02 herbivory plant defense and case studies

[Herbivory] Four herbivore feeding strategies

Folivory (leaves), seed predation, root feeding, sap feeding

[Herbivory] Main challenges for folivores

Digesting cellulose and dealing with plant defensive structures and compounds

[Herbivory] Plant cell wall components

Cellulose, hemicellulose, pectin, lignin and others

[Herbivory] Why can't vertebrates digest cellulose?

They don't produce the enzyme cellulase; fungi and bacteria do

[Herbivory] Solution to the cellulose problem

Mutualistic associations with microorganisms housed in a fermentation chamber

[Herbivory] Foregut fermentation (ruminants)

Rumen fermentation before the absorption site; efficient cellulose breakdown; can synthesize own proteins; slow, so animal must select high-N food

[Herbivory] Hindgut fermentation (non-ruminants)

Cecum fermentation after the absorption site; less efficient; all amino acids come from plants; faster digestion so animal can eat lower-quality food

[Herbivory] Grazers vs browsers

Grazers eat grass; browsers eat woody vegetation

[Herbivory] Hypsodonty

High-crowned teeth, an adaptation of grazers to tooth wear from silica-rich grass

[Herbivory] Browser teeth

Cutting surfaces, adapted to high-lignin woody vegetation

[Herbivory] Mastodon vs mammoth

Mastodon dentition = browser; mammoth dentition = grazer (high-crowned)

[Plant defense] Three plant strategies against herbivory

Avoidance, tolerance, defense

[Plant defense] Avoidance example

Masting (synchronized mass seed production) to overwhelm seed predators

[Plant defense] Tolerance

Compensation and overcompensation in growth after damage

[Plant defense] Structural defense examples

Acacia thorns, tomato trichomes

[Plant defense] Constitutive (quantitative) chemical defense

Constantly produced; tends to be C-based (e.g., condensed tannins in oaks); slows or inhibits digestion

[Plant defense] Induced (qualitative) chemical defense

Upregulated during herbivore attack; often N-rich (e.g., nicotine, alkaloids); deters feeding or is toxic/lethal

[Plant defense] Condensed tannins

C-based constitutive/quantitative defense that slows digestion

[Plant defense] Nicotine/alkaloids

N-rich induced/qualitative defenses that deter feeding or poison

[Plant defense] Plant carbon allocation pools

Leaf mass, stem mass, roots, reproduction, storage, defense

[Plant defense] Allocation tradeoff

Fixed carbon is limited, so investing more in one pool means less in another

[Plant defense] Resource availability hypothesis (Coley et al. 2005)

Plants in resource-poor environments grow slowly, have long-lived costly leaves, and invest heavily in defense (e.g., tannins)

[Plant defense] Fast-growing plants and defense (Coley 1988)

Fast-growers in resource-rich environments invest little in defense (opportunity cost); they get eaten more but resources are easy to replace

[Plant defense] Growth vs defense tradeoff

Fast-growing plants are less defended and eaten more; slow-growing plants are heavily defended

[Prey defense] Anti-predator traits

Armor, toxins, mimicry, camouflage, size, speed/agility

[Case study] Klamathweed and beetles

Herbivores (biocontrol beetles) can crash plant populations

[Case study] Opuntia and Cactoblastis

Moth herbivore dramatically reduced invasive prickly pear cactus

[Case study] Anolis lizards and spiders

Predators strongly affect prey abundance

[Case study] Doherty et al. 2016

Invasive predators are a major driver of global biodiversity loss

[Case study] Bonsall et al. 2002

Host-parasitoid systems show strong population effects: beetles with parasitoids fluctuate and stay lower than beetles alone

[Case study] Snow geese grazing

Light grazing enhances NPP; heavy grazing makes NPP plummet