Population Dynamics Chapter 6 Populations

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Population Dynamics Chapter 6 Populations

• AP Environmental Science
• GNHS

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4 types of Population Fluxes

• Population flux changes in pops over
• time.
• Advantage Allows vegetation and organism
  reproduction time to recover
• Types 1) stable 3) irregular
• 2) irruptive 4) cyclic

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Stable Pop Flux

• Pop fluctuates around carrying capacity
• either slightly above or below
• Typical of species in undisturbed tropical
  forestslittle variation in average temp or
  rainfall.

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Stable Pop Flux Example
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Irruptive Pop Flux

• Pop is normally stable but occasionally explodes
  (erupts) to peak and then crashes to stable lower
  level.
• Ex Racoon, house mouse

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Irruptive Pop Flux
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Irregular Pop Flux

• Chaotic behavior in population size
• No recurring pattern
• May be due to chaos in ecosystem

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Cyclic Pop Flux

• Fluctuations in size that occur over a regular
  time period.
• Includes predator-prey
• (lynx and hare)

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Population Dynamics Outline

• Characteristics of a Population
• Population Dynamics and Carrying Capacity
• Reproductive Strategies
• Conservation Biology
• Human Impacts
• Working with Nature

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Characteristics of a Population

• Population - individuals inhabiting the same area
  at the same time and can interbreed.
• Population Dynamics Population change due to
• Population Size - number of individuals
• Population Density - population size in a certain
  space at a given time
• Population Dispersion - spatial pattern in
  habitat
• Age Structure - proportion of individuals in each
  age group in population

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Population Size

• Natality
• Number of individuals added through reproduction
• Crude Birth Rate - Births per 1000
• Total Fertility Rate Average number of children
  born alive per woman in her lifetime
• Mortality
• Number of individuals removed through death
• Crude Death Rate Deaths per 1000

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Population Growth

• Populations show two types of growth
• Exponential
• J-shaped curve
• Growth is independent of population density
• Logistic
• S-shaped curve
• Growth is not independent of population density

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Population Growth Mathway

• Benefits
• Prediction of future generations
• Creation of population trends
• Assists in determining type of growth
• exponential or logistics

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Population Growth - Mathway

• Basic variables of population growth
• Npopulation number
• r rate of growth
• t Time in days, months, years, generations
• d delta or change in (ex. dN change in
• 
  population)
• K carrying capacity

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Population Growth

• Population growth depends upon
• birth rates
• death rates
• immigration rates (into area)
• emigration rates (exit area)
• Pop Pop0 (b i) - (d e)
• Zero Population Growth
• (b i) (d e)

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How is r determined?

• r births deaths
• Total Population (rN)
• Does not include immigration or emigration!
• Example 20,000 births 15,000 deaths
• 500,000 organisms
• Growth Rate (r) .01 (x 100) 1.0

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Exponential Growth Model (J)
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Growth Rate ExampleWhat type of growth is this?
Time N Rate (r) r x N
T1 2 10 20
T2 20 10 200
T3 200 10 2000
T5 2000 10 20,000
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J-curve Exponential Growth
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Population Growth Rate Practice
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Exponential Growth
Time N r r x N
0 10 1.5 15
1 15 1.5 23
2 23 1.5 35
3 35 1.5 53
4 53 1.5 80
5 80 1.5 120
6 120 1.5 180
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Exponential Growth

• Rules If r ? 0, then dN is negative and
• population is declining.
• If r gt 0, then dN is positive and
• population increases over
  time
• If r 0, then dN is 0 ? no change in
• population

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Logistics Growth Model (S)
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Logistics Growth

• Solve for the right side of the equation.
• You must know your carrying capacity (K)
• Example
• Look at the N/K part.
• If K100 wolves, the maximum pop
• If N 100 wolves, then N/K 100 1
• 100

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Logistics (cont)

• If 1-N/K 1-1 0 and rN (0) 0 and dN/dt 0.
  
• This means no change in population because the
  population carrying capacity.
• 6. What if N50 and K100, please calculate the
  outcome using the formula.

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Logistics (cont)

1. Then N/K 50/100 ½.
2. 1-N/K 1-1/2 ½
3. Rate of increase is ½ rN or half of the
   reproductive rate.
4. Try it with N120 and K100, what is the
   reproductive rate going to be?

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Logistics Growth from Model
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Population Density

• Population Density (or ecological population
  density) is the amount of individuals in a
  population per unit habitat area
• Some species exist in high densities - Mice
• Some species exist in low densities - Mountain
  lions
• Density depends upon
• social/population structure
• mating relationships
• time of year

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Population Doubling

• Rule of 70 used for determining how long it
  takes for a population to double.
• If a population grows at a rate of 7, how long
  would it take to double?
• 70, 70 / 14..7 doubling .7 10
  
• r ( form) rr (decimal form) ,.07
  yrs.
• THIS IS THE DOUBLING TIME OF A POPULATION!!!is.
  It states that to find the doubling time of a
  quantity growing at a given annual percentage
  rate, divide the percentage number into 70 to r

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Population Dispersion
Population dispersion is the spatial pattern of
distribution There are three main
classifications Clumped individuals are lumped
into groups ex. Flocking birds or herbivore
herds due to resources that are clumped or
social interactions most common
http//www.johndarm.clara.net/galleryphots/
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Population Dispersion
http//www.calflora.net/bloomingplants/creosotebus
h2.html
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Age Structure

• The age structure of a population is usually
  shown graphically
• The population is usually divided up into
  prereproductives, reproductives and
  postreproductives
• The age structure of a population dictates
  whether is will grow, shrink, or stay the same
  size

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Age Structure Diagrams
Positive Growth Zero Growth
Negative Growth (ZPG) Pyramid
Shape Vertical Edges Inverted
Pyramid
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Population Dynamics Outline

• Characteristics of a Population
• Population Dynamics and Carrying Capacity
• Reproductive Strategies
• Conservation Biology
• Human Impacts
• Working with Nature

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• Biotic Potential
• factors allow a population to increase under
  ideal conditions, potentially leading to
  exponential growth
• Environmental Resistance
• affect the young more than the elderly in a
  population, thereby affecting recruitment
  (survival to reproductive age)

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Biotic Potential

• Ability of populations of a given species to
  increase in size
• Abiotic Contributing Factors
• Favorable light
• Favorable Temperatures
• Favorable chemical environment - nutrients
• Biotic Contributing Factors
• Reproductive rate
• Generalized niche
• Ability to migrate or disperse
• Adequate defense mechanisms
• Ability to cope with adverse conditions

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Environmental Resistance

• Ability of populations of a given species to
  increase in size
• Abiotic Contributing Factors
• Unfavorable light
• Unfavorable Temperatures
• Unfavorable chemical environment - nutrients
• Biotic Contributing Factors
• Low reproductive rate
• Specialized niche
• Inability to migrate or disperse
• Inadequate defense mechanisms
• Inability to cope with adverse conditions

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Exponential Growth

• As early as Darwin, scientists have realized that
  populations have the ability to grow
  exponentially
• All populations have this ability, although not
  all populations realized this type of growth
• Darwin pondered the question of exponential
  growth. He knew that all species had the
  potential to grow exponentially
• He used elephants as an example because elephants
  are one of the slowest breeders on the planet

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Exponential Growth
One female will produce 6 young over her 100 year
life span. In a population, this amounts to a
growth rate of 2 Darwin wondered, how many
elephants could result from one male and one
female in 750 years? 19,000,000 elephants!!!
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Exponential Growth Graph
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Population Dynamics and Carrying Capacity

• Basic Concept Over a long period of time,
  populations of species in an ecosystem are
  usually in a state of equilibrium (balance
  between births and deaths)
• There is a dynamic balance between biotic
  potential and environmental resistance

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Carrying Capacity (K)

• Exponential curve is not realistic due to
  carrying capacity of area
• Carrying capacity is maximum number of
  individuals a habitat can support over a given
  period of time due to environmental resistance
  (sustainability)

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Logistic Growth

• Because of Environmental Resistance, population
  growth decreases as density reaches carrying
  capacity
• Graph of individuals vs. time yields a sigmoid or
  S-curved growth curve
• Reproductive time lag causes population overshoot
• Population will not be steady curve due to
  resources (prey) and predators

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Population Dynamics Outline

• Characteristics of a Population
• Population Dynamics and Carrying Capacity
• Reproductive Strategies
• Conservation Biology
• Human Impacts
• Working with Nature

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Reproductive Strategies

• Goal of every species is to produce as many
  offspring as possible
• Each individual has a limited amount of energy to
  put towards life and reproduction
• This leads to a trade-off of long life or high
  reproductive rate
• Natural Selection has lead to two strategies for
  species r - strategists and K - strategists

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r - Strategists

• Spend most of their time in exponential growth
• Maximize reproductive life
• Minimum life

K
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R Strategists

• Many small offspring
• Little or no parental care and protection of
  offspring
• Early reproductive age
• Most offspring die before reaching reproductive
  age
• Small adults
• Adapted to unstable climate and environmental
  conditions
• High population growth rate (r)
• Population size fluctuates wildly above and below
  carrying capacity (K)
• Generalist niche
• Low ability to compete
• Early successional species

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K - Strategists

• Maintain population at carrying capacity (K)
• Maximize lifespan

K
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K- Strategist

• Fewer, larger offspring
• High parental care and protection of offspring
• Later reproductive age
• Most offspring survive to reproductive age
• Larger adults
• Adapted to stable climate and environmental
  conditions
• Lower population growth rate (r)
• Population size fairly stable and usually close
  to carrying capacity (K)
• Specialist niche
• High ability to compete
• Late successional species

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Survivorship Curves

• Late Loss K-strategists that produce few young
  and care for them until they reach reproductive
  age thus reducing juvenile mortality
• Constant Loss typically intermediate
  reproductive strategies with fairly constant
  mortality throughout all age classes
• Early Loss r-strategists with many offspring,
  high infant mortality and high survivorship once
  a certain size and age

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Population Dynamics Outline

• Characteristics of a Population
• Population Dynamics and Carrying Capacity
• Reproductive Strategies
• Conservation Biology
• Human Impacts
• Working with Nature

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Conservation Biology

• Careful and sensible use of natural resources by
  humans
• Originated in 1970s to deal with problems in
  maintaining earth's biodiversity
• Dedicated to protecting ecosystems and to finding
  practical ways to prevent premature extinctions
  of species

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Conservation Biology

• Three Principles
• Biodiversity and ecological integrity are useful
  and necessary to all life on earth and should not
  be reduced by human actions
• Humans should not cause or hasten the premature
  extinction of populations and species or disrupt
  vital ecological processes
• Best way to preserve earths biodiversity and
  ecological integrity is to protect intact
  ecosystems that provide sufficient habitat

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Habitat Fragmentation

• Process by which human activity breaks natural
  ecosystems into smaller and smaller pieces of
  land
• Greatest impact on populations of species that
  require large areas of continuous habitat
• Also called habitat islands

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1949 1964 Habitat fragmentation in northern
Alberta 1982 1991
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Population Dynamics Outline

• Characteristics of a Population
• Population Dynamics and Carrying Capacity
• Reproductive Strategies
• Conservation Biology
• Human Impacts
• Working with Nature

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Human Impacts

• Fragmentation and degrading habitat
• Simplifying natural ecosystems
• Strengthening some populations of pest species
  and disease-causing bacteria by overuse of
  pesticides
• Elimination of some predators

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Human Impacts

• Deliberately or accidentally introducing new
  species
• Overharvesting potentially renewable resources
• Interfering with the normal chemical cycling and
  energy flows in ecosystem

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Population Dynamics Outline

• Characteristics of a Population
• Population Dynamics and Carrying Capacity
• Reproductive Strategies
• Conservation Biology
• Human Impacts
• Working with Nature

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Working with Nature

• Learn six features of living systems
• Interdependence
• Diversity
• Resilience
• Adaptability
• Unpredictability
• Limits

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Basic Ecological Lessons

1. Sunlight is primary source of energy
2. Nutrients are replenished and wastes are disposed
   of by recycling materials
3. Soil, water, air, plants and animals are renewed
   through natural processes
4. Energy is always required to produce or maintain
   an energy flow or to recycle chemicals

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Basic Ecological Lessons

1. Biodiversity takes many forms because it has
   evolved over billions of years under different
   conditions
2. Complex networks of and feedback loops exist
3. Population size and growth rate are controlled by
   interactions with other species and with abiotic
4. Organisms generally only use what they need

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Four Principles for Sustainable

1. We are part of, not apart from, the earths
   dynamic web of life.
2. Our lives, lifestyles, and economies are totally
   dependent on the sun and the earth.
3. We can never do merely one thing (first law of
   human ecology Garret Hardin).
4. Everything is connected to everything else we
   are all in it together.