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Chapter 15: Ecosystems and Communities
Organisms and their environments
by Mark Manteuffel, St. Louis Community College
Learning Objectives
• Be able to explain the following:

What are ecosystems?

How do energy and chemicals move through
ecosystems?
Learning Objectives
• Be able to explain the following:

How do species interactions influence the
structure of communities?

How do communities remain stable or
change over time?
15.1–15.2
Ecosystems
have living and
nonliving
components.
15.1 What are ecosystems?
A
community of biological organisms plus
the non-living components with which the
organisms interact.
Take-home message 15.1
 An
ecosystem is a community of biological
organisms plus the non-living components
in the environment with which the
organisms interact.
Take-home message 15.1
 Ecosystems
are found not just in obvious
places such as ponds, deserts, and tropical
rainforests but also in some unexpected
places, like the digestive tracts of
organisms or the shell of a beetle.
15.2 A variety of biomes occur
around the world, each
determined by temperature
and rainfall.
Biomes
 What
is the average temperature?
 What is the average rainfall (or other
precipitation)?
 Is the temperature relatively constant or
does it vary seasonally?
 Is the rainfall relatively constant or does it
vary seasonally?
Biomes
 Temperature
and precipitation dictate:
• Primary productivity levels
 the amount of organic matter produced
 The
numbers and types of primary
producers:
• are the chief determinants of the amount and
breadth of other life in the region.
Take-home message 15.2
 Biomes
are the major ecological
communities of earth, characterized
mostly by the vegetation present.
 Different
biomes result from differences in
temperature and precipitation, and the
extent to which they vary from season to
season.
15.6–15.8
Energy and
chemicals flow
within
ecosystems.
15.6 Energy flows from producers to
consumers.
First Stop: Primary Producers
Second Stop: Primary
Consumers—the Herbivores
Third Stop: Secondary
Consumers—the Carnivores
Fourth Stop: Tertiary Consumers—
the “Top” Carnivores
Chains or Webs?
 Food
chain
• Pathway from photosynthetic producers
through the various levels of animals
 Food
web
• Involve harvesting energy from multiple stops
in the food chain
Food Chain
Energy Flow
Food Web
Energy Flows
 Losses
at every “step” in a food chain
 Inefficiency
of energy transfers
Take-home message 15.6
 Energy
from the sun passes through an
ecosystem in several steps known as
trophic levels.
 First,
primary producers convert light
energy to chemical energy in
photosynthesis.
Take-home message 15.6
 Herbivores
then consume the primary
producers, the herbivores are consumed
by carnivores, and the carnivores, in turn,
may be consumed by top carnivores.
Take-home message 15.6
 Detritivores
and decomposers extract
energy from organic waste and the
remains of organisms that have died.
 At
each step in a food chain, some usable
energy is lost as heat.
15.7 Energy pyramids reveal
the inefficiency of food
chains.
10% efficiency
Biomass
 10%
rule
 Where
does the rest go?
 Expended
feces
in cellular respiration or lost as
In humans, why is
vegetarianism more
energetically efficient than
meat-eating?
The 10% rule in application
Why are big, fierce animal
species so rare in the world?
Take-home message 15.7
 Energy
pyramids reveal that the biomass
of primary producers in an ecosystem
tends to be far greater than the biomass
of herbivores.
Take-home message 15.7
 Similarly,
the biomass transferred at each
successive step along the food chain tends
to be only about 10% of the biomass of
the organisms consumed.
 As
a consequence of this inefficiency, food
chains rarely exceed four levels.
15.8 Essential chemicals
cycle through ecosystems.
The recycling of molecules
Chemical Reservoirs

Each chemical is stored in a non-living part of
the environment.

Organisms acquire the chemical from the
reservoir.

The chemical cycles through the food chain.

Eventually, the chemical is returned to the
reservoir.
The Three Most Important
Chemical Cycles
1. Carbon
2. Nitrogen
3. Phosphorus
Why are global CO2 levels
rising?
Fossil fuels
Global CO2 levels are rising in general,
but they also exhibit a sharp rise and
fall within each year.
Why?
Nitrogen is like a bottleneck
limiting plant growth.
Fertilizers
Take-home message 15.8
 Chemicals
essential to life—including
carbon, nitrogen, and phosphorus—
cycle through ecosystems.
Take-home message 15.8
 They
are usually captured from the
atmosphere, soil, or water by growing
organisms; passed from one trophic
level to the next as organisms eat
other organisms; and returned to the
environment through respiration,
decomposition, and erosion.
Take-home message 15.8
 These
cycles can be disrupted as
human activities significantly increase
the amounts of the chemicals utilized
or released to the environment.
15.10. Each species’ role in a
community is defined by its niche.
More than just a place for living, a
niche is a complete way of living.
No two species occupy the same
niche.
Take-home message 15.10
A
population of organisms in a
community fills a unique niche,
defined by the manner in which they
utilize the resources in their
environment.
Take-home message 15.10
 Organisms
do not always completely
fill their niche; competition with
species that have overlapping niches
can reduce their range.
15.11 Competition can be hard to
see, but it still influences
community structure.
Take-home message 15.11
 Populations
with completely overlapping
niches cannot coexist forever.
 Competition
for resources occurs until one or
both species evolve in ways that reduce the
competition, through character displacement,
or until one becomes extinct in that location.
15.15–15.16
Communities
can change
or remain
stable over
time.
15.15. Many communities
change over time.
Secondary Succession
 Much
faster than primary succession
• life and soil are already present
Take-home message 15.15
 Succession
is the change in the species
composition of a community over time,
following a disturbance.
 In
primary succession, the process begins
in an area with no life and no soil.
Take-home message 15.15
 In
secondary succession, the process
occurs in an area where life is already
present.
 In
both types, the process usually takes
place in a predictable sequence.
THREATS TO BIODIVERSITY &
THE ENVIRONEMNT
BIODIVERSITY
• Biodiversity is the variety of different
types of life found on earth. It is a
measure of the variety of organisms
present in different ecosystems.
~ UNITED NATIONS ENVIRONMENT PROGRAM
Invasive Species
• A non-native species that is imported or
introduced to a native habitat.
• Problems:
– No natural predators
– Outcompete native species for resources
• Examples:
– Zebra mussels (animal)
– Purple Loosestrife (plant)
Examples
Habitat Destruction
• Through land development, habitats can
be completely destroyed or fragmented.
Both lead to a decrease of habitats for
native species.
Habitat Fragmentation
Pollution
Two types of pollution:
1. Point source: a specific point of
polluting air or water (ex: pipe draining
into a river from a factory)
2. Non-point source: no specific point is
located but many widespread points
(ex: car exhaust)
Point source
Non-point Source
Bio magnification
the
accumulation
of toxins
through the
trophic levels
of a food
chain.
Ecological “HOT SPOT”
Areas in the world with large
amounts of biodiversity but the
habitats and species are endanger of
extinction due to human impact.
NO MORE NOTES EVER!!!