Chapters 55
Concept 5: Ecosystems – Analyzing productivity, energy
flow, and chemical cycling.
 Ecosystems (Ch 55)
 How energy flows though the ecosystem by
understanding the terms that relate to food chains and
food webs
 The difference between gross primary productivity and
net primary productivity
 The carbon and nitrogen biogeochemical cycles
Ecosystems
 consist of all the organisms living in a community, as
well as the abiotic factors with which they interact
 Ecosystems range from a microcosm (aquarium) to a
large area such as a (forest, lake)
 Ecosystem Dynamics involve two main processes: energy
flow and chemical cycling
Flow of Energy
 The first law of thermodynamics states that energy
cannot be created or destroyed, only transformed
 Energy enters an ecosystem as solar radiation, is
conserved, and is lost from organisms as heat
 The second law of thermodynamics states that every
exchange of energy increases the entropy of the
universe
 In an ecosystem, energy conversions are not completely
efficient, and some energy is always lost as heat
Cycling of Chemicals
• The law of conservation of mass states that matter
cannot be created or destroyed
• Chemical elements are continually recycled within
ecosystems
• Ex) In a forest ecosystem, most nutrients enter as dust or
solutes in rain and are carried away in water
Overall: Ecosystems are open systems, absorbing energy and mass and
releasing heat and waste products
Trophic Levels
 Autotrophs - build molecules themselves using
photosynthesis or chemosynthesis as an energy source
 Ex) plants and algae
 Ex) chemosynthetic bacteria
on hydrothermal vents
 Heterotrophs - depend on the biosynthetic output of
other organisms
Trophic Levels
Energy and nutrients pass from:




Primary producers (autotrophs) to
Primary consumers (herbivores) to
Secondary consumers (carnivores) to
Tertiary consumers (carnivores that feed
on other carnivores)
 Detritivores, or decomposers, are
consumers that derive their energy from
detritus, nonliving organic matter
 Prokaryotes and fungi are important detritivores
 Decomposition connects all trophic levels
Try This!
 Which of the following is absolutely essential to the
functioning of an ecosystem?
 A) producers
 B) producers and herbivores
 C) producers, herbivores, and carnivores
 D) detritivores
 E) producers and detritivores
Primary Productivity (Lab 12!)
 The amount of light energy converted to chemical
energy (organic compounds) by an ecosystem’s
autotrophs during a given period of time
 Background:
 Photosynthesis (required light energy)

carbon dioxide + water → glucose + oxygen
 Cellular Respiration (generates ATP – energy currency)

glucose + oxygen → carbon dioxide + water
Primary Productivity
• Gross primary production (GPP)
– Total primary production of the ecosystem
• Net primary production (NPP)
– GPP minus energy used by primary producers for
respiration
• Only NPP is available to consumers
• Ecosystems vary greatly in NPP and contribution to the
total NPP on Earth
Ecological Efficiency
 Describes the proportion of energy represented at one trophic
level that is transferred to the next trophic level
 On average, efficiency is only ~10%
 10 percent of the productivity of one trophic level is transferred to
the next level. The remaining 90% is consumed by
individual metabolic activity or to detritovores
 Applications:


Farming: Energy required to raise and sustain carnivores is far
greater than that of herbivores… we eat cows, we ride horses
Bioaccumulation as you go up the trophic levels


Ex)High mercury in tuna and swordfish
Ex) High toxicity levels in orcas
Ecological Pyramids
 Used to show relationship between trophic levels
 Horizontal bars or tiers: represent relative size in terms
of either:



Energy (productivity)
Biomass
Numbers of organisms
 Tiers are stacked in the order in which energy is
transferred.
Try This
 Which of the following is not true of a pyramid of
production?
 A) Only about 10% of the energy in one trophic level is passed




into the next level.
B) Because of the loss of energy at each trophic level, most
food chains are limited to three to five links.
C) The pyramid of production of some aquatic ecosystems is
inverted because of the large zooplankton primary consumer
level.
D) Eating grain-fed beef is an inefficient means of obtaining
the energy trapped by photosynthesis
E) A pyramid of numbers is usually the same shape as a
pyramid of production
Biogeochemical Cycles
 Describes the flow of essential elements from the
environment to living things and back to the
environment.
 p. 1209-1214 in Campbell
 For each of the following essential elements, you much
know:
 The reservoirs (major storage location)
 The process of assimilation (incorporation into plants
and animals)
 The process of release (how it returns to the
environment)
Biogeochemical Cycles
 Hydrolytic Cycle (water cycle)
 Carbon Cycle (required for the building of all organic
compounds)
 Nitrogen Cycle (required for the manufacture the building
blocks of proteins and nucleic acids)
 Phosphorus Cycle (required for the manufacture of ATP and all
nucleic acids. Cycle is similar to other mineral cycles like
calcium)
Try This
 The finding of harmful levels of DDT in grebes (fish-
eating birds) following years of trying to eliminate
bothersome gnat populations in a lakeshore town is an
example of...
Try This
 The finding of harmful levels of DDT in grebes (fish-
eating birds) following years of trying to eliminate
bothersome gnat populations in a lakeshore town is an
example of...
 BIOLOGICAL MAGNIFICATION
Concept 5: Ecosystems – Analyzing productivity, energy
flow, and chemical cycling.
 Ecosystems (Ch 55)
 How energy flows though the ecosystem by
understanding the terms that relate to food chains and
food webs
 The difference between gross primary productivity and
net primary productivity
 The carbon and nitrogen biogeochemical cycles