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159 Cards in this Set

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What are some ways that plants affect predators and parasitoids of herbivores?
- Supplemental or emergency food
- Shelter for natural enemies
- Chemical cues for location
- Secondary metabolites
- Physical traits for location
Describe specificity in terms of herbivore-plant-parasitoid interactions mediated by plant volatiles.
Specificity in:
-how each natural enemy perceives plant signals/traits
-signals/traits produced by different plants (both constitutive & induced signals)
-response depends not only on plant signals but herbivores present
Define signal transduction (pathways).
Process by which information from the extracellular environment is conveyed into the cell interior with a change in cellular response.
True or False?
Plant allelochemicals may have a negative effect on natural enemies.
True! Plant allelochemicals MAY have a negative effect on natrual enemies. Considering post-oviposition and post-attack, and negative effect on development time, adult weight and survival.
Provide 2 examples of negative effects of plant allelochemicals on their natural enemies.
1) Ladybird beetle (Predator),Sorgum aphid (Herbivore), Resistant sorghum cultivars (Plant):
-Development time increases
-Adult weight & survival reduced

2) Ichneumonid wasp (Parasitoid), Noctud caterpillar (Herbivore), and Tomato (Plant) - tomatine allelochemicals
-Detrimental effects on the time of development, survival and adult size of parasitoid
Provide examples of how herbivores may utilize plant toxins against their generalist natural enemies in marine & terrestrial habitats.
Marine systems:
- Amphipods are adapted to eating chemically defended plants - build a shelter they carry around; are rejected by predatory fish.
- Camouflaged crabs use algae in the Pacific and Caribbean for chemical defense against local fish.

Terrestrial Habitats:
- Herbivores feed on iridoid glycoside-containing plants - sequester these chemicals & gain protection from vertebrate and invertebrate natural enemies.
Define sequestration.
Use of plant toxins by herbivore for defense
What adaptations are involved in sequestration?
a) Herbivore must be willing to ingest the hosts secondary chemicals
b) Herbivore must be tolerant of chemicals
c) Herbivore must digest chemical without metabolising it into a nontoxic form
d) Herbivore must deposit chemicals in particular tissues or store them
Provide an example of sequestration.
-Monarch butterflies use cardiac glycosides from the plants they ingest, which induces vomiting by the birds that try to eat them.
-The Euphydryas butterflies' caterpillars sequester iridoid glycosides from host plants during larval feeding and retain the compounds as adults. These compounds protect this herbivore by making it unpalatable to vertebrate predators such as birds.
How can secondary chemicals protect insect herbivores against their enemies?
- The degree to which an insect is subjected to parasitism depends on the plant on which it occurs.
- Acceptance or rejection of prey by predators can depend on the chemicals in the diet of the prey
- Potentially detrimental and beneficial influence of plants on the virulence of pathogens of insects
Provide an example of how natural enemies are affected by plant physical factor - texture or size of plant tissues and organs.
- Pine moths mine a wide range of sizes of pine buds
- When they feed on pines with large buds and robust stems it suffers less parasitism than when it feeds on small buds
- This variation is presumed to be associated with the limitations imposed by the size of the female's ovipositor.
Provide an example of how distinct physical plant characteristics consequences to the effectiveness of parasitoids.
- Parasitism rates of Pieris rapae are generally high on leaves of open growing varieties (Brussel sprouts) and lower on heading varieties (cabbage), where larvae espace attack by feeding in folds of the leaves
What are some implications to animal-plant interactions for the variation of affects of parasitoids and plants?
- Consequence: predators and parasitoids kill a portion of herbivore individuals on a plant and that, in turn, affects the nature and outcome of the interaction between the host plant and surviving herbivores.
- Different plants differ in their abilities to influence natural enemies and thus in their influence on the natural enemies' ability to reduce the survival and impact of a particular herbivore.
- Plants differ in their ability to influence large suites of natural enemies that might effectively reduce the survival & impact of a large number of herbivores co-occurring on the plant.
Plant traits can affect a SMALL/LARGE suite of co-occurring herbivore species???
Plant traits can affect a large suite of co-occurring herbivore species.
Responses of particular natural enemies may be specific but ______?
Responses of particular natural enemies may be specific but many natural enemy species may respond to the same plant traits.
Provide an example of differential parasitism and how the plant traits can affect a large suite of co-occurring herbivore species.
- Differential parasitism was demonstrated among the Lepidoptera on tree species in different families.
- Differential parasitism based on host plant: Significantly higher on box elder compared to black willow
- Total parasitism of caterpillars of the same species was significantly greater on box elder vs. black willow
What are other factors that natural enemies may respond to?
- Plant
- Plant patch
- Landscape differences in plant architecture
- Species diversity (plant density, microclimate created by plants)
Provide an example of the effect of plant patch on natural enemies.
Whether the herbivore's host plant grows isolated from other plants or clumped with other plants can signficiantly influence the natural enemies of herbivores.
-Example: Syrphid & anthocorid predators of aphids find brussels sprouts and the aphids on these plants more readily when they are among weeds than when plants are on bare ground.
Describe primary plant compounds.
Necessary for normal plant metabolism including the production of lipids, carbohydrates, proteins, etc.
Describe secondary plant compounds.
Generally not directly involved in the normal growth, development, or reproduction of plants. They may perform ecological roles such as defense from herbivores, but they often do not.
Even in the best host plant, the concentration of elemental nutrients is HIGHER/LOWER in insect herbivore tissues than in plant tissues.
Even in the best host plant, the concentration of key elemental nutrients is HIGHER in insect herbivore tissues than in plant tissues.
____ is the major nutritional element required by herbivores and it is the most limiting.
Nitrogen is the major nutritional element required by herbivores and it is the most limiting.
What are some variables affecting nitrogen levels in plants?
- Plant or tissue age
- Type of plant tissue
- Plant species
- Growth form
- Growing conditions
- Location of plant in the habitat & associated difference in soil richness
Herbivore fitness increases as _____ availability increases.
Herbivore fitness increases as nitrogen availability increases.
Name 2 exceptions to the statement "Herbivore fitness increases as nitrogen availability increases."
1) Total nitrogen content is sometimes a poor index of nutritional protein levels.
2) High nitrogen in plants may reflect the presence of nutritionally useless compounds (such as alkaloids, structural proteins, etc.)
______ is critical for herbivores and _____ levels are associated with nitrogen levels.
Protein is critical for herbivores and protein levels are associated with nitrogen levels.
The nutritional value of protein is most accurately reflected in the array of _______ available.
The nutritional value of protein is most accurately reflected in the array of amino acids available.
Why is Phosphorus an important primary plant compound?
Phosphorus is:
a) a significant nutrient - found in complex organic compounds in many tissues; a sugar-phosphate backbone forms the helical structure of every DNA molecule.
b) a component of ATP - a fundamental energy source in living organisms providing fuel for biochemical reactions.
What are some important primary plant compounds?
- Nitrogen
- Phosphorus
- Carbohydrates (starches, fructosans, and sugars)
- Lipids (triglycerides, phospholipids, glycolipids)
Even though sugars are not of high nutritional value, they are important plant compounds... Why?
Sugars:
-Universal phagostimulants (feeding stimulants): particularly, sucrose and fructose
- Phagostimulants act only after pre-ingestion cues bring the herbivore to the "best" plant
- Hexose and sucrose (sugars) occur in cytoplasm, particularly in photosynthetically active tissues
It is common for _____ and _____ levels to be inversely correlated in leaves.
It is common for protein and sugar levels to be inversely correlated in leaves.
Characteristics of secondary plant compounds
- Usually occur only in special, differentiated cells
- Often not necessary for the cells themselves but may be useful for the plant as a whole
- A particular compound is idosyncratic in terms of its distribution and concentration in the tissues of a given species.
- More than 100,000 characterized secondary compounds
- May have originally evolved for other functions and only secondarily adapted for use against herbivore
- Secondary compounds perform many functions in plants that may have nothing to do with defense against herbivory
- Some play important, well-known roles in chemical defense
- Affect herbivore feeding and oviposition behavior
- May determine whether or not herbivores accept or reject a howl plant or specific plant parts
- Many act as allelochemicals
- Are variable in time & space
Provide some examples of functions provided by secondary compounds.
- Structure to cells walls (lignin)
- Pigmentation of lowers and other tissues
- Regulators of plant growth (flavonols)
- Aids in nutrient cycling (tannins & phenolic acids)
- Antibiotics serving to protect against plant pathogens
- UV protectants
Characteristics of flavonols and flavones
- Mostly colorless pigments in the leaves of plants
- Control light admittance to leaves (photosynthesis and UV protection)
- Involved in leaf color change in the fall
Explain the basic process of leaf color change in the fall involving flavonols.
As chlorophyll breaks down, large quantities of flavonols are converted to anthocyanins.
Characteristics of flavonoids
- Allow selective admittance of blue-green and red light for photosynthesis
- Affects interaction of plants with other organisms: they inhibit or encourage bacteria & mychorizzae associations
- Have anti-oxidative or antimicrobial effects (as a consequence they have been used as anticarcinogenic and cardio-protective compounds)
Define allelochemicals
Allelochemicals are compounds that affect the behavior or growth of members of another species.
Characteristics of allelochemicals
- May serve as attractants, repellants, toxins, or allergens
- May prevent some species from feeding on them and encourage others to feed on them
- Some allelochemicals that are toxic to polyphages actually increase growth or in some way affect behavior to the advantage of adapted monophages
Briefly explain the effects of allelochemicals on herbivore host-plant selection behavior.
Herbivores may respond to a chemical that brings it to a favored plant or warns of toxicity. The allelochemical may be the toxin itself or a "token chemical stimulus" always associated with a toxin.
-Plant chemicals can repel or attract
What are some abiotic factors that may significantly affect the type and concentration of secondary chemical defenses?
- Soil richness
- Light availability
- Ligh intensity
Give examples of how changes in nutrient availability to plants can result in significant variation in secondary plant chemistry.
- Nitrogen fertilization often increases the concentration of nitrogen-based secondary plant defense compounds (e.g., alkaloids, cyanogenic glycosides, non-protein amino acids)
- Nitrogen fertilization may significantly reduce carbon-based secondary compounds (e.g., tannin, salicin, tremuloidin)
______ fluctuations in the production of secondary compounds may be dramatic in some plants.
Diurnal fluctuations in the production of secondary compounds may be dramatic in some plants.
Provide examples/evidence for the fact that temporal and spatial changes in light intensity results in significant variation in secondary plant chemistry.
- The year to year increases in phenolics in sorghum is correlated most strongly with overall levels of sunlight
- The concentration of nitrogen-based compounds such as the cyanogenic compounds in bracken fern is 50% greater in plants growing in shady areas compared to those in open areas (because nitrogen is not going into growth and protein production and is thus available for defensive compounds).
The concentration of carbon-based and nitrogen-based defenses are ____ related.
The concentration of carbon-based and nitrogen-based defenses are inversely related.
_____ varies greatly among herbivores; as some species feed on a single plant species and others feed on hundreds of plant species in scores of plant families.
Diet breadth varies greatly among herbivores; as some species feed on a single plant species and others feed on hundreds of plant species in scores of plant families.
Define monophagous species.
Feed on only one plant taxon - one plant species or species of one family (narrow diet breadth)
Define oligophagous species.
Feed on plants of several families but on only a limited number of plant species.
Define polyphagous species.
Feed on plant species of two or more families and often on dozens or even hundreds of plant species (wide diet breadth).
Define absolute monophage.
Feed on only one plant species over its entire geographical range.
Define functional monophage.
Feed on only one plant species in a particular habitat but switch to a different plant species in a different habitat.
Examples of absolute monophages
1) Koala - specialist on eucalyptus leaves throughout its range in Australia although it will eat other food
2) Giant Panda - lives almost entirely on bamboo in the wild although it can function as a carnivore if necessary
Host plant _____ often changes with the herbivore's age or developmental stage.
Host plant specificity often changes with the herbivore's age or developmental stage.

Example: Young insect larvae tend to be more selective than older larvae in accepting host plants.
Of all herbivores, the large majority of species are fairly host-plant specific. Why?
Because most herbivores are insects, which have a relatively limited host plant range.
Most insect herbivores are relatively specialized.
Most are oligophagous or monophagous, even at the order level.
What are most terrestrial and marine herbivores classified as?
Terrestrial vertebrate herbivores: polyphages
Marine herbivores (invertebrate & vertebrate): polyphages
Provide a possible explanation for the dominance of monophagy seen in insects.
The dominance of monophagy in insects may reflect constraints on evolution of the insect's nervous system, as related to the detection of plant deterrents. Some have proposed that polyphagous insects are less sensitive to deterrents (prime factors in host selection). Monophagous insects are generally more sensitive to deterrents.
Feeding Specialization Hypothesis
What is the feeding specialization hypothesis?
If an herbivore specializes on a particular plant species, it has a competitive advantage over other herbivores.
Provide rationale behind the feeding specialization hypothesis.
- Familiarity with a plant improves searching efficiency and reduces exposure to natural enemies and other mortality agents.
- Specialists may use plant chemicals as cues, enabling them to locate host plants readily.
- Specialist herbivores may use plant chemicals in sex pheromones, thereby increasing chances of mating.
- Specialists may also use plant toxins as protection against natural enemies.
Provide an example of how a specialist species uses plant toxins as protection against natural enemies.
Monarch butterflies sequester cardenolides (cardiac glycosides) from milkweed plants, which the caterpillars ingest. The cardenolides make the adult Monarchs fould tasting to provide protection against birds. The cardenolides act as emetics that make birds vomit when they ingest the adult butterflies.
Provide an example of how a specialist species uses plant chemicals in sex pheromones, to increase their chances of mating.
Some Lepidoptera use plant compounds called pyrrolizidine alkaloids (PAs) to produce pheromones.
-Larvae of the tiger moth may feed on many palnts, but seek plants with PAs.
-PAs are sequestered by larvae and stored by adulthood when they are used by male moths to synthesize a pheromone.
-The pheromone is disseminated from an eversible organ called the coremata on the adult moth's abdomen.
Name another example of how a specialist species uses plant toxins as protection against natural enemies (involving PAs).
PAs are sequestered by some salt marsh caterpillars to protect their eggs from predators.
Behavioral responses to plant chemical defenses may be _____ or herbivores may evolve the ability to _____.
Behavioral responses to plant chemical defenses may be innate or herbivores may evolve the ability to learn.
Provide an example of vertebrates learning to associate traits of foods and their value.
Peppers have secondary chemicals called capsaicinoids (capsaicin) that make them pungent, and are producd by the cells surrounding the pepper fruit's placenta.
While these capsaicinoids repel mammals, they have no effect on birds which lack the receptor to detect capsaicinoids. Therefore, the compounds are not irritants to the birds as they are to mammals, which have the receptor.
Chili pepper seeds consumed by birds pass through the digestive tract unharmed, allowing birds to disperse the seeds of pepper plants.
Peppers attract and are eaten by many bird species.
Birds ensure spread of the peppers' seeds, since they are strong fliers.
What are some advantages to polyphagy?
- The ease of finding a host plant minimizes the cost of searching for food.
- The ability to switch hosts increases the probability that the herbivore will obtain high quality food: an important factor, given the great amount of variation of plant quality, in time and space.
How does size and diet breadth affect vertebrate herbivores?
- Large body size and relatively low food conversion efficiencies force large vertebrates to eat large amounts of food.
- A polyphagous existence helps the big eaters to meet this requirement.
What are some feeding adaptations that have allowed some large vertebrates to cope with low quality host plants?
- By slowly processing their food, hooved mammals (ungulates) are able to cope with low nitrogen, high fiber, low moisture and high allelochemical concentrations in poor quality plants.
- Complex digestive tracts
- Specialized mouthparts
- Both above are adaptations to low food quality, and they rely on slow food intake and processing of food.
Do vertebrates exhibit any food preferences?
Yes! Vertebrates DO exhibit preferences.
If given a choice, large grazers typically select diets that are higher in proteins.
Examples: Sheep and cattle select leaves over stems, and green over dry/old leaves. Sheep selectively seek plants that are more easily digested.
Define the Nutrient Constraint Hypothesis.
- Proposes that no one species of plant can satisfy the nutritional needs of a mammalian (vertebrate) herbivore.
- A polyphagous lifestyle may be favored when any one plant host fails to provide all needed nutrients required for development (such as amino acids, vitamins, trace elements, etc.)
Define the Detoxification Limitation Hypothesis.
- Proposes that the detoxification system of mammalian herbivores is unable to process large amounts of secondary compounds.
- Polyphagous herbivores are more likely to efficiently process the relatively smaller quantities of specific toxins in a mixed diet.
Provide an example of the detoxification limitation hypothesis.
When sheep consume large amounts of mimosine that occurs in some plants they eat, they suffer decreased weight gain, loss of hair and infertility.
If they eat mimosine in small doses at first, then in progressively higher doses, their gut flora develop the ability to detoxify and degrade the chemical.
Is it true that polyphages and monophages appear equally well adapted in many ways? If so/not, explain why.
In the case of insect herbivores, polyphages and monophages do appear to be equally well adapted in many ways.
Because:
- Monophages do not appear to be any more efficient at processing their food than polyphages.
- Research has not demonstrated a correlation between host plant specialization and increased food utilization.
- Monophages and some polyphages appear to be proficient at detoxifying plant allelochemicals.
How do herbivores compensate for sub-optimal diets?
1) Physiological mechanisms
(Gut retention time, Adjustments in growth & performance, Metabolic transformations, Egestion, Binding)
2) Behavioral Mechanisms
(Compensatory feeding, Emesis, Diet supplementation, Learning, Host plant switching, Emigration)
3) Evolved life-history/Ecological Adaptations
(Using what's bad for other herbivores, Phenological matching)
Provide an example of how increased retention time of food in the gut improves assimilation efficiency in some species.
The spider monkey, which feeds on fruits, retains food material in its gut ~4.5 hours (fruits are a higher value food).
Gut retention time of the leaf-eating howler monkey, which feeds on leaves, is ~20 hours (leaves are a lower quality food).
Provide an example of how increasing the gut retention time may be detrimental if certain toxins are present.
Toxins in tree and shrub resins reducce or inhibit gut microbes and thus slow cellulose fermentation in mammals or inhibit caecal functioning in birds like the ptarmigan.
Give an example of how herbivores compensate for changes in the quality of food by altering growth rate, development and other performance parameters, or changing host plants.
Insect herbivores grow more slowly and lay fewer eggs on poor diets.
True/False? Physiological changes such as altering growth rate, development and other performance parameters are linked to behavioral changes.
True!
These physiological changes are often linked to behavioral changes associated with foraging and preference.
What are some metabolic and physiological mechanisms to cope with plant chemical defenses?
1) Detoxification
2) Egestion
3) Binding
What is the result of the metabolic and physiological mechanisms used to cope with plant chemical defenses?
The 3 processes (detoxification, egestion and binding) result in the production in by-products that are excreted or retained as non-toxic substances.
What are the chemical pathways by which detoxification occurs?
1) Oxidation
2) Hydrolysis
3) Reduction
4) Conjugations
Oxidation
Loss of electrons
Hydrolysis
Water mediated cleavage
Reduction
A gain of electrons
Conjugations
Where two harmful chemicals are united into one inactive and readily excreted product
What are the group of enzymes called that bring about oxidation?
Mixed Function Oxidases (MFO's) or Polysubstrate Monooxygenases (PSMO's)
How do MFO's-PSMO's work in oxidation?
- MFO's-PSMO's convert allelochemicals into more reactive compounds that are then metabolized by other enzymes.
Where are MFO's-PSMO's located in living organisms?
MFO's-PSMO's occur in the endoplasmic reticulum of cells of several tissues including the liver in mammals and in the midgut wall in invertebrates.
Wide-spread in the _____ of invertebrate herbivores, mixed-function oxidases, such as P450 can metabolize many different plant ________ chemicals.
Wide-spread in the midgut of invertebrate herbivores, mixed-function oxidases, such as P450 can metabolize many different plant secondary chemicals.
Give examples of MFO's metabolizing different plant chemicals in specific herbivores.
a) Spider mites adapted to bean - P450 enzymes triggered on bean hosts.
b) DDT-resistant house flies are able to convert DDT [dichloro diphenyl tricloroethane] (toxic to house flies) to DDE [dichloro diphenyl dichloroethene](not toxic to house flies)
_____ of some herbivorous mammals and many birds may chemically transform certain secondary plant compounds.
Gut microbes of some herbivorous mammals and many birds may chemically transform certain secondary plant compounds.
True/False?
Gut microbes appear to process all secondary plant compounds.
False!
Gut microbes appear to process some but certainly not all secondary plant compounds.
True/False?
In some cases, metabolic processes convert toxins to less toxic forms but the same processes can form more toxic compounds.
True!
In some cases, metabolic processes convert toxins to less toxic forms but the same processes can form more toxic compounds.
True/False?
Functions of gut microbes are very well understood in their role in detoxifying secondary chemicals.
False!
Researchers acknowledge that the functions of gut microbes are so poorly understood that their role in detoxifying secondary chemicals is problematic.
Define egestion.
Process that avoids intoxication by blocking the toxins' passage through the gut wall and rapidly eliminating them (getting rid of the toxin quickly).
An effective method for dealing with secondary chemicals.
Provide an example of the use of the egestion method.
The tobacco hornworm can egest as much as 98% of nicotine in its food. 93% of the nicotine is egested within 2 hours of consumption. Nicotine causes changes in the insect's gut within the first 2 hours, insect is trying to get rid of the nicotine.
Describe the method - Binding of plant defenses
Some mammalian herbivores produce substances that bind plant compounds which disrupt digestive processes.
Binding - keeps toxin, but renders it into a nontoxic byproduct
Give examples of binding of plant defenses.
a) Feeding rats on sorghum (a plant with high levels of tannin) induces proline-rich salivary proteins, which have a high binding affinity for tannins. The onset of synthesis of these proteins coincides with increased weight gain in the rats.
b) Mule deer are adapted to feeding on tanniferous forage through the production of salivary proteins that bind tannins
c) Human herbivores: kaopectate's active ingredient is bismuth subsalicylate; it binds or neutralizes the toxins of some bacteria, rendering them nontoxic.
_____ boost the insect's immune system, engulfing harmful bacteria or fungi (for example).
Hemocytes boost the insect's immune system, engulfing harmful bacteria or fungi (for example).
What is compensatory feeding?
Adjustments in feeding rates and efficiency
Give examples of compensatory feeding observed in nature.
a) Insect adjusts its feeding behavior to compensate for nitrogen deficiency in plants. When nitrogen declines, the cabbage butterfly larvae increase their food consumption.
- Leaves of milkweed can differ in their nitrogen content in successive years; During low nitrogen years, larvae of the monarch butterfly may eat ~75% more leaf biomass.
When does compensatory feeding work?
Compensatory feeding may maximize acquisition of nitrogen and nutrients.
When does compensatory feeding not work?
It may be less effective when host plants are defended by leaf toughness, feeding deterrents, resins and other digestibility reducers.
Define emesis
A behavioral mechanism to cope with plant toxins that induces vomiting in the organism that ingests the toxin.
What happens when you eat poorly cooked food contaminated with Salmonella or "bad" seafood?
The treatment for many poisonings requires removal of the toxic substance from the stomach before absorption occurs (emesis).
What is geophagy?
Intentional soil eating; a behavioral adaptation among animals allowing for the consumption of plant materials that otherwise couldn't be tolerated.
Give examples of geophagy.
- Parrots consume clay, rich in minerals that bind toxins (such as strychine, quinine and quinidine)
- People in many societies add clay to bitter foods such as wild potatoes to absorb some of the toxins they contain
- The indigenous people of the Andes eat the poisonous potatoes with a "dip" made of clay and seasoned with herbs. With the clay neutralizing toxic effects of the potatoes, the indigenous people of the Andes were able to begin consuming them and cultivating non-toxic varieties.
What is aversion learning?
The capacity to learn and thus avoid plant defenses. Learning to avoid distasteful or toxic foods has been observed in vertebrates and even in insect herbivores and may play a role in behavioral avoidance of toxic plants.
Even in the absence of strict aversion, learning may assist in coping with toxins.
Describe the behavioral adaptation - switching host plants.
Shifts in host plant selection - Herbivores often switch to different host plants as the quality of one host plant declines.
Give an example of the adaptation switchin host plants.
The butterfly Battus philenor changes its ovipositional behavior as the season advances and the quality of its preferred food Aristolochia reticulata declines.
_____ is the most immediate herbivore response to declining food availability and quality.
Emigration is the most immediate herbivore response to declining food availability and quality.
When does emigration occur?
Many species of invertebrates and vertebrates will leave habitats when food resources are low.
Provide examples of emigration.
a) Emigration is low among squirrels in years with a favorable mast crop and high when little seed is set.
b) Froghoppers and leafhoppers feed on plant sap and move from plant species to plant species as plant nitrogen levels change.
c) In some aphids, deterioration of food resources is marked by a switch from wingless (apterous) morphs to winged (alate) morphs capable of emigration.
How is leaf quality determined?
Leaf quality is reflected in nitrogen and water content
Leaf quality generally INCREASES/DECLINES with leaf age.
Leah quality generally declines with leaf age.
What is phenological matching?
An ecological adaptation used by herbivores that use plants when they are at their best/peak.
Some herbivores have evolved a tight synchrony between leaf budbreak (when leaf quality is greatest), and egg hatch to cope with seasonal declines in food quality.
Provide an example of phenological matching?
- White oak budbreak is late relative to egg hatch of Alsophila pometaria, an early season moth and scarlet oak buds break about the same time.
- In stands where scarlet oak dominates, Alsophila populations (and thus herbivory) are high, whereas in white-oak dominated sites Alsophila cannot maintain a high population.
- Because the moth is polyphagous and 1st instars are widely dispersed by wind onto white oaks; in scarley oak-dominated stands, white oaks suffer greater herbivory than white oaks in white oak-dominated stands.
- In white-oak dominated stands, scarlet oak is less susceptible to defolation. In scarlet-oak dominated stands, white oak is more suceptible to defoliation.
Define Taxis Response.
A directed response either toward or away from an environmental stimulus
Define Kinesis.
A movement that lacks directional orientation and depends upon the intensity of stimulation.
For example, animals move more slowly and turn more frequently in "good" habitats than in "bad" habitats.
What are the different types of taxis seen in orientation to plant signals?
a) Tropotaxis
b) Klinotaxis
c) Menotaxis
Define Tropotaxis.
Difference between two receptors
Define Klinotaxis.
Temporal comparison of information coming from one receptor
Define Menotaxis.
Moving by maintaining a set anle to the wind or light direction
What are the types of kinesis in orientation to plant signals?
a) Orthokinesis
b) Klinokinesis
Define Orthokinesis.
Altering speed of movement
Define Klinokinesis.
Change in rate of turning
How do herbivores respond to plant cues?
- Some are attracted to suitable habitat from long distances by sight or smell via a taxis response.
- Most habitat selction operates by kinesis.
How do insect herbivores gather information on potential host plants?
A sensory system using:
- Taste (chemoreception)
- Smell (olfactory cells)
- Touch (mechanosenses)
- Sight (through the compound eye)
Provide examples of herbivores that exhibit kinesis responses.
a) Rodents (squirrels) appear to find scattered seeds as readily as they do clumped seeds.
b) Tephritid flies aggregate equally in areas of abundant and scarce food sources of knapweed.
Explain how an ecosystem might be likened to "Nature's Wall Street."
- The engine of evolution that drives the diversity of life resides inside local ecosystems.
- An ecosystem might be likened to nature's "wall street" for it is the place where natural selection determines the winners and losers in life.
- The organisms in an ecosystem have adjusted and changed to one another and their physical environment over long periods, each member altering its characteristics in response to changes in other organisms and the non-living environment.
Define Species Diversity (Species Richness).
Number and distribution of species in one location
Define Species Abundance.
Density (number per unit area) of members of a species
Define Herbivory.
The consumption of herbaceous vegetation
Define Habitat.
The part of the physical environment in which an organism lives
Define Patch.
An area of distinct habitat type
How do differences in the size and density of plants in patches alter the abiotic conditions in which herbivores live?
- Plant patches provide unique resources for herbivores, and their natural enemies strongly influence the interactions of the herbivores, natural enemies and host plants.
- Plant canopies can modify temperature, humidity, and wind spped and the biological phenomena affected by these factors.
What are the 2 hypotheses that were generated to explain the relationship in insect species richness and habitat size?
1) Encounter Frequency Hypothesis
2) Habitat Heterogeneity Hypothesis
Define the Encounter Frequency Hypothesis.
The number of insect species associated with a plant depends on the probability of encounter. The more widespread the plant is, the greateer the probability of encounter will be.
Define the Habitat Heterogeneity Hypothesis.
The more widespread a plant is, the more kinds of habitats it will occur and therefore the potential for encounters with insect herbivores will increase.
What are some generalizations about the relationship between habitat size and species diversity?
- The larger the area is, the higher the carrying capacity will be for species.
- More diverse habitats will permit species to exist in suitable enclaves from competition, and the net result will be reduced rates of extinction with increased habitat size.
- There are exceptions; many factors in an ecosystem will determine the species composition in a habitat patch.
Provide an example of how the structure and size of plants affects the likelihood of encounters with herbivores.
- Some species exhibit preferences solely because of structural differences of potential host plants.
- The horse lubber grasshopper will feed on mesquite trees when encountered. However, because most of its foraging time is spend on the ground, it tends more often to encounter lower growing plants.
_____ changes in plant structure may strongly influence the rank order of herbivory.
Seasonal changes in plant structure may strongly influence the rank order of herbivory.
What is the result of seasonal changes in plant structure and its influence on the rank order of herbivory?
Seasonal appearance of herbivores and their predators in a predictable sequence.
Provide an example of seasonal appearance of herbivores due to seasonal changes in plant structure.
a) In the Serengeti, zebras are the first large mammals to enter tall grass communities following seasonal rains, feeding on stems and leaves. Wildebeast are next, feeding on the grass leaves that become more accessible after zebra feeding. Then Thompson's gazelles arrive to feed on the short growth grasses and herbs that develop only after wildebeast grazing.
Is there a predictable relationship in plant patch size and the abundance of herbivores and level of herbivory?
Most studies have failed to show a consistent relationship
The greater the patch size, the GREATER/LESS the diversity of species.
The greater the patch size, the greater the diversity of species.
How do plant species diversity and density affect the abundance of herbivores and herbivory?
The density of a plant species in a habitat generally determines the quality of the plant's resources for herbivores and the herbivores' impact on the plants.
Provide examples of how the density of a plant species in a habitat determines the quality of the plant's resources for herbvores.
- Isolated plants of Capsella bursa-pastoris can produce 23,000 seeds per plant compared to 200 seeds per plant growing in crowded conditions.
- An isolated wheat plant can produce more than 50 grams of seed, whereas the plant grown at standard crop densities only produces ~2 grams of seeds.
True/False?
Plant eaters seek out patches of specific plant density.
False!
Although plant density can influence herbivores, it is unclear whether most plant eaters seek out patches of specific plant density.
- Assumption: herbivores do not generally respond to plant density per se.
- Herbivore orientation to host palnts and the time spent on them may depend more on the height, size and shape of host plants and the associated non-host plants.
Provide examples of how herbivore responses to plant density may be circumstance specific.
- The butterfly Anthocaris carda mines tends to oviposit on isolated plants and therefore selected plants at the edges of host plant patches.
- Clumped dester annuals suffer ~68% grazing mortality by vertebrates compared to 35% mortality suffered by plants seperated by more than 10 meters.
True/False?
Plant patch patterns can significantly affect the succes and rate of a herbivore's colonization of new plant patches.
True!
Plant patch patterns can significantly affect the success and rate of a herbivore's colonization of new plant patches.
Immigration rates of herbivores and their natural enemies INCREASE/DECREASE with increasing distance form the nearest large plant population.
Immigration rates of herbivores and their natural enemies decrease with increasing distance from the nearest large plant population.
Habitat ______ seems to have more impact on parasitoids than their herbivore hosts.
Habitat fragmentation seems to have more impact on parasitoids than their herbivore hosts.
- Parasitoids are less apt to move to patches than when the habitat is fragmented.
Why does plant scarcity appear to have minimal influence on the population dynamics of herbivores?
Because the immediate response of most herbivores to declining food resources is emigration.
Although, localized or temporary depletion of small plant patches may occur.
Provide examples of localized or temporary depletion of small plant patches.
a) Sea urchins can eliminate local patches of algae
b) Vertebrates can deplete some grassland patches
Provide an example of how plant species diversity in patches can have a significant impact on herbivore abundance and diversity.
In agroecosystems, the number of invertebrate herbivores per plant and the level of herbivory are often higher in monocultures (single crop species) than in polycultures (mixed crop species).
What are the 2 hypothesis that explain the observed differences between monocultures and polycultures?
1) Resource Concentration Hypothesis
2) Enemy Hypothesis
Define Resource Concentration Hypothesis.
Predicts that herbivore density will be lower in diverse than simple vegetational systems because herbivores' host plants are more widely spread (less concentrated) in the diverse systems and therefore harder to find. Also, some plants in the diverse systems may repel the herbivores.
Define Enemy Hypothesis.
Predicts that herbivore density will be lower in diverse than simple vegetational systems because the herbivores' natural enemies will be more abundance in the diverse systems.
Lower herbivore density and herbivory in polycultures may be partially due to ______.
Lower herbivore density and herbivory in polycultures may be partially due to associational resistance.
Define Associational Resistance.
Reduction in abundance of herbivores when their host plants are surrounded by non-host plants
According to the enemy hypothesis, why should enemies benefit from polycultures?
a) Wider range of microclimates
b) Greater variety of prey
c) More alternate food resources, such as nectar and pollen: many species of predators and parasitoids feed on plant materials to subsist during times of prey shortages or to obtain certain supplementary nutrients.