Learning objectives

Describe how energy is transferred in an ecosystem and contrast
that to nutrient transfer Explain how pollutants are
concentrated at higher trophic levels Describe how humans
have altered global biogeochemical cycles (esp. carbon)

Ecosystems

Communities of organisms + abiotic components The
biotic and abiotic components of an ecosystem are linked by flows of
energy and nutrients

Energy flow through ecosystems

Primary production transforms the energy in sunlight or inorganic
compounds into chemical energy (stored in sugars) and use this energy
for maintenance (respiration) and growth & reproduction (adding tissue)

Gross primary productivity (GPP)

The total amount of chemical energy (sugar) produced in a given area
and time period

Net primary productivity (NPP)

Energy used for growth = biomass This is the energy
available for other organisms

How Efficient Are Autotrophs at Capturing Solar Energy?

0.8% Why so inefficient? Photopigments
Photosynthesis reduced in winter and dry conditions
Enzyme efficiency varies with temperature

What Happens to the Biomass of Autotrophs?

Consumers eat living organisms Primary consumers eat
primary producers Secondary consumers eat primary
consumers Tertiary consumers eat secondary consumers
Decomposers (detritivores) feed on detritus, the waste
products or dead remains of other organisms Components
linked by the movement of energy and nutrients

Nutrients cycle through ecosystems

Food chain

A food chain connects trophic levels
� Describes how energy moves from one
trophic level to another
� Decomposer food chain begins with dead stuff
� Grazing food chain begins with live
primary producers

Food webs

Productivity (biomass) pyramid

The �10% rule�: Only 10% of the energy stored as biomass at one
trophic level can be stored as biomass in the next trophic level.

Tuna sandwich

Biomagnification

Increase in concentration of certain molecules (esp. persistent
organic pollutants) up the food chain

Bigeochemical cycles

Circulation of chemical nutrients like carbon, oxygen, nitrogen,
water through the biological and physical world.

Global carbon cycle

Global carbon cycle Movement of carbon among three
(four) �reservoirs� terrestrial ecosystems, oceans,
atmosphere, (fossil fuels) OCEAN = largest
reservoir Photosynthesis takes carbon from atmosphere into
tissue Respiration releases carbon from tissue into
atmosphere

Threats to biodiversity

Species are vanishing faster than at virtually any other time
in Earth�s history Modern rates of extinction are 100 to
1000 times greater than the average, or �background,� rate

Habitat destruction

� Logging and burning, Grazing livestock, Development
� At current rate, lose 28% wet tropical forest in your lifetime
� Wet tropical forest = biodiversity �hotspots�

Habitat degredation

Habitat fragmentation
� Some fragments too small for some species
� Reduces dispersal & population sizes
� Creates edge habitat
� -> DRAMATIC LOSS OF DIVERSITY & BIOMASS

Overxploitation

Unsustainable removal of wildlife for human use
Overhunting (esp. marine species), pet trade

Invasive species

Nonnative species disrupting native species

Why is biodiversity important

Biodiversity has both economic and biological benefits.
Greater biodiversity is associated with Greater
NPP More primary biomass brings more energy to
ecosystem Greater stability Resistance,
resilience Ecosystem services Pollination,
filtration, decomposition

Biophilia

The urge to affiliate with other forms of life.