The hierarchical nature and processes of different levels of ecological systems:

Species Interactions Ch 17 Herbivory

Objectives Herbivory Effects on plants How demonstrate herbivory effects Herbivore selectivity Plant deterrents to herbivory What limits herbivory?

Pairwise interspecific interactions ***Which is: +/-, +/0, +/+, -/-, -/0 ? Mutualism Commensalism +,0 Amensalism -,0 Herbivory Predation Parasitism Disease Competition Amenalism: huge tree and seedling competing for resources; seedling makes infinitesmal dent into tree’s resources. Really very asymmetrical competition. Commensalism: epiphytes on trees; remoras (sharpsuckers) have sucker on dorsal fin; attadh to shark or rays 1) saves energy due to limited swimming 2) gathers food ccraps when host is feeding Parasite: consumes part of blood or tissues of host, usually without killing the host. Pathogen: parasitic organism that causes a disease in its host.

Pairwise interspecific interactions Mutualism (+/+) Commensalism (+, 0) Amensalism (-, 0) Herbivory (+/-) Predation (+/-) Parasitism Disease Competition (-/-) Amenalism: huge tree and seedling competing for resources; seedling makes infinitesmal dent into tree’s resources. Really very asymmetrical competition. Commensalism: epiphytes on trees; remoras (sharpsuckers) have sucker on dorsal fin; attadh to shark or rays 1) saves energy due to limited swimming 2) gathers food ccraps when host is feeding Parasite: consumes part of blood or tissues of host, usually without killing the host. Pathogen: parasitic organism that causes a disease in its host.

Fluidity of interspecific relationships: Can evolve from one type to another. Switch + and - signs of interaction, e.g. +/+ to +/-.

In food chains, all life forms are both consumers and victims of consumers. Predators Parasites Parasitoids Pathogens Herbivores

Herbivory: Effects on plants C41.7 Larva of moth eating way through mesophyll of oak leaf.

Outbreaks of herbivorous insects can defoliate forests. Canada Tent caterpillars, gypsy moths, fungus on chestnut…pine bark beetle in BC on trainride Spruce budworm

Herbivory has great effects on plants: 1) individual/ecosystem 2) population 3) community If prefer dominant species---> What is a keystone herbivore? If prefer subdominant species---> Mauna Loa Hawaii: area at L is protected from cattle grazing. GB: Herbivores can change relative densisites of plants species: Herbivores that prefer dominant plants cause increased diverstiy Herbivores that prefer subordinant plants cause decreased diversity. Figure 1

How do we test the hypothesis that herbivores control plant populations? Describe, then explain these results.

Herbivores feed on plants - and also inoculate them with pathogens and rot-causing microbes.

Does herbivore control plant species? If…. then… Natural enemies hypothesis: Biological control: Prickly pear introduced into Australia without natural enemy. Biological control: introduced cactus moth from SA; moth feeds on growing shoots and introduces pathogens - greatly reduced cactus. But not eradicated…manages to disperse to predator-free areas. Figure 2

(biological control agent) In spite of plant defenses, herbivores can control plant population size. Weed introduced to west; from Europe ; has high amounts of alkaloids - toxic to cattle and sheep. Biological control: introduced beetles of genus Chrysolina from Australia. Reduced weed abundance by 99%.. Klamath weed + beetle (biological control agent)

***What are plant deterrents to herbivory? Structural defense Low nutritional content; sequester nutritious parts Mutualistic defense (ant-acacia) Secondary compounds Figure 3

Chemical defenses (secondary compounds) are toxic to herbivores.

Types of secondary compounds growth regulators toxins against generalist herbivores specialists evolve to detoxify toxin often N-based lignin, alkaloids, non-protein amino acids, cyanogenic glycosides--->HCN digestive inhibitors against specialists often C-based tannins, phenolics, terpenoids Digestive inhibitors bind to proteins and inhibit their digestion. So slow growth of larvae

Chemical defenses Constitutive: high levels at all times Induced: increase greatly after attack Theory: Cost of defense is too high to maintain under light herbivory. (but how quickly can they make them? Hypothesis: Plants ‘eavesdrop’ on neighbors - signal to make defense. Refer to article they read at beginning of semester.Wild tobacco growing near clipped sagebrush became more resistant to herbivores than tobacco plants near unclipped sagebrush. Eavesdropping may be restircted to species that are strongly inducible and to those species that relase high concentrations of cues.

What is evidence that plant defenses are induced by herbivory? #2 to #1 Mite 2 lower on cotton plants that had been previously exposed to closely related mite sp 2 than on control plants with no previous mite exposure. Inductionof chemical defenses by cotton plants following exposure to one mite species results in reduced populations of adult mites of another species.- and their eggs. Mite sp 1 attacks. Plant responds by making defense chemical. Mite sp 2 attacks but in much lower numbers.

Are herbivores ‘lawnmowers’ or selective feeders ***Are herbivores ‘lawnmowers’ or selective feeders? What 3 factors may explain results? K14.14 Selectivity is major reason why the world is not completely green for a herbivore. Selectivity may be caused by plant secondary substances such as phenols.Also differences in nutritional quality. Figure 4

Describe the major pattern in this figure. Generate a WHY ***Describe the major pattern in this figure. Generate a WHY ? Develop an ‘If…then’. Herbivores of oak leaves More species of caterpillars eat oak leaves in spring than later in season. April October Figure 5

Hypothesis/prediction: If oak leaves become less suitable insect food as they age, then caterpillars fed young leaves will grow better than if fed slightly older leaves. Diet larval weight % adults emerge young leaves 45 76 old leaves 18 0 ***What is conclusion? Do data support the hypothesis? “Figure” 6

H1: Increase in toughness H2: Increase in secondary chemicals ***What are three changes as a leaf ages that could account for the previous results? (3 alternative hypotheses) H1: Increase in toughness H2: Increase in secondary chemicals H3: Decrease in nutrient quality Toughness index Figure 7 Leaf age

***Develop predictions for H1 toughness and H2 chemical defense. If leaf toughness explains seasonal feeding pattern of oak insects, then larvae should grow equally well when eating ground-up old vs. young leaves. If chemical defenses have increased with leaf age, then larvae should grow better on ground-up leaves of young than old leaves. ***Are predictions ‘operational’? Do they contain independent and dependent variables? ‘Figure’ 8

***Results Larvae fed ground-up leaves Larval weight Young leaves 37 Old leaves 35 ***Which hypothesis is supported? Why hasn’t NS favored insect mouth parts able to cope with tough leaves? 3rd alternative hypothesis is still possible; Maybe poorer nutrition in later summer; then NS toward early feeding. “Figure” 9

***What factors limit herbivory? Predators Herbivores Plants Nutrients Herbivores consume only @ 10% of plant productivity (up to 30-60% in grasslands). Why so little? ***What factors limit herbivory? Predators Herbivores Plants Nutrients Abiotic factors The ‘world is green’ hypothesis: Herbivores consume a small % of vegetation because they are held in check by a variety of factors. What limits herbivory? top-down vs. bottom-up control: predators limit number of herbivores? vs. plants deter herbivores?

Top-down control. Tri-trophic predators interactions. herbivores Top-down control Tri-trophic predators interactions herbivores plants nutrients/light Bottom-up control Top-down: predators control herbivores Bottom up: plants (or nutirents that control plants) control herbivore (e.g. light or nutrients lower plant productivity which lowers herbivore producitify Also intraspecific competition may control herbivores; or other abioltic factors “Figure” 10

Observation/question: Despite many potential herbivores, why do leaves lose low leaf area? Observation: Birds eat insect herbivores. ***Hypothesis: If bird predation on insect herbivores indirectly reduces the amount of leaf area consumed, ***Prediction: then leaf area consumed will be greater for plants with bird-exclusion cages than those without cages. ‘Figure ‘ 11

Experimental set-up…caged tree saplings

Results: 1) number of insects: 70% greater on saplings without birds than with birds. “Figure” 12 2) % leaf area missing: 35% without birds 22% with birds *** What’s conclusion? Support for hypothesis? Tri-trophic interaction; top-down control. Bird predation: directly reduces # of herbivores indirectly reduces leaf damage by herbivores New questions: Will 1) decreases in bird populations due to forest fragmentation or 2) change in phenology increase insect damage?