HERBIVORY
Herbivory = the eating or consumption of plants (primary prodoucers) or plant
material, by animals known as primary consumers.
Organisms can be divided into heterotrophs and autotrophs. All the energy in
a biotic community enters through plants, so herbivores are a critical link.
Because plants have a low nitrogen content (not very nutritional), herbivores
have to eat a lot of it and be efficient at digesting. Plant food we eat nowadays is
selected for higher nutritional value.
99% of terrestrial biomass is made of plants.
Eating plants has advantages – they are abundant, do not run and rarely fight
back. Why aren’t all animals herbivores?
Special adaptations are required for herbivores to digest plants:
- The right shape and size for best access to the plants is needed
- Strong jaws, durable teeth, bill, or other mouthparts
- Large rumen (first stomach) to digest cellulose using symbiotic micro-
organisms
Herbivores come in different flavours depending on feeding specialisation:
- Specialists e.g. koalas, monarch caterpillars
- Generalists e.g. deer, cows, leaf-cutter ants
- The effect of herbivores on the ecosystem will depend on its specialisation
Do herbivores impact plant species?
Herbivores can:
- Reduce plant growth rate
- Reduce plant reproductive output – either directly as seed predators or
indirectly by reducing plant biomass.
- Examples: outbreaks of herbivorous insects can defoliate forests, and cattle
grazing can radically alter plant communities.
Effects of herbivores on diversity:
- Herbivores that prefer dominant plants cause increased diversity
- Herbivores that prefer subordinate plants cause decreased diversity
Positive effects of herbivory?
- In 276 studies of grazed systems around the world, approx. 17% showed a
positive relationship between grazing and aboveground production.
- Herbivores can induce plant growth – e.g. clipping can induce fruit production,
moderate grazing by snow geese increases plant biomass
- Herbivores can be valuable controllers of invasive plants – an invasive species
is a species new to an area, where it grows unchecked (lack of competitors,
Herbivory = the eating or consumption of plants (primary prodoucers) or plant
material, by animals known as primary consumers.
Organisms can be divided into heterotrophs and autotrophs. All the energy in
a biotic community enters through plants, so herbivores are a critical link.
Because plants have a low nitrogen content (not very nutritional), herbivores
have to eat a lot of it and be efficient at digesting. Plant food we eat nowadays is
selected for higher nutritional value.
99% of terrestrial biomass is made of plants.
Eating plants has advantages – they are abundant, do not run and rarely fight
back. Why aren’t all animals herbivores?
Special adaptations are required for herbivores to digest plants:
- The right shape and size for best access to the plants is needed
- Strong jaws, durable teeth, bill, or other mouthparts
- Large rumen (first stomach) to digest cellulose using symbiotic micro-
organisms
Herbivores come in different flavours depending on feeding specialisation:
- Specialists e.g. koalas, monarch caterpillars
- Generalists e.g. deer, cows, leaf-cutter ants
- The effect of herbivores on the ecosystem will depend on its specialisation
Do herbivores impact plant species?
Herbivores can:
- Reduce plant growth rate
- Reduce plant reproductive output – either directly as seed predators or
indirectly by reducing plant biomass.
- Examples: outbreaks of herbivorous insects can defoliate forests, and cattle
grazing can radically alter plant communities.
Effects of herbivores on diversity:
- Herbivores that prefer dominant plants cause increased diversity
- Herbivores that prefer subordinate plants cause decreased diversity
Positive effects of herbivory?
- In 276 studies of grazed systems around the world, approx. 17% showed a
positive relationship between grazing and aboveground production.
- Herbivores can induce plant growth – e.g. clipping can induce fruit production,
moderate grazing by snow geese increases plant biomass
- Herbivores can be valuable controllers of invasive plants – an invasive species
is a species new to an area, where it grows unchecked (lack of competitors,
