Lecture XXI: Ecosystems

Question 1

Recall: Ecosystem

Answer 1

All of the living organisms in a given area (the community or biotic component of an ecosystem)

Plus,

The physical environment (abiotic factors) they interact with.

Question 2

Biomes

Answer 2

A biome is any of the world’s major ecosystem types.

Question 3

What characterizes Biomes

Answer 3

Terrestrial biomes are typically characterized by the predominant vegetation and the adaptations seen in organisms to thrive in the specific environment. Examples of terrestrial biomes are: dessert, tropical rainforest, savanna, temperate grassland, northern coniferous forest etc..

Question 4

Aquatic Biomes

Answer 4

Aquatic biomes are characterized by the physical environment and the adaptations that organisms have to survive within it. Lakes, rivers, wetlands, intertidal zones, oceanic pelagic zone, coral reefs and marine benthic are examples of aquatic biomes.

Question 5

Biotic Components of Ecosystems

Answer 5

Primary Producers (autotrophs)

Consumers (heterotrophs)

Decomposers (heterotrophs)

Question 6

Primary Producers

Answer 6

The only group that can utilize simple carbon molecules (CO2) and convert it into biomass in the form of complex organic macromolecules.

Many are photoautotrophic, meaning they have the ability to convert radiant energy from the sun into chemical bond energy through photosynthesis.

They form the base of all ecosystem food chains (webs).

Question 7

Consumers:

Answer 7

Consumers unlike producers are heterotrophic, they must acquire carbon through the consumption of food (organic compounds).

Most consumers are chemoheterotrophic, they also acquire their energy from the food they ingest.

 Primary Consumers
- Ingest producers as their carbon and energy source. Herbivores
Secondary, Tertiary….. Consumers
Ingest other consumers
Omnivores/Carnivores

Question 8

Decomposers

Answer 8

Decomposers like consumers are heterotrophic, they must acquire carbon from organic molecules. They differ from consumers in the way that they acquire it.

Instead of ingesting food like consumers, decomposers secrete digestive enzymes into the external environment and then absorb small organic molecules as they become available.

Question 9

Ecosystem Trophic Levels

Answer 9

Within each ecosystem there is a different feeding relationship between the organisms that exist there. Energy and nutrients pass from one organism to the next. Each link in the chain is called a trophic level.

Question 10

What type of abiotic factors could limit the number and type of species that can live within an ecosystem?

Answer 10

The number of trophic levels found within an ecosystem is strongly influenced by the abiotic environmental factors that exist there.

Amount of sunlight
Nutrient availability (water, phosphorous, carbon, nitrogen)
Temperature

Ecosystems with more sunlight (energy) and nutrients available can support a greater number of living organisms (more biomass) and will have greater species diversity than ecosystems with low sunlight and nutrient availability.

Question 11

Food Web:

Answer 11

A Food Web

In nature simple food chains are uncommon.

More complex interactions occur forming a food web between trophic levels.

Generally, each species feeds on, or is fed upon by, more than one species.

Question 12

Energy Flow

Answer 12

Radiant Energy from the sun

Primary Producers
Capture less than 10% of radiant E in photosynthesis
Convert it into chemical E (stored in bonds of organic molecules)

Primary Consumers
-Herbivores
Ingest producers
Break bonds of organic molecules in cellular respiration producing ATP. Other molecules used to build up their tissues.

Secondary and Tertiary Consumers
-Omnivores/ Carnivores
Ingest consumers.
Organic molecules used the same way as primary consumers.

Energy is lost at each trophic level in the form of heat.

Energy flow is linear

Energy is lost with each trophic level.

All levels are connected to decomposers.

Question 13

Energy Budget

Answer 13

The total amount of energy available for an ecosystem
Based on Primary Production, the amount of radiant energy that is converted into chemical energy by primary producers.

The greater the primary production in an ecosystem the greater the ecosystem’s energy budget is.

Question 14

Primary Production: Gross vs. Net

Answer 14

Gross Primary Production (GPP) = Total primary production in an ecosystem (radiant E → chemical E)

However, plants need to use some of that energy for their own metabolism (R).

What is left over and stored in the plants tissues is the energy available to consumers:
Net Primary Production or NPP (E available to consumers)

NPP = GPP - R

Question 15

Evatranpirations rate

Answer 15

Primary Production is for the most part determined by the amount of available sunlight. However, in Terrestrial Ecosystems it is also influenced by Water, Temperature, and Availability of other Nutrients.

Primary production in terrestrial ecosystems is correlated with the evapotranspiration rate that occurs there.

The evapotranspiration rate is a measure of the amount of water entering the atmosphere from the ground through the process of evaporation and through transpiration from plants, so it is a measure of both temperature and available water.

Question 16

Secondary Production

Answer 16

Is the amount of chemical E ingested by primary consumers (Herbivores) that is converted into their own tissue growth (biomass).

Question 17

Bioaccumulation and Biomagnification of Toxins within Ecosystems

Answer 17

So far, we have considered how energy flows through ecosystem food chains (webs). An issue that faces organisms today is the tendency of certain toxins to accumulate or build up within food chains.

When a toxin is present in the environment it may begin to appear in the tissues of living organisms. This is called bioaccumulation.

When the toxin is passed from one trophic level to the next and increases in concentration it is called biomagnification.

Question 18

How are nutrients cycled?

Answer 18

Unlike energy, nutrients are in a closed system and are never lost. Nutrients are, however cycled between abiotic and biotic components in ecosystems.

Question 19

Rate of Nutrient Cycling

Answer 19

The rate of nutrient cycling is closely linked to the number of decomposers active within an ecosystem.

Question 20

Eutrophication

Answer 20

The process by which elevated nutrient levels lead to an overgrowth of algae and the subsequent depletion of water oxygen levels in aquatic ecosystems. Cultural eutrophication refers to the enrichment of water with nutrients derived from human activities such as fertilizer use and sewage dumping.

Phosphorous is usually the limiting nutrient in aquatic ecosystems, so when it is added, primary production increases dramatically.

Question 21

The Phosphorous Cycle

Answer 21

Reservoirs:
Sedimentary rock
 Soil
 Ocean
 Living organisms

Primary producers uptake (assimilate) phosphate and then pass it up the food chain.

Question 22

Carbon Cycle

Answer 22

Primary Reservoir is the atmosphere, but also sediments, soil, fossil fuels, plant and animal biomass.

Photosynthesis removes substantial amounts of carbon from the abiotic environment. Called Carbon fixation.

Carbon returns to the abiotic environment through Respiration, Combustion and Decomposition.

Carbon is essential to build the backbone of all macromolecules (proteins, lipids, carbohydrates and nucleic acids.

Question 23

The Water Cycle

Answer 23

Reservoirs:
-Oceans  97%
Glaciers and ice caps 2%
 Fresh water bodies 1%
 Living organisms

Processes:
Evaporation
Condensation
Precipitation
Transpiration

Question 24

Nitrogen Cycle:

Answer 24

Nitrogen (N2)is in abundance in the atmosphere, but most living organisms cannot use it in this form.

They must rely on nitrogen fixing bacteria to convert nitrogen into a usable form.

Once N2 has been converted into nitrate, producers can assimilate it and pass it up through the trophic levels.

Question 25

1. Nitrogen Fixation

Answer 25

N2 → NH3

Performed by nitrogen fixing bacteria only.

Question 26

2. Ammonification

Answer 26

Organic molecules containing nitrogen
Nucleic acids
Proteins
From decaying organisms.
Through decomposers, becomes NH3, and gains an H+ from soil and becomes NH4

Question 27

3. Nitrification

Answer 27

NH4+ → NO3-
Ammonium
From decomposers and also converted from ammonia from nitrogen fixation

Nitrification only performed by nitrifying bacteria

Question 28

4. Assimilation

Answer 28

NO3-
—-> Taken up by roots
Plants

Nitrate used to make organic molecules such as amino acids and nucleic acids to build plant tissue.

Question 29

5. Denitrification

Answer 29

NO3- —-> N2 (Nitrogen gas
- Returns to the atmosphere)

Denitrification is only performed by denitrifying bacteria

Question 30

Ecosystem Restoration

Answer 30

Bioremediation: Using organisms like prokaryotes, fungi and plants to detoxify polluted ecosystems. They can process toxins such as heavy metals. Once absorbed they are removed and succession can occur.