , phytoplankton , and decaying plant material are all likely to be represented in the microphytobenthos on the surface sediment , and consumers may select between them . Spartina and Gracilaria samples were rinsed prior to processing . "
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    ABSTRACT: Nonnative species that form novel habitats strongly affect ecosystem processes. The effects of these ecosystem engineers can be both positive and negative but the mechanisms behind their effects are not well described. In this study we determined the relative importance of three main mechanisms by which invasive ecosystem engineers can facilitate native fauna. The engineer may provide new physical structure that reduces harsh abiotic conditions or gives refuge from predation (both engineering mechanisms), or provide a new profitable food resource (a trophic mechanism). The invasive seaweed Gracilaria vermiculophylla is a novel addition to estuarine intertidal mudflats of the southeastern United States. The epifaunal amphipod Gammarus mucronatus is up to 100 times more abundant on Gracilaria-invaded mudflats compared to uninvaded mudflats. Feeding assays, a survivorship experiment and stable isotope analysis demonstrated that Gammarus consumes little Gracilaria and cannot survive on Gracilaria alone. However, the structural engineering effects of Gracilaria greatly enhanced the survivorship of Gammarus in the presence of predators during high tide and when exposed to harsh abiotic conditions during low tide. Our results demonstrate that invasive ecosystem engineers can dramatically affect the distribution and abundance of native species by providing a novel protective structure.
    Full-text · Article · Oct 2014 · Ecology
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    • "Stable isotopes offer multiple insights about food webs, as tracers of C and N, for trophic level assessments, and as proxies for trophic structuring within species and within whole assemblages , including bottom-up and top-down forcing (Vander Zanden et al. 1999, Layman et al. 2012). Stable isotope approaches can thereby be useful for monitoring changes in community trophic interactions under different management scenarios or strategies, including ecological restoration (Gratton & Denno 2006). Establishing rates of recovery of trophic structure or diversity can help determine monitoring strategies and success criteria for restoration . "
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    Full-text · Article · Mar 2014 · Marine Ecology Progress Series
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    • "One such invader, a Eurasian lineage of the common reed, Phragmites australis (hereafter referred to as Phragmites), is increasingly dominant in wetlands across North America (Marks et al. 1994; Chambers et al. 1999; Saltonstall 2003; Kettenring et al. 2012b in this issue). Phragmites invasions are often associated with decreases in plant biodiversity (Chambers et al. 1999; Keller 2000; Bertness et al. 2002), declines in habitat quality for fish and wildlife (Fell et al. 2003, 2006; Gratton and Denno 2006; Chambers et al. 2012), disruptions to biogeochemical cycles (Meyerson et al. 1999, 2000; Findlay et al. 2003) and other ecosystem services (but see Kiviat 2013 and Kettenring et al. 2012b in this special issue, which highlight Phragmites benefit to wildlife or lack/weaknesses of data on actual impacts). Phragmites invasion is becoming an increasingly large management concern in a variety of systems: tidal marshes along the Atlantic Coast (Chambers et al. 1999; Warren et al. 2001; Bertness et al. 2002); the Great Lakes (Tulbure et al. 2007; Carlson et al. 2009; Uzarski et al. 2009; Willcox 2013); inland brackish wetlands of the Great Basin (Kettenring and Mock 2012; Kettenring et al. 2012a)a n dt h eG u l fC o a s t( Kettenring et al. 2012b in this special issue). "
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    Full-text · Article · Feb 2014 · AoB PLANTS
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