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Population Ecology-J Curve, S
curve and Age Distribution !!
POPULATION
A group of organisms of the same species occupying a
particular space at a particular time.
POPULATION ECOLOGY
Population ecology is a study of populations in relation to
the environment.
It deals with the factors that influence the population’s
size, growth, density, distribution, age structure and many
other features.
DENSITY AND DISPERSION
DENSITY: IS the number of individuals per unit area or volume.
DISPERSION: is the pattern of spacing among individuals within
the boundaries of the population.
POPULATION SIZE
Population size depends on a balance between
NATALITY=Birth Rate (b)
MORTALITY=Death Rate (d)
If birth rate (b)>death rate (d) —- r is (+); population is
increasing in size.
If (b) < (d) —–r is (-); population is shrinking.
If (b) = (d) —–r is (0); population size is constant.
Besides natality and mortality, population size also depends
on the movement of individuals between population s
(migration)
IMMIGRATION RATE (i)=movement of individuals into a
population
EMIGRATION RATE (e)=movement of individuals out of a
population.
FACTORS THAT AFFECT FUTURE POPULATION
GROWTH
POPULATION GROWTH
Two factors influence the dynamics of a population
BIOTIC POTENTIAL:
Promotes positive growth
intrinsic factors(litter size, gestation period)
ENVIRONMENTAL RESISTANCE:
Limits growth
extrinsic factors(weather, food supply etc. )
PATTERNS OF POPULATION GROWTH
1.
EXPONENTIAL GROWTH:
Exponential population
growth is population increase
under idealized condition
Under this condition the rate of reproduction is at its
maximum, called the intrinsic rate of increase.
The equation of exponential growth is
J-shaped curve of exponential population growth is a
characteristics of some population that are rebounding.
Exponential growth can not be sustained for long in any
population.
A more realistic population model limits growth by
incorporating carrying capacity
Carrying capacity (k) is the maximum population size the
environment can support.
LOGISTIC GROWTH:
2.
In the logistic population growth model the per capita
rate of increase declines as carrying capacity is
reached.
The logistic growth equation includes k,the carrying
capacity
What
limits
population
size around carrying capacity?
1. DENSITY DEPENDENT FACTORS:
Competition(habitat space, food resource, mates)
Disease
Predation
2. DENSITY INDEPENDENT FACTORS:
Weather condition
Catastrophes
Natural disasters
SURVIVORSHIP CURVES
1. A survivorship curve traces the decline of a group of
new borns over time.
2. Survivorship curve plot the probability of surviving to
a certain age for a representative member of the
population.
TYPES OF SURVIVORSHIP CURVES
1. TYPE I; CONVEX CURVE: Most individuals live to adulthood
with most mortality occurring during old age.(i.e.,
humans red deer, elephants)
2. TYPE II; STRAIGHT LINE: An individual’s chance of dying
is independent of its age (i.e., small birds, mammals)
3. TYPE III; CONCAVE CURVE: Few individuals lives to
adulthood, with the chance of dying decreasing with
age.(i.e., oysters, red wood trees, snapping turtles)
AGE DISTRIBUTION
1. The age distribution of a population is the portion of
individuals at different ages.
2. It has a significant impact on future population growth.
3. Population that have remained constant for a long time
have stable age distribution, which reflect an
individual’s chance of living a given amount of time.
4. Rapidly growing populations will have disproportionate
number of young individuals.
POPULATION PYRAMIDS
A population pyramid is also called an age pyramid or age
picture diagram.
It is a graphical illustration that shows the age distribution
of various age groups in a population.
TYPES OF POPULATION AGE PYRAMIDS
Population age pyramid has mainly four types.
1. STABLE PYRAMID: a population pyramid showing
unchanging pattern of fertility and mortality.
an
2. STATIONARY PYRAMID: a population pyramid typical of
countries with low fertility and low mortality.
3. EXPANSIVE PYRAMID: a population pyramid that is very
wide at the base, indicating high birth and death rates.
4. CONSTRICTIVE PYRAMID: a population pyramid that comes in
at the bottom. the population is generally older on
average, as the country has long life expectancy a low
death rate, but also a low birth rate.
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