The Impact of Vertebrate Herbivores on Wetland Vegetation in Atchafalaya Bay, Louisiana

Evers, D. Elaine; Sasser, Charles E.; Gosselink, James G.; Fuller, Deborah A.; Visser, Jenneke M.

doi:10.2307/1352543

Cited by 67 publications

(52 citation statements)

References 29 publications

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“…We limited our meta-analysis to studies that presented data for individual taxa, either where only one herbivore taxon was present or where the effects of different taxa were experimentally separated through careful exclosure design (e.g. Evers et al, 1998;Wong, Kwong & Qiu, 2009). …”

Section: Methods (1) Data Collationmentioning

confidence: 99%

Herbivore regulation of plant abundance in aquatic ecosystems

et al. 2016

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Herbivory is a fundamental process that controls primary producer abundance and regulates energy and nutrient flows to higher trophic levels. Despite the recent proliferation of small-scale studies on herbivore effects on aquatic plants, there remains limited understanding of the factors that control consumer regulation of vascular plants in aquatic ecosystems. Our current knowledge of the regulation of primary producers has hindered efforts to understand the structure and functioning of aquatic ecosystems, and to manage such ecosystems effectively. We conducted a global meta-analysis of the outcomes of plant-herbivore interactions using a data set comprised of 326 values from 163 studies, in order to test two mechanistic hypotheses: first, that greater negative changes in plant abundance would be associated with higher herbivore biomass densities; second, that the magnitude of changes in plant abundance would vary with herbivore taxonomic identity. We found evidence that plant abundance declined with increased herbivore density, with plants eliminated at high densities. Significant between-taxa differences in impact were detected, with insects associated with smaller reductions in plant abundance than all other taxa. Similarly, birds caused smaller reductions in plant abundance than echinoderms, fish, or molluscs. Furthermore, larger reductions in plant abundance were detected for fish relative to crustaceans. We found a positive relationship between herbivore species richness and change in plant abundance, with the strongest reductions in plant abundance reported for low herbivore species richness, suggesting that greater herbivore diversity may protect against large reductions in plant abundance. Finally, we found that herbivore-plant nativeness was a key factor affecting the magnitude of herbivore impacts on plant abundance across a wide range of species assemblages. Assemblages comprised of invasive herbivores and native plant assemblages were associated with greater reductions in plant abundance compared with invasive herbivores and invasive plants, native herbivores and invasive plants, native herbivores and mixed-nativeness plants, and native herbivores and native plants. By contrast, assemblages comprised of native herbivores and invasive plants were associated with lower reductions in plant abundance compared with both mixed-nativeness herbivores and native plants, and native herbivores and native plants. However, the effects of herbivore-plant nativeness on changes in plant abundance were reduced at high herbivore densities. Our mean reductions in aquatic plant abundance are greater than those reported in the literature for terrestrial plants, but lower than aquatic algae. Our findings highlight the need for a substantial shift in how biologists incorporate plant-herbivore interactions into theories of aquatic ecosystem structure and functioning. Currently, the failure to incorporate top-down effects continues to hinder our capacity to understand and manage the ecological dynamics of habitats ...

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Section: Methods (1) Data Collationmentioning

confidence: 99%

Herbivore regulation of plant abundance in aquatic ecosystems

et al. 2016

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“…These can result from the introduction of non-native species (e.g. nutria: Evers et al 1998;feral horses: Turner 1987;feral cattle: Martin 2003), from the absence or reduction of predators which leads to increased herbivore populations (e.g. littorinid snails: Silliman & Bertness 2002; sesarmid crabs: Holdredge et al 2009), and from agricultural subsidies that enhance food supply to herbivore populations (e.g.…”

Section: Introductionmentioning

confidence: 99%

Foliar DMSO:DMSP ratio and metal content as indicators of stress in Spartina alterniflora

McFarlin¹,

Alber²

2013

Mar. Ecol. Prog. Ser.

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We evaluated 2 potential indicators of stress, viz. the ratio of dimethylsulfoxide to dimethylsulfoniopropionate (DMSO:DMSP) and foliar metals, in Spartina alterniflora collected from areas affected by 4 different disturbances (sudden marsh dieback, horse grazing, increased snail densities, wrack deposition) across 20 marshes in Georgia, USA. The DMSO:DMSP ratio was a stronger and more consistent indicator of stress than either DMSP or DMSO concentrations alone, with significantly higher ratios occurring in leaves and stems collected from affected compared to healthy areas in all 4 disturbance types. Foliar metal concentrations also differed in affected compared to healthy areas. Of 20 metals evaluated, concentrations of 19 were increased in leaves collected from edge and affected areas. Multidimensional scaling using the entire suite of metals showed separation between plants from affected and healthy areas, but no difference among disturbance types. In contrast, chlorophyll a concentrations were not significantly different between affected and healthy areas, and did not correlate with variation in either of the 2 indicators. These results suggest that the DMSO:DMSP ratio and foliar metal suite are sensitive indicators of sublethal stress in Spartina, capable of identifying stress before there are visible signs such as chlorophyll loss. The fact that both indicators were consistent across a variety of disturbance types suggests that they may be primarily responsive to general oxidative stress and thus, broadly useful tools for evaluating the health of salt marsh habitat in the field. Spartina alterniflora salt marsh near St. Simons Island, GA, with a dieback area along the edge of the tidal creek.

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“…Since its introduction, the nutria population has increased rapidly, becoming the dominant grazer in fresh and oligohaline marshes (Lowery 1974, Condrey et al 1995. The change in species composition due to nutria grazing has been shown in Louisiana for the nearby Atchafalaya delta (Shaffer et al 1992, Evers et al 1998, oligohaline wiregrass marshes (Taylor et al 1994), and mesohatine wiregrass marshes (Nyman et at. 1993).…”

Section: Discussionmentioning

confidence: 95%

Long-term vegetation change in Louisiana tidal marshes, 1968–1992

et al. 1999

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The Louisiana coastal marshes form some of the most extensive wetlands within the continental United States. The problem of land loss in these coastal marshes is well-documented, but very little is known about possible changes in vegetation composition that might be associated with this loss. We analyzed vegetation data collected from 1968 to 1992 in the tidal wetlands of Terrebonne parish and described five vegetation types that occur in this region. Our data did not show the predicted change to more salt-tolerant vegetation. This is probably due to the influence of the Atchafalaya River in the study area. However, we documented a large change in the dominant vegetation of the fresh marsh. Panicum hemitornon-dominated marshes occupied 51% of the study area in 1968 and only 14% in 1992. This vegetation type was replaced with Eleocharis baldwinii-domJnated marshes (3% in 1968 to 41% in 1992). This change occurred adjacent to an area of significant conversion to open water. Based on limited available data from the literature, we ev',duated three potential driving factors in this change-grazing, water-level increase, and water quality-but could not determine the cause of change definitively.

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The Impact of Vertebrate Herbivores on Wetland Vegetation in Atchafalaya Bay, Louisiana

Cited by 67 publications

References 29 publications

Herbivore regulation of plant abundance in aquatic ecosystems

Herbivore regulation of plant abundance in aquatic ecosystems

Foliar DMSO:DMSP ratio and metal content as indicators of stress in Spartina alterniflora

Long-term vegetation change in Louisiana tidal marshes, 1968–1992

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