Arthropod Food Web Restoration Following Removal Of An Invasive Wetland Plant
ABSTRACT 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 . "
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.Ecology 10/2014; 95(10):2699-2706. DOI:10.1890/14-0127.1 · 5.00 Impact Factor
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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 . "
ABSTRACT: Ecological succession has long been a focal point for research, and knowledge of underlying mechanisms is required if scientists and managers are to successfully promote recovery of ecosystem function following disturbance. We addressed the influence of bottom-up processes on successional assemblage shifts in salt marshes, ecosystems with strong physical gradients, and how these shifts were reflected in the trophic characteristics of benthic fauna. We tracked the temporal development of infaunal community structure and food-web interactions in a young, created salt marsh and an adjacent natural marsh in Mission Bay, California, USA (1996-2003). Macrofaunal community succession in created Spartina foliosa habitats occurred rapidly, with infaunal densities reaching 70% of those in the natural marsh after 1 yr. Community composition shifted from initial dominance of insect larvae (surface-feeding microalgivores) to increased dominance of oligochaetes (subsurface-feeding detritivores) within the first 7 yr. Isotopic labeling of microalgae, N2-fixing cyanobacteria, S. foliosa and bacteria revealed direct links (or absence thereof) between these basal food sources and specific consumer groups. In combination with the compositional changes in the macroinvertebrate fauna, the trophic patterns indicated an increase in food-web complexity over time, reflecting resource-driven marsh succession. Natural abundance stable isotope ratios of salt marsh consumers (infaunal and epifaunal macroinvertebrates, and fish) initially reflected distinctions in trophic structure between the created and natural marsh, but these diminished during successional development. Our findings suggest that changing resource availability is one of the important drivers of succession in benthic communities of restored wetlands in Southern California.Marine Ecology Progress Series 03/2014; 500:43-55. DOI:10.3354/meps10686 · 2.64 Impact Factor
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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). "
ABSTRACT: Studies on invasive plant management are often short in duration and limited in the methods tested, and lack an adequate description of plant communities that replace the invader following removal. Here we present a comprehensive review of management studies on a single species, in an effort to elucidate future directions for research in invasive plant management. We reviewed the literature on Phragmites management in North America in an effort to synthesize our understanding of management efforts, identify gaps in knowledge and improve the efficacy of management. Additionally, we assessed recent ecological findings concerning Phragmites mechanisms of invasion and integrated these findings into our recommendations for more effective management. Our overall goal is to examine whether or not current management approaches can be improved and whether they promote reestablishment of native plant communities. We found: (i) little information on community-level recovery of vegetation following removal of Phragmites; and (ii) most management approaches focus on the removal of Phragmites from individual stands or groups of stands over a relatively small area. With a few exceptions, recovery studies did not monitor vegetation for substantial durations, thus limiting adequate evaluation of the recovery trajectory. We also found that none of the recovery studies were conducted in a landscape context, even though it is now well documented that land-use patterns on adjacent habitats influence the structure and function of wetlands, including the expansion of Phragmites. We suggest that Phragmites management needs to shift to watershed-scale efforts in coastal regions, or larger management units inland. In addition, management efforts should focus on restoring native plant communities, rather than simply eradicating Phragmites stands. Wetlands and watersheds should be prioritized to identify ecosystems that would benefit most from Phragmites management and those where the negative impact of management would be minimal.AoB PLANTS 02/2014; 6. DOI:10.1093/aobpla/plu001 · 2.27 Impact Factor