Transcript Population Dynamics - Currituck County Schools

Population Dynamics
Population Dynamics
• Populations of plants and animals change
over time due to:
• climate change,
• natural disaster,
• Changes in predator or prey abundance,
• Anthropogenesis.
Characteristics of Populations
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Size
Density
Dispersion
Age Distribution
Population Measurements of
Population Characteristics
• 1. Size – measure the number of
individuals in a population at a given time.
• Methods: Quadrant and transect.
Population Measurements of
Population Characteristics
• 2. Population density – the number of
individuals of a population in a certain
space at a given time.
• Terrestrial ecologists express density as
the number of individuals per unit area.
• Aquatic ecologists express density as the
number of individuals per unit volume.
Human Population Density
Population Dispersion
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3. Population dispersion – the spatial pattern in which the members
of a population are found in their habitat.
a. Clumped Dispersal: (MOST COMMON) resources are usually
patchy in nature. Additionally, some animal species form grazing
herds, schools of fish, flocks of birds, and troops of primates to
protect against predators, during migration, during mating season, or
because they are social animals.
b. Uniform Dispersal: (RARE) occurs mostly when individuals of the
same species compete for resources that are scarce or when a
species defends its territory by physical or chemical means.
Example, Creosote bush in desert biome. It competes for water
(limiting factor) by excreting toxic chemicals that prevent seedlings of
other creosote bushes from growing near it.
c. Random Dispersal (RARE) occurs when resources or conditions in
the environment are fairly uniform and competition is limited. This
condition is rare because environments are rarely uniform. Random
dispersion is most common in weedy species that have a broad
tolerance range for environmental conditions (‘generalists”)
(a) Clumped (elephants)
(b) Uniform (creosote bush)
(c) Random (dandelions)
Age Structure
4. Age Structure – the proportion of individuals in
each age group in a population.
a. Pre-reproductive
b. Reproductive
c. Post-reproductive
A population with a large % of its individuals in the
pre-reproductive category has a high potential
for growth = “population momentum”.
Human Age Structure Diagrams
What Limits Population Growth?
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Births
Deaths
Immigration
Emigration
Population change = (b + i) – (d + e)
Biotic Potential
• Populations vary in their capacity for growth.
When environmental factors are optimal,
populations grow.
Biotic Potential = Population Growth
• The intrinsic rate of increase (r) is the rate at
which a population could grow if it had unlimited
resources.
“r” is expressed as the # of individuals per existing
individual per unit time. Example, # of new
peppered moths per existing # of peppered
moths/year.
Biotic Potential
• Where (dN/dt) is the rate of increase of the
population and N is the population size, r
is the intrinsic rate of increase. This is
therefore the theoretical maximum rate of
increase of a population per individual
Populations with High Intrinsic
Rates of Increase = “r” Strategists
(Generalists)
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Many small offspring
Little or no parental care
Early reproductive age
Most offspring die before reaching reproductive age
Small adults
Adapt quickly to environmental changes
High population growth rate
Population size fluctuates greatly above/below carrying capacity
Generalist niche
Low ability to compete
Early successional species (rabbit, quali, ringneck pheasant, dove,
bobolink, gopher, pioneer plant species and weeds)
Environmental Resistance
• Environmental resistance limits the growth of a
population when all of the limiting factors in the
environment work synergistically.
• This results in specialization of species (k-strategists):
• Low reproductive rates
• Specialized niche
• Competition of resources
• Loss of habitat which causes increased competition
making organisms susceptible to disease and weakening
them preventing them from reproducing.
• Environmental Resistance = Population Decrease
POPULATION SIZE
Growth factors
(biotic potential)
Abiotic
Favorable light
Favorable temperature
Favorable chemical environment
(optimal level of critical nutrients)
Biotic
High reproductive rate
Generalized niche
Adequate food supply
Suitable habitat
Ability to compete for resources
Ability to hide from or defend
against predators
Ability to resist diseases and parasites
Ability to migrate and live in other
habitats
Ability to adapt to environmental
change
© 2004 Brooks/Cole – Thomson Learning
Decrease factors
(environmental resistance)
Abiotic
Too much or too little light
Temperature too high or too low
Unfavorable chemical environment
(too much or too little of critical
nutrients)
Biotic
Low reproductive rate
Specialized niche
Inadequate food supply
Unsuitable or destroyed habitat
Too many competitors
Insufficient ability to hide from or defend
against predators
Inability to resist diseases and parasites
Inability to migrate and live in other
habitats
Inability to adapt to environmental
change
Figure 9-4
Page 166
Environmental
resistance
Population size (N)
Carrying capacity (K)
Biotic
potential
Exponential
growth
Time (t)
SYNERGY
• Together, biotic potential AND
environmental resistance determine the
carrying capacity (K) which is the number
of individuals of a given species that can
be sustained indefinitely in a given area.
Exponential Growth Curve
• Exponential Growth – a
population that does not
have resource limitations
grows exponentially.
• Exponential growth starts
out slowly and then
proceeds faster and faster
as the population grows.
• “ J-shaped curve
Logistic Growth Curve
• Logistic growth involves
exponential population
growth when the
population is small and a
steady decrease in
population growth with
time as the population
approaches “K”.
• Logistic curves yield
sigmoidal curves or “S”
curves.
What Happens When the
Population Exceeds “K”?
• 1. As populations use up resources they
“overshoot” the carrying capacity (k) of the
habitat. (+FBL)
• The overshoot occurs BECAUSE of a
“reproductive lag time” = the period
required for the br to decrease and dr to
increase in response to overconsumption
of resources. (-FBL is delayed, therefore,
recovery is delayed).
Population size (thousands)
160
Hare
140
Lynx
120
100
80
60
40
20
0
1845
1855
1865
1875
1885
Year
1895
1905
1915
1925
1935
2.0
Overshoot
Number of sheep (millions)
Carrying capacity
1.5
1.0
.5
1800
1825
1850
1875
Year
1900
1925
Results
• Population crashes!
• The only way to avoid a crash in population is if
individuals of that species emigrate out of the habitat and
into a new one with more favorable conditions.
• Once the existing “k” of the habitat has been exceeded,
the environment becomes degraded and the new “k” is
lowered.
• Recall Easter Island!
How Does Population Density
Affect Population Growth?
1. Density-independent population controls –
factors that will affect the size of a population
regardless of it’s density.
• Examples are:
• Natural disasters (floods, hurricanes,
earthquakes, landslides, severe drought,
unseasonable weather, fire, destruction of
habitat, tsunamis)
• EX. Hurricane Katrina (2005), Indonesian
Tsunami (2005)
New Orleans After Hurricane
Katrina
Limiting Factors for Population
Density
2. Density-dependent population controls – when
limiting factors in the environment have a significant
effect on the size of a population as it’s density per unit
area increases. These include:
• Competition for resources
• Parasitism
• Disease
• This means that populations with a high density per unit
area generally have lower birth rates and higher death
rates = slow growth rates due to “k” of the environment.
Density-Dependent Example in
Animals
• If there are a large number of prey (zebra)
in the savanna biome where competition is
high for limited resources THEN more
zebra will become weakened, susceptible
to disease, and die.
• Most impacted = young, weak,and the
elderly.
Density-Dependent Example in
Humans
• Infectious Disease – bubonic plague
• The bacterium that causes this disease lives in
rodents and is transferred to humans via fleas
(vector species).
• Fleas feed on humans (become infected) and
then bite humans transferring the disease.
• The disease spread rapidly through crowded
cities, where sanitary conditions were poor and
rats were abundant.
• Over 25 million people died.
POPULATION CURVES IN NATURE
Number of individuals
1. Stable – population
fluctuates slightly
© 2004rooks/Cole – Thomson Learning
above/below “k”.
(undisturbed tropical
rain forest)
(d) Irregular
(a) Stable
(c) Cyclic
(b) Irruptive
Time
2. Irruptive – normally
have fairly stable
population that may
occassionally
“explode” or “irrupt” to
a high peak and then
crash to a lower, more
stable level. Can
occur due to more
predators/less food in
habitat. (racoon)
3. Cyclic “boom-bust
cycles” (Linx-rabbit,
lion-zebra)
4. 4. Irregular unpredictable
What Can We Learn From Nature?
Living systems have six key features:
• Interdependence
• Diversity
• Resilience
• Adaptability
• Unpredictability
• limits
Important Ecological Principles to
Promote Sustainability
• We are part of, not apart from, the earth’s
dynamic web of life.
• Our lives, lifestyles, and economies are
totally dependent on the sun and the earth
(solar capital and earth capital).
• We can never do merely one thing without
it affecting everything else.
Solutions
• Build societies based on conservation and
not waste.
• Preserve what we can’t replace.
• Work with nature to help restore what we
have degraded or destroyed.
“Everything is connected to
everything else; we are all in it
together”