Population%20Ecology

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Population Ecology

• How do populations grow?

Growth birth rates gt death rates Decline
birth rates lt death rates Zero Growth birth
rates death rates
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Population Growth Models

• Exponential Growth
• Logistic Growth

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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,..
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Exponential Growth Model

• Does Exponential Growth occur in the real world?

Yes No . Can only occur over short-time
period..something always regulates growth
(Finite resources!)
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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

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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
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Logistic Growth Graph
initial carrying capacity
new carrying capacity
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Overshooting Capacity

• Population may temporarily increase above
  carrying capacity
• Overshoot is usually followed by a crash
  dramatic increase in deaths

Reindeer on St. Matthews Island
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Limiting Factors

• Density-Dependent Factors food, space, water,
  mates

• directly related to population density

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Density-dependent Effects
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Limiting Factors

• Density-Independent Factors fire, floods, wind,
  urbanization

• unrelated to population density

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Resource Consumption

• United States has 4.6 of the worlds population
• Americans have a disproportionately large effect
  on the worlds 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

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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

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Community Ecology
Community grouping of all species living
interacting in the same area, includes
populations of different species
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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
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Richness Evenness Diversity
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Properties of Communities (cont)
4) Prevalent vegetation form
- vertical profile (trees, shrubs, grasses)
- determine other organisms that are present
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Properties of Communities (cont)
5) Trophic Structure (feeding structure)
- who eats whom?
- determine energy flow in community
- determine community structure
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Energy Flow in Communities
food chain sequence of organisms linked by
energy nutrient flow
trophic level feeding level/position of organism
in food chain
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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
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Trophic Levels
Decomposers (detritus feeder) consume and
convert dead material for use by producers
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Food Webs
food web interconnected food chains all
trophic interactions in community
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Bioaccumulation Biomagnification
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Properties of Communities (cont)
6) Stability
- recovery from disturbance (e.g., fire)
- depends on type of community type of
disturbance
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What Happens in a Community?
1) Competition individuals contest over a
resource (food, space, water, mates) major
factor determining structure

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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

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What Happens in a Community?
Types of Competition
B) Intraspecific competition within the same
species, e.g., 2 male bobcats compete for space

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Principle of Competitive Exclusion (Gauses
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

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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

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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
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Predation Community Diversity

• Predation maintains diversity

• Paines experiments with sea stars (a predator)

• keystone predator predator which reduces
  density of most competitive species in community
  leads to gt diversity

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What Happens in a Community? (cont.)
3) Ecological Succession temporal sequence of
one community replacing another predictable

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Major Ecosystem Processes

1. Energy Flow energy moves through system

2) Nutrient Cycling chemical elements recycled
in system
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Energy Flow

• Solar energy primary energy source

Of incoming solar radiation 66 absorbed
34 reflected (albedo)
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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)
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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)
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Pyramid of Energy Flow

• Primary producers trapped about 1.2 of the solar
  energy that entered the ecosystem
• 616 passed on to next level

decomposers detritivores 5,080
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top carnivores
carnivores
383
herbivores
3,368
20,810 kilocalories/square meter/year
producers
Figure 30.8a Page 544
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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)

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Hydrologic Cycle
atmosphere
precipitation onto land 111,000
wind-driven water vapor 40,000
evaporation from land plants (evapotranspiration)
71,000
evaporation from ocean 425,000
precipitation into ocean 385,000
surface and groundwater flow 40,000
land
ocean
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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

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Hubbard Brook Experiment
losses from disturbed watershed
time of deforestation
losses from undisturbed watershed
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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

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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

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Carbon Cycle Marine
diffusion between atmosphere and ocean
combustion of fossil fuels
bicarbonate and carbonate in ocean water
aerobic respiration
photosynthesis
marine food webs
death, sedimentation
incorporation into sediments
uplifting
sedimentation
marine sediments
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Carbon Cycle Land
atmosphere
combustion of fossil fuels
volcanic action
aerobic respiration
combustion of wood
photosynthesis
terrestrial rocks
deforestation
weathering
land food webs
soil water
peat, fossil fuels
death, burial, compaction over geologic time
leaching, runoff
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Carbon in the Oceans

• Most carbon in the ocean is dissolved carbonate
  and bicarbonate
• Ocean currents carry dissolved carbon

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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

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Greenhouse Effect

• Greenhouse gases impede the escape of heat from
  Earths surface

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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

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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

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Nitrogen Cycle

• Nitrogen is used in amino acids and nucleic acids
• Main reservoir is nitrogen gas in the atmosphere

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Nitrogen Cycle
gaseous nitrogen in atmosphere
nitrogen fixation
food webs on land
fertilizers
uptake by autotrophs
excretion, death, decomposition
uptake by autotrophs
loss by denitrification
ammonia, ammonium
wastes, remains
nitrate
ammonification
nitrification
loss by leaching
nitrification
loss by leaching
nitrite
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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

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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

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Phosphorus Cycle

• Phosphorus is part of phospholipids and all
  nucleotides
• It is the most prevalent limiting factor in
  ecosystems
• Main reservoir is Earths crust no gaseous phase

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Phosphorus Cycle
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Human Effects

• In tropical countries, clearing lands for
  agriculture may deplete phosphorus-poor soils
• In developed countries, phosphorus runoff is
  causing eutrophication of waterways

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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

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Biosphere

• Oceans
• cover ¾ of Earth
• Temperature rainfall patterns (climate)

• Huge oxygen sources -- algae
• estuary fresh water meets salt water life-rich
  area

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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