involves the predation of plants or algae.
Monophagous herbivores, which are usually insects, feed on one plant species or just a few
closely related species.
Polyphagous species, which are mainly mammals, feed on many different host species,
Strategy Example
1. Mechanical defenses -Thorns, sticky hairs, silica
2. Chemical defenses- Alkaloids, phenolics, terpenoids
3. Mutualisms with defensive agents- Bull’s horn acacia and ants
4. Associational resistance- Purple loosestrife growing next to Myrica
5. Mimic semiochemicals- Ecdysteroids mimic insectmolting
Hormone
Mechanical
many leaves also exhibit sticky hairs or trichomes on the leaves that trap and kill small insects.
Other plants produce sticky resins that gum up the mouthparts of insects when they puncture the
leaf veins.
Low-lying plants are generally more spinose than larger plants,
In temperate locations, evergreen species such as holly, Ilex spp., are often the only browse
available in winter and are spiny.
grasses and palms sequester silica, which makes them difficult to chew.
Both fibers and silica, which are indigestible to animals, grind down mammalian teeth and insect
mandibles, reducing feeding effi ciency.
Chemical
referred to as secondary metabolites, or secondary chemicals.
Most of these chemicals smell bad or are bitter tasting or toxic, and
they deter herbivores from feeding and plant pathogens from colonizing and establishing.
with flowers, the smell may be pleasant and serve to attract animals such as pollinators.
Many fruits are also chemically defended and such defenses may change as fruits ripen.
Alkaloids
Alkaloids are bitter-tasting molecules and often have an unpleasant odor.
For example, an alkaloid in chile peppers called capsaicin elicits a burning sensation. This molecule
is so potent that one-millionth of a drop can be detected by the human tongue.
Capsaicin may serve to discourage mammals from eating the peppers.
birds, which serve to disperse seeds, do not experience the burning sensation of capsaicin.
Other alkaloids are poisonous, like the alkaloid atropine, Animals that eat this plant and
consequently ingest atropine become very sick and may die.
, In humans, for example, atropine causes the heart to speed up to dangerous rates because the
nerve inputs that normally keep a check on heart rate are blocked by atropine.
Phenolics
Common categories of phenolics are the flavonoids, tannins, and lignins.
Flavonoids are produced by many plant species and create a variety of flavors and smells.
These can play a role as deterrents to eating a plant or as attractants that promote pollination.
The flavors of chocolate and vanilla largely come from a mixture of flavonoid molecules.
o Tannins are found in many plant species and typically act as a deterrent to animals, either because
of a bitter taste or due to toxic effects.
o They also can inhibit the enzymes found in the digestive tracts of animals if consumed in large
amounts.
o Tannins are found abundantly in the leaves of many plant species, tea for example, and they
impart a brown color to water.
Lignins are also large phenolic polymers synthesized by plants.
The lignins form polymers that bond with other plant wall components such as cellulose. This
strengthens plant cells and enables a plant to better withstand the rigors of environmental stress.
It also makes wood very tough to digest.
Terpenoids
terpenoids are volatile, they are responsible for the odors emitted by many types of plants, such as
menthol produced by mint
The odors of terpenoids may attract pollinators or repel animals that eat plants
terpenoids often impart an intense flavor to plant tissues. Many of the spices used in cooking are
rich in different types of terpenoids. Examples include cinnamon, cloves, and ginger
terpenoids, like the carotenoids, are responsible for the coloration of many species. An example is
β-carotene that gives carrots their orange color. Carotenoids are also found in leaves, but their
color is masked by chlorophyll, which is green.
Chemical defense strategies change according to plant type and environmental conditions
Plant chemical defenses can be classified as quantitative or as qualitative, depending on the
volume of defense present in the plant.
Quantitative defenses are substances that are ingested in large amounts by the herbivore as it
eats and that prevent energy gain from the digestion of food.
Examples are tannins and resins in leaves,
These compounds are not toxic in small doses, but they have cumulative effects.
The more leaf the herbivores ingest, the more difficult it is for them to digest it.
Qualitative defenses are toxic substances that are effective in very small doses.
Monophagous herbivores, which are usually insects, feed on one plant species or just a few
closely related species.
Polyphagous species, which are mainly mammals, feed on many different host species,
Strategy Example
1. Mechanical defenses -Thorns, sticky hairs, silica
2. Chemical defenses- Alkaloids, phenolics, terpenoids
3. Mutualisms with defensive agents- Bull’s horn acacia and ants
4. Associational resistance- Purple loosestrife growing next to Myrica
5. Mimic semiochemicals- Ecdysteroids mimic insectmolting
Hormone
Mechanical
many leaves also exhibit sticky hairs or trichomes on the leaves that trap and kill small insects.
Other plants produce sticky resins that gum up the mouthparts of insects when they puncture the
leaf veins.
Low-lying plants are generally more spinose than larger plants,
In temperate locations, evergreen species such as holly, Ilex spp., are often the only browse
available in winter and are spiny.
grasses and palms sequester silica, which makes them difficult to chew.
Both fibers and silica, which are indigestible to animals, grind down mammalian teeth and insect
mandibles, reducing feeding effi ciency.
Chemical
referred to as secondary metabolites, or secondary chemicals.
Most of these chemicals smell bad or are bitter tasting or toxic, and
they deter herbivores from feeding and plant pathogens from colonizing and establishing.
with flowers, the smell may be pleasant and serve to attract animals such as pollinators.
Many fruits are also chemically defended and such defenses may change as fruits ripen.
Alkaloids
Alkaloids are bitter-tasting molecules and often have an unpleasant odor.
For example, an alkaloid in chile peppers called capsaicin elicits a burning sensation. This molecule
is so potent that one-millionth of a drop can be detected by the human tongue.
Capsaicin may serve to discourage mammals from eating the peppers.
birds, which serve to disperse seeds, do not experience the burning sensation of capsaicin.
Other alkaloids are poisonous, like the alkaloid atropine, Animals that eat this plant and
consequently ingest atropine become very sick and may die.
, In humans, for example, atropine causes the heart to speed up to dangerous rates because the
nerve inputs that normally keep a check on heart rate are blocked by atropine.
Phenolics
Common categories of phenolics are the flavonoids, tannins, and lignins.
Flavonoids are produced by many plant species and create a variety of flavors and smells.
These can play a role as deterrents to eating a plant or as attractants that promote pollination.
The flavors of chocolate and vanilla largely come from a mixture of flavonoid molecules.
o Tannins are found in many plant species and typically act as a deterrent to animals, either because
of a bitter taste or due to toxic effects.
o They also can inhibit the enzymes found in the digestive tracts of animals if consumed in large
amounts.
o Tannins are found abundantly in the leaves of many plant species, tea for example, and they
impart a brown color to water.
Lignins are also large phenolic polymers synthesized by plants.
The lignins form polymers that bond with other plant wall components such as cellulose. This
strengthens plant cells and enables a plant to better withstand the rigors of environmental stress.
It also makes wood very tough to digest.
Terpenoids
terpenoids are volatile, they are responsible for the odors emitted by many types of plants, such as
menthol produced by mint
The odors of terpenoids may attract pollinators or repel animals that eat plants
terpenoids often impart an intense flavor to plant tissues. Many of the spices used in cooking are
rich in different types of terpenoids. Examples include cinnamon, cloves, and ginger
terpenoids, like the carotenoids, are responsible for the coloration of many species. An example is
β-carotene that gives carrots their orange color. Carotenoids are also found in leaves, but their
color is masked by chlorophyll, which is green.
Chemical defense strategies change according to plant type and environmental conditions
Plant chemical defenses can be classified as quantitative or as qualitative, depending on the
volume of defense present in the plant.
Quantitative defenses are substances that are ingested in large amounts by the herbivore as it
eats and that prevent energy gain from the digestion of food.
Examples are tannins and resins in leaves,
These compounds are not toxic in small doses, but they have cumulative effects.
The more leaf the herbivores ingest, the more difficult it is for them to digest it.
Qualitative defenses are toxic substances that are effective in very small doses.
