ECOSYSTEMS & HUMAN INTERFERENCES I

Ecosystem: the biological communities & their abiotic environment

Ecosystems are Characterized by:Energy flowMineral cycling

• Ecosystems are not self-contained (leaky!)

• Natural ecosystems are affected by human activities

The Biotic Community

Living organisms in an ecosystem are divided into two trophic levels:

Autotrophs: primary producersHeterotrophs: consumers (secondary P., Include:

HerbivoresCarnivoresOmnivoresDetritivoresDecomposers

Decomposers

Energy flowEnergy flow Mineral cyclingMineral cycling

Reflection & Absorption

Dec

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Oxidation (Respiration etc.)

Heat

Light

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Mader, 2001

• Gross Primary Productivity (GPP): the total energy captured from the sun by autotrophs

• Net Primary Productivity (NPP): GPP – Respiration = Energy passed on to herbivores

Secondary Production

The amount of chemical energy in consumers’ food converted to new biomass per unit time.

The efficiency of energy transfer between trophic levels is usually less than 20%

33/200x100=16.5%

Which is more efficient for human population: eating corn or beef?

??

Trophic Efficiency and Ecological Pyramids

Trophic efficiency is the % of production transferred from one trophic level to the next.

Pyramids of production represent the multiplicative loss of energy from a food chain

Ecological Pyramids Energy & biomass pyramids are upright. As a rule, only 10% of energy or biomass are passed on to

the next level.

Energy Pyramid

Biomass Pyramids Represent the ecological consequence of low

trophic efficiencies. Most biomass pyramids narrow sharply from

primary producers to top-level carnivores because energy transfers are inefficient.

Numbers Pyramids

Show how the levels in the pyramids of biomass are proportional to the number of individuals present in each trophic level.

Inverted Pyramids

In lakes & open sea algae & cyanobacteria are the main primary producers.

Algae multiple fast but also consumed at a higher rate therefore the pyramid appears inverted