Plant And Animal Interactions- Test 2

Front 1

Assumptions that lead to the inference that insect herbivores do not strongly affect dynamics of plant populations

Back 1

-Insect herbivory has negligible effects on the number of seeds that plants produce.
-Strong density-dependence at the seed and seedling life-stages results in additional seed input rarely translating into increased plant population size in the next generation

Front 2

Methods for Studying Insect Herbivore Effects on Plant Populations

Back 2

Experimental:
Insect Exclusion (Insecticide, Cages)
-Can have phytotoxic effects (insecticide)
-Not 100% Effective
-Insecticide plants receive excess water
Artificial Damage
-How realistic is damage?
-Timing? Spatial Dist.? Correct Magnitude?
Observational
-Herbivore preference analysis
-How to separate from confounding variables?

Front 3

Do insect herbivores reduce plant lifetime seed production?

Back 3

Rauscher and Feeney
-2 year experiment
-Mortality higher in exposed insects
-Final root mass of protected plants was larger than
exposed
-Exposed plants= 1 seed, Protected= 30 seeds
So, yes. In this experiment they do.

Front 4

Does increased seed output translate into increased population size?
What experiment might you do to test this assumption?

Back 4

-Seed addition experiment or increase microsite availability
-Erikson & Ehrlich: More seeds=more pop., more seed+more microsites= even more pop.
-Russell: Seed addition increased # of reproductive adults. Seed limitation of recruitment to adulthood was not uncommon

Front 5

Evidence that floral herbivory and pre-dispersal seed predation can limit plant population growth

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-Louda and Potvin: spraying flower heads with insecticide increased the number of reproductive adults in the next generation 2-3X
-Kelley and Dyer: Floral feeding insects decreased λ from 0.93 to 0.87
-Fagan and Bishop: Trophic interactions during primary succession, herbivores slow a plant reinvasion
-Louda and Rodman: With shade from willows removed, insect damage to C. cordifolia increased ==> sharp decrease in C. cordifolia pop. density. Insect herbivory restricts C. cordifolia distribution to shady habitats. Shaded plants have more glucosinolates

Front 6

Species richness

Back 6

the number of species that co-occur in a community

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Species diversity

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a quantity that is based upon both the species richness and the evenness of representation of those species in an ecological community

Front 8

Succession

Back 8

the non-seasonal directional sequence of changes in species composition that occur in a community after a disturbance

Front 9

Mechanisms by which herbivores could influence plant community composition

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1. Insect herbivory is so intense on a plant species that it directly keeps the plant species quite rare in the community or eliminates the plant species from the community

2. Insect herbivory changes abundances of plant species by altering the competitive relationships among plant species (Parker and Root: Guttierezia serothrae population => Larger grasshopper population => more herbivory upon Machaeranthera canescens)

Front 10

Conclusions from Carson and Root (2000)

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-Insect herbivore outbreaks can have dramatic effects on plant communities by suppressing the competitive dominants

-Out-breaks may occur frequently enough that they affect perennials multiple times during their life-spans

-At non-out-break levels insect herbivory can allow competitively subordinate species to persist in a community

-Following an out-break, non-out-break levels of insect herbivores can prevent the recovery of competitive dominants, prolonging the effects of the out-break on the community

Front 11

Do aboveground or belowground insect herbivores have larger effects on plant community composition?

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-Schadler et. al. 2004: Secondary succession is influenced by belowground herbivory on a productive site. (i.e. root herbivory by insects allows for greater species richness by suppressing otherwise dominant plants)

Front 12

Janzen-Connell Hypothesis

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Density-dependent or distance-dependent pathogen transmission or herbivory by specialist insects drive high tree species diversity in tropical forests.

"No-Grow" zones are enforced by specialist pathogens around a given tree. This effect creates a refuge of non-competition for other plant species.

Front 13

Root (1973) Organization of a plant-arthropod association in simple and diverse habitats: the fauna of collards. Describe results of study.

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specialist insect herbivores are more concentrated in dense host plant patches. More insect herbivore biomass and less insect diversity in a monoculture.

Front 14

Two explanations for larger specialist herbivore populations in more concentrated host plant patches

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Enemies hypothesis and Resource Concentration

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Enemies hypothesis

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Natural enemies limit herbivore populations more in diverse plant communities. Diverse plant communities support more diverse predator communities and more stable predator populations.

Front 16

Resource concentration hypothesis

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host plant concentration and specialist herbivore density are positively related because concentrated host patches are easier to find and herbivores remain longer in concentrated patches

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Direct effects (interactions)

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effect of one species on another that is not mediated by a third species

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Indirect effects (interactions)

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effect of one species on another through affecting the abundance or behavior of a third species

Front 19

Associational resistance

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host plant species receive less damage by herbivores in diverse plant communities than in species-poor communities

Front 20

Intercropping

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traditional agricultural practice of planting unrelated crop species in alternating rows to reduce insect herbivore damage

Front 21

Direct mechanisms by which high host plant concentration could produce higher specialist herbivore densities

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Concentrated host patches are easier to find – higher immigration rates

Concentrated host patches are harder to lose accidentally – lower emigration rates

In-patch herbivore reproduction and survival is greater in concentrated host plant patches

Front 22

Matter SF 1997 Population density and area: the roles of between- and within patch processes

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Emigration rate unaffected number of ramets / patch; Immigration rate was negatively related to number of ramets / patch for females

Emergence density of beetles and beetle survival were positively related to number of ramets / patch --- within patch herbivore population dynamics are important

Front 23

Important differences between vertebrates and invertebrates that may contribute to differences in feeding ecology

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Body size: larger body size – increased volume of gut flora, food can be held longer for digestion

Bite size: larger bite size – less ability to be discriminating in the plant tissue types and even plant species consumed

Endotherms vs. Ectotherms: producing metabolic heat to warm the body requires greater energy intake

Front 24

Extent to which animals digest plant material depends on

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Volume of microbial fluid

Amount of time that partially digested food is retained in the gut

Proportion of lignin, silica or other indigestible material in the food, presence of digestibility-reducing compounds (tannins)

Front 25

Grazing

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herbivory on herbaceous plant materials

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Browsing

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herbivory of woody plant materials. The proportion of woody plant material in a mammalian herbivore’s diet is positively correlated with liver size (detoxification)

Front 27

Herbivore Dentition

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Omnivores or soft plant tissue eaters have low crown molars

Herbivores (grass eating) have high crown molars

Front 28

Fermentation

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breakdown of complex organic molecules, like cellulose and hemicellulose, under anaerobic conditions to produce simply fatty acids that can be absorbed in the small intestine

Front 29

Foregut Fermentors

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-Ruminants= antelope, deer, cattle, sheep
-Non-ruminants= hamster, hippo, vole, kangaroo

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Hindgut Fermentors

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-Cecal Digesters (large cecum): elephant, rabbit, rat
-Sacculated Colonic Digesters: horse, man, pig
-Unsacculated Colonic Digesters: cat, dog

**less efficient than foregut, less nutrient absorption***

Front 31

Ruminant

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foregut fermenting mammals with four-chambered stomach, including two chambers (rumen and reticulum) specialized for bacterial fermentation

Front 32

Microbes in digestive system benefit protein nutrition by

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1. Microbe bodies are high in protein (use plant material to grow microbes, digest microbes)

2. Microbes can synthesize essential amino acids

Front 33

How do small vertebrate herbivores, who have shorter gut retention times and less extensive gut flora, obtain sufficient energy?

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Coprophagy: eating of feces; passing the plant material through the digestive track a second time

Eat plant parts that have lower cellulose and lignin content

Front 34

Optimal foraging theory

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conceptual models to predict animal foraging behavior using the assumption that the foraging strategy that will be favored by natural selection is the strategy that maximizes the rate of energy intake

Front 35

Associational susceptibility

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indirect interaction in which a prey species suffers greater predation pressure near another species than where the prey species occurs with other con-specifics

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Associational resistance

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indirect interaction in which a prey species experiences less predation pressure near other species than where the prey species occurs with other con-specifics

Front 37

Compensatory Continuum Hypothesis

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A plant is capable of a continuum of responses to herbivory depending upon the tissue type damaged, the timing of damage and resource availability to the plant. A plant’s tolerance should be greatest in high-resource, low-competition environments

Front 38

Growth Rate Model

Back 38

A plant’s tolerance to herbivory should be greatest under low resource or high competition environments where undamaged plants are growing at a slow rate