Conditions for collapse: Chronic nutrient enrichment increases native insect density linked to salt marsh dieback

Tomasula, Jewel; Maguire, Billie; Rippel, Tyler M.; Lopez, Eddie; Perez, Stéphanie; Arab, Ali; Murphy, Shannon; Wimp, Gina M.

doi:10.1016/j.biocon.2022.109882

Cited by 2 publications

(2 citation statements)

References 59 publications

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“…However, despite altered traits, feeding assays revealed Littoraria consumption was similar across treatments and plant age (Fig. 5), a finding in contrast to previous work showing that elevated nutrients can increase grazer damage (Bertness et al 2008, Tomasula et al 2023. Our study did find that nutrient only treatments decreased both fiber and silica content of Spartina, although these structural defenses were most likely lost in the process of creating agar-based foods (Long et al 2011, Hughes et al 2015, potentially influencing our feeding assay results.…”

Section: Discussioncontrasting

confidence: 77%

Resource availability and plant age drive defense against herbivory in salt marshes

Wittyngham¹,

Carey

Johnson³

2023

Oikos

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The resource‐availability hypothesis (RAH) and the intraspecific RAH (RAHintra), posit that resources, (i.e. nutrients) control plant antiherbivore defenses. Both hypotheses predict that in low‐resource environments, plant growth is slow, and constitutive defense is high. In high‐resource environments, however, the RAH predicts that plant growth is fast, and constitutive defense is low, whereas the RAHintra predicts that increased resources attract more herbivores, and this intensified grazing pressure leads to high constitutive defense. Salt marshes are nutrient‐limited ecosystems threatened by eutrophication and chronic herbivory, yet we know little about how these stressors shape saltmarsh plant antiherbivore defenses, which influence trophic interactions and ecosystem resilience. We manipulated resource availability via nutrient addition and herbivory via the marsh periwinkle Littoraria irrorata, on the saltmarsh foundation species Spartina alterniflora, in mesocosms. Because plant age can also influence trait variation, we measured traits in both original and clonally‐grown new stems. Feeding assays then evaluated how treatments and plant age affected subsequent Littoraria consumption of Spartina. Nutrient addition stimulated growth, while decreasing defensive traits (e.g. fiber and silica content), following the RAH. Herbivory enhanced belowground production and increased stem diameter, yet did not induce defensive traits, contrary to our expectations. Herbivory plus nutrients increased Spartina biomass and reduced phenolics, a defensive trait, further supporting the RAH. Regardless of treatment, clonally‐grown new stems had greater variation in measured traits. Despite altered traits, however, treatments and plant age did not affect Littoraria consumption. Our results support the RAH and part of the RAHintra and suggest: 1) nutrient availability is a primary driver of plant trait change and 2) plant age controls the magnitude of trait variation in Spartina. Further, our findings indicate that eutrophic conditions may not always increase top‒down control by herbivores, and in some instances can enhance saltmarsh resilience against sea‐level rise via stimulated Spartina biomass production.

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Section: Discussioncontrasting

confidence: 77%

Resource availability and plant age drive defense against herbivory in salt marshes

Wittyngham¹,

Carey

Johnson³

2023

Oikos

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“…Understanding the effects of salinity and vegetation texture on the ecological functioning and structure of tidal marsh insect communities within Gulf Coast tidal marshes is particularly important as these marshes are currently experiencing heavy decline due to anthropogenic activities (Couvillion et al, 2017; Watzin & Gosselink, 1992), and because the proposed restoration efforts have the potential to induce eutrophication (Coastal Protection and Restoration Authority of Louisiana, 2007, 2012, 2017; Elsey‐Quirk et al, 2019) and heavy pressure by herbivorous insects (Bertness et al, 2008; Sala et al, 2008; Tomasula et al, 2023). Therefore, the purpose of this study was to conduct an extensive, year‐long inventory of insect families within Louisiana's coastal marshes and to test how insect functional feeding groups vary across multiple salinity zones in two major estuaries with respect to the several aspects of vegetation texture: plant composition, density (ground cover), and between structurally different plant species.…”

Section: Introductionmentioning

confidence: 99%

The influence of salinity and vegetation texture on the ecological roles of insects in tidal marshes in Louisiana

Aker,

Husseneder,

Foil

2023

Ecosphere

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Tidal marsh insect communities are influenced by both salinity and aspects of vegetation texture (vegetation diversity, plant density, and architectural structure). These factors affect the abundances and intra‐ and interguild interactions of these insects and should result in broad‐scale variation in the distribution and ecological functioning of tidal marsh insect communities along these gradients. However, this assumption has not been tested within Gulf Coast marshes, and the insect communities and their ecological roles are not well known. This study identifies how family‐level insect biodiversity varies by salinity and which factors are most important in affecting the distribution of insect functional feeding groups within Louisiana's coastal marshes. Insect family diversity was found to decrease as salinity increased for several indices. Vegetation texture and the underlying salinity gradient were found to be important factors affecting the distribution of free‐living sucking, stem‐boring, parasitic, and filtering functional feeding groups.

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Conditions for collapse: Chronic nutrient enrichment increases native insect density linked to salt marsh dieback

Cited by 2 publications

References 59 publications

Resource availability and plant age drive defense against herbivory in salt marshes

Resource availability and plant age drive defense against herbivory in salt marshes

The influence of salinity and vegetation texture on the ecological roles of insects in tidal marshes in Louisiana

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