ECOSYSTEMS, BEHAVIOR
AND HUMAN INFLUENCES
CHAPTERS 36, 37, 38
ENERGY FLOWS THROUGH
ECOSYSTEMS
• A community is the collection of organisms that live
in a particular place.
• The place where a community lives is called the
habitat.
• The combination of the community and habitat is
called the ecosystem.
ENERGY FLOWS THROUGH
ECOSYSTEMS
• You can think of the organisms in an ecosystem as
chemical machines fueled by energy captured in
photosynthesis.
• Producers first capture the energy - these are the
autotrophs, such as plants, algae, and some bacteria.
• Consumers are the heterotrophs that obtain their energystoring molecules by consuming plants or other animals.
ENERGY FLOWS THROUGH
ECOSYSTEMS
• Ecologists assign every
organism in an ecosystem
to a trophic level.
Tertiary consumer
Trophic
level 4
Sun
Top
carnivore
• Food energy passes through an Trophic
level 3
ecosystem from one trophic
Carnivore
level to another.
Primary consumer
• How many steps from the
Trophic
sun?
level 2
Herbivore
• When the path is a simple
linear progression, it is called
Producer
a food chain.
Trophic
level 1
• The chain ends with
decomposers that break
down dead organisms or
their excretions.
Decomposers
Bacteria
Secondary consumer
Fungi
ENERGY FLOWS THROUGH
ECOSYSTEMS
• Producers - the lowest trophic level of any
ecosystem.
• Green plants occupy this role in most terrestrial ecosystems
while algae do in most aquatic systems.
• Herbivores - occupy the second trophic level and
eat producers.
• They are the primary consumers.
ENERGY FLOWS THROUGH
ECOSYSTEMS
• Carnivores - occupy the third trophic level and eat
producers; carnivores are secondary consumers.
• Some carnivores also eat plants, and are called omnivores.
• The fourth trophic level, if present, is composed of tertiary
consumers, or top carnivores.
ENERGY FLOWS THROUGH
ECOSYSTEMS
• Detrivores (also known as
scavengers) are special
consumers that eat dead
organisms.
• Decomposers are organism that
break down organic substances,
making them available to other
organisms.
• Bacteria and fungi are the principal
decomposers in land ecosystems.
ENERGY FLOWS THROUGH
ECOSYSTEMS
• Much of the energy
captured by plants
is lost as energy
passes through the
ecosystem.
• 80–95% of the
energy available at
one trophic level is
not transferred to
the next.
17%
Growth
33%
Cellular
respiration
50%
Feces
ENERGY FLOWS THROUGH
ECOSYSTEMS
Algae and
cyanobacteria
• Food chains usually
consist of only three or
four steps,
• So much energy is lost at
each step that very little
energy remains in the
system after it has been
incorporated into the
bodies of organisms at four
successive trophic levels.
Small
heterotrophs
Trout
Smelt
Human
1.2 calories
1000 calories
150 calories
30 calories
6 calories
ENERGY FLOWS THROUGH
ECOSYSTEMS
• In most ecosystems,
the path of energy is
not linear because
individuals often feed
at several trophic
levels.
• A food web describes
this more complex path
of energy flow.
Top carnivores
Carnivores
Birds of prey
Herbivores
Photosynthesizers
Decomposers
Humans
Birds
Birds
Mammals
Mammals
Inorganic
nutrients
Arthropods
Fish
Meiofauna
Inorganic
nutrients
Bacteria and fungi
Algae
Inorganic
nutrients
Mollusks
Annelids
BIOGEOCHEMICAL CYCLES
• Unlike energy, the physical components of
ecosystems are passed around and reused within
ecosystems.
• This is termed cycling by ecologists.
• The paths of water, carbon, and soil nutrients as they pass
from the environment to living organisms and back form
closed circles called biogeochemical cycles.
THE WATER CYCLE
• Water cycles within an ecosystem in two ways.
• Environmental water cycle - water vapor in the atmosphere
condenses and falls to earth as precipitation.
• It reenters the atmosphere by evaporation from lakes, rivers, and
oceans.
• organismic water cycle - surface water is taken up by plant
roots.
• After passing through the plant, water evaporates from a plant
leaf and re-enter the atmosphere via transpiration.
THE WATER CYCLE
THE CARBON CYCLE
• The earth’s atmosphere contains plentiful carbon,
present as CO2.
• The carbon cycles between the atmosphere and living
organisms.
• Plants trap the carbon in organic molecules by photosynthesis.
• The carbon is returned to the atmosphere by respiration,
combustion, and erosion.
• Some carbon is locked up for a long time in wood;
plants that become buried in sediment can be
gradually transformed into coal or oil (fossil fuels).
• The burning of fossil fuels leads to this carbon being
released back to the atmosphere.
THE CARBON CYCLE
OCEAN ECOSYSTEMS
• Shallow waters -
Shallow waters
Limit of light
Intertidal region
penetration
Open sea surface
the small area of water
that occurs mostly along
the shoreline and
4
Continental
Deep-sea
contains the most
shelf
waters
species.
• Part of this area consists
of the intertidal zone,
which is periodically
exposed to air.
• Partly enclosed bodies • Open-sea surface - contains a lot
of water, such as river
of phytoplankton that drift with the
mouths and coastal
current and perform 40% of all the
bays, have
photosynthesis that takes place on
intermediate salinities
earth.
and are called
• Deep-sea waters - very few
estuaries.
organisms live below 300 meters
and are often bizarre.
FRESHWATER ECOSYSTEMS
• Freshwater ecosystems
include lakes, ponds, rivers,
and wetlands.
• All freshwater habitats are
strongly connected to land
habitats, with wetlands
(marshes and swamps)
constituting intermediate
habitats.
• A large amount of organic
and inorganic material
continually enters bodies of
freshwater from nearby land
communities.
FRESHWATER ECOSYSTEMS
• Ponds and lakes have
three zones in which
organisms live.
• Littoral (shallow
“edge”).
• Limnetic (open-water
surface).
• Profundal (deep-water)
• No light penetrates here.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Limnetic zone
Littoral zone
Profundal zone
(a)
Littoral zone
FRESHWATER ECOSYSTEMS
• Lakes can also be divided
into two categories based
on their production of
organic material.
• In oligotrophic lakes,
organic matter and nutrients
are relatively scarce.
• Eutrophic lakes have an
abundant supply of minerals
and organic matter.
(b) Oligotrophic lake
b-c: © Corbis RF
(c) Eutrophic lake
LAND ECOSYSTEMS
• A biome is a terrestrial ecosystem.
• Each biome is characterized by a particular climate and a
defined group of organisms.
• Biomes that normally occur at high latitudes also follow
an altitudinal gradient along mountains.
Polar ice
Tundra
Taiga
Mountain zone
Temperate
deciduous forest
Temperate evergreen forest
Warm, moist evergreen forest
Tropical monsoon forest
Tropical rain forest
Chaparral
Temperate grassland
Savanna
Semidesert
Desert
LAND ECOSYSTEMS
• Grasslands (also
called prairies)
grow in temperate
areas.
• Many of the
original grasslands
have been
converted to
agricultural lands.
LAND ECOSYSTEMS
• Deciduous forests
are forests of trees
that drop their
leaves in the winter.
• Deer, bears,
beavers, and
raccoons, are the
familiar animals of
these regions.
LAND ECOSYSTEMS
• The taiga is a
great band of
coniferous trees
that extends
across vast areas
of North America
and Asia.
• Most of the trees
occur in dense
stands of one or
two species.
LAND ECOSYSTEMS
• Tundra is open,
often boggy,
grassland that
occurs in the far
north beyond
the taiga.
• Permafrost, or
permanent ice,
usually exists
within 1 meter of
the surface.
Tundra
LAND ECOSYSTEMS
• Chaparral consists of evergreen, often spiny
shrubs and low trees.
• These communities occur in
“Mediterranean” regions, those with a dry
summer climate.
LAND ECOSYSTEMS
• Polar ice caps lie over the Arctic Ocean in
the north and Antarctica in the south.
• This region receives almost no precipitation
and freshwater is scarce.
LAND ECOSYSTEMS
• Tropical upland forests occur at slightly
higher altitudes than rainforest or where
local climates are drier.
• Most trees or deciduous.
• Rainfall is seasonal - monsoon seasons alternate
with dry seasons that approach drought conditions.
APPROACHES TO THE STUDY OF
ANIMAL BEHAVIOR
• Behavior can be defined
as the way an animal
responds to stimuli in its
environment.
• Proximate causation deals
with how the behavior works.
• How questions
• Ultimate causation deals with
why the behavior evolved.
• Why questions
INSTINCTIVE BEHAVIORAL
PATTERNS
• Ethology is the study of animal behavior in natural
conditions.
• Behavior in animals is often innate and based on preset
paths in the nervous system.
• The trigger for the behavior is a sign stimulus.
• The response is called the fixed action pattern.
INSTINCTIVE BEHAVIORAL
PATTERNS
• Konrad Lorenz studied egg retrieval in geese.
• Egg retrieval behavior is triggered by a sign stimulus
which is the appearance of an egg outside of the
nest.
• The innate releasing mechanism in the goose’s brain
triggers the fixed action pattern:
• The goose will extend its neck toward the egg, get up, and
roll the egg back to the nest under its bill.
INSTINCTIVE BEHAVIORAL
PATTERNS
• Niko Tinbergen
studied sign stimuli
in the mating
behavior of male
stickleback fish.
• He was able to
produce the
aggressive display in
males by
challenging them
with unfishlike
models, so long as
the sign-stimulus—a
red color—was
present.
Accurate clay model without red
Aggressive
postures of
breeding male
sticklebacks
Clay models with red underside
GENETIC EFFECTS ON BEHAVIOR
• Many animal behaviors are strongly
influenced by genes passed from parent to
offspring.
• Behavioral genetics investigates the inheritance
of genes connected to behavior.
• For example, identical twins reared in different
environments show many similarities, indicating
that genes play a key role in determining
human behavior.
GENETIC EFFECTS ON BEHAVIOR
• In mice, the fosB
gene determines
whether or not
female mice will
nurture young.
• When a female lacks
the fosB allele, she
will ignore her
newborn babies.
HOW ANIMALS LEARN
• In many cases, animals alter their behavior
as a result of previous experiences.
• This is called learning.
• Nonassociative learning is the simplest type of
learning - it does not require an animal to form
associations between two stimuli or between a
stimulus and a response.
• Sensitization occurs when repeating a
stimulus produces a greater response.
• Habituation is a decreased response to a
repeated stimulus.
HOW ANIMALS LEARN
• Associative learning is a form of learning in which
behavior is modified, or conditioned, because of an
association.
• Classical conditioning occurs when paired stimuli
are presented, causing the animal to form an
association between the stimuli.
• Pavlov’s dog learned to associate a bell with food.
HOW ANIMALS LEARN
• As an animal matures, it
may form preferences or
social attachments to other
individuals.
• This process is called imprinting
and is sometimes considered a
type of learning.
• For example, young birds
of some species begin to
follow their mother or the
first object they see after
hatching.
BEHAVIORAL ECOLOGY
• Behavioral ecology is the
study of how natural selection
shapes behavior.
• Niko Tinbergen observed that
after gull nestlings hatched,
the parents quickly removed
the shells.
• From experiments, he found
that eggshell removal reduces
predation of unhatched eggs
and increases the survival of
offspring.
A COST-BENEFIT ANALYSIS OF
BEHAVIOR
• Behavioral ecologists examine the evolutionary
advantage of behavior by asking if it provides an
evolutionary benefit greater than its cost.
• Optimal foraging theory predicts that animals will
select food items that maximize their net energy
intake per unit of foraging time.
A COST-BENEFIT ANALYSIS OF
BEHAVIOR
• Territoriality is a behavior in which an individual
defends a portion of its home range and uses it
exclusively.
• Territories are defended by displays that advertise that the
territories are occupied and by overt aggression.
• The adaptive value of territoriality depends on the trade-off
between the benefits and the costs.
MIGRATORY BEHAVIOR
• Many animals breed in one
part of the world and spend
the rest of the year in another.
• Migrations are long-range
two-way annual movements.
• Compass sense is an
innate ability to move in a
particular direction or
bearing.
• Map sense is a learned
ability to adjust a bearing
depending on the animal’s
location.
Breeding
range
Wintering
range
Holland
Switzerland
Spain
REPRODUCTIVE BEHAVIORS
• Sexual selection is competition for mating
opportunities.
• Intrasexual selection - occurs between members of the
same sex.
• Leads to the evolution of structures used in combat, such as
antlers.
• Intersexual selection - is also called mate choice and
occurs between members of the opposite sex.
• Leads to the evolution of complex courtship behaviors and of
ornaments.
COMMUNICATION WITHIN
SOCIAL GROUPS
• In animals living in groups, information is
communicated between group members.
• An alarm call is given by an animal acting as a “guard”
and warns the group of a predator.
• Alarm pheromone is secreted by social insects and triggers
attack behavior by the group.
• Trail pheromone is secreted by social insects to lead colony
members to a food source.
COMMUNICATION WITHIN
SOCIAL GROUPS
• Honeybees have an extremely complex dance
language that directs nestmates to rich nectar sources.
• A waggle dance is performed by a scout upon its
return to the hive.
• The dance traces a figure-eight pattern and
conveys information about the direction and
distance of the food source.
20°
(a)
(b)
POLLUTION
• Our world is a highly interactive biosphere, and
damage done to any one ecosystem can have ill
effects on many others.
• Biologists call widespread effects on the worldwide
ecosystem global change.
• The pattern of global change that has become evident
within recent years is one of the most serious problems
facing humanity’s future.
POLLUTION
• Pollution takes many forms:
• Air pollution is a major problem in the world’s
cities
• Some cities, such as New York and Boston, are gray-air
cities because of sulfur oxides from industrial pollution.
• Other cities, such as Los Angeles, are brown-air cities
because pollutants in the air react with sunlight to form
smog.
• Water pollution - despite improved methods of sewage
treatment, lakes and rivers are becoming increasingly
polluted with sewage.
• Fertilizers and insecticides also get washed from the land
to the water.
POLLUTION
• Large quantities of many
toxic chemicals,
although no longer
manufactured, still
circulate in the
ecosystem.
• For example, chlorinated
hydrocarbons, a class of
compounds that includes
DDT, have all been
banned for normal use in
the U.S.
• These chemicals break down
slowly and accumulate in
animal fat tissue.
• As they pass through the food
chain, they become
increasingly concentrated in a
process called biological
magnification.
DDT Concentration
25 ppm in
predatory birds
2 ppm in
large fish
0.5 ppm in
small fish
0.04 ppm in
zooplankton
0.000003 ppm
in water
ACID PRECIPITATION
• Acid rain is pollution-acidified precipitation
produced when sulfur products of industry
combine with water vapor in the air and
then fall back to earth as rain or snow.
• Acid precipitation destroys life.
• At least 1.4 million acres of forests in the Northern
Hemisphere have been adversely affected.
• Tens of thousands of lakes in the northeastern U.S. and
Canada are dying biologically as their pH levels fall
below 5.0.
• Industrial scrubbers and the Clean Air Act revision
of 1990 have begun to address this problem.
• The chemical bonds in CO2
transmit radiant energy
from the sun but trap the
longer wavelengths of
infrared light (or heat).
• This creates a greenhouse
effect of this trapped heat.
• Other greenhouse gases
include CFCs, nitrogen
oxides, and methane.
380
376
372
368
61
364
360
60.5
356
352
60
348
344
340
59.5
336
332
59
328
324
58.5
320
316
58
312
'58 '62 '66 '70 '74 '78 '82 '86 '90 '94 '98 '02 '06
Temperature (degrees Fahrenheit)
• Industrial society’s
burning of fossil fuels has
released huge amounts
of carbon dioxide into
the atmosphere.
Carbon dioxide concentration (parts per million)
GLOBAL WARMING
Year
GLOBAL WARMING
• The earth’s greenhouse effect is intensifying.
• Global warming is a rise in the average global
temperatures associated with increased CO2
concentration in the atmosphere.
• Some possible effects of global warming include:
• Changes to rainfall patterns.
• Increases in agricultural yield but increased risks
of drought.
• Melting of ice in glaciers, causing sea level to
rise.
THE OZONE HOLE
• Living things were able to leave the oceans and
colonize the surface of the earth only after a protective
shield of ozone had been added by photosynthesis.
South
Pole
Southern hemisphere ozone hole area
(millions of square kilometers)
• The ozone shield protects the earth from harmful radiation.
• Starting in 1975, the earth’s ozone shield began to disintegrate,
leaving a mysterious zone of lower-than-normal ozone
concentration, an ozone hole.
2005
2003
2000
1995–2004 average
27
24
21
18
15
12
9
6
3
0
August
(left): NASA
September
October
November
December
THE OZONE HOLE
• Chlorofluorocarbons (CFCs) were found to
be responsible for the breakdown of ozone.
• Originally thought to be harmless, these
chemicals are used as coolants in refrigeration
and cooling, gas in aerosol contains, and as the
foaming agent in Styrofoam.
• CFCs easily catalyze the conversion of O3 (ozone)
into O2.
• The drop in worldwide ozone is about 3% and is
estimated to have led to an increase in perhaps
as much as 20% in lethal melanoma skin cancers.
LOSS OF BIODIVERSITY
• Current rates of extinction are alarmingly high,
constituting a crisis in biodiversity.
• Biologists have identified three factors that play a role in
extinction:
• Habitat loss - this is the single most important cause.
• Species overexploitation - species that are hunted or harvested
by humans have historically been at risk of extinction.
• Introduced species - the introduction of exotic species results in
extinction because these species have no native predators to
keep their populations in check.
rain forest
cover
Africa
Before human
1950
colonization
1985
2000
REDUCING POLLUTION
• The pattern of global change that is
overtaking our world is very disturbing.
• We must quickly find ways to reduce the
harmful impact of human activities on the
biosphere.
• It is important that these areas be
addressed:
•
•
•
•
Reducing pollution
Preserving nonreplaceable resources
Curbing population growth
Finding other sources of energy
REDUCING POLLUTION
• Two approaches have been devised to curb
pollution in the U.S.
• Antipollution laws set standards for what can be
released into the environment.
• Pollution taxes are assessed in order to balance the
conflicting demands of environmental safety and
economic growth.
PRESERVING NONREPLACEABLE
RESOURCES
• In the U.S., there are three sorts of
nonreplaceable resources that are being
reduced at alarming rates:
• Topsoil - over one quarter of topsoil has been lost since
1950.
• Groundwater - groundwater in aquifers is being depleted or
polluted.
• Biodiversity - loss of species creates instability in ecosystems
and reduces productivity.
THE TRAGEDY OF THE COMMONS
"Freedom in a Commons
Brings Ruin to All"
The essence of Hardin's original essay:
Picture a pasture open to all. It is expected that each
herdsman will try to keep as many cattle as possible
on [this] commons....What is the utility...of adding
one more animal?...Since the herdsman receives all
the proceeds from the sale of the additional animal,
the positive utility [to the herdsman] is nearly +1....
Since, however, the effects of overgrazing are shared
by all the herdsmen, the negative utility for any
particular decision-making herdsman is only a
fraction of -1. Adding together the...partial utilities,
the rational herdsman concludes that the only
sensible course for him to pursue is to add another
animal to [the] herd. And another; and another....
Therein is the tragedy. Each man is locked into
a system that [causes] him to increase his herd
without limit—in a world that is limited....Freedom
in a commons brings ruin to all.
—G. Hardin, "The Tragedy of the Commons,"
Science 162, 1243 (1968), p. 1244
CURBING POPULATION
GROWTH
• Such growth cannot
continue because our world
cannot support it.
7
6
Billions of people
• In the last 300 years, the
human birthrate has
stabilized, but the death
rate has fallen.
• The world population
reached 7 billion people
in 2010, and will double in
about 58 years.
5
Significant advances
in medicine through
science and
technology
4
Industrial
revolution
3
2
Bubonic plague
"Black Death"
1
4000
B.C.
3000 B.C.2000 B.C. 1000 B.C. 0
Year
1000
2000 2004
CURBING POPULATION
GROWTH
• The rate at which a population can be expected to
grow in the future can be assessed graphically by
means of a population pyramid.
Age
85+
80–84
75–79
70–74
65–69
60–64
55–59
50–54
45–49
40–44
35–39
30–34
25–29
20–24
15–19
10–14
5–9
0–4
Kenya 2005
United States 1964
United States 2005
Male
Female
“Baby boomers”
Depression
3.0 2.5 2.0 1.5 1.0 0.5
0.5 1.0 1.5 2.0 2.5 3.0
12 10
8
6
4
2
0
2
4
6
8 10 12
Population (in millions)
12 10
8
6
4
2
0
2
4
6
8 10 12
CURBING POPULATION
GROWTH
• We in the developed countries need to pay more
attention to lessening the impact of our resource
consumption.
• An ecological footprint is the amount of
productive land required to support an individual
at the standard of living of a particular population
through the course of his or her life.
• The ecological footprint of an individual in the
U.S. is 10 times greater than that of someone in
India.
• http://www.myfootprint.org/
PRESERVING ENDANGERED
SPECIES
• Once you understand why a particular species is
endangered, it becomes possible to think of
designing a recovery plan, including:
•
•
•
•
•
Habitat restoration
Captive propagation
Sustaining genetic diversity
Preserving keystone species
Conservation of ecosystems
PRESERVING ENDANGERED
SPECIES
• Executing these plans can be expensive.
• Preserving ecosystems and monitoring species
before they are threatened is the most effective
means of protecting the environment and
preventing extinctions.
PRESERVING ENDANGERED
SPECIES
• Habitat restoration
• No restoration is truly pristine.
• Removing introduced species can restore a habitat.
• Cleanup, such as pollution removal, and rehabilitation can
successfully restore habitat.
• Captive propagation
• Since DDT was banned, researchers were able to use reestablished peregrine falcon populations that had
disappeared.
PRESERVING ENDANGERED
SPECIES
• Sustaining genetic diversity
• In black rhinos, the lack of genetic variability
poses the greatest challenge to the species.
PRESERVING ENDANGERED
SPECIES
• Preserving keystone
species
• Bats known as “flying foxes”
are often the only pollinators
of certain plant species, but
they are hunted by humans.
• Some populations have been
helped by legal protection,
habitat restoration, and
captive breeding programs.
• Conservation of ecosystems
• Often, the best way to preserve biodiversity is to
focus on preserving intact ecosystems, rather than
focusing on particular species.
FINDING CLEANER SOURCES OF
ENERGY
• The pollution generated by burning coal and oil,
the increasing scarcity of oil, and the potential
contributions of CO2 to global warming, all make it
desirable to find alternative energy sources.
• There are many possible candidates including
• Nuclear power
• Solar power
• Wind power
• Biomass—using ethanol produced from plants
ALTERNATIVE ENERGY SOURCES
INDIVIDUALS CAN MAKE THE
DIFFERENCE
• There are environmental success stories, where one or
a few individuals make a difference in solving
environmental problems.
• For starters, many U.S. families recycle.
• Other examples include cleaning up the Nashua
River (in New England) and Lake Washington (in
Seattle).