Herbivory

heterotroph

an organism that obtains its nutrition from another organism

Secondary chemicals (or compounds or metabolites) (Internet)

are organic compounds that are not directly involved in the normal growth, development, or reproduction of an organism. Unlike primary metabolites, absence of secondary metabolites does not result in immediate death, but rather in long-term impairment of the organism's survivability, fecundity, or aesthetics, or perhaps in no significant change at all. Secondary metabolites are often restricted to a narrow set of species within a phylogenetic group. Secondary metabolites often play an important role in plant defense against herbivory and other interspecies defenses.

Phenological defenses

predator saturation/ satiation via mast fruiting (e.g., oaks, bamboos) to swamp granivores. Another example is mast fruiting - producing a massive amount of seeds at an interval of years to overwhelm granivores

Autotroph

produces its own food--e.g., a plant or a "chemoautotroph" living in deep sea vents and using sulphur and methane oxidizing agent and as source of energy

Mast fruiting

producing a massive amount of seeds at an interval of years to overwhelm granivores

Top-down control (Internet)

refers to when a top predator controls the structure or population dynamics of the ecosystem. The classic example is of kelp forest ecosystems. In such ecosystems, sea otters are a keystone predator. They prey on urchins which in turn eat kelp.

What did Marquis and Whelan (1994) show? What does it support?

showed cascading top-down effect in a terrestrial food web, lending empirical support to these cascades being a consequence of the HSS theory

First batch of graphs from Marquis and Whelan (1994); 3 different dependent variables

*Different letters over bar indicate statistically significant differences

What are two types of tannins?

1. Condensed tannins - attach to cellulose and fiber-bound proteins, acting against microbial and fungal attack, also affecting some vertebrates 2. Hydrolyzable tannins - inactivate digestive enzymes of herbivores

Examples of quantitative defenses (2)

1. E.g., tannins (phenolics) in oak trees Can affect plant choice: a variety of browsers (goats, kudus, impalas) rejected diverse plants with > 5% condensed tannins 2. Resins (terpenoids) common in conifers E.g., those in long-leaf pine fight off attacks of southern pine beetle (pitch tube with beetle illustrated)

Results (words only) form Marquis and Whelan (1994) (3)

1. Greatest herbivore density & leaf damage in cages where protected from insectivorous birds 2. Leaf biomass greatest where herbivores least abundant: spray & control (fewer caterpillars) had more biomass than cages (with most caterpillars) 3. Indirect effects of birds shown by larger leaf sizes in controls compared to cages, and in spray treatment (simulates "super carnivores") compared to controls.

Lessons from prickly pear (3)

1. Invasive plant, introduced without its co-evolved herbivore control agents, can spread rapidly and become a pest 2. A specialized herbivore may get the plant totally under control 3. However, this example involved introduced organisms, and thus a potentially artificial situation: How general is this phenomenon of herbivores controlling plant populations? In a 1991 review of efforts to control plant weeds biologically using herbivores (N = 701 cases), noticeable control by herbivore occurred in only 26% of cases, so herbivores certainly are not always effective!

Examples of mechanical defenses against leaf browsers and grazers (4)

1. Leaf toughness (e.g., silica in grasses, horsetails) 2. Thorns, spines 3. Movement (leaves close when touched in "sensitive plants") 4. Spined leaf margins, branches, trunks, etc.

What are the different types of plant defenses? (5)

1. Mechanical defenses (against grazers or browsers for example) 2. Phenological defense 3. Biotic Defense 4. Hormonal defense 5. Biochemical defense ("Green Desert")

Describe the assumptions and assertions of the HSS study 2; 3 subs in 1st)

1. Most terrestrial ecosystems have just three trophic levels a. Plants generally limited by resource availability (not by herbivores) b. Herbivores generally limited by their predators and parasites c. Carnivores generally food-limited, since their predators rarer 2. Any system with an odd number of trophic levels follows this scheme

Some generalizations about situations where mechanical defenses have evolved (4)

1. Open sites, such as deserts, where plants are close to ground & thus vulnerable to browsers, grazers (also benefit of producing thorns, etc., outweighs costs because of expense of replacing lost tissue in desert) 2. Presumably the sharp thorns on trunks & branches evolved to defend against large climbing herbivores...but which ones? - pleistocene megafauna 3. Plants with only one meristem (such as palms) often spiny, to protect apical meristem 4. Evergreens such as American holly (common in Louisiana forests) may be spiny because they face severe herbivore pressure in winter when deciduous plants have lost their leaves

What are the two broad classes of chemical defensive compounds? (no examples)

1. Quantitative defenses = substances eaten in "relatively" large amounts by herbivores that impede or slow digestion, expose herbivores to predators & parasites. Tend to be carbon-based. 2. Qualitative defenses - often toxic compounds that can deter feeding or affect herbivores after ingestion of small doses. Often nitrogen-based

What are some examples of secondary compounds used against herbivores?

1. THC (tetrahydrocannabinol) in marijuana is an alkaloid, a nitrogenous secondary compound 2. Mustards in the family Cruciferae contain glucosinolates, another nitrogenous class of defensive compounds 3. Queen Anne's lace in family Umbelliferae contains furanocoumarins, belonging to the flavanoids (phenolic, carbon-based compounds) 4. Tobacco contains nicotine, another alkaloid

Why is the Earth Green? (list only) (2)

1. Top-down control of herbivores by predators (HSS theory) 2. Plants fight back!

Consequences of the HSS theory and comments about how well-tested it is (4)

1. Top-down trophic cascade of effects from carnivore to plant 2. Carnivores tend to compete with each other for food, and plants also, but herbivores tend to compete less (controlled by predators) 3. Theory was based on much empirical support, but few if any direct tests at the time of indirect effects such as benefit of carnivores to plants by controlling herbivores 4. Indirect effects traditionally better tested in aquatic systems

Ecological effects of herbivores (3; 3 subs in first)

1.Reduce plant fitness: Reduce plant growth rate and reproductive output a. Directly as seed predators b. Indirectly by reducing plant biomass (e.g., browsing, grazing) c. Insect herbivores can completely defoliate plants, even forests! 2. Control plant distribution and abundance 3. Alter plant community structure and composition - through alterations of plant distribution patterns and relative abundances

Describe the classic example of herbivores controlling their "prey"

1839 - Prickly pear (Opuntia stricta) introduced to Australia By 1925 it covered large areas, destroying rangeland. Herbivores were introduced to try to control the plant: Cactus moth larvae (Cactoblastis cactorum) was introduced from South America, with great success controlling prickly pear

How often (approximately) do herbivores control their "prey"

26% (not often) according to a review

What are we seeing in forests now because of a lack of wolves?

A browse line from deer

What is an example of herbivores altering plant species dominance patterns by feeding selectively on dominant interspecific competitors?

Bison in Great Plains feed selectively on C4 plants (tall grasses), allowing more light at ground level and a greater proportion of C3 plants to thrive

Biochemical defense (idea of a "green desert")

Chemical plant compounds - often referred to as secondary chemicals (i.e., 2º metabolites) Plants produce a huge variety of compounds, in widely varying amounts

Describe the honey locus tree

Common in Jean Lafitte National Historical Park Highly rewarding sugars surrounding seeds in bean-like pods

Describe the evolutionary "arms race" between plants and herbivores

Complex plant-herbivore interactions may have resulted from a long evolutionary history Recall: the co-evolutionary arms race involving angiosperm plants and their specialized plant herbivores is one explanation for why beetles are so rich in species

List some examples of plant-feeding strategies (7)

Folivores, granivores (seed eaters), palynivores (pollen feeders), mucivores (sap eaters), frugivores, nectarivores, and xylophages (wood eaters)

What is the name of the theory that is the first reason why the Earth is green?

HSS study/theory: Theory put forth in basic form by Hairston, Smith, & Slobodkin (HSS) in 1960

Herbivores can alter _____ ______ ______ patterns by feeding ______ on _______ _______ __________

Herbivores can alter plant species dominance patterns by feeding selectively on dominant interspecific competitors

Conclusions

Herbivores may completely control the plants on which they feed, consuming essentially all the available leaf tissue biomass Herbivores, in terrestrial environments at least, normally do not consume much of the green (photosynthetic) biomass...why? Plants fight back with diverse weapons--part of a co-evolutionary arms race involving plants and their herbivores Herbivores are a major factor influencing agricultural productivity, and scientists have developed a variety of strategies, such as integrated pest management, to try to control herbivores

What kind of defense did we discuss with fir trees?

Hormonal defense

What is an example of qualitative defenses?

Hypericum (Klamath weed) contains alkaloid hypericin, evolved to protect it from many insect herbivores...and it's also toxic to cattle.

Why is herbivory important?

Important because plants are the ultimate source of energy for food webs in most environments

Explain what "Why is the Earth Green?" is asking?

In other words, why don't herbivores eat more of the available terrestrial plant biomass? What controls the abundance of herbivores?

What is a way that plants save energy while defending themselves?

Induced defenses: These are facultative defenses (physical and chemical) augmented (up-regulated, produced) in proportion to consumption of plant material by herbivore (e.g., oaks increase production of tannins in response to herbivory; browsed Acacia drepanolobium trees in Kenya have longer thorns than unbrowsed trees) Plant only puts energy into defenses when needed! (a kind of phenotypic plasticity)

What is an importance of herbivory to humans? (3 tools we use to deal with)

Intense scientific effort goes into controlling the negative impacts of herbivores in agricultural systems: 1. Pesticides 2. Biological controls (e.g., Aphytis parasitoid wasps to control citrus scale) 3. Integrated pest management (use of biological control, coupled with judicious use of pesticides)

Trophic relationships (me)

Interactions between different levels of food chains and webs. An example would be predator-prey interactions

Why is American holly spiny?

It faces severe herbivore pressure in the winter when deciduous plants have lost their leaves

Why hasn't the honey locus tree lost its spines?

It probably hasn't had enough time evolutionarily

What experiment showed cascading top-down effect in a terrestrial food web?

Marquis and Whelan (1994)

Biotic defense (through an example)

Mutualisms - myrmecophtes, e.g., some acacias, cecropias, pitcher plants, etc. use highly aggressive, stinging ants to protect foliage

What was our second (not the "classic") example of herbivores controlling their "prey?"

Native Eucalyptus trees of Australia were 100% taller when native herbivorous insects were experimentally removed compared with controls

What are induced defenses an example of?

Phenotypic plasticity

What are some generalizations about the two kinds of chemical defenses?

Quantitative defenses tend to be found in plants that are highly apparent to herbivores (long-lived, large), especially K-selected species like oak trees Qualitative defenses tend to be most important in species that are un-apparent, especially herbaceous and other r-selected (weedy) species But note that many exceptions exist to the above assertions

Green desert

Refers to how, even though the planet is green (dominated by plants), from the herbivore perspective it's a desert because plants are so well-protected (especially due to biochemical defenses) that relatively few plants are available to them as food

Hormonal defense

Reproductive inhibition (e.g., fir trees) via production of insect hormone derivatives (secondary compounds) that inhibit metamorphosis of herbivores

Trophic cascade

Sherry: indirect effect that skips a trophic level Internet: occur when predators in a food web suppress the abundance or alter the behavior of their prey, thereby releasing the next lower trophic level from predation

What is herbivory?

The consumption of plants (primary producers - autotrophs) or plant material by primary consumers (heterotrophs). It is a + / - interaction - like parasitism & predation

Presumably the sharp thorns on trunks & branches evolved in plants like the honey locust tree to defend against large climbing herbivores...but which ones?

The pleistocene megafauna (they are remnants of past evolutionary pressures

Induced defenses (with example)

These are facultative defenses (physical and chemical) augmented (up-regulated, produced) in proportion to consumption of plant material by herbivore (e.g., oaks increase production of tannins in response to herbivory; browsed Acacia drepanolobium trees in Kenya have longer thorns than unbrowsed trees) Plant only puts energy into defenses when needed! (a kind of phenotypic plasticity)

Why are palms spiny?

They only have one meristem, so the spines are needed to protect the apical meristem

What were the treatments (3) and predictions (2) in Marquis and Whelan (1994)?

Three treatments on white oak saplings in Illinois: 1. sprayed saplings with insecticide to remove insect herbivores (caterpillars) 2. excluded birds with cages & thus protected caterpillars, 3. controls (untreated trees) Predictions: 1. Insect herbivore densities on plants would be in following order: cages > control > insecticide 2. + indirect effects (plant benefits) would be observed in following order: insecticide > control > cages

What do the two basic answers to "Why is the Earth Green?" involve?

Two basic answers involve trophic interactions: 1. Predators and parasites 2. Plants themselves

Evolutionary Arms Race (internet)

a struggle between competing sets of co-evolving genes, traits, or species, that develop adaptations and counter-adaptations against each other, resembling an arms race. These are often described as examples of positive feedback.