Download Population Biology

Chapter 6
POPULATION
BIOLOGY
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OUTLINE
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DYNAMICS OF POPULATION GROWTH
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FACTORS THAT INCREASE OR DECREASE
POPULATIONS
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FACTORS THAT REGULATE POPULATION
GROWTH
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CONSERVATION BIOLOGY
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OPTION 1 = $_______________________
OPTION 2 = $_______________________
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BIOTIC POTENTIAL
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BIOTIC POTENTIAL refers to unrestrained
biological reproduction. Biological organisms
can produce enormous numbers of offspring if
their reproduction is unrestrained.
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ENVIRONMENTAL RESISTANCE refers to the
total of all factors that limit population growth.
These are also known as LIMITING FACTORS
 As population increases so does
environmental resistance!!
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DYNAMICS OF POPULATION GROWTH
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POPULATION - all the members of a single
species living in a specific area at the same
time
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EXPONENTIAL GROWTH - growth at a constant
rate of increase per unit time; has no limit
dN/dt = rN
The change in the Number of individuals (dN)
per change in time (dt) equals the rate of growth
(r) times the number of individuals in the
population (N). r is often called the INTRINSIC
CAPACITY FOR INCREASE.
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EXPONENTIAL GROWTH
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Number of individuals added to a population at
the beginning of exponential growth is
relatively small. But numbers increase quickly
because a % increase leads to a much larger
increase as the population grows.
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J CURVE when the equation is graphed
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Exponential growth is a simple, idealized
model. In the real world there are limits to
growth.
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EXPONENTIAL GROWTH
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***RULE OF 70 YOU MUST KNOW THIS
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RULE OF 70 is used to determine the
approximate doubling time of a population
Doubling Time =
70
% growth rate
1. If a country was doubling its population every
35 years what would its growth rate be?
2. Currently, human pop growth rate is 1.2% In
what year do you predict the world population
will have doubled?
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CARRYING CAPACITY
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CARRYING CAPACITY - limit of sustainability
that an environment has in relation to the size
of a species population
OVERSHOOT - population exceeds the carrying
capacity of the environment and death rates
rise as resources become scarce
POPULATION CRASH - growth becomes
negative and the population decreases
suddenly
BOOM AND BUST - population undergoes
repeated cycles of overshooting followed by
crashing
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BOOM & BUST OR J CURVE
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GROWTH TO A STABLE POPULATION
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LOGISTIC GROWTH - growth rates regulated by
internal and external factors until coming into
equilibrium with environmental resources
 dN/dt = r N (1 - N/K)
 Terms have the same definitions as previous
slide, with K added to indicate carrying
capacity.
 Growth rate slows as population approaches
carrying capacity.
 S CURVE when the equation is graphed
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LOGISTIC GROWTH CURVE OR S CURVE
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J vs S POPULATION CURVES
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r AND K SELECTED SPECIES
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r SELECTED SPECIES rely upon a high
reproductive rate to overcome the high mortality
of offspring with little/no parental care.
ie: A clam releases a million eggs in a lifetime
but the larva are so small that few survive.
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K SELECTED SPECIES have few offspring but
more parental care so most young survive.
ie: An elephant reproduces every 4 or 5 years.
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REPRODUCTIVE STRATEGIES
r-selected
species
K-selected
species
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FACTORS AFFECTING
POPULATION GROWTH
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EXTERNAL FACTORS include habitat quality,
food availability and interaction with other
organisms.
INTERNAL FACTORS include physiological
stress due to overcrowding, maturity, body
size, and hormonal status.
These factors are DENSITY DEPENDENT,
meaning as population size increases the effect
intensifies.
DENSITY INDEPENDENT effects (drought, an
early frost, flooding, landslides, etc.) also may
decrease population size.
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FACTORS THAT INCREASE POPULATION
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NATALITY – birth rate
 FECUNDITY - physical ability to reproduce
 FERTILITY - measure of actual number of
offspring produced
IMMIGRATION - organisms introduced into new
ecosystems
 Dispersal of organisms by wind or water
currents over long distances. Sometimes
carried by animals or on rafts of drifting
vegetation.
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FACTORS THAT DECREASE POPULATION
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EMIGRATION – individuals leaving an area
MORTALITY - death rate
 SURVIVORSHIP - percentage of cohort
surviving to a certain age
 LIFE EXPECTANCY - probable number of years
of survival for an individual of a given age
- Increases as humans age. By older age,
most individuals destined to die early have
already done so.
- Has risen in nations/areas with good
nutrition, sanitation and medical care
- Women live longer than men.
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LIFE SPAN
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LIFE SPAN - longest period of life reached by a
given type of organism
 Bristlecone pine lives 4,600 years.
 Human maximum lifespan is 120 years.
 Microbes may live a few hours.
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Differences in relative longevity among species
are shown as survivorship curves.
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SURVIVORSHIP CURVES
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FOUR GENERAL PATTERNS: (NOTE THE #’s)
I. Full physiological life span if organism
survives childhood
Example: top consumers, Humans
II. Probability of death unrelated to age
- Example: Sea gull, rodents
IV. Mortality peaks both early and late in life.
- Example: Deer, crabs
III. Mortality peaks early in life.
- Example: oysters, sea turtles, oak tree
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SURVIVORSHIP CURVES
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FACTORS THAT REGULATE POP. GROWTH
ENVIRONMENTAL RESISTANCE
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DENSITY DEPENDENT FACTORS
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Have more influence as the population density
increases
They slow population growth
Impact large % of population
Disease, competition, predation, stress and
stress related issues – aggression, decreased
fertility and immunity, pathological behaviors
due to high density
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FACTORS THAT REGULATE POP. GROWTH
ENVIRONMENTAL RESISTANCE
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DENSITY INDEPENDENT FACTORS
 Not influenced by the size of the population
 All organisms are affected equally regardless
of population density
 Fire, floods, weather, natural disasters,
human-caused habitat disruption, etc.
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FACTORS THAT REGULATE POP. GROWTH
ENVIRONMENTAL RESISTANCE
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INTRINSIC FACTORS - operate within or between
individual organisms in the same species
 competition, territoriality, stress, etc
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EXTRINSIC FACTORS - imposed from outside
the population
 predation, climate, natural disasters, etc.
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FACTORS THAT REGULATE POP. GROWTH
ENVIRONMENTAL RESISTANCE
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ABIOTIC FACTORS - Caused by non-living
environmental components. Tend to be density
independent, and do not really regulate
population although they may be important in
increasing or decreasing numbers.
ie: climate, weather, natural disasters, fire
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BIOTIC FACTORS - Caused by living organisms.
Tend to be density dependent. They regulate
population size by decreasing natality or
increasing mortality.
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DENSITY DEPENDENT FACTORS
(biotic factors)
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INTERSPECIFIC INTERACTIONS
(between different species)
 predator/prey, mutualism, commensalism, etc
 Resource partitioning, invasives, etc
Predator-Prey
Oscillating Cycles
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DENSITY DEPENDENT FACTORS
(biotic factors)
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INTRASPECIFIC INTERACTIONS - competition
for resources by individuals within a population
 As population density approaches the
carrying capacity, resources become limited.
Control of access to resources by territoriality;
owners of territory defend it and its resources
against rivals.
STRESS-RELATED DISEASES occur in some
species when conditions become overcrowded.
DISEASES – tend to spread faster with a higher
population density
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CONSERVATION BIOLOGY
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Critical question in conservation biology is the
minimum population size of a species required
for long term viability.
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SPECIAL CASE OF ISLANDS
 ISLAND BIOGEOGRAPHY
- MacArthur and Wilson proposed that
species diversity is a balance between
colonization and extinction rates.
- Small islands vs Large islands
- Far from mainland vs closer to mainland
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CONSERVATION GENETICS
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In a large population, genetic diversity tends to
be preserved. A loss/gain of a few individuals
has little effect on the total gene pool.
However, in small populations small events can
have large effects on the gene pool.
GENETIC DRIFT
 Change in gene frequency due to a random
event
FOUNDER EFFECT
 Few individuals start a new population.
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CONSERVATION GENETICS
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DEMOGRAPHIC BOTTLENECK - just a few
members of a species survive a catastrophic
event such as a natural disaster
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Founder effects and demographic bottlenecks
reduce genetic diversity. There also may be
INBREEDING due to small population size.
Inbreeding may lead to the expression of
recessive genes that have a harmful effect
on the population.
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GENETIC DRIFT
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POPULATION VIABILITY ANALYSIS
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MINIMUM VIABLE POPULATION is the minimum
population size required for long-term survival
of a species.
ie:
 The number of grizzly bears in North America
dropped from 100,000 in 1800 to 1,200 now.
The animal’s range is just 1% of what is once
was and the population is fragmented into 6
separate groups.
Biologists need to know how small the bear
groups can be and still be viable in order to
save the grizzly.
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METAPOPULATIONS
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METAPOPULATION - a collection of populations
that have regular or intermittent gene flow
between geographically separate units
 SOURCE HABITAT - Birth rates are higher
than death rates. Surplus individuals can
migrate to new locations.
 SINK HABITAT - Birth rates are less than
death rates and the species would disappear
if not replenished from a source.
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METAPOPULATION
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