Topic 9 - Biol 213

Ecosystem

A community of living organisms (biotic) interacting with each other and their non-living physical environment (abiotic)

Abiotic Ecosystem Components

Non-living physical and chemical elements including sunlight, climate, nutrients, air, water, and soil

Biotic Ecosystem Components

Living organisms within an ecosystem including plants, fungi, animals, and microorganisms

Solar Energy Distribution on Earth

~33% is reflected into space, ~42% heats the Earth's surface, and less than 1% is captured by autotrophs

Autotrophs

Organisms that synthesize their own organic compounds by converting ambient energy into biologically accessible chemical energy

Photoautotrophs vs Chemoautotrophs

Photoautotrophs capture solar energy using pigments excited by photons

Gross Primary Productivity (GPP)

The total rate at which primary producers convert solar energy into chemical energy

Net Primary Productivity (NPP)

The remaining chemical energy stored by producers after subtracting the energy used for their own respiration/maintenance

NPP Units of Measurement

Measured in energy captured per area per time (kJ/m²/year) or biomass created per area per time (g/m²/year)

Primary Productivity Key Environmental Drivers

Mean annual primary productivity increases with higher mean annual temperature, precipitation, sunlight intensity/duration, and nutrient availability

Limiting Nutrients for Photoautotrophs

Nitrogen and Phosphorus are the most common limiting nutrients for photoautotrophs

Heterotrophs

Organisms that obtain energy by consuming other organisms, depending directly or indirectly on autotrophs

Secondary Production

The generation of consumer biomass driven by the energy transfer from producers to consumers

Trophic Energy Transfer Efficiency (~10% Rule)

Each trophic level contains only about 10% of the energy present in the level directly below it due to metabolic inefficiencies

Trophic Levels

1 = Producers, 2 = Primary Consumers, 3 = Secondary Consumers, 4 = Tertiary Consumers, 5 = Quaternary/Apex Predators

Ingestion

The total amount of energy consumed by a heterotroph from lower trophic levels

Egestion

The portion of ingested energy that cannot be digested and is excreted as waste

Assimilation

The total energy absorbed into a consumer's body, calculated as Ingestion minus Egestion

Secondary Productivity (SP)

The net energy stored as consumer growth/reproduction, calculated as Assimilation minus Respiration

Net Production Efficiency (NPE)

The proportion of assimilated energy stored as secondary productivity, calculated as NPE = (SP / Assimilation) * 100

Ecological Efficiency (EE)

The proportion of primary producer energy (NPP) converted into consumer biomass, calculated as EE = (SP / NPP) * 100

Bottom-up Trophic Control

Ecosystem control where the abundance of organisms at lower trophic levels (producers) determines the biomass of higher trophic levels

Top-down Trophic Control

Ecosystem control where apex predators at the top of the food web regulate the abundance of herbivores and producers below them

Sample Problem: Calculating Assimilation

Assimilation = Ingestion (500 kJ/m²/yr) - Egestion (200 kJ/m²/yr) = 300 kJ/m²/yr

Sample Problem: Calculating Secondary Productivity

Secondary Productivity = Assimilation (300 kJ/m²/yr) - Respiration (200 kJ/m²/yr) = 100 kJ/m²/yr

Sample Problem: Calculating Net Production Efficiency

NPE = (Secondary Productivity [100] / Assimilation [300]) * 100 = 33.3%

Sample Problem: Calculating Ecological Efficiency

EE = (Secondary Productivity [100] / Plant Production NPP [1000]) * 100 = 10%

In top-down control, ecosystem structure is strongly influenced by:

Number of predators at high trophic levels

Which nutrients are most commonly limiting to primary productivity?

Nitrogen and phosphorous

On average, approximately what fraction of the energy in one trophic level is transferred to the next?

10%

Ecological efficiency describes:

Consumer production relative to production at the trophic level below

Autotrophs are organisms that:

Convert ambient energy into chemical energy stored in organic compounds

True or false: In natural populations, an organism's trophic position is always a whole number.

False (trophic positions can be non-integers due to complex diet webs)

Net primary productivity (NPP) equals:

GPP - producer maintenance cost

How do you calculate Assimilation for a consumer?

Assimilation = Ingestion - Egestion

How do you calculate Secondary Productivity?

Secondary Productivity = Assimilation - Respiration

How do you calculate Net Production Efficiency (NPE)?

NPE = (Secondary Productivity / Assimilation) * 100

If an herbivore ingests 300 kJ/m2/yr, egests 90 kJ/m2/yr, and respires 150 kJ/m2/yr, what is its Assimilation?

210 kJ/m2/year

If an herbivore ingests 300 kJ/m2/yr, egests 90 kJ/m2/yr, and respires 150 kJ/m2/yr, what is its Secondary Productivity?

60 kJ/m2/year

If an herbivore ingests 300 kJ/m2/yr, egests 90 kJ/m2/yr, and respires 150 kJ/m2/yr, what is its Net Production Efficiency (NPE)?

28.57%