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<p>Large mammalian herbivores affect both plants and the small animals that live in and feed on those plants. The response of plant and animal communities to mammalian herbivory is variable worldwide, but rarely studied in North American salt marshes. We studied mammalian grazing (cattle, feral horses, and mowing as a type of “artificial grazing”) on three barrier islands on the coast of Georgia, USA. The three grazing treatments differed in location, intensity, and type of herbivore. They all altered invertebrate community composition, but in different ways. Cattle grazing had the most negative impact on plant height, chlorophyll content, and leaf toughness, and on the density of invertebrates, while artificial grazing sometimes increased densities of planthoppers, herbivorous <i>Chaetopsis</i> spp. flies, and spiders. Although the responses to grazing of some plant traits and some invertebrate taxa were variable, plant height and katydid (<i>Orchelimum fidicinium</i>) density were consistently reduced by the three grazing types. In laboratory experiments, katydids (the easiest herbivore to work with in the laboratory) did not have a feeding preference for grazed versus ungrazed plants, but grew better on ungrazed plants. Our results indicate that moderate levels of grazing do not harm salt marsh invertebrates in this geographic area, and may even benefit some species. Heavy grazing, however, strongly suppresses both plants and marsh invertebrates. Future studies should evaluate both grazing intensity and the different responses of different invertebrate taxa to improve guidance to managers about vertebrate grazing in salt marshes.</p>

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Effects of Large Mammal Herbivory on Salt Marsh Invertebrate Communities Vary with Grazing Type

  • 期刊论文

  • 发表日期：

    2025年4月28日

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  • Kori J. Lugar,
  • Steven C. Pennings

摘要

Large mammalian herbivores affect both plants and the small animals that live in and feed on those plants. The response of plant and animal communities to mammalian herbivory is variable worldwide, but rarely studied in North American salt marshes. We studied mammalian grazing (cattle, feral horses, and mowing as a type of “artificial grazing”) on three barrier islands on the coast of Georgia, USA. The three grazing treatments differed in location, intensity, and type of herbivore. They all altered invertebrate community composition, but in different ways. Cattle grazing had the most negative impact on plant height, chlorophyll content, and leaf toughness, and on the density of invertebrates, while artificial grazing sometimes increased densities of planthoppers, herbivorous Chaetopsis spp. flies, and spiders. Although the responses to grazing of some plant traits and some invertebrate taxa were variable, plant height and katydid (Orchelimum fidicinium) density were consistently reduced by the three grazing types. In laboratory experiments, katydids (the easiest herbivore to work with in the laboratory) did not have a feeding preference for grazed versus ungrazed plants, but grew better on ungrazed plants. Our results indicate that moderate levels of grazing do not harm salt marsh invertebrates in this geographic area, and may even benefit some species. Heavy grazing, however, strongly suppresses both plants and marsh invertebrates. Future studies should evaluate both grazing intensity and the different responses of different invertebrate taxa to improve guidance to managers about vertebrate grazing in salt marshes.