TOPIC 2: Ecology

2.1 Individuals, Populations, Communities & Ecosystems

2.2 Energy & Biomass in Ecosystems

2.3 Biogeochemical Cycles

2.4 Climate & Biomes

2.5 Zonation, Succession & ∆Ecosystems

Guiding Questions

• How can flows of energy and matter through ecosystems be modeled?
• How do human actions affect the flow of energy and matter, and what is the impact on ecosystems?

2.2 SL Knowledge & Understandings (6hrs)

1. Ecosystems are sustained by supplies of energy and matter.
2. The first law of thermodynamics states that as energy flows through ecosystems, it can be transformed from one form to another but cannot be created or destroyed.
3. Photosynthesis and cellular respiration transform energy and matter in ecosystems.
4. Photosynthesis is the conversion of light energy to chemical energy in the form of glucose, some of which can be stored as biomass by autotrophs.
5. Producers form the first trophic level in a food chain.
6. Cellular respiration releases energy from glucose by converting it into a chemical form that can easily be used in carrying out active processes within living cells.
7. Some of the chemical energy released during cellular respiration is transformed into heat.
8. The second law of thermodynamics states that energy transformations in ecosystems are inefficient.
9. Consumers gain chemical energy from carbon (organic) compounds obtained from other organisms. Consumers have diverse strategies for obtaining energy-containing carbon compounds.
10. Because producers in ecosystems make their own carbon compounds by photosynthesis, they are at the start of food chains. Consumers obtain carbon compounds from producers or other consumers, so form the subsequent trophic levels.
11. Carbon compounds and the energy they contain are passed from one organism to the next in a food chain. The stages in a food chain are called trophic levels.
12. There are losses of energy and organic matter as food is transferred along a food chain.
13. Gross productivity (GP) is the total gain in biomass by an organism. Net productivity (NP) is the amount remaining after losses due to cellular respiration.
14. The number of trophic levels in ecosystems is limited due to energy losses.
15. Food webs show the complexity of trophic relationships in communities.
16. Biomass of a trophic level can be measured by collecting and drying samples.
17. Ecological pyramids are used to represent relative numbers, biomass or energy of trophic levels in an ecosystem.
18. Pollutants that are non-biodegradable, such as polychlorinated biphenyl (PCB), dichlorodiphenyltrichloroethane (DDT) and mercury, cause changes to ecosystems through the processes of bioaccumulation and biomagnification.
19. Non-biodegradable pollutants are absorbed within microplastics, which increases their transmission in the food chain.
20. Human activities, such as burning fossil fuels, deforestation, urbanization and agriculture, have impacts on flows of energy and transfers of matter in ecosystems.

2.2 Additional HL Knowledge & Understandings (⁺2hrs)

• Autotrophs synthesize carbon compounds from inorganic sources of carbon and other elements. Heterotrophs obtain carbon compounds from other organisms.
• Photoautotrophs use light as an external energy source in photosynthesis. Chemoautotrophs use exothermic inorganic chemical reactions as an external energy source in chemosynthesis.
• Primary productivity is the rate of production of biomass using an external energy source and inorganic sources of carbon and other elements.
• Secondary productivity is the gain in biomass by consumers using carbon compounds absorbed and assimilated from ingested food.
• Net primary productivity is the basis for food chains because it is the quantity of carbon compounds sustainably available to primary consumers.
• Maximum sustainable yields (MSYs) are the net primary or net secondary productivity of a system.
• Sustainable yields are higher for lower trophic levels.
• Ecological efficiency is the percentage of energy received by one trophic level that is passed on to the next level.
• The second law of thermodynamics shows how the entropy of a system increases as biomass passes through ecosystems.

Expected & Ancillary Vocabulary

• community
• ecosystem
• respiration
• photosynthesis
• primary producer
• biomass
• trophic level
• autotroph
• heterotroph
• producer
• consumer
• decomposer
• ecological pyramids (numbers, biomass, productivity)
• bioaccumulation
• biomagnification
• food chain
• food web
• ​

• 1^st & 2^nd laws of thermodynamics
• ​

↗ Clickable IGO’s, GO’s, NGO’s & Citizen Science (IA?) →

2.2.1 (6.1.3) Energy Flows Through Ecosystems

Insolation

• The amount of solar radiation in a given area.
• electromagnetic (EM) radiation
• often called solar irradiance

Measuring

• SI units: W∙ m^-2
• energy industry uses over time
• J ∙ s^-1 = W
• 1 kW∙ m^-2 = 24 kWh ∙ m^-2∙ day^-1
• Avg. 1 366 W∙ m^-2 @ top of atmosphere

then, attenuation starts (gradual loss of intensity)

• 1 000 W∙ m^-2 @ sea level on a clear day
• after scattering & reemission
• varies with sun angle & atmospheric conditions

2.2.1 (2.4.3) Insolation

2.2.1 (2.4.x) Other Energy

Thermal energy

• radioactive decay
• geological
• VIDEO: hydrothermal vents
• VIDEO: 2 m Soil depth in Quebec, Canada

2.2.1 (2.3.x) Matter Cycles in Ecosystems

Solids, liquids & gases

• soil (or other substrate)
• inorganic & organic
• nutrients
• carbon, nitrogen, phosphorus, sulfur, other minerals & ions
• water
• air (N₂, O₂, CO₂…)

2.2.2 Thermodynamics

Study of heat and its relation to energy and work

• Developed by Sadi Carnot (French physicist 1796-1832)
• Refined by Lord Kelvin (William Thomson; British physicist 1824-1907)
• Applied to engines, phase transitions, transport, black holes, engineering, the Universe…
• Began with “Father of chemistry” Antoine Lavoisier (1743-94), united by Albert Einstein’s (1879-1955)

E = mc²

2.2.2 (x.x.x) Laws of Thermodynamics

0^th Law - if 2 systems are in thermal equilibrium with a 3^rd system, they are in equilibrium with each other.

1^st Law - energy cannot be created or destroyed (always conserved), only transferred or transformed

(potential ←→ kinetic; E = mc2)

2^nd Law - entropy (chaos/disorder) of an isolated system never decreases, as it spontaneously evolves to thermal equilibrium (homogenous temp., no work available)

3^rd Law - there is no practical means to reach Absolute Zero (0 K = -273.15 ºC)

2.2.3 Photosynthesis & Cellular Respiration

Reduced to the following equation… what is missing?

2.2.4 (x.x.x) Photosynthesis

Primary producers (in most ecosystems) convert light energy into chemical energy within chloroplasts

2.2.5_21 (4.3.1) Producers/Autotrophs/Photosynthesizers

Troph-: (Gr.) τροφή - food; nourishment

All life requires carbon, hydrogen, nitrogen, oxygen (CHON), plus phosphorus & sulfur (CHONPS)

Plants, phytoplankton, algae… primary producers

• phototrophs, lithotrophs, chemotrophs
• synthesizes abiotic energy into food
• fundamental base to food chains & trophic pyramids
• provide habitat for other organisms
• supply nutrients to soil
• bind soil to stop erosion

2.2.6 (2.3.6) Cellular Respiration

The conversion of organic matter into chemical energy, CO₂, and H₂O.

• ATP (adenosine triphosphate) directly fuels the majority of biological reactions
• humans hydrolyze (reduce) 10²⁵ ATP molecules to ADP each day
• ADP uses ADP reduced back to ATP using free energy from oxidation of organic molecules

2.2.7 (2.3.19) Aerobic & Anaerobic Respiration

Aerobic

• O₂ not a limiting resource
• 15x more efficient
• generates 38 ATP Mol. (losses make it 32/30) per glucose
• loses less thermal energy
• within mitochondria
• plant respiration accounts for ~½ of terrestrial CO₂ release

Anaerobic (fermentation)

• bacteria or archaea
• generates 2 ATP molecules per glucose
• multicellular organisms use it in strenuous activity within muscles

2.2.7 (x.x.x) Energy Accounting (Exothermic)

Enthalpy (Chem.), H = E + PV

• total heat content of a system
• negative for exothermic (heat released)
• thermodynamics
• ΔH = H_products - H_reactants < 0

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C₆H₁₂O_{6 (s)} + 6 O_{2 (g)} → 6 CO_{2 (g)} + 6 H₂O _(l) + energy

• ΔH = −2 880 kJ per mol of C₆H₁₂O₆
• Lindeman’s 10% Law

2.2.8 (2.2.29) 2^nd Law of Thermodynamics

Living organisms are constantly fighting the 2^nd Law…

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…and a lot of heat is lost in the process.

2^nd Law TOK

How do we measure time?

2.2.9_21 (2.3.1) Consumers - Heterotrophs

cannot "fix" carbon, cannot produce its own food

• “feed” on macronutrients of carbohydrates (CHO), lipids (CHO), proteins (CHON⁺PS)
• digestion breaks down complex molecules (carbohydrates, proteins, lipids) into simpler compounds (glucose, amino acids, fatty acids)

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2.2.9 Consumers - Decomposers

Bacteria

• one gram of soil has 52 000 000 bacterial cells
• more biomass than all other living things

Fungi

• "roots" are called hyphae
• primary decomposers in forests
• break down lignin (organic polymer, like cellulose, found in woody plants)

Detritivores

• millipedes, worms, wood lice, dung flies, slugs
• often eaten by consumers

Scavengers

• carrion-eaters
• hawks, vultures, eagles, hyenas, Tasmanian devils, maggots, flesh-flies

2.2.10 (x.x.x) Food Chains

Shows

• flow of energy from one organism to the next
• feeding relationships between spp
• arrows connect spp & point to the → consumer

Almost always starts with the sun, except likely origin of life → hydrothermal vents

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2.2.11 (x.x.x) Trophic Level

The position an organism, population, or community of spp occupies in a food chain.

• Primary producers
• Primary consumer/herbivore
• keep each other within K with negative feedback loops
• disperse seeds & pollinate
• Secondary consumer/carnivore
• remove old, weak & diseased animals
• regulate lower trophic spp
• Tertiary consumer…
• …
• Top carnivore/apex predator (niche)
• Decomposers/Detritivores/saprotrophs
• break down dead organisms
• release nutrients back to soil
• control spread of disease

2.2.11 (2.1.20) Carbon = Energy

2^nd Law implications:

• total biomass always decreases the further up a food chain &/or trophic level
• more energy spent “feeding”

Raymond Lindeman - American ecologist (1915-1942)

• PhD thesis on trophic dynamics
• “10% law”

Energy stores are light to chemical to mechanical to thermal to…

2.2.12 (x.x.x) Ecological Efficiency (Assimilation)

Lindeman did not call it a "law", citing ecological efficiencies ranging from 0.1% to 37.5%. Losses are due to

• transfer.
• cellular respiration breakdowns.
• incomplete digestion (faeces).

Used as a general rule when numbers not given

Aquatic ecosystems usually higher

• phytoplankton biomass can cycle 100–300 times per year for zooplankton (consumers)
• consumers typically ~15%

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2.2.12 (x.x.x) More Efficiencies

1. Determine if the ecosystem at right follows Lindeman’s 10% law, and explain why or why not. [4]

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• FYI: 1 kcal = 4 184 J = 4.184 kJ = 1 Cal
• 1 calorie = energy required to raise 1 g of H₂O 1 ºC
• 1 Calorie (capital C) for 1 kg

Why is transfer so low?

• 2^nd law of thermodynamics
• cellular respiration
• heat loss to environment
• energy is reflected (producers)
• pieces cannot be digested
• waste of digestion (also 2^nd law)
• organisms die & decompose before being eaten

2.2.13 Energy → Biomass = Productivity

the production of biomass per unit area (usually m²) per unit time (usually yr) thus, kg m^-2 yr^-1

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Primary productivity: gain by producers in energy or biomass per unit area per unit time.

light → chemical

Secondary productivity: gain by heterotrophs in energy or biomass per unit area per unit time.

feeding & absorption

2.2.13 (x.x.x) Gross & Net Productivity (GP & NP)

Gross productivity (GP)

• total gain in biomass per unit area per unit time

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Net productivity (NP)

• gain by producers
• in energy or biomass per unit area per unit time
• after respiratory losses
• potential available to next trophic level

2.2.14 (x.x.x) Height of Trophic Pyramids

Terrestrial Food

Sun → producer → you

Sun → producer → consumer → you

RARELY: Sun → producer → consumer → consumer → you

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Marine Food

Sun → producer → you

Sun → producer → consumer → you

Sun → producer → consumer → consumer → you

Sun → producer → consumer → consumer → consumer → you

Sun → producer → consumer → consumer → consumer → consumer → you

Sun → producer → consumer → consumer → consumer → consumer → consumer → you

2.2.15 (x.x.x) Food Webs…

…complex interrelated network of food chains in an ecosystem.

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• Shows species eaten in multiple food chains
• Shows species consuming in multiple food chains
• More realistic
• Can become complicated…

2.2.15 …or Very Complicated

2.2.16 (x.x.x) Measuring Biomass

…dry mass of organic matter. Usually g∙m^-2 for a given time (yr)

1. Using a quadrat with known area,
1. place the quadrat in sampling location.
2. work the frame through the standing plants to ground such that:
1. No stems rooted outside of the frame are lying inside the frame
2. No stems rooted inside the frame are lying outside the frame
3. remove foreign material fallen into the plot from the outside (e.g., oak leaves)
2. Clip plants rooted within frame close to ground level and place in a labeled paper bag. Roots may also be collected with inorganics (soil, rock, etc.) removed
3. Mass bag & dried plant material in ± grams & record
4. Place bags into drying oven @ 60 ⁰C for minimum 24 hrs
5. Mass bag and dried plant material in ± grams & record
6. Measure mass three times with 1 or 2 days between each measurement (no oven). If mass is relatively similar across all three measurements, then the majority of the water has evaporated
7. Use biomass of sample quadrat to multiply & calculate area surveyed

2.2.16 IA? Notes on Drying

The mass of clipped plant material includes water inside the plant (within and between cells) and water on leaves and stems such as dew and precipitation. Therefore, the mass of freshly harvested plant material is highly variable and depends on recent weather, atmospheric conditions, and the water status of the plant.

Generally, the mass of all fresh, or “green”, samples are measured in the field and then a subset of these samples are brought back to the lab to be oven-dried. Alternatively, all the samples can be collected and brought back to the lab and dried.

Recommended Drying Procedure:

• Dry sample within 24 hours of clipping. The sooner the better.
• Place samples (in paper bags) in a forced-air oven at 60-70°C
• Most samples will take 24-48 hours to dry
• To determine if a sample is dry, a few bags can be removed from the oven, mass and returned to the oven. A few hours later, (4-8 hours) the bags can measured again. Samples are dry when no changes in mass occur between measures. This is called “drying to a constant mass”.
• Samples must be stored in a dry place or they will absorb atmospheric moisture and gain mass.
• Air-dried samples are sometimes used to compare production. If an oven is not available and if samples are collected in a very dry environment (where molding is unlikely), the samples can be placed in a dry warm place to dry-out over several days to reach an “air-dried” weight.
• Excerpted from University of Idaho College of Natural Resources

If impossible to dry samples, book values can be used to convert fresh field measurements to dry mass:

Grass:

• before heading = 35 to 30% dry matter (or 65-70% moisture)
• headed out = 35 to 40% dry matter
• after bloom = 45 to 50%
• mature seeded = 55 to 60%
• leave dry/stem partly dry = 80 to 85%
• apparent dormancy = 90 to 95%

Forbs:

• very lush = 15 to 20%
• mature, seed-stage = 35 to 40%
• seed ripe, leaves drying = 60%
• dry and dormant = 90 to 100%

Shrubs/Trees (deciduous):

• lush new leaves = 20 to 35%
• older, full-sized leaves = 50%

Shrubs/Trees (evergreen):

• lush new leaves = 55%
• older, full-sized leaves = 65%

2.2.16 (x.x.x) Non-destructive Biomass - Tree IA?

Above Ground Biomass & Diameter @ Breast Height (1.3 m) modelling

Table 1: Distribution of number of harvested trees within diameter at breast height (dbh), total tree height (H_t) and wood density (ρ) classes

where B_i is mass of tree i, D_i is diameter at breast-height, μ_i is mean biomass of all trees with diameter D_i, a and b are the allometric coefficient & exponent respectively, & φ is the dispersion parameter.

2.2.17 (x.x.x) Ecological Pyramids

Quantify information at various trophic levels for easier comparison

Size of bars are relative to one another

Three types, pyramid of

• numbers
• biomass
• productivity

Usually narrower at the top, but not always

2.2.17 (x.x.x) Pyramid of Numbers

Shows the proportional number of organisms at each trophic level in a food chain

Seasonal snapshot (time dependent)

Graphically: producers → top carnivores

Not necessarily pyramidal

2.2.17 Pyramid of Biomass

Units – mass per unit area (example: g∙m^-2)

Mostly pyramidal shaped

(Individual biomass) x (individuals)

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2. Outline a method to obtain biomass in one of the graphs at right. [3]

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2.2.17 Pyramid of Productivity

Energy generated @ each trophic level (GP)

Energy available to next level (NP)

Not time-dependent (data taken year-round)

Always pyramidal (in healthy ecosystems)

Shows changes over a year

Units: energy per unit area per time (J∙m^-2yr^-1)

2.2.17 Pyramid Summary

2.2.17 Pyramid Summary

2.2.18 (x.x.x) Bioaccumulation

The buildup of persistent (non-biodegradable) substances in an organism or trophic level.

2.2.18 (1.3.3) Biomagnification

“PCBs, which were banned in the 1970s, break down very slowly. As much as they refuse to dissolve in water, they love to work their way into the lipids, or fat tissue, found in living things. Once PCBs check in, they don’t check out. They remain in fatty tissue, working their way up the food web in higher and higher concentrations, a process known as biomagnification.

Even when PCBs reach the top of the marine food web, where killer whales are the apex predator, their destructive behavior is not over. When animals die, their tissues are broken down by scavengers and bacteria, allowing PCBs to recycle back through the food web again and again. Adding to the overall contamination are historic PCBs still washing off the land along with very low levels allowed in some paints and dyes.”

• Encyclopedia of Puget Sound

2.2.18 (1.3.12) Bioaccumulation & Biomagnification

The buildup of persistent (non-biodegradable) substances over a lifetime.

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The buildup of persistent (non-biodegradable) substances along a food chain

The higher the trophic level, the more concentration possible

2.2.18 (1.3.3) Bioaccumulation & Biomagnification

The combination of both…

2.2.19 (x.x.x) Non-biodegradable Pollutants

Named toxins

• PCB (polychlorinated biphenyl)
• “forever” chemical
• methylmercury
• neurotoxin
• DDT (dichlorodiphenyltrichloroethane)
• of Silent Spring “fame”
• microplastics
• Nurdles

Toxicity measurements

• Direct - concentration (ppm, ppb, ppt, etc.)
• Indirect - indicator spp, tissue or cell damage (LD50 - lethal dose in 50% of population)

2.2.20 (6.2.x) Human Activities on Carbon

Massive impact on other matter cycles, too

• water
• nitrogen
• phosphorous
• sulfur
• silicon dioxide (sand)
• other inorganics
• lithium
• coltan
• precious metals
• ​
• ​

2.2 Additional HL Knowledge & Understandings

• Autotrophs synthesize carbon compounds from inorganic sources of carbon and other elements. Heterotrophs obtain carbon compounds from other organisms.
• Photoautotrophs use light as an external energy source in photosynthesis. Chemoautotrophs use exothermic inorganic chemical reactions as an external energy source in chemosynthesis.
• Primary productivity is the rate of production of biomass using an external energy source and inorganic sources of carbon and other elements.
• Secondary productivity is the gain in biomass by consumers using carbon compounds absorbed and assimilated from ingested food.
• Net primary productivity is the basis for food chains because it is the quantity of carbon compounds sustainably available to primary consumers.
• Maximum sustainable yields (MSYs) are the net primary or net secondary productivity of a system.
• Sustainable yields are higher for lower trophic levels.
• Ecological efficiency is the percentage of energy received by one trophic level that is passed on to the next level.
• The second law of thermodynamics shows how the entropy of a system increases as biomass passes through ecosystems.

2.2.21 (x.x.x) Auto- & Heterotrophs

Photoautotrophs

2.2.21 (x.x.x) Photo- & Chemoautotrophs

Photoautotrophs

2.2.23 (x.x.x) Primary Productivity

GPP & NPP

2.2.24 (x.x.x) Secondary Productivity

MSY

2.2.25 (2.5.10) NPP

MSY

2.2.26 (x.x.x) Sustainable Yields

MSY

2.2.27 (x.x.x) Trophic Level & Sustainable Yields

MSY

2.2.28 (x.x.x) Ecological Efficiency

Efficiency

2.2.29 (2.2.8) The 2^nd Law of Thermodynamics

How many ways to define it?