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**Herbivore Overview**:
– Etymology: Derived from Latin words meaning ‘small plant, herb’ and ‘to eat, devour.’
– Definition: Organisms primarily eat autotrophs like plants.
– Evolution: Traces back to less than 20 million years after the first land plants evolved.
– Food Chain: Herbivores are primary consumers, followed by carnivores and omnivores.
– Feeding Strategies: Grazing, browsing, selective foraging, and optimal foraging theory.

**Herbivore Foraging Behavior**:
– Rate of return equation by S. Holling in 1959.
– Marginal value theorem: Describes balance between eating all food in a patch or moving to a new patch.
– Giving Up Density (GUD) and Giving Up Time (GUT) parameters.
– Herbivores spend more time handling vegetation in dense forests.
– Optimal foraging theory predicts animal behavior while searching for resources.

**Plant-Herbivore Interactions**:
– Influence on community structure and functional processes.
– Impact on plant diversity and richness variably.
– Coevolution and phylogenetic correlation between herbivores and plants.
– Abiotic factors like climate impacting plant-herbivore communities.
– Interactions sustaining greater herbivore richness with plant diversity.

**Herbivore Defense and Plant Defense**:
– Herbivores use feeding choice, herbivore modification, and plant modification strategies.
Plant defense traits divided into tolerance and resistance.
– Physical defenses like thorns, spines, and trichomes.
– Chemical defenses include carbon-based (terpenes, phenolics) and nitrogen-based defenses (alkaloids, cyanogens).
Plant defenses attract natural enemies and include physical and chemical mechanisms.

**Impacts and Conservation**:
– Trophic cascades affecting plant communities through herbivores.
– Economic impacts of herbivores on agriculture and ecotourism.
– Overgrazing leading to ecosystem degradation.
– Conservation efforts for sustainable herbivore management.
– Balancing herbivore populations with ecosystem needs for long-term sustainability.

Herbivore (Wikipedia)

A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthparts adapted to rasping or grinding. Horses and other herbivores have wide flat teeth that are adapted to grinding grass, tree bark, and other tough plant material.

A deer and two fawns feeding on foliage
A sawfly larva feeding on a leaf
Tracks made by terrestrial gastropods with their radulas, scraping green algae from a surface inside a greenhouse

A large percentage of herbivores have mutualistic gut flora that help them digest plant matter, which is more difficult to digest than animal prey. This flora is made up of cellulose-digesting protozoans or bacteria.

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