Transcript Population Dynamics Notes

Population Dynamics
Population Dynamics Outline
• Characteristics of a Population
• Population Dynamics and Carrying Capacity
• Reproductive Strategies
• Human Impacts
Characteristics of a Population
• Population - individuals inhabiting the same area
at the same time
• 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
Population Size
• Natality
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Number of individuals added through reproduction
Crude Birth Rate - Births per 1000
CBR= (Births/Population)*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
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
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/
Population Dispersion
Uniform: Individuals are regularly
spaced in the environment - ex.
Creosote bush due to antagonism
between individuals, or do to regular
spacing of resources rare because
resources are rarely evenly spaced
Random: Individuals are randomly
dispersed in the environment ex.
Dandelions due to random
distribution of resources in the
environment, and neither positive nor
negative interaction between
individuals rare because these
conditions are rarely met
http://www.calflora.net/bloomingplants/creosotebush2.html
www.agry.purdue.edu/turf/ tips/2002/clover611.htm
Population Histogram
• A population histogram shows the age
structure of a population and 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
Population Histograms
Positive Growth
Pyramid Shape
Zero Growth
(ZPG)
Vertical Edges
Negative Growth
Inverted Pyramid
Population Dynamics Outline
• Characteristics of a Population
• Population Dynamics
• Carrying Capacity
• Reproductive Strategies
• Human Impacts
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:
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Reproductive rate
Generalized niche
Ability to migrate or disperse
Adequate defense mechanisms
Ability to cope with adverse conditions
Environmental Resistance
• Ability of populations of a given species to
decrease in size (limiting factors)
– Abiotic Contributing Factors:
• Unfavorable light
• Unfavorable Temperatures
• Unfavorable chemical environment - nutrients
– Biotic Contributing Factors:
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Low reproductive rate
Specialized niche
Inability to migrate or disperse
Inadequate defense mechanisms
Inability to cope with adverse conditions
• 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 survival to reproductive
age
Population Growth
• Population growth depends upon
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birth rates
death rates
immigration rates (into area)
emigration rates (exit area)
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
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
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!!!
Exponential Growth Graph
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
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)
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
Population Dynamics Outline
• Characteristics of a Population
• Population Dynamics and Carrying
Capacity
• Reproductive Strategies
• Human Impacts
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
r - Strategists
• Spend most of their
time in exponential
growth
• Maximize
reproductive life
• Minimum life span
K
R Strategists
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Many small offspring
Little or no parental care and protection of offspring
Early reproductive age
Most offspring die before reaching reproductive age
Small in size
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
K - Strategists
• Maintain
population at
carrying capacity
(K)
• Maximize
lifespan
K
K- Strategist
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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
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
Population Dynamics Outline
• Characteristics of a Population
• Population Dynamics and Carrying
Capacity
• Reproductive Strategies
• Human Impacts
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
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
1949
1964
Habitat
fragmentation
in northern
Alberta
1982
1991
Human Impacts
• Deliberately or accidentally
introducing new species
• Overharvesting potentially renewable
resources
• Interfering with the normal chemical
cycling and energy flows in ecosystem
Four Principles for
Sustainablity
1. We are part of, not apart from, the
earth’s 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.