Principles of Ecology
Learning Targets
 Describe the different niches organisms occupy in food
chains and diagram a model of a food web that includes
several food chains.
 Compare and contrast how matter and energy move
through ecosystems and explain how each process relates
to the laws of conservation of mass and energy.
 Discuss the potential ecological, environmental, and social
impacts of a primary plant-based or primary meat-based
diet in a human society.
 Identify how living organisms influence global and local
cycles of matter (ex. Carbon, nitrogen, phosphorus, and
water cycles)
 Energy flows through an
ecosystem from producers to
consumers. Energy flows from
one trophic level to the next.
(troph = feeding)
 Nutrients (matter) cycle in an
ecosystem.
 The processes of photosynthesis
and aerobic respiration are
important in nutrient cycling
and energy flow.
Primary Producers – plants, algae, photosynthetic bacteria,
some archaea cells.
Most are photoautotrophs.
Some are chemoautotrophs
(use chemicals in the environment
instead of sunlight to produce food)
• Food Chains – show the trophic relationship between
organisms in an ecosystem.
• A single food chain is just one link in a food web
Primary
Producer
Primary
Producer
Primary
Producer
Primary
Consumer
Primary
Consumer
Secondary
Consumer
Primary
Consumer
Secondary
Consumer
Secondary
Consumer
Tertiary
Consumer
Tertiary
Consumer Quaternary Consumer
 Food Webs show all the interacting food chains in an
ecosystem.
 Energy flow in an ecosystem is not efficient between
trophic levels, which can be seen in an energy pyramid.
Only about 10% of all energy is passed
from one trophic level to the next
Tertiary
consumers
Secondary
consumers
 Biomass pyramids also
decline as the trophic level
increases.
Primary
consumers
Primary
producers
 Why?
10 J
The 10% rule
100 J
1,000 J
10,000 J
 Energy lost in
the form of heat.
 Energy used for
metabolic
purposes.
 Indigestible
material
Figure 54.11
Trophic level
1,000,000 J of sunlight
Dry weight
(g/m2)
Tertiary consumers
1.5
Secondary consumers
11
Primary consumers
Primary producers
37
809
 The dynamics of energy flow through ecosystems have important
implications for the human population.
 Consider the resources needed to grow, feed, process, and transport
beef.
 Discussion Question: As human populations continue to
grow, will humans be able to sustain a diet that relies on
animals for protein?
Trophic level
Secondary
consumers
Primary
consumers
Primary
producers
 Decomposers and Detritivores play an important role
in recycling nutrients in an ecosystem.
 The chemical cycling in an ecosystem is an
essential component of ecosystem function.
 Also called Biogeochemical Cycles
THE CARBON CYCLE
CO2 in atmosphere
Photosynthesis
THE NITROGEN CYCLE
THE PHOSPHORUS CYCLE
N2 in atmosphere
Rain
Cellular
respiration
Assimilation
Burning of
fossil fuels
and wood
Higher-level
Primary
consumers
consumers
Carbon compounds Detritus
in water
Decomposition
Denitrifying
NO3 bacteria
Nitrogen-fixing
bacteria in rootDecomposers
Nitrifying
nodules of legumes Nitrification
bacteria
Ammonification
NO2 
NH3 NH4+
Nitrogen-fixing
Nitrifying
soil bacteria
bacteria
Geologic Weathering
of rocks
uplift
Runoff
Plants
Consumption
Plant uptake
3
Soil of PO4
Leaching
Sedimentation
Decomposition
 The Carbon Cycle is a global biogeochemical cycle
 What are some living and non-living reservoirs of carbon?
 What are some of the processes that occur that change carbon
from one form to another?
 In what form(s) is carbon utilized by living things?
 The nitrogen cycle is a global biogeochemical cycle
 What sort of organisms convert nitrogen from one form to
another?
 Why are each of these processes essential for an ecosystem
food web?