NRES 419 Exam 2

Diversity-stability hypothesis

More diverse communities are more likely to contain resistant species, which compensate for species lost during a perturbation.

Diversity-productivity hypothesis

More diverse communities more fully utilize limiting resources and have increased productivity.

1. Plant spatial distribution 2. Total plant productivity 3. Plant diversity and relative abundance 4. Community integration

Mutualistic interactions have community level consequences, affecting:

Underlying every mutualism is an intrinsic conflict between parties—each is under selection for increased exploitation of the other. Cheater moths inflict a cost on the host by consuming seeds, but not pollinating. Evidence suggests that host shifts (moth moving to a new yucca species) preceded the evolution of cheating. The host shift allows escape from obligate mutualism, because another moth species already pollinates the yucca (Pellmyr et al. 1996).

A moth that lays more eggs would have a higher fitness, but might drive the plant (and itself) to extinction. What keeps the moth from cheating?

A) Diversity B) Diversity Index

A) generally, some combination of richness and evenness B) a numeric score used to express richness and evenness in a single number (e.g. Shannon-Wiener Index, Simpson's Index)

A) Species Richness B) Species Evenness

A) the number of species in some area B) the distribution of individuals among species

Potential evapotranspiration

Ability of the atmosphere to remove water from the surface through evaporation and transpiration, given unlimited water supply. Driven by sun's energy and wind.

- Vomiting, diarrhea - Convulsions - Hallucinations - Burning sensations - Blackened hands and feet - Gangrene

Claviceps fungi on grasses produce ergot alkaloids that cause ergotism in animals and humans. What are the symptoms?

Orographic effect

As winds carry air up the windward side of mountains, the air cools and water vapor condenses. When the air moves down the leeward side it expands and warms, increasing its capacity to absorb and retain water, creating a rain shadow.

O2

Common N-fixing bacteria are Rhizobium and Bradyrhizobium, which invade the roots of legumes, inducing the formation of nodules. Nitrogenase, the enzyme that catalyzes fixation, is inhibited by what?

Spatial heterogeneity (as in the preceding example) • Along a gradient, one species may dominate one end (α12 > α21), and another species the other end (α12 < α21). Trophic interactions • Herbivory and other trophic interactions can alter the outcome of competition Temporal heterogeneity • Changes in the habitat over time, like interannual changes in rainfall, can favor one species over another; competitive advantage constantly shifts (α changes) • Disturbances (e.g. floods, droughts, fires) can interrupt competitive exclusion

Describe some external factors that influence the outcome of competition

• Returned to soil in organic matter, and converted back to inorganic forms • PO43- gets bound to metals (Fe, Al, Mn) in soil, forming insoluble, and unavailable, compounds • Through erosion, pollution and discharge, P ends up in aquatic ecosystems and eventually the ocean • It can make its way back to land in the form of anadromous fish and seabird guano

Describe steps in the Phosphorus cycle?

Distribution of biomes results from: 1) solar insolation and relative seasonality, 2) global air circulation, especially the prevailing direction of moisture-laden winds, 3) the position of geological factors like mountain ranges

Distribution of biomes results from...

1. Diversity is being reduced at a scale relevant to ecosystem functions. - Diversity is declining globally. - At regional and local scales, however, diversity is increasing—in many cases through addition of exotic species. 2. Reductions in commonly measured ecosystem variables are undesirable. - However, it is often not clear that any particular level of ecosystem function (like productivity) is inherently good or bad.

Do biodiversity-function relationships bolster the case for conservation?

Unidirectional, cyclic

Energy flow through ecosystems is _________, but nutrient flows are _________.

Areas that experience increased drying will have greater drought risk. This leads to more frequent and intense fires . . . which releases more C to the atmosphere and reduces forest cover and C uptake.

Explain how increased fire frequency and severity is an example of positive feedback.

Many fleshy-fruited plants contain seeds capable of, or even requiring, passage through an animal gut. Dispersal agents may preferentially distribute seeds to sites where germination is more likely.

Explain plant transport mutualisms?

Some groups of plants are characterized by distinctive defense chemicals, and they are often only eaten by insects belonging to certain families that have evolved strategies to cope (Ehrlich and Raven 1964). Example: • Milkweeds contain cardiac glycosides, toxic to vertebrates. • Monarchs and milkweed beetles co-opt the toxin for their own anti-predator defense are conspicuously colored.

Explain the plant-herbivore coevolution.

• For plants, the cost may be up to 20% of GPP - Plants decrease investment when N is abundant - N-fixing plants mostly occur in high light environments - They also get targeted by herbivores

Fixation is expensive—uses large amount of ATP - So, it pays to have friends with lots of energy. N-fixers associated with plants fix more N. How do plants adapt to deal with this cost?

Nutrient runoff stimulates production and decomposition of organic matter. Decomposition uses up available oxygen more rapidly than it can be resupplied. Lack of oxygen kills fish, shrimp and other animals.

How are hypoxic zones formed?

• Latitudinal and elevational range shifts • Phenological changes • Increased incidence of pests and diseases • Non-native species invasions • Altered species interactions

How are plant populations responding to ongoing climate change?

• Nitrite reduces ability of hemoglobin to carry oxygen in blood, causing anemia, especially in infants • Nitrite can be converted in body into the carcinogens Nnitrosamines and N-nitrosamides, which damage DNA

How can excess nitrogen negatively affect human health?

• Reduces canopy density so all leaves receive sufficient light for photosynthesis • Alters plant hormone balance, stimulating vigorous compensatory growth

How can herbivory benefit a plant?

Over the longer term, herbivores can alter plant species composition, favoring well-defended species with lower litter quality

How can herbivory decrease nutrient turnover?

- Plant material is converted to readily decomposed urine and feces - Herbivores also concentrate and transport nutrients to new locations

How can herbivory increase nutrient turnover?

If mutualisms strongly favor a dominant competitor, they can decrease plant diversity Tall fescue, a Eurasian grass, is often infected with a beneficial fungal endophyte that passes from parent to offspring via the seed. The endophyte produces alkaloids that are toxic to herbivorous insects and mammals, giving fescue an advantage over competitors

How can mutualisms decrease diversity?

Increased AM fungal diversity led to increased plant diversity, nutrient capture and biomass.

How can mutualisms increase diversity?

Deprives pathogen of a host on which to increase, especially for those pathogens that lack a dormant structure

How do Crop Rotations help limit pathogen spread?

Niering et al. (1963): Nearly all successful saguaro seedlings are found close to a shadeproducing object, usually another plant. "Nurse plant" effects of this type appear to be common among desert plants. In general, positive plant-plant interactions may be more common in physically stressful environments.

How do plant-plant facilitation can increase productivity by decreasing stress?

• Removal of plants—harvesting • Topsoil loss from erosion • Fire—large gaseous loss of N • Leaching of DON, NO3- , NO2- • Ammonia (NH3) volatilization • Loss of gaseous NO and N2O during nitrification • Denitrification—Reduction of NO3- and NO2- to N2 gas by anaerobic microbes

How do you lose nitrogen from ecosystems?

• Insects are ectothermic. Therefore, temperature largely determines range distributions. • Warming causes: • Reduced cold-related mortality • Shorter generation times • Insects can also expand ranges and invade new habitats more quickly than plants.

How does Climate Change alter pest population dynamics?

• Nitrogen oxides (NO and NO2) come mainly from motor vehicle exhaust, industrial boilers and electric utilities • Toxic—irritates lungs and lowers resistance to respiratory infections • Contributes to ozone smog formation and acid rain • Causes nitrogen saturation of ecosystems

How does NOx contribute to air pollution?

• Nitrogen inputs increase plant growth • Some life history strategies allow plants to capitalize on N increases, others don't • N-addition often favors invasive and weedy species over more sensitive native species

How does excess N shift plant communities?

Human activities tend to increase inputs and outputs relative to internal transfers, making cycling more open.

How does human activities change the proportion between open and closed cycling?

• Dissolution of CO2 in ocean produces acidity (H+) as it equilibrates with bicarbonate and carbonate ions • CO2 + H2O ↔ H+ + HCO3- ↔ 2H+ + CO32- • Rising dissolved CO2 concentration has resulted in 30% increase in ocean acidity • Acidity dissolves the calcium carbonate shells of marine organisms including corals and foraminifera • It also reduces the rate at which CO2 dissolves in the ocean, making oceans a weaker CO2 sink

How does increase in CO2 lead to ocean acidification?

Water temperature is more stable than land mass temperature, and buffers temp on nearby land— water gives up energy in the winter and absorbs it in the summer

How does proximity to water control temperature?

Transpiration tends to conserve nutrients in the system by removing excess water that would promote loss.

How does transpiration affect nutrient cycling?

If the search for 20th century climate analogs is restricted to a more realistic 500 km radius, the extent of disappearing climate increases to 37-85% of the global land surface.

How fast can species move compared to how fast they should move?

- Agriculture • Application of ammonia or urea fertilizer • Increased production of legumes - Industry and transportation • Fossil fuel combustion releases nitric oxide (NO) and nitrogen dioxide (NO2), collectively referred to as NOx - Sewage

How have humans altered the nitrogen cycle?

Humans have increased P flux by mining phosphate rock. Land use change has increased P flux from land to ocean by 50-300%. Phosphorous often causes lake eutrophication.

How have humans altered the phosphorus cycle?

• Nitrous oxide (N2O) is an important greenhouse gas, causing 6% of global warming • However, airborne N inputs stimulate plant growth and carbon sequestration • . . . so cooling and warming effects of N-deposition roughly cancel each other out

How is N linked to climate change and what are its effects?

Hotter, drier climate may cause the collapse of some ecosystems, changing the vegetation and releasing the C stored in vegetation and soil. The Amazonian rainforest may shift to drier caatinga scrub vegetation. Short-term fluctuations in CO2 in the atmosphere have been attributed to heat and drought in western Amazonia and SE Asia, leading to C losses through decreased vegetation productivity and/or increased respiration.

How is Rainforest drying and desertification a positive feedback?

H2SO4, HNO3, HCl acids are formed by reactions with water in the atmosphere and SO2, NOx, and HCl gases

How is acid deposition formed?

Albedo: shortwave reflectance of the ecosystem surface Varies 10-fold among ecosystems from snow to dark surfaces of lakes and wet soil Snow and ice contribute to cold conditions required for their persistence. As temperature increases, boreal forests migrate northward, decreasing albedo, furthering warming, and increasing forest expansion even more—a positive feedback.

How is albedo an example of positive feedback?

Number; Size

Neighbor density affects both number of individuals and size of individuals

Individualistically

Niche theory predicts that each species will respond to a climatic variable in its own way. Therefore, species might be expected to respond __________ to changes in climate.

3 (or odd) trophic levels: more green world because secondary consumers control primary consumer populations 4 (or even): less green world because tertiary consumers control secondary consumer populations and primary consumer populations deplete producers

Oksanen et al. (1981): "Greenness" of the world depends on the number of trophic levels. What does this mean?

Number; density

Pathogens require a minimum ________ and ________ of hosts to spread.

Bee pollinated flowers often have: • Bilateral symmetry • A landing platform • Partially closed flowers • Bright, often yellow or blue, flowers • Nectar guides • Moderate quantities of partially concealed nectar

Plant mutualisms provide some of the best evidence for coevolution. How does bee pollinated flowers show evidence for coevolution?

Self-thinning

Progressive density-dependent mortality occurs in even-aged stands of plants as they mature.

• Thermal expansion of water • Melting glaciers and ice caps

Sea level rise is caused by what two factors?

Actual evapotranspiration

Sum of water lost to both evaporation and transpiration over a year. Determined by gradient of vapor pressure between ground surface and atmosphere.

below

The atmosphere is heated from _______, and re-radiates heat back to earth.

Precipitation

There have been major increases in the flux of N to the atmosphere. How does it return to the earth?

Gause's Competitive Exclusion Principle

Two species with the same niche cannot coexist indefinitely.

- Dense, genetically uniform monocultures - Uniform microclimate - Efficient pathogen transmission - Allows evolution of higher virulence—more virulent strains have greater fitness under these circumstances - Also, global travel and world trade of agricultural products spread pathogens beyond centers of origin, introducing pathogens to naïve plant populations

Virulence is affected by an evolutionary tradeoff between pathogen replication within a host and transmission between hosts. What are some examples of this in crop fields?

- Municipal wastewater - Acid mine drainage - Urban stormwater runoff - Agricultural runoff - Agricultural wastewater - Landfill leachate

Wetlands are sinks for phosphorous and major sites for denitrification. What have they been used to treat?

Grazers Browsers Seed predators

What are classifications of herbivores?

In 50 years, under low carbon emissions scenarios, ChampaignUrbana might feel like Monroe, LA, and under high emissions scenarios, like Waco, TX.

What are climate projections for Illinois?

- This process releases H+ ions, acidifying soil - Also releases nitric oxide (NO) and nitrous oxide (N2O)

What are consequences of nitrification?

• Advanced spring activities: - Earlier shooting and flowering of plants - Increases growing season length, but also increases the chance of encountering a late frost • Later onset of autumn activities: - In Europe, leaf color changes delayed 0.3-1.6 days per decade (Menzel et al. 1999)

What are some Phenological changes due to climate change?

• Characteristic of parasitic plants - Strong host preference: Attach only to a subset of available hosts - Broad host ranges: Many simultaneously parasitize multiple hosts - Holoparasites—lack chlorophyll, derive all resources from host - Hemiparasites—contain chlorophyll, derive partial resources from host

What are some characteristics of parasitic plants?

• Terpenoids - Includes essential oils like menthol, camphor, citronella • Phenolics - Includes tannins and lignin • Nitrogen compounds - Cyanogenic glycosides - Glucosinolates - Alkaloids (e.g. caffeine, morphine, strychnine)

What are some classes of defense compounds?

• Over time, plants acclimate to higher CO2 by reducing stomatal conductance, allowing plants to sustain Cuptake while reducing water demand. • Over the longer term, CO2 uptake becomes nutrient limited, as nutrients become sequestered in live and dead materials. • Increased productivity could also be counteracted by increased tree death due to warming and associated disease and pest outbreaks.

What are some constraints on CO2 fertilization?

Level of contact: • Symbiotic • Non-symbiotic Level of dependence: • Obligate • Facultative Level of specificity: • Specific • Non-specific

What are some different levels of mutualisms?

• Danthonia grass is infected by the fungus Atkinsonella - Infection actually increases plant survival, but decreases reproduction • Sedge genus Cyperus is infected by Balansia - Plant biomass increases 4x - Induces vivipary in the plant - Fungus spreads maternally through plantlets

What are some examples of castrating fungi hijack plant life history tradeoffs?

- Spines (modified leaves), prickles (outgrowth from stem cortex), thorns (modified branches) - Tough, leathery leaves - Hairs with barbs, sometimes poisons - Protection of meristems from grazing - Gummy substances to trap insects - Shedding leaves

What are some examples of mechanical defenses?

• Indirect defense via predators - Semiochemicals • Plants release volatile organic compounds when attacked • Predators and parasitoids detect these as feeding cues • Direct defense, examples: - Toxic fungal endophytes - Housing and feeding natural enemies of herbivores

What are some examples of mutualistic defenses?

• Blackbody radiation • Increased NPP due to CO2 fertilization and higher temperature

What are some examples of negative feedback?

• Arctic methane release • Increased decomposition • Rainforest drying • Increased fire • Decreased CO2 uptake by oceans • Increased water vapor • Ice-albedo feedback

What are some examples of positive feedback?

• Atmospheric deposition - Wet deposition—Precipitation deposits nutrients - Dry deposition—Dust and ash carry nutrients • Leaching: removal of soluble constituents from soil or litter by percolating water • Fire - Breaks down litter, increases pH, releases nutrients in ash • Earth movement including volcanoes, mountain uplift and other tectonic activity

What are some physical factors that influences cycles?

• Range of plant responses, depending on species and dose: - Fertilization - No response - Growth and yield reductions - Injury to foliage - Plant death

What are some plant responses to sulfur oxides?

Effects on stocks and fluxes of energy and materials: • Niche complementarity—species exploit different resources • Functional facilitation—e.g. decomposition of a log requires a consortium • Sampling effect—increased chance of including a high-functioning species • Dilution effect—lower density of each species leads to reduced per capita effects of specialized pathogens or predators Effects on stability of ecosystem functions: • Insurance effects—species respond differently to stressors; many species =less chance of losing a function entirely following the stressor • Portfolio effects—independent fluctuations of many species may show lower variability in the aggregate than fluctuations of any one species

What are some potential effects of diversity?

• Preserving and restoring migration corridors • Assisted migration: deliberately moving species from their current range to a new range • 'Futuristic restoration': establishing ecosystems that are likely to persist in the future rather than relying on past conditions as a guide for restoration

What are some solutions with adapting to climate change?

• Weathering of rocks is the primary source of P for ecosystems • P is limited in old, highly weathered soils

What are sources of phosphorus?

• Mainly SO2, but also SO3 • Mostly from anthropogenic sources, primarily coal combustion - Coal is 0.2-7% S - Scrubbers on coal plants can remove most of it

What are sulfur oxides?

• Microbial decomposition - Immobilization, mineralization - Large C:N ratios (>32:1) favor immobilization • Litter - Amount, constituents, decomposition rate - Litter quality: more lignin = slower turnover • Evergreen vs. deciduous plants - Evergreen trees use more nutrients in wood than is lost in litterfall each year

What are the biotic factors influencing cycling?

• Effects on plants are mainly indirect, through the soil - Acidic input displaces cations like Ca and Mg, leading to nutrient depletion - Anion inputs (nitrate, sulfate) also leach cations - Soil acidification mobilizes toxic metals like Al which attack roots

What are the effects of acid rain?

Mortality • Uncommon in mature plants • However, seed and seedling predation can be severe seed predators can consume 10-100% of seeds Decreased seed production • Consumption of reproductive structures • Reduced vegetative growth to support seed production Reduced and altered growth • Destruction of photosynthetic tissue and storage organs • Consumption of meristems alters growth form

What are the effects of herbivores on plants?

10% of NPP is typically consumed in terrestrial ecosystems (the other 90% goes to decomposers)

What are the effects of herbivory on productivity?

• 'Killers' - Adult mortality - Seedling mortality (e.g., damping-off diseases) • 'Debilitators' - Reduce growth - Reduce fitness • 'Castrators' - Destroy reproductive structures

What are the effects of pathogens and parasites on plants?

- The entry of nutrients into ecosystems - Internal transfer among organisms - Losses of nutrients from ecosystems

What are the general three steps of nutrient cycling?

Gall formers Chewers Leaf miners Stem borers Suckers Root feeders

What are the herbivorous insect guilds?

1. Sediment and rocks 2. Ocean 3. Soil and biota 4. Atmosphere

What are the major pools of Carbon?

A. Proportional response—each species contributes equally to function B. Redundancy—many species perform the same function C. Idiosyncratic response—certain species have larger effects than others, but functional response is unpredictable

What are the three ways that function respond to biodiversity loss?

1. Atmospheric—elements with an important gaseous phase (e.g. nitrogen) 2. Sedimentary—elements without an important gaseous phase that move in sedimentary cycles (e.g. phosphorous)

What are the two movement pathways?

• Fungi • Oomycetes • Bacteria • Viruses • Nematodes

What are the types of pathogens and parasites?

• Vector transmission • Direct transmission • Maternal transmission • Indirect transmission via multiple hosts

What are types of transmission?

• Most pathogens are highly hostspecific • Limiting host availability can limit pathogen spread • Crop rotation

What are ways to limit pathogen spread?

Diverse communities are more stable

What did Charles Elton argue?

Replaced taxonomic diversity (number of species) with trophic complexity as the measure of "diversity" in the diversity-function relationship.

What did MacArthur and Hutchinson conclude?

Plants have something very valuable to offer heterotrophic partners—energy. In exchange, plants get nutrition, protection, and transport of propagules and gametes.

What do plants offer and receive in mutualisms?

A stem exclusion phase in forest trees

What does self-thinning lead to?

• Primary form of C in atmosphere is CO2 • Atmospheric pool is the smallest, but the most active C pool • Carbon is removed from the atmosphere by photosynthesis and released to air by respiration and fossil fuel combustion

What does the atmospheric pool consist of?

Vegetation holds about the same amount of C as atmosphere • Soils hold 2-3 times more C than atmosphere • Permafrost soils, in particular, contain a large C pool • Net ecosystem production (NEP) is a measure of an ecosystem's ability to act as a sink for C

What does the biosphere pool consist of?

• Carbon is in the form of dissolved organic C, dissolved inorganic C (bicarbonate, carbonate and free CO2), and particulate organic C • 97% of ocean C is in intermediate and deep waters • Deep water C is stored for 100s-1000s of years before returning to surface in upwelling areas

What does the oceanic pool consist of?

• Sediments and rocks store over 99% of the Earth's C • Includes limestone and kerogens (fossil C) • A very stable pool—turnover time is millions of years

What does the sediment and rock pool consist of?

Methane (CH4)

What is 23x more potent per molecule than CO2?

• All organisms together are limited by the amount of energy fixed in photosynthesis (NPP). • The world is green. In most communities, producers are not limited by herbivores, therefore they must be resource (light, water, nutrients) limited. • Therefore, herbivores have plenty of food—they must not be food limited. Instead, herbivores must be limited by predators and parasites. • That means that predators and parasites must limit their own food. • And it also means that herbivores must not compete for resources.

What is Hairston, Smith and Slobodkin (1960)—"Green World Hypothesis"?

• Ecosystems have the capacity to store excess nitrogen, but with continued inputs they become saturated. • Beyond this saturation threshold, inputs exceed plant and microbial demand. • The system then becomes 'leaky', N cycling becomes open, and N is lost to streams and groundwater.

What is Nitrogen Saturation and what are its effects?

• Mitochondria, plastids (like chloroplasts) and possibly other organelles in eurkaryotic cells originated through symbiosis. • The organelles were originally free-living bacteria that were incorporated as endosymbionts into another cell.

What is The Endosymbiotic Life Hypothesis?

• Blackbody: an ideal, opaque, non-reflective body • As the temperature of a blackbody increases, the emission of infrared radiation back into space increases • This increases the amount of outgoing radiation as the Earth warms—a negative feedback

What is a blackbody and why is it an example of a negative feedback?

Density dependent effects are those that increase with increased crowding due to: • Aggressive interactions among individuals • Build-up of waste products • Effects of density on resources Density dependent populations reach a threshold size called the carrying capacity, K

What is a density-dependent population?

Nitrogen gas (N2) ---Nitrogen fixation--->Organic nitrogen---Ammonification--->Ammonium (NH4)---Nitrification--->Nitrate (NO3)---Denitrification

What is a simplified version of the nitrogen cycle

• Infects conifers, stealing water and nutrients • Barely regulates its own stomata, increasing whole tree water use • Decreases leaf water potential • Forces stomatal closure throughout tree to compensate for water loss - less CO2 uptake • Decreases tree growth rate by up to 80%

What is an example of a parasidic plant?

Pseudomyrmex ants live in the specialized hollow thorns of acacia trees. The trees provide extrafloral nectaries at the base of leaves and nutrient-rich Beltian bodies on the tips of leaflets. The ants attack anything that touches the plant, keeping it free of herbivorous insects.

What is an example of a protection mutualism?

• Winter moths (Operophtera brumata) lay eggs in oak canopies in early winter • Caterpillars hatch based on temperature cues and feed on young leaves • Hatch too early → starvation Hatch too late → less digestible food • Oak bud burst has advanced, but egg hatching has advanced even faster • Leads to mis-timing between trophic levels

What is an example of altered species synchrony due to Climate Change?

Spruce budworm • Mature fir and spruce in boreal forest • Irruptions linked to habitat structure After disturbance, fir gradually replaces birch and other deciduous species; then spruce replaces fir • Trigger: large areas of mature fir • Devastates both fir and spruce, restarts succession

What is an example of herbivore outbreaks affecting structure?

Male Euglossine bees (orchid bees) collect fragrances from nectarless orchids, storing the fragrances on specialized grooves on their hind legs. These orchid species are pollinated only by male Euglossine bees, and put all of their pollen in a single packet, the pollinium, which gets stuck to the bee as it leaves the flower. The fragrances are released by the bees during sexual displays.

What is an example of highly specialized, obligate pollination mutualisms?

Example of increased plant nutrition due to mutualisms: plant-microbial mutualisms increase plant access to limiting nutrients

What is an example of increased plant nutrition due to mutualisms?

Nicotine: Present in plants of the Solanaceae family Stimulates the release of several neurotransmitters and hormones in humans Once widely used as an insecticide, it has now been banned in the US. However, neonicotinoids are still widely used.

What is an example of use of secondary metabolites by humans?

A doubling of CO2 can increase photosynthetic rate by 30-50%. The 35% increase in CO2 has caused an increase in C gain by ecosystems. Human-induced warming has been less severe than it would have been without this increased production. This negative feedback may not be permanent.

What is the CO2 fertilization effect and why is it an example of a negative feedback?

• Armillaria soldipes fungus causes root disease in trees • In 2001, a single 2400-year-old, 8.9 km2 Armillaria was discovered in Malheur National Forest, OR • Largest known organism by area • Weighs perhaps 605 tons

What is the Humongous Fungus?

- Mitochondria and plastids contain their own DNA that is similar to bacterial DNA - They have unique membranes - They replicate within cells through a process like binary fission - They have internal structure and biochemistry similar to bacteria

What is the evidence for The Endosymbiotic Life Hypothesis?

Natural sources: volcanos Major source is fossil fuel combustion, which produces gaseous sulfur dioxide (SO2).

What is the natural source of sulfur and how have humans increased sulfur cycling by 50%?

• As microbes break down dead organic matter, N is released as dissolved organic nitrogen (DON) through action of exoenzymes. • Microbes break down DON, using the C to support growth and respiration, and secrete NH4+ into the soil. This is termed nitrogen mineralization or ammonification. • When N-limited, microbes absorb NH4+, termed immobilization.

What is the process of mineralization?

• Nitrifying bacteria in soil oxidize NH4+, yielding energy to fix carbon (reduce CO2) • NH4+ is first oxidized to nitrite (NO2-) and then to nitrate (NO3-), the form of N most commonly used by plants

What is the process of nitrification?

Causes of spatial distribution of novel climates: poleward shift of thermal zones and large changes in tropical and subtropical precipitation Disappearing climates: concentrated in tropical mountains and on poleward sides of continents

What is the projected risk of novel and disappearing climates in year 2100?

Variations in moisture and temperature determine the types of plants that grow in a given climate and rates at which biological processes occur.

What is the relationship of biomes to climate?

Climate

What is the single best predictor of the structure and function of plant ecosystems?

• Direct elimination of species - Chestnut blight resulted in loss of American chestnuts (Castanea dentata) from forests in Eastern U.S. • Indirect effects on plants from animal pathogens - Anthrax outbreaks reduced impala populations in Lake Manyara National Park, Tanzania in 1977 and 1983. Evenaged stands of Acacia established during these years. • Altered species distribution

What the effects of pathogens on plant communities?

• Increased productivity • Decreased plant species number • Decreased C4:C3 biomass • Decreased C:N ratio in litter and roots • Increased mineralization rates, and decreased immobilization • Decreased nitrogen retention in the ecosystem • Altered carbon storage

What were the effects of 12 years of nitrogen addition on grassland plots (Wedin and Tilman 1996)?

Seedlings planted in larger openings grew larger Thus, location relative neighbors is also critically important

What were the findings of Ross and Harper 1972 when they varied patch size and placed a seed in the middle?

- Northern range boundaries have moved northward an average of 6.1 km per decade - Upper elevation boundaries have moved upward an average of 6.1 m per decade

What were the results of the meta-analysis of plant and animal range shifts in the Northern Hemisphere over the past 20-140 years (Parmesan and Yohe 2003)?

Temperature is generally lower at high altitude—air cools at it rises due to lower pressure, this makes it expand and lose energy. Generally, increasing elevation by 100 m is equivalent to 1 degree of latitude; thus we have arctic plants growing near the equator.

What's Humboldt's Rule?

• Rare and short-lived plant species are less apparent to herbivores and should produce a small set of qualitative defense compounds. • Long-lived or common plants are more apparent and should produce a large amount of quantitative defenses.

What's the Apparency Theory (Feeny 1976)?

• Uses fossil fuels to convert N2 to NH3 • Developed by Fritz Haber and Carl Bosch in 1914 • Responsible for increases in agricultural production, and in turn, increases in world population over 20th century

What's the Haber-Bosch process?

• Soil fertility and leaf longevity determine defensive strategies. • High resource environments with high leaf turnover: herbivory may be intense, but the cost of herbivory is low because leaves are easily replaced—little need for investment in defense. Important to use cheaper, mobile defenses like qualitative inhibitors. • Resource limited environments with long-lived leaves: Cost of herbivory is high; leaves are too expensive to waste. Plants can use immobile defenses like tannins and lignin.

What's the Resource Availability Theory (Coley et al. 1985)?

• Constitutive defenses - Always present in the plant - Include mechanical defenses, digestibility reducers, toxins - Often require large amounts of resources that are slowly mobilized • Inducible defenses - Deployed in response to wounding - May appear within a few minutes or during the next growing season - Less costly when herbivory is variable

What's the difference between Constitutive and Inducible defenses?

Fundamental niche: Range of resources an organism can use in the absence of competitors Realized niche: What organism actually uses when competitors are present

What's the difference between a fundamental niche and a realized niche?

1. Community ecology, which traditionally emphasizes community structure and diversity, and relationships among species 2. Ecosystem ecology, which traditionally ignores diversity and emphasizes processes, functions and the flow of materials and energy

What's the difference between community ecology and ecosystem ecology?

Negative Feedback: Perturbation damped toward initial condition Positive Feedback: Perturbation amplified away from initial condition

What's the difference between negative and positive feedback?

• Carbon and water are exchanged freely between plants and the atmosphere. • In contrast, N and P are tightly cycled within ecosystems. - More than 90% of N and P absorbed by plants comes from recycled nutrients

What's the difference between open and closed cycling and examples of each?

Qualitative: toxins, low concentration, targets=generalists, low dosage, high mobility, low energy Quantitative: digestibility reducers, high concentration, targets= generalists and specialists, high dosage, low mobility, high energy

What's the difference between qualitative and quantitative chemical defenses?

• Resistance mechanisms: prevent an attack by a pathogen or parasite • Tolerance mechanisms: allow plants to withstand the negative effects of a pathogen or parasite. Resistance and tolerance come at a cost—usually a reduced investment in growth or reproduction.

What's the difference between resistance and tolerance mechanisms and what do they have in common?

The Law of Constant Yield

When density is sufficiently high and resources become limited, the effects of competition will result in a constant biomass due to a proportional decrease in the size of the individuals.

• Solar insolation • Re-emission from atmosphere • Altitude • Circulation patterns

Where does variation in average annual temperature stem from?

Actual evapotranspiration It increases with precipitation and temperature, and accounts for most of the global variation in productivity.

Which climatic factor best predicts productivity?

Water vapor is a greenhouse gas! As atmosphere is warmed, saturation vapor pressure increases, and atmosphere holds more water vapor. More water vapor traps more longwave radiation so the atmosphere warms even more, doubling the amount of warming. However, although clouds emit infrared radiation back to Earth (warming) they also reflect incoming shortwave radiation (cooling). Net effect depends on type and altitude of clouds.

Why are Cloud and water vapor feedbacks an example of positive feedback?

N fixed becomes available to other plants through production and decomposition of N-rich litter.

Why are legumes important in agricultural rotations?

• Plant defenses, not just productivity, might limit herbivores • Herbivores might compete for other resources like territories or nest sites • Most communities don't have neat trophic levels

Why are trophic levels complicated in relation to herbivory?

Increased warming and CO2 lead to higher productivity, especially at high latitudes, but only up to a point. On the other hand, decomposition increases exponentially with temperature. This leads to net C loss. Also, thawing of permafrost exposes thousands of years worth of organic C to decomposition. Microbial metabolism may also release enough heat ("dung-heap effect") to facilitate further melting.

Why is decomposition feedback an example of positive feedback?

• Sun's rays most perpendicular at equator • Shorter atmospheric path near equator (less radiation absorbed, reflected, scattered by atomosphere) • Therefore more energy absorbed by Earth, per unit area, at equator

Why is it the hottest at the equator?

Warming is triggering the release of methane from arctic permafrost and from methane hydrate on the sea floor. Methane is naturally released by some ecosystems due to anaerobic decomposition. Permafrost melts, releasing methane from land. Sea ice stabilizes methane deposits on and near the shore, preventing breakdown of methane hydrates. Ice melts, releasing methane from the sea.

Why is methane release a positive feedback mechanism?

• Why was mutualism ignored for so long? - It's hard to see—often involving microbes - Darwin's influence on ecology, and his focus on competition and predation • Progress came through struggle and competition - Political—mutualism was considered anti-capitalist and was associated with left-wing and socialist causes during the first part of the 20th century

Why were mutualisms ignored for so long?