Transcript Ecology Unit

Ecology
The
Biosphere
Population Ecology
Community Ecology
Ecosystems
Introduction to Ecology
and the Biosphere
Chapter 50
Abiotic Factors of the Biosphere

Climate
– Water/Rainfall
– Temperature

Rocks and Soil
– Particle size
– pH

–Light
–Wind
–Mineral composition
Periodic Disturbances
– Catastrophic events: fire, flood, earthquake, etc.
Global Climate Patterns

Determined by:
– input of solar energy
• Shape of earth—latitudinal variation
• 23.5° tilt of earth’s axis—seasonal variation
– earth’s movement in space
Global Air Circulation,
Precipitation, and
Winds
Local and Seasonal Effects on
Climate

Proximity to bodies of water
– Oceanic currents along continental coasts
– Large inland bodies of water—lakes

Topographic features
– Mountain ranges
Rain Shadows
Seasonal Turnover of Lakes/Ponds

Lake stratification and biannual mixing
– Temperature
– Density
water densest at 4°C,
it sinks below water that is
warmer or colder
Chapter 52
Population Ecology
Overview: Earth’s Fluctuating
Populations

To understand human population growth,
we must consider general principles of
population ecology
Population ecology = study of populations
relative to environment, including
environmental influences on density and
distribution, age structure, and population
size
 Population = group of individuals of a
single species living in the same general
area

Density and Dispersion
Density is the number of individuals per unit
area or volume
 Dispersion is the pattern of spacing among
individuals within the boundaries of the
population

– Environmental and social factors influence spacing
of individuals in a population
Clumped distribution may be
influenced by resource
availability (living in groups
increases the effectiveness of
hunting, spreads the work of
protecting and caring for
young)
Uniform distribution may be
influenced by social interactions
such as territoriality
Random distribution—the
position of each individual is
independent of other individuals
Demography
Study of theory and statistics behind
population growth and decline
 N = size of the population

Demographic Statistics
Birth rate = number of offspring produced
per time period
 Death rate = number of deaths per time
period
 Sex ratio = proportion of males and females
in a population
 Generation time = time needed for
individuals to reach reproductive maturity

Demographic Statistics

Age structure = statistic
that compares the relative
number of individuals in
the population from each
age group
Copyright © 2002 Pearson Education, Inc., publishing as
Benjamin Cummings


Immigration rate = rate at which individuals
relocate into a given population
Emigration rate = rate which individuals relocate
out of a give population
Demographic Statistics
These statistics together determine the size
and growth rate of a given population
 Population Growth = (Births +
immigration) - (deaths + emigration)
 If birth rates are greater
than death rates:




Fictional "Tribbles" from Star
Trek:
Defining characteristic of the
Tribbles is their extreme
reproductive rate. Over half
of a Tribbles metabolism is
devoted to reproduction,
allowing them to bear a litter
of young every twelve hours.
With an average litter of ten,
a single Tribble can therefore
create a population of
1,771,561 within three days,
and an amazing
304,481,639,541,400,000,000
,000,000,000,000,000,000,00
0,000,000,000,000,000,000,0
00 in thirty days!
Population Growth
Short generation time = faster
rate of population growth
Population Growth and Size

Biotic potential = maximum growth rate of
a population given unlimited resources,
unlimited space, and lack of competition or
predators
– Rate varies from species to species

Carrying capacity = maximum number of
individuals that a population can sustain in a
given environment without destroying the
habitat
Limiting Factors Control Population
Sizes

Density-dependent factors come into play
when population approaches and/or passes
the carrying capacity
– Food supplies, waste products, populationcrowding diseases

Density-independent factors have nothing
to do with the population size
– Floods, droughts, earthquakes, other natural
disasters and weather conditions
Population Growth


Exponential Growth =
population grows as if there
are no limitations as to how
large it can get (biotic
potential)
A population increases slowly at first (the "lag
phase") and then grows increasingly rapidly as time
passes (the "log phase"). When numbers are low, a
doubling does not produce much addition to the
population, but as numbers increase, each successive
doubling adds larger and larger increments.
Population Growth

Logistic Growth =
population growth
slows to
zero and population
size
tends to stabilize
because of
environmental
resistance
(limiting factors)
Exponential growth can be represented by the
following equation:
dN/dt = rN
where:

– dN/dt is the instantaneous rate of change in population
size
– r is the intrinsic rate of increase of the population
– N is population size at any given point in time


The S-shaped (sigmoid) curve that shows the
effect of environmental resistance upon population
growth can be represented by the following
equation, often referred to as the logistic equation:
dN/dt = rN (K-N) / K
where K is the carrying capacity (maximum value
of N for a given set of environmental conditions)
Point of
Maximum growth
(K/2)
Carrying Capacity
Population size (N)
2,000
dN
dt = 1.0N
1,500
Exponential
growth
K = 1,500
Logistic growth
1,000
dN
dt = 1.0N
1,500 – N
1,500
500
0
0
10
5
Number of generations
15
Life History Strategies

K-selected populations are of a roughly
constant size whose members have low
reproductive rates.
– Offspring require extensive postnatal care until
sufficiently matured (humans)

R-selected populations experience rapid
growth
– Offspring are numerous, mature rapidly, and
require little postnatal care (bacteria)
Predator-Prey Cycling


Many populations
undergo boom-andbust cycles
Boom-and-bust cycles
are influenced by
complex interactions
between biotic and
abiotic factors
Community Ecology
Chapter 53
Interactions Between Populations
of Different Species
Interspecific interactions—occur b/w
populations of different species
 Coevolution—a change in one species acts
as a selective force on another species

Interactions Between Populations
of Different Species

Predation (+/–)—consumption
of one organism by another
– Predator eats prey
– Parasitism (+/–)—specialized
predator (parasite) lives on/in its
host, not killed immediately
• Endoparasitism—live inside host
(tapeworms/viruses)
• Ectoparasitism—live on surface
of host (mosquitoes/aphids)
– Herbivory (+/–)—herbivores
consume plants
Plant Defenses Against Hebivores

Physical defenses
– thorns, hooks/spines on
leaves

Chemical defenses
– Make plant distasteful or
poisonous
• Morphine from opium
poppy
• Nicotine from tobacco
Animal Defenses Against Predators

Behavioral defenses
– Alarm cries
– Distraction displays

Cryptic coloration/shape
(camouflage)
– Blend in with environment
– Asposematic coloration
• Red/black; yellow/black

Mechanical/chemical defenses
– Quills, spines, and other similar structures
– Toxins—distasteful or poisonous
• Monarch butterfly stores toxin of milkweed as larvae
• Poisonous toads secrete toxin
Animal Defenses Against Predators

Mimicry—prey resembles species that cannot
be eaten
– Batesian mimicry: Imitate color patterns or
appearance of more dangerous organisms

Mimicry can be used to lure prey
– Snapping turtle wriggles tongue like a worm to
attract and capture small fish
Interspecific Competition (–/–)

Competition occurs when 2 or more
populations overlap in their niches
– Limiting resources
• Food
• Space
• Mates

Generally, one will out-compete the other
Competitive Exclusion Principle

Two species cannot coexist in a community if their
niches are identical
Competition in Nature


Two possible Outcomes
1. Weaker competitor becomes extinct
2. One or both species may evolve enough to
use a different set of resources
Competition cannot operate for long periods of
time
Resource Partitioning
Evolution Drives Reduced Niche Overlap
12
10
8
6
4
2
0
12
Number of individuals
Population 1
Population 2
10
8
6
4
2
0
2
4
6
8 10 12 14 16 18 20
2 4 6 8 10 12 14 16 18 20
Height of nesting site in apple trees
Character
Displacement
Joseph H. Connell Study
Symbiotic Relationships

Non-Beneficial
– Parasitism (+/–)—host harmed

Beneficial
– Commensalism (+/0)—one partner benefits
while not harming the other
• Cattle egrets—egrets eat ectoparasites/cattle are
groomed
– Mutualism (+/+)—both partners benefit
• Lichens-association b/w fungus and algae
• Nitrogen-fixing bacteria and legumes
Community Structure
Predators can moderate competition among its
prey species
 Keystone species can alter the whole community

Effects of a Keystone Predator:Sea Star (Pisaster)
20
15
With Pisaster
Without Pisaster
10
5
68
19
69
19
70
19
71
19
72
19
67
19
66
19
65
19
64
19
63
0
19
Number of Species
Present
25
Year
Community Structure
Introduction of a species (exotic species)
into a community can have drastic affects
on the existing community members
 Habitats that are more varied can support a
more diverse community

– provides more ecological niches
Nonequilibrium and
Disturbances in a Community

Storms, fire, floods, droughts, overgrazing,
or detrimental human activities:
– Remove organisms
– Alter resource availability
Create opportunities for new species that
have not previously occupied the habitat
 Humans are the biggest disturbance

– Logging, agriculture, overgrazing
Ecological Succession

Primary succession
– Begins in a virtually lifeless area where soil has not
formed
– Lichens and mosses colonize first
– Soil gradually forms and small plants and shrubs take
root

Secondary succession
– Occurs where an existing community has been cleared
by some disturbance that leaves soil in tact
– Earliest plants to recolonize are often those that grow
from wind-blown or animal-borne seeds
Ecological Succession
Competition among early species shape the
succession of an area
 Tolerance to abiotic conditions determines
early species

Ecosystems
Chapter 54
Trophic Relationships

Ecosystems divided into trophic levels
(feeding levels)
– Primary producers—autotrophs (mostly
photosynthetic)
– Primary consumers—herbivores
– Secondary consumers—carnivores that eat
herbivores
– Tertiary consumers—carnivores that eat other
carnivores
– Detrivores—consumers that eat dead or
decaying matter
Food Webs

Feeding
relationships
woven into
elaborate
interconnections
between species
Energy Flow in Ecosystems
Each level in a food web contains a
different quantity of stored chemical energy
 When consumers eats producers or 2
consumers eat 1 producers, some energy is
lost in the each transfer from one level to
the next

– Gross primary productivity= [total chemical
energy generated by producers]
– Net primary productivity= [total chemical
energy – respiration by plants]
Pyramid of Net
Productivity:
10% of energy at
each level converted
to new biomass
Pyramids of
Standing Crop
Biomass
Sharp
decrease in
biomass at
successively
higher levels
Small crop of 1
producers
support larger
crop of 1
consumers
Pyramid of Numbers:
In higher trophic levels, the
small amount of biomass
contained in a few organisms
Biogeochemical Cycles
Chemical elements available only in limited
amounts
 Movement of essential elements between
the biotic and abiotic environment

Carbon Cycle
 Nitrogen Cycle
 Phosphorus Cycle
 Water Cycle

*
Carbon Cycle
Human Impacts

Greenhouse Effect
– Increase of atmospheric CO2
• Combustion of fossil fuels
• Burning of wood from deforestation
– Increase in numbers of C3 plants in areas
previously inhabited by C4 plants
– Increase in global temperature
*
Nitrogen Cycle
Human Impacts

Agricultural effects
– Cultivation—turns up soil and increases rate of
decomposition of organic matter; Releases
more nitrogen
– Harvesting removes nitrogen from ecosystem
– Adding industrially synthesized fertilizers to
soil has resulted in doubling globe’s supply
• Excess nitrogen leeches into soil and into rivers,
streams, and lakes and ground water—
– high amounts are toxic to aquatic organisms and
humans
– Algal blooms in lakes speed up eutrophication
*
Phosphorus Cycle
Water Cycle
The human population is disrupting
chemical cycles throughout the biosphere

As the human population has grown, our
activities have disrupted the trophic structure,
energy flow, and chemical cycling of many
ecosystems
Nutrient Enrichment

In addition to transporting nutrients from
one location to another, humans have added
new materials, some of them toxins, to
ecosystems
Agriculture and Nitrogen
Cycling
Agriculture removes nutrients from ecosystems
that would ordinarily be cycled back into the soil
 Nitrogen is the main nutrient lost through
agriculture; thus, agriculture greatly impacts the
nitrogen cycle
 Industrially produced fertilizer is typically used
to replace lost nitrogen, but effects on an
ecosystem can be harmful

Contamination of Aquatic
Ecosystems




Critical load for a nutrient is the amount that plants can
absorb without damaging the ecosystem
When excess nutrients are added to an ecosystem, the
critical load is exceeded
Remaining nutrients can contaminate groundwater and
freshwater and marine ecosystems
Sewage runoff causes cultural eutrophication, excessive
algal growth that can greatly harm freshwater
ecosystems
Acid Precipitation


Combustion of
fossil fuels is the
main cause of acid
precipitation
North American
and European
ecosystems
downwind from
industrial regions
have been damaged
by rain and snow
containing nitric
and sulfuric acid
4.6
4.3
4.6
4.3
4.6
4.3
4.1
Europe
North America
4.6
5.0
5.3
5.4
5.3
5.3
5.2
5.2
5.5
5.2
5.5
5.6
5.4
5.2
5.3
5.3
5.5
6.0
5.9 5.5
5.3
5.2
5.3
5.4
5.4
5.3 5.0
5.05.1 4.9 5.4
5.1
6.3
5.7
5.6
4.9
5.4
5.3
5.0
5.2
5.4
5.1
5.5
5.2 4.8
5.3
4.5 4.6 4.7
5.4
5.2 5.15.0
4.8
4.7
5.2
4.5 4.6
4.8
4.3 4.5 4.5
5.2 4.9
5.5
4.5
5.6
4.5 4.5 4.6
4.9 4.7
4.7
4.3 4.4
4.5
4.6
5.1 4.7
4.6
4.5
4.7
5.4
4.5
4.1 4.4
5.3
5.3
4.8
4.4 4.4
4.6
4.3
4.6
4.6
4.6 4.5
4.4
4.5
4.7
4.5
4.5 4.5
4.7
4.7
4.6
4.8
4.6
5.4
4.6
4.8 4.6
4.5
5.0
4.5 4.5
4.7
4.8
4.9
4.5
4.6
4.5
Field pH
4.5 4.7
5.0
4.7
4.8 4.7 4.7
5.0
4.8 5.1 4.7
5.3
4.7
4.7
5.2–5.3
5.0
5.4
4.7 4.6
4.7
4.9
5.1–5.2
4.8
4.7
4.8
5.3
4.8
4.9
5.0–5.1
4.8
4.7
4.9–5.0
4.9
4.8
4.7
5.6
6.1
5.2
5.7
5.0 5.0
5.1
5.1
5.7
5.1
5.0
5.0
4.8
4.7
4.7
4.7
4.9


By the year 2000, acid precipitation affected the entire contiguous
United States
Environmental regulations and new technologies have allowed
many developed countries to reduce sulfur dioxide emissions
4.8–4.9
4.7–4.8
4.6–4.7
4.5–4.6
4.4–4.5
4.3–4.4
<4.3
Toxins in the Environment

Concentration of PCBs
Herring
gull eggs
124 ppm

Lake trout
4.83 ppm
Smelt
1.04 ppm
Zooplankton
0.123 ppm
Phytoplankton
0.025 ppm

In some cases, harmful
substances persist for long
periods in an ecosystem
One reason toxins are harmful
is that they become more
concentrated in successive
trophic levels
In biological magnification,
toxins concentrate at higher
trophic levels, where biomass
is lower
Atmospheric Carbon Dioxide

One pressing problem caused by human
activities is the rising level of atmospheric
carbon dioxide
Rising Atmospheric CO2

Due to the burning of fossil fuels and other
human activities, the concentration of
atmospheric CO2 has been steadily
increasing
The Greenhouse Effect and
Global Warming
The greenhouse effect caused by
atmospheric CO2 keeps Earth’s surface at a
habitable temperature
 Increased levels of atmospheric CO2 are
magnifying the greenhouse effect, which
could cause global warming and climatic
change



Life on Earth is protected
from damaging effects of
UV radiation by a
protective layer or ozone
molecules in the
atmosphere
Satellite studies suggest
that the ozone layer has
been gradually thinning
since 1975
Ozone layer thickness (Dobson units)
Depletion of Atmospheric Ozone
350
300
250
200
150
100
50
0
1955 1960 1965 1970 19751980 1985 19901995 2000 2005
Year (Average for the month of October)

Destruction of atmospheric ozone probably
results from chlorine-releasing pollutants
produced by human activity
Chlorine atoms
Chlorine from CFCs interacts with ozone
(O3), forming chlorine monoxide (CIO) and
oxygen (O2).
O2
Chlorine O3
CIO
O2
Sunlight causes
Cl2O2 to break down
into O2 and free
chlorine atoms. The
chlorine atoms can
begin the cycle
again.
Sunlight
CIO
Cl2O2
Two CIO molecules
react, forming chlorine
peroxide (Cl2O2).

Scientists first described an “ozone hole”
over Antarctica in 1985; it has increased in
size as ozone depletion has increased
October 1979
October 2000