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Population Ecology
• How do populations grow?
Growth = birth rates > death rates
Decline = birth rates < death rates
Zero Growth = birth rates = death rates
Population Growth Models
• Exponential Growth
• Logistic Growth
Exponential Growth Model
• J-shaped curve
• If conditions perfect, then population
grows by constant factor over time =
unchecked growth
Ex:
You count 2 deer in 1995
1996 = 4 deer
1997 = 8 deer
1998 = 16 deer,……..
dN
 rN
dt
dN
 N
 rN 1  
dt
 K
Exponential Growth Model
• Does Exponential Growth occur in the
real world?
Yes & No …. Can only occur over shorttime period…..something always
regulates growth (Finite resources!)
Logistic Growth Model
• S-shaped curve
• Population grows exponentially for short
time & then growth is checked by a
limiting factor
• carrying capacity (K): # of individuals
that the environment can maintain
dN
 rN
dt
dN
 N
 rN 1  
dt
 K
Logistic Growth Model
• Does Logistic Growth occur in the real
world?
Yes & No …. Population growth is limited
& populations do grow to near a K …
but population dynamics do not end at K
Logistic Growth Graph
initial carrying
capacity
new carrying
capacity
Overshooting Capacity
• Population may
temporarily increase
above carrying
capacity
• Overshoot is usually
followed by a crash;
dramatic increase in
deaths
Reindeer on St. Matthew’s Island
Limiting Factors
• Density-Dependent Factors: food,
space, water, mates
• directly related to population density
Density-dependent Effects
Limiting Factors
• Density-Independent Factors: fire,
floods, wind, urbanization
• unrelated to population density
Resource Consumption
• United States has 4.6% of
the world’s population
• Americans have a
disproportionately large
effect on the world’s
resources (30% of
consumption)
• Per capita, Americans
consume more resources
and create more pollution
than citizens of less
developed nations
– 1 American = 20-40
persons from less
developed nation
Human Population Problems
• Over 6 billion people alive
• About 2 billion live in poverty
• Most resources are consumed by the
relatively few people in developed
countries
Community Ecology
Community: grouping of all species living &
interacting in the same area, includes
populations of different species
Properties of Communities
1) Species Richness = # species in a comm.
2) Species Evenness = relative abundance of
different species
3) Species Diversity = richness & evenness
e.g., Four species (A,B,C,D) in 2 different
communities
Comm 1 – 25A 25B 25C 25D
Comm 2 – 97A 1B 1C 1D
Richness
Evenness
Diversity
Properties of Communities (cont)
4) Prevalent vegetation form
- vertical profile (trees, shrubs, grasses)
- determine other organisms that are
present
Properties of Communities (cont)
5) Trophic Structure (feeding structure)
- who eats whom?
- determine energy flow in community
- determine community structure
Energy Flow in Communities
food chain: sequence of organisms linked
by energy & nutrient flow
trophic level: feeding level/position of
organism in food chain
Trophic Levels
Producer: (autotrophs) anchor of chain;
produce all organic matter for other
organisms
Heterotrophs (consumers)
Primary consumer: directly consume
producers = herbivores
Secondary consumer: consume herbivores
Tertiary & Quaternary consumers: consume
secondary & tertiary consumers,
respectively
Trophic Levels
Decomposers: (detritus feeder) consume
and convert dead material for use by
producers
Food Webs
food web: interconnected food chains; all
trophic interactions in community
Bioaccumulation = Biomagnification
Properties of Communities (cont)
6) Stability
- recovery from disturbance (e.g., fire)
- depends on type of community & type of
disturbance
What Happens in a
Community?
1) Competition: individuals contest over a
resource (food, space, water, mates…) –
major factor determining structure
What Happens in a
Community?
Types of Competition
A) Interspecific: competition between
different species, e.g., blue jay & chickadee
compete for sunflower seed at feeder
What Happens in a
Community?
Types of Competition
B) Intraspecific:
competition within
the same species,
e.g., 2 male bobcats
compete for space
Principle of Competitive
Exclusion (Gause’s experiments)
• Two species
which compete
for same
resource cannot
coexist in same
place at same
time
• Implications =
different
locations or
different times
• Relates directly
to niche concept
Niche Concept
Niche: functional role (“occupation”) &
position (spatial & temporal) of a species in
its community
• Principle of Competitive Exclusion = 2
species cannot occupy the same niche
What Happens in a
Community? (cont.)
2) Predation: one species consumes another
species
Predator: consumer of the other species
Prey: the food species or the species to be
consumed
Predation & Community
Diversity
• Predation
maintains
diversity
• Paine’s
experiments
with sea stars
(a predator)
• keystone predator: predator which reduces
density of most competitive species in
community – leads to > diversity
What Happens in a
Community? (cont.)
3) Ecological Succession: temporal sequence
of one community replacing another;
predictable
Major Ecosystem Processes
1) Energy Flow = energy moves through
system
2) Nutrient Cycling = chemical elements
recycled in system
Energy Flow
• Solar energy – primary energy source
Of incoming solar radiation:
66% absorbed
34% reflected (albedo)
Solar Energy
• Of solar radiation absorbed:
- ~22%
water cycle
- nearly all
transform to heat &
radiates
emissivity: relative ability of Earth to
release energy (e.g., radiate heat into
space; link to global warming)
Solar Energy
• Tiny amount of solar energy into
photosynthesis (~1%)
photosynthesis (PNS): use solar energy to
convert CO2 & H2O into sugar; by-product
= O2
primary production: all organic matter
resulting from PNS; raw material for other
organisms (gross production vs. net
production)
Pyramid of Energy Flow
• Primary producers trapped about 1.2% of the
solar energy that entered the ecosystem
• 6–16% passed on to next level
21
top carnivores
decomposers + detritivores = 5,080
carnivores
herbivores
383
3,368
producers
20,810 kilocalories/square meter/year
Figure 30.8a
Page 544
Nutrient Cycles
What does the Law of Conservation of
Matter state?
• circular flow of chemicals = recycling
• Inputs & relationship to energy flow?
• Water, Carbon (C), Nitrogen (N),
Phosphorus (P), Sulfur (S)
Hydrologic Cycle
atmosphere
wind-driven water vapor
40,000
evaporation precipitation
from ocean into ocean
425,000
385,000
precipitation
onto land
111,000
evaporation from land
plants (evapotranspiration)
71,000
surface and
groundwater
flow 40,000
ocean
land
Hubbard Brook Experiment
• A watershed was experimentally stripped of
vegetation
• All surface water draining from watershed
was measured
• Removal of vegetation caused a six-fold
increase in the calcium content of the runoff
water
Hubbard Brook Experiment
losses from
disturbed watershed
time of
deforestation
losses from
undisturbed watershed
Global Water Crisis
• Limited amount of fresh water
• Desalinization is expensive and requires large
amounts of energy
• Aquifers are being depleted
• Groundwater is contaminated
• Sewage, agricultural runoff, and industrial
chemicals pollute rivers
Carbon Cycle
• Carbon moves through the atmosphere and
food webs on its way to and from the ocean,
sediments, and rocks
• Sediments and rocks are the
main reservoir
diffusion between
atmosphere and ocean
bicarbonate and
carbonate in
ocean water
photosynthesis
combustion of fossil fuels
aerobic
respiration
marine food
webs
death,
incorporation sedimentation
into sediments
uplifting
sedimentation
marine sediments
Carbon Cycle: Marine
atmosphere
combustion of
fossil fuels
volcanic action
terrestrial
rocks
weathering
photosynthesis
aerobic combustion
respiration of wood
deforestation
land food
webs
soil water
leaching,
runoff
death, burial,
compaction over
geologic time
Carbon Cycle: Land
peat,
fossil
fuels
Carbon in the Oceans
• Most carbon in the ocean is dissolved
carbonate and bicarbonate
• Ocean currents carry dissolved carbon
Carbon in Atmosphere
• Atmospheric carbon is mainly
carbon dioxide
• Carbon dioxide is added to atmosphere
– Aerobic respiration, volcanic action, burning
fossil fuels
• Removed by photosynthesis
Greenhouse Effect
• Greenhouse gases impede the escape
of heat from Earth’s surface
Carbon Dioxide Increase
• Carbon dioxide levels fluctuate seasonally
• The average level is steadily increasing
• Burning of fossil fuels and deforestation are
contributing to the increase
Other Greenhouse Gases
• CFCs: synthetic gases used in plastics and
in refrigeration
• Methane: released by natural gas
production, livestock
• Nitrous oxide: released by bacteria,
fertilizers, and animal wastes
Nitrogen Cycle
• Nitrogen is used in amino acids and nucleic
acids
• Main reservoir is nitrogen gas in the
atmosphere
Nitrogen Cycle
gaseous nitrogen
in atmosphere
nitrogen
fixation
food webs on land
fertilizers
uptake by
autotrophs
ammonia, ammonium
loss by
leaching
excretion, death,
decomposition
uptake by
autotrophs
wastes, remains
nitrate
ammonification
nitrification
nitrification
nitrite
loss by
denitrification
loss by
leaching
Nitrogen Fixation
• Plants cannot use nitrogen gas
• Nitrogen-fixing bacteria convert
nitrogen gas into ammonia (NH3)
• Ammonia and ammonium can be
taken up by plants
Human Effects
• Humans increase rate of nitrogen loss by
clearing forests and grasslands
• Humans increase nitrogen in water and air
by using fertilizers and by burning fossil
fuels
• Too much or too little nitrogen can
compromise plant health
Phosphorus Cycle
• Phosphorus is part of phospholipids and
all nucleotides
• It is the most prevalent limiting factor in
ecosystems
• Main reservoir is Earth’s crust; no
gaseous phase
Phosphorus Cycle
mining
FERTILIZER
GUANO
excretion
agriculture
uptake
by
autotrophs
MARINE
FOOD
WEBS
weathering
DISSOLVED
IN OCEAN
WATER
uptake
by
autotrophs
weathering
DISSOLVED IN
SOIL WATER,
LAKES, RIVERS
death,
decomposition
sedimentation
LAND
FOOD
WEBS
death,
decomposition
settling
out
leaching, runoff
uplifting
TERRESTRIAL ROCKS
MARINE SEDIMENTS
over geologic time
Human Effects
• In tropical countries, clearing lands for
agriculture may deplete phosphorus-poor
soils
• In developed countries, phosphorus runoff
is causing eutrophication of waterways
Ecosystem Management
• Optimal level of resource management
• Entire systems vs. pieces
• Goal = minimize human impacts on
ecosystems so as to insure their integrity
& health & therefore our health
• Manage at larger scale, e.g., Great Lakes
Region Ecosystem NOT Michigan only
Biosphere
• Oceans
- cover ¾ of Earth
- Temperature & rainfall patterns
(climate)
- Huge oxygen sources -- algae
- estuary: fresh water meets salt water;
life-rich area
Biomes
Terrestrial community of common climate
& unique species assemblages
1) Tundra – permafrost
2) Boreal Forest -- conifers
3) Deciduous Forest – broad-leaves
4) Tropical Rain Forest – 70% of life
5) Tropical Savannah -- fire
6) Grassland -- treeless
7) Desert – low rainfall