Ecosystems

What is an Ecosystem?

• All the organisms living in a community (biotic) and all the abiotic factors that they interact with.

• Ecosystems receive energy from sunlight,• Turned into chemical energy by autotrophic

organisms consumed by heterotrophs • Energy flows through ecosystems• Matter is recycled throughout them.

Ecosystems in relation to Thermodynamics

• Energy cannot be destroyed only transformed = energy in an ecosystem brought in by the sun and released as heat. The total amount of energy stays the same.

• Chemical elements in ecosystems travel from trophic level to trophic level in an endless cycle unlike energy that needs the sun’s constant supply of energy.

Trophic Relationships in an Ecosystem

• Autotrophs/primary producers: support all other levels

• Heterotrophs/Primary Consumers/Herbivores: eat primary producers.

• Heterotrophs/Secondary Consumers: eat primary consumers

• Tertiary Consumers: eat Secondary Consumers• Detritivores/Decomposers: consumers that get

energy from organic material called detritus (dead things, feces).

Decomposers/Detritivores

• They make chemical energy available for producers in an ecosystem

• They decompose organic materials and transport chemical materials into soil, water and air.

• Main decomposers = fungi and prokaryotes

Factors Limiting Production in Ecosystems

• Primary Production= amount of light energy turned into chemical energy by autotrophs

• Solar Radiation: 1% of this is converted to chemical energy by primary producers, this is still enough for primary producers to produce 170 billion tons of organic material/year.

• Gross Primary Production (GPP): all primary production in ecosystem/ amount of light E turned into chemical E.

• Net Primary Production (NPP): GPP – E used by primary producers and consumers to live: Shows the storage of chemical energy that is available for consumers to use.

Production

• Forest has large biomass but primary production is lower than grasslands because grasslands do not accumulate plants (organisms eat them).

• Ecosystems have large ranges of production they create.

• Terrestrial Ecosystems make 2/3 of the worlds net primary production, marine ecosystems make 1/3.

Factors Inhibiting Primary Production in Marine Ecosystems

• Light: only penetrates to a certain depth in the water.• Limiting Nutrient: something that needs to be added so that

the production can increase in an area. (Nitrogen, Phosphorus)• Nitrogen limits phytoplankton growth in ocean.• Iron concentrations are low in oceans because dust from land

gives iron to oceans so central Pacific/Atlantic don’t have a lot of iron.

• If there is not a lot of iron and iron is added then cyanobacteria grows and fixes nitrogen, then phytoplankton population increases.

• Nutrients available determine marine ecosystem primary production

Temperature and Moisture: Limit Terrestrial Production

• Warm, wet conditions = high production• Dry, cold conditions = low productions• Moderate Conditions = moderate production• Evapo-transpiration : amount of water

transpired by different plants and then evaporated by the land. (Increases when precipitation increases and light E available)

• Nitrogen + Phosphorus also limit terrestrial production.

Energy Transfer

• Trophic Efficiency is the percentage of production that is transported from one trophic level to the next one

• Most energy available at one level is not transported to the next level (only 5-20%)

• Ecosystems cannot have many top-trophic level carnivores because so much energy is lost up the trophic levels

Movement of Nutrients through Ecosystem

• Limited amounts of chemical elements are available to ecosystems. They are recycled throughout the ecosystem through biotic and abiotic factors.

• Carbon, Nitrogen, Sulfur, and Oxygen are recycled globally.

• Phosphorus, Potassium, Calcium, trace elements are recycled locally (Soil).

• Ecologists study chemical cycling in an ecosystem by adding radioactive isotopes to different elements they are tracing.

Biogeochemical Cycles (Water Cycle)

• Water Cycle: all organisms need it and it’s availability in an ecosystem affects processes.

• Processes in the Water Cycle – Evaporation, Condensation, Precipitation

• Transpiration by plants and groundwater flow that brings water to oceans

Biogeochemical Cycle (Carbon Cycle)

• The framework of organic molecules is carbon.• Autotrophs take CO2 and make organic molecules

that autotrophs and heterotrophs can then use.• Carbon comes from fossil fuels, soil, aquatic soil,

oceans, plant + animal biomass, and the atmosphere• Photosynthesis fixes CO2 in the atmosphere• CO2 is also added into the atmosphere by cellular

respiration (producers, consumers).• Fossil Fuels and volcanoes also add CO2 into

atmosphere

Biogeochemical Cycle (Nitrogen Cycle)

• Limiting Plant Nutrient• Mostly found in the atmosphere as nitrogen

gas, but also found in soil, and aquatic sediment

• Enters ecosystem through bacterial nitrogen fixation in roots of plants

Biogeochemical Cycle (Phosphorus Cycle)

• Plants synthesize phosphate and plants absorb it to synthesize organic molecules

• Mostly comes from marine rocks• When rocks disintegrate soil receives more

phosphate

How Decomposition and Vegetation effect Nutrient Cycling

• Rate of nutrient cycling in different ecosystems are extremely different because of the rate of decomposition. Warm temperatures and moisture increase the rate of decomposition.

Human Impact• Interrupts nutrient cycling.• Farming depletes nutrients in some areas and creates too

many in another.• Humans add toxic materials to ecosystems.• Acid Rain• Ozone depletion• Climate change

Toxins

• Humans bring toxins into ecosystems.• Organisms ingest them and they accumulate

in their bodies.• Biological Magnification: Toxins becoming

more concentrated in successive trophic levels in a food web.

• Top-Level carnivores most affected by toxins in ecosystem.

• Many toxins cannot be degraded.

Acid Precipitation

• Burning of fossil fuels (coal) releases sulfur and nitrogen oxides.

• The acids return to the earth as acid rain, snow, sleet, or fog. (pH under 5.6)

• Lowers pH of soil and water• Causes problems for plants and animals.• Fish populations decline. (Freshwater lakes)

Ozone depletion

• CFC : fluorocarbons: released into air and deplete ozone: emissions have been reduced due to policies in various countries– Freon, AC units– Burning styrofoam– aerosols

Climate Change• Burning fossil fuels increased CO2 levels in atmosphere.• Deforestation: not using the CO2• If the rate of CO2 levels keep increasing it will be double what

it was at the beginning of the Industrial Revolution.• CO2 makes Earth retain more heat. (Greenhouse Effect)• Increased temperature = melting polar icecaps = sea levels

rising = flooding coastal areas• Ozone layer thinning which makes increased UV radiation.