Transcript Population Dynamics Miller 11th Edition Chapter 10

Population Ecology
Ch. 9
Population Ecology Outline
• 9-1: Population Dynamics and Carrying
Capacity
• 9-2: Reproductive Patterns and Survival
• 9-3: Effects of Genetic Variations n Pop. Size
• 9-4: Human Impacts and Working with
Nature
9-1: Population Dynamics and Carrying Capacity
• Population - individuals of the same species,
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 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 3 main
patterns of dispersion:
1. 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
2) Uniform: Individuals are regularly
spaced in the environment - ex.
Creosote bush due to antagonism
between individuals.
http://www.calflora.net/bloomingplants/creosotebush2.html
3) 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
www.agry.purdue.edu/turf/ tips/2002/clover611.htm
Age Structure
• The age structure of a population is usually shown
graphically.
• The population is usually divided up into
– Prereproductives (not mature enough to reproduce)
– reproductives (capable of reproduction)
– Postreproductives (too old to reproduce)
• The age structure of a population dictates whether
is will grow, shrink, or stay the same size.
Age Structure Diagrams
Positive Growth
Pyramid Shape
Zero Growth
(ZPG)
Vertical Edges
Negative Growth
Inverted Pyramid
Limits to Pop. Growth
Biotic Potential- Ability of populations of a given
species to increase in size
Abiotic Growth Factors (biotic potential)
• Favorable Light conditions
• Favorable Temperatures
• Favorable Chemical environment – optimal levels of nutrients
Biotic Growth Factors:
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High reproductive rate
Generalized niche
Ability to migrate or disperse
Adequate defense mechanisms against predators
Ability to cope with adverse conditions – migration, resistance to
diseases, adapt to evtl. changes, etc.
Biotic Potential continued…
• Intrinsic rate of increase (r) – rate at
which a pop. could grow if it had
UNLIMITED resources.
• Not realistic!
• No pop. can grow indefinitely due to factors
that will slow growth eventually.
Limits to Pop. Growth continued…
• Environmental Resistance- all the factors that can
limit the growth and size of pops.
Abiotic Decreasing Factors:
• Unfavorable light conditions – too little or too much
• Unfavorable Temperatures
• Unfavorable chemical environment - nutrients
Biotic Decreasing Factors:
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Low reproductive rate
Specialized niche
Inability to migrate or disperse
Too many competitiors
Inadequate defense mechanisms
Inability to cope with adverse conditions- not resistance to
disease or unable to adapt to envtl. changes
Environmental Resistance continued…
• There is a dynamic balance between
biotic potential and environmental
resistance.
• Carrying capacity (K) - maximum number
of individuals a habitat can support over a
given period of time due to environmental
resistance (sustainability)
Population Change 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)
Measuring Pop. Growth
• Population growth depends upon
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birth rates
death rates
immigration rates (into area)
emigration rates (exit area)
Pop. change = (b + i) - (d + e)
Population Growth Diagrams
• 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 (J curve)
Fixed rate of increase,
starting slowly and
growing rapidly
Exponential curve is not
realistic for long
periods of time, due to
carrying capacity of
area.
Logistic Growth
(S curve)
• Because of environmental
resistance, population
growth decreases as
density reaches carrying
capacity
• Graph of individuals vs.
time yields a sigmoid or Scurved growth curve
• Reproductive time lag
causes population
overshoot
• Population will not be
steady curve due to
resources (prey) and
predators
Density-Dependent Controls
• Competition for resources
• Predation
• Parasitism
• Disease
Density-Independent Controls
• Natural disasters
• Severe weather
• Pollution
• Pesticide spraying
9-2: Reproductive Patterns
and Survival
• 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
K
• Maximize
reproductive life
• Minimum life
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 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
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
Late successional species
r and K strategists summary animation
Survivorship Curves
• Late Loss (Type I) : K-strategists that produce
few young and care for them until they reach
reproductive age thus reducing juvenile
mortality
• Constant Loss (Type II): typically intermediate
reproductive strategies with fairly constant
mortality throughout all age classes
• Early Loss (Type III) : r-strategists with many
offspring, high infant mortality and high
survivorship once a certain size and age
Population
Growth Self Quiz!
Late Loss
Constant Loss
Early Loss
9-3: Effects of Genetic Variations in Pop. Size
Variations in genetic diversity can affect small, isolated
populations. Most large pops. genetic diversity remains fairly
constant.
Genetic variations that can affect small populations could include:
1. Founder effect – few individ. colonize a new area that’s
geographically isolated from others in the population
2. Demographic Bottleneck effect – When a pop. is destroyed by
natural disaster, and only a few individs. Survive; May lack genetic
diversity to carry on and rebuild population.
3. Genetic drift – random changes in genes frequencies that could
lead to unequal reproductive success; founder effect could cause
genetic drift
4. Inbreeding – when individuals of small pops. mate and could
increase likelihood of passing on defective genes to offspring and
affect long term survival.
Genetic changes in a pop.
due to the Bottleneck effect
Genetic Drift
9-4: Human Impacts and Working with Nature
Nine major ways humans impact the environment to
meet OUR needs and wants:
1.
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9.
Fragmentation, degrading and destroying habitats
Simplifying/ homogenizing natural ecosystems (1 crop)
Using, wasting and destroying NPP that support all consumers.
Strengthening some populations of pest species and diseasecausing bacteria by overuse of pesticides
Elimination of some predators (sharks)
Deliberately or accidentally introducing new species (exotic)
Overharvesting potentially renewable resources (farmland, fish)
Interfering with the normal chemical cycling and energy flows in
ecosystem (excessive CO2 emissions)
Increasingly more dependent on nonrenewable energy (fossil
fuels)
Working with Nature:
Principles of Sustainability
To maintain a balance between our altered
environments and natural environments, we
need to learn the important features of
nature.
• Nature sustains itself through:
(diagram on back cover of book!)
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Uses of unlimited solar energy
Biodiversity
Nutrient recycling
Population Control
Ecological Principles for Sustainability
(Message of the book and this class! )
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.