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ESS Test - Topics 2.3 2.4

ESS Test
Topics 2.3 & 2.4
Flows of energy and matter
★ The fate of solar radiation reaching the Earth
★ Productivity
★ Flows of energy and matter
Main concepts:
➔ As Solar radiation enters the atmosphere some energy becomes unavailable for ecosystems as it is
absorbed by organic matter or reflected back
➔ The loss of radiation is through reflection and absorption
➔ Pathways of energy:
◆ Light energy to chemical energy
◆ Transfer of chemical energy from one trophic level to another, with different efficiencies
◆ ultraviolet and visible light to heat energy
◆ Reradiation of heat energy to the atmosphere
➔ Conversion of energy into biomass for a period of time = productivity
➔ Gross secondary productivity = total energy / biomass assimilated by consumers. (food eaten - fecal
➔ Net primary productivity = GPP - respiratory losses
➔ Net secondary productivity = GSP - respiratory losses
➔ Maximum sustainable yields = net primary/net secondary productivity of a system
➔ Flows of matter: transfers and transformations
➔ Carbon and nitrogen cycles: illustrate flow of matter using flow diagrams
➔ Storages in the carbon cycle: organisms, forests, atmosphere, soil, fossil fuels and oceans
➔ Flows in the carbon cycle: consumption, death and decomposition, photosynthesis, respiration, dissolving
and fossilisation.
➔ Storages in the nitrogen cycle: organisms, soil, fossil fuels, atmosphere and water bodies
➔ Flows in the nitrogen cycle: nitrogen fixation, absorption, assimilation, consumption, excretion, death and
decomposition, denitrification
➔ Human activities: burning fossil fuels, deforestation, urbanization and agriculture impact energy flows as
well as the carbon and nitrogen cycle
Key points
Almost all energy comes from the sun
Solar radiation is made up of visible wavelengths (lights) and those invisible to humans (ultraviolet and
60% of energy is absorbed by atmospheric gases and dust particles
Nearly all ultraviolet light is absorbed by ozone
Infrared light (heat) is absorbed by carbon dioxide, clouds and water vapours
Ultraviolet and visible light energy (short wave) are converted to heat energy (long wave)
The systems depend on the amount of energy that reaches the ground, not the atmosphere. This amount
varies according to time, season, clouds, etc
Most energy is reflected or absorbed and re radiated as heat
35% of energy is reflected back to space by ice, snow, water and land
Some of the energy absorbed heats up the land and seas
Only 1-4% of energy is available to plants on the surface
Green plants: light energy to chemical energy
Chemical energy: one trophic level to another
The fate of solar radiation reaching the Earth
Energy from sun → photons
Energy leaving the sun → 63 million J s-1 m-2
Solar energy reaching the atmosphere → 1400 s-1 m-2 → 1400 watts per second → Earths solar constant
100% entering solar radiation → 69% absorbed → 31%total reflection
Photosynthesis → solar energy into food
Plants absorption:
40% of energy that hits the leaf → only 9% can de used (red&blue wavelengths)
5% reflected
50% lost
5% passes right through the leaf
9% can only be used → GPP
4.5% used to stay alive
5.5% → NPP
All solar radiation → 0.06% captured by plants → GPP
Left over of that energy captured → NPP → amount of food available to all animals
Efficiency of conversion of energy to food:
2-3% in terrestrial ecosystems
1% aquatic ecosystems
Gross: total amount made of something as a result of an activity
Net: amount left after reductions made
Primary: plants
Secondary: animals
Biomass: living mass of an organism / dry mass
Productivity: conversion of energy into biomass over a given period of time → rate of growth or biomass increase
→ m-2 yr-1
Gross productivity: total gain in energy or biomass per unit area per unit time → biomass gained before
Net productivity: gain in energy or biomass per unit area per unit time after reductions from respiration
Gross primary productivity: total gain in energy or biomass per unit area per unit time in green plants →
energy fixed by photosynthesis → light energy into chemical energy (sugars)
Can be measured by calculating the amount of sugars plants produce → difficult → easier to look at the NPP
Net primary productivity: rate at which plants accumulate dry mass → g m-2
Glucose produced by plants used for:
Growth, maintenance and reproduction → energy is lost as heat
Depositions: stored dry mass and then potential food source for consumers
NPP = rate at which plants photosynthesize (GPP) - rate which they respire
Accumulation of dry mass → biomass
Total amount of plant material → amount of energy that is available to all the animals.
Lost from food chains → dies and decays
Eaten by herbivores
Amount of biomass:
spatially : some biomes have higher NPP rates (tropical forest vs tundra)
Temporally: seasonal patterns of productivity change according to basic resource availability (light, water,
Net Secondary Productivity
Only food that crosses the wall of the alimentary canal is absorbed and used to power life processes (assimilated food
Some is used in cellular respiration
Some is removed as nitrogenous waste (urine)
Stored in dry mass of new body tissue
Some plant material is released as feces (egestion) → not absorbed → no energy
NSP herbivores = energy from food ingested - energy lost in egestion - energy used respiration
Gross secondary productivity
Total energy / biomass assimilated by consumers
GSP = food eaten - fecal loss
Plants → autotrophs
Animals → heterotrophs
NSP (net secondary productivity)
Total gain in energy / biomass per unit area per unit of time by consumers after losses of respiration
NSP = GSP - respiratory losses
Assimilate 80% of energy from their diets
Egest less than 20%
Chase moving animals → higher energy intake → increased respiration
Biomass locked up in the prey foods → skeletal parts are non-digestible (bones, horns, antlers) → assimilate
maximum of energy from digestible food
Assimilate 40% of energy from diet
Egest 60%
Feed on static plants
Flows of energy and matter
Energy flows through systems
Matter flows through ecosystems
(nutrients, oxygen, carbon dioxide, water)
How much?
Infinite (sun always shining)
Cycles and recycles repeatedly
All organisms → gove out energy → all the time
All organisms → release → nutrients,
carbon dioxide, water
Higher to lower → light to heat → +entropy
May change form but does not degrade
Temporarily as chemical energy
Long and short term in chemical forms
Transfers and transformations
Both matter and energy move and flow through ecosystems
Both types of flow → use energy
Transfer + simple - energy → transformations
Cycles and flows
Energy → flows in one direction
Solar radiation --------> released as heat through decomposers’ respiration
Biogeochemical cycles:
Cycle of chemical nutrients
Nutrients absorbed by organisms → circulate through trophic levels → released via the detritus food chain
Nutrient cycles
Biogeochemical cycle:
Organic phase (element is in a living organism) → determines how much is available to Liv. org.
Inorganic phase (element is outside living organisms) → major reservoir → rocks and soils → slower flow
Examples: water, carbon, nitrogen, sulphur and phosphorus
Similar characteristics
Movement of matter
Energy travels from the sun
Nutrients and matter are finite and recycled and reused (decomposer food chain)
Organisms die and are decomposed and nutrients are released
Carbon cycle
Where is it stored?
Carbon or carbon dioxide sinks:
● Organic (w/ carbon dioxide molecules):
○ Organisms - living plants and animals
○ Fossilized life forms - fossil fuels
● Inorganic (simple carbon molecules):
○ Locked up in sedimentary rocks and fossil fuels - most is stored here
○ The oceans - carbon is dissolved / locked up as carbonates in shells
○ Soil
○ Atmosphere
Carbon flows
Occurs in the ecosphere
Four main storages:
- Soil
- Living things
- Oceans
- Atmosphere
Carbon not in the atmosphere → stored in carbon dioxide sinks → complex organic molecules
Carbon between living and non-living chemical cycles → fixed by photosynthesis and released through respiration
Also released through combustion of fossil fuels and biomass
Photosynthesis → recaptures carbon → carbon fixation
Carbon releasement: plant harvest for food - wood for firewood - fossil fuels - cut down trees
This changes the balance of the carbon cycle
Human activity disrupted the balance of the global carbon cycle → increased combustion - land use changes deforestation
The carbon budget
Carbon sinks and flows → gigatonnes of carbon (GtC) → 1 billion tones
Humans and the carbon cycle
Annual current global emissions → fossil fuels → 5.5 GtC + 1.6 GtC deforestation = 7.1 GtC
● 20% burning natural gas
● 40% bruning coal
● 40% burning oil
2.4-3.2 GtC → atmosphere
2.4 GtC → oceans
0.5 GtC → Forests
1.8 GtC unaccounted for
Amount of carbon in other reservoirs:
Atmosphere → 750 GtC
Standing biomass → 650 GtC
Soils → 1,500 GtC
Oceans → 1720 GtC
Nitrogen cycle
● Organisms
● Soil
● Fossil fuels
● Atmosphere
● Water
Nitrogen fixation
○ Absorption
○ Assimilation
○ Consumption
Death & decomposition
Three basic stages: nitrogen fixation, nitrification and denitrification
Nitrogen fixation:
Atmospheric nitrogen is made available to plants through fixation
Gaseous nitrogen ----> ammonium ions happens by:
➔ Bacteria in the soil
➔ Bacteria in root nodules of leguminous plants
➔ Cyanobacteria in soil or water
➔ Lightning: causes the oxidation of nitrogen gas
➔ Haber process: nitrogen-fixing process used to make fertilizers
Conversion of ammonium ions to nitrites
Nitrites to nitrates
Denitrifying bacteria reverse the nitrification process
Located in waterlogged and anaerobic conditions
Ammonium - nitrites - nitrates → nitrogen gas
Decomposition also provides nitrogen for plants
+ Nitrogen than other processes
Animals: insects, worms, fungi, bacteria
Breakdown protein → ammonium ions - nitrite ions - nitrate ions
Take up nitrogen → assimilate / build complex molecules
Protein synthesis → inorganic nitrogen compounds → complex amino acids → proteins
Humans and the nitrogen cycle
Removal of humans and plants → remove nitrogen from cycle
Add nitrogen → fertilizers
Energy flow diagrams
Show energy entering and leaving a trophic level
Assimilation and productivity efficiencies
Efficiency of assimilation = Gp * 100 / food eaten
Efficiency of biomass productivity = NP * 100 / GP
Trophic efficiency
Efficiency from one trophic level to another → 10% → general
May be 5% to 20% → depends on energy lost through heat and respiration
Trophic inefficiencies:
Not everything is eaten
Digestion is inefficient
Heat is lost
Some energy is assimilated in other processes → eg: reproduction
Energy budgets
Quantity of energy entering, staying within and leaving the animal/population
Human activities and ecosystems
Process, effect or activity derived from humans → anthropogenic
Energy subsidy: additional energy that we have to put into the system above which comes from the suns’ energy
Some systems → due to energy subsidies → higher NPP
Advantage: feed more people → food production + efficient → energy has to come from somewhere
Maximum sustainable yield:
Largest crop or catch that can be taken from the stock of a species without depleting the stock → NP of a system
Energy: yield ratio
Energy in and energy out in the form of food
Agriculture + sophisticated → ratio goes down
1:30 → 30 units of food for each unit of input energy as work
Energy input can be increased → but has to keep flowing through the ecosystems
Biomes, zonation and succession
★ Biomes
★ Succession and zonation
★ K- and r-strategists’ reproductive strategies
Main concepts
★ Biomes: collections of ecosystems sharing similar climatic conditions
○ Can be grouped in five major classes: aquatic, forest, grassland, desert and tundra
★ Main factors governing the distribution of biomes: insolation, precipitation, temperature
★ Tricellular model of atmospheric circulation explains the distribution of precipitation and temperature,
which influences the structure & productivity of terrestrial biomes
★ Climate change is altering the distribution of biomes = biome shifts
★ Zonation: changes in community along an environmental gradient due to factors such as changes in altitude,
latitude, tidal level or distance from shore
★ Succession: process of change over time in an ecosystem involving pioneer/intermediate/complex climax
○ Changes in patterns of: energy flow/gross&net prod/diversity/mineral cycling
★ Greater habitat diversity → greater species → greater diversity
★ R and K strategist species: have reproductive strategies that are better adapted to pioneer and climax
★ Early stage of succession → GP low → initial conditions
○ Energy lost through respiration→ low
○ Np is high → system is growing
★ Later stage of succession → GP high → increased consumer community
○ Balanced by respiration → NP almost 0
★ Variety of nutrients and energy → stability of complex ecosystems
★ No climax community → set of alternative stable states
○ Depend on climatic factors, properties of local soil, etc
★ Human activity can divert succession → modifying the ecosystem → fire, agriculture, grazing pressure,
deforestation, etc.
★ Ecosystem’s capacity to survive →> relies on → resilience and diversity
How many biomes are there?
Biome: collections of ecosystems sharing similar climatic conditions
Biosphere: part of Earth inhabited by organisms (upper part of the atmosphere; deepest part of ocean)
Freshwater (swamp forests, lakes and onds, stream, rivers)
Marine (rocky shore, mud flats, coral reef, deep ocean)
Deserts: hot & cold
Forests: tropical, temperate, boreal
Grassland: tropical, savanna, temperate
Tundra: arctic & alpine
Each have their own limiting factors, productivity and biodiversity.
Insolation, precipitation and temperature affect the distribution of biomes
Why biomes are where they are
Biomes affected by:
Climate (temperature and precipitation)
Terrain (slope, aspect, altitude)
Temperature → hotter near equator / colder near poles
Latitude: distance from north/south from the equator
Altitude: height above sea level
Increase latitude/altitude → colder
Ocean currents and winds:
They distributor surplus heat energy → from the equator towards the poles
Air moving horizontally = wind
Winds cause ocean currents → water responsible for transferring heat
Water changes from states → gives out/takes in heat = latent heat
Solid → liquid → gas takes in
Gas → liquid → solid gives out
This change distributes heat around the earth
Earth is tilted 23.5 degrees on its axis
Insolation + precipitation + temperature → most important abiotic factors influencing biomes
+temperature +evaporation → important the relationship between precipitation and evaporation
P / E ratio: precipitation to evaporation ratio
P/E ratio = 75/50 → 1.25 → greater than 1
Rains a lot → little evaporation
Loss of minerals when washed away
P/E ratio = 5/50 → 0.1 → less than 1
Lots of evaporation
Leaves salts behind → increased soil salinity
P/E ratio = 1 → P & E are about the same → soil is rich and fertile
Different biomes have different productivity:
May be to limiting factors
Low raw material availability
Low energy source availability
Solar radiation + heat limited in poles
Water limited in desert
Productivity is greater in low latitudes → nearer the equator
Near equator:
Temperatures are high
Sunlight input is high
Precipitation is high
Towards the poles:
Temperatures decline
Sunlight availability declines
Rate of photosynthesis is lower → GPP and NPP are lower
Arctic & antarctica:
Low temperatures
Frozen grounds
Long periods in winter
Low precipitation
All this reduces rate of photosynthesis → lower productivity
Desert and semi arid areas:
Absence of moisture → lower productivity
Climate change and biome shift
Increase in global temperature → biomes are moving
Climate changes:
➢ Temperature increase of 1.5 to 4.5°c by 2100
➢ Greater warming in higher latitudes
➢ +warming in winter than summer
➢ Dryer areas; wetter areas
➢ Stronger storms
Changes are happening fast → organisms change slowly → adapt fast by moving to other areas
➢ Poles where its cooler
➢ Higher to mountains → +altitude +cold
➢ Towards equator → wetter
Examples of biome shifting:
Sahel region (africa): woodlands → savannas
Artic: tundra → shrubland
Plants migrate slowly → seeds
Animals migrate longer distances → whales, albatrosses
Obstacle to migration: mountain ranges, seas, human activities
Hotspot: areas predicted to have a high turnover of species due to climate change
❖ Himalayas
❖ Equatorial eastern africa
❖ Mediterranean
❖ Madagascar
❖ North america great plains and lakes
Changes → new opportunities for exploitation of resources:
● Dreacease ice → drill oil → arctic ocean
● New trade route → north-west passage (north america and north pole)
Tropical rainforest:
➔ Hot and wet areas & Broadleaved forest
➔ Almost in the equator
➔ High rainfall / temperatures (26 - 28°c) / insolation
➔ Rain washes nutrients
➔ High levels of biodiversity
➔ Large trees, vines, climbers, orchids
➔ Stratification within plants and trees
➔ Many niches available
➔ 40% NPP of terrestrial ecosystems
➔ Fast rate of decomposition, photosynthesis and respiration
Rapid recycling of nutrients
50% of world’s population lives near a tropical forest → too many exploiting
Issue: logging, clear-felling, conversion to grazing
Examples: Amazon rainforest, borneo rainforest
➔ Dry areas: hot during the day / cold at night
➔ Classification: tropical / temperate / cold
➔ Cover 20-30% of Eartgs surface → 30° from equator
➔ Limited water → E > P
➔ Low biodiversity
➔ Soil rich in nutrients
➔ Plant drought-resistant → cacti and succulents
➔ Reptiles: snakes, lizards / small mammals: kangaroo rat
➔ NP → secondary and primary → low
➔ Population density low → rich in oil and nutrients
➔ Issues: desertification → area becomes a desrt because of overgrazing/drought
➔ Examples: Atacama desert (chile), Sahara desert (africa)
Temperate grasslands
➔ Flat areas dominated by grasses and herbaceous plants➔ 40-60° from equator
➔ P = E or P>E
➔ Temperature range high & low precipitation
➔ Grasses, no trees, and burrowing animals (rabbits), antelopes, wolves, coyotes
➔ Not high NP
➔ Used fro agriculture
➔ Issues: overgrazing
➔ Example: pampas in Argentina
Temperate forests
➔ Mild climate, deciduous forests
➔ 40-60° from equator
➔ P>E
➔ Freezing winter - wide range of temperatures -30°c to 30°c
➔ Fewer species than tropical rainforests, woodlands show stratification
➔ Flowering plants, mosses, lichens
➔ Forest floor → thick leaf litter
➔ Rapid recycling of nutrients, som lost through leaching → produces brown soil
➔ Well developed food chains → autotrophs, herbivores, carnivores
➔ Deciduous trees → conifer trees towards pole latitudes / increase altitude / vertical slope
➔ 2nd highest NPP
➔ Issues: most cleared for farming, urban developments
➔ Example: US pacific northwest
Arctic tundra
➔ Cold, low precipitation, long&dark winters
➔ 10% of earths surface
➔ Permafrost soil and no trees
➔ High winds
➔ Low temperatures → low rate of photosynthesis, respiration and decomposition
➔ Slow growth and recycling of nutrients
➔ Limited water, temperature, insolation and nutrients
➔ spring&summer: animals active, plants start growing
Low growing plants: grasses, mosses, small shrubs
Animals adapted: thick fur, small ears → small mammals and predators (lemmings, voles, fox, owl
Low biodiversity, inorganic matter and minerals
Very low NP
Used for mining and oil
Issues: take time to recover from disruption, global warming may make them disappear
Examples: siberia, alaska
Deep ocean
➔ Ocean and seafloor beyond continental shelves
➔ 65% of earth’s surface
➔ +depth +pressure → temperature variates until -2°c
➔ No light below 1000m
➔ Low nutrients and productivity
◆ 200m: phytoplankton and cyanobacteria main producers → eaten by fish, invertebrates
◆ 200-1000m: +pressure → fish are muscular and strong, large eyes
◆ 1000-4000m: high diversity, dark, fish have bioluminescence
◆ 4000m: huge pressure, cold, dark → shrimps, jellyfish
◆ Bottom surface: debris from shells and bones, volcanic rocks
➔ Rocks rich in manganese and iron
➔ Issues: pollution
➔ Examples: arctic, atlantic, pacific oceans
Succession and zonation
Succession: process of change over time in an ecosystem involving pioneer/intermediate/climax communities
How an ecosystem changes over time
● Dynamic and temporal
● Progressive changes
Zonation: change in community along an environmental gradient due to factors such as changes in altitude, latitude,
tidal level, distance from shore
how an ecosystem is changing along an environmental gradient
● Spatial and static
● Abiotic gradient
Abiotic and biotic factors influence each niche
➢ Temperature: decreases → +latitude / +altitude
➢ Precipitation: +altitude → -precipitation
➢ Solar insolation: +altitude + insolation
➢ Soil type: warmer zones → fertile / +altitude = acidic soil
➢ Interactions between species
Human activities alter zonation
➔ Change in species composition over time
➔ Two types: primary and secondary
➔ Early stages: GPP and respiration are low → NPP is high
➔ Later stages: GPP high → respiration increases → NPP approaches zero P:R = 1
➔ Climax community → reached at the end of succession → species composition stops changing
➔ +complex + stable ecosystem
➔ Interruption of succession: human activities
◆ May recover or not
➔ +diversity + resilient
Primary succession
❖ Bare inorganic surface
❖ Colonization by organisms in new land created/uncovered → river deltas, volcanic eruptions
1. Bare Surface: lifeless abiotic environment available for colonization → nutrient poor, erratic water supply
2. Colonization: first species to colonize pioneers (usually r-selected species)
3. Establishment: species diversity increases; invertebrates visit and live in the soil → increase org. mater.
4. Competition: new species colonize; larger plants enable K-selected specie establish → pioneer r-species
cannot compete with k-species
5. Stabilization: late colonizers become established; complex food webs develop
6. Climax community: stable and self-perpetuating; steady state dynamic equilibrium; maximum possible
development a community can reach
Secondary succession
❖ Established community is suddenly destroyed
❖ Fire, flood, human activity
❖ Soil already developed
● Size of organisms increases
● Energy flow + complex: simple food chain → complex
● Soil depth, humus, water-holding capacity, mineral content and cycling increase
● Biodiversity increases → climax community is reached
● NPP/GPP rise and then fall
● Productivity : respiration ratio falls
Species diversity in successions
+species + diversity
Increase in species diversity continues until balance is reached
Pioneer species are never totally wiped off
Communities are affected by periods of disturbance
Trees die, fires, floods, landslides, earthquakes, hurricanes, etc
Arrested and deflected successions
Succession may be stopped by an abiotic factor → ‘arrested’
This leads to a sub-climax community → can only continue development if factor is romevoed
Affected by natural event or human activity
Leads to plagioclimax community → pasture, arable farmland, plantations
Human activity stops → development continues
Significance of changes during succession
Biodiversity increases during succession → +species arrive → then decreases when climax com. Is reached
Mineral cycling: slow at early stages → increases during succession
K- and r-strategists’ reproductive strategies
K- / r-strategists
K- / r-selected species
k and r determine the shape of the population growth curve
K: carrying capacity
R: shape of exponential part of the growth curve
K- & r-strategists: approach different species take into getting their genes into the next generation to ensure survival
of species
K-strategists: humans and large mammals
➢ Small numbers of offspring
➢ Energy + time in parental care
➢ Offspring survives
➢ Good competitors
➢ Population size close to carrying capacity
➢ Stable climax ecosystems: k out competes r
R.strategists: invertebrates and fish
➢ Lots of energy in production of eggs
➢ No energy used in raising them
➢ Lay eggs and leave
➢ Reproduce quickly
➢ Colonize habitats quickly
➢ Make good use of short-lived resources
➢ Exceed carrying capacity → predominate unstable ecosystems
Many species combine both
Survivorship curve
Shows the fate of a group of individuals of a species