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8/7/2019 Lecture 8 Population Properties
http://slidepdf.com/reader/full/lecture-8-population-properties 1/21
ECOLOGY OF POPULATIONS
Population Properties
LECTURE 8
8/7/2019 Lecture 8 Population Properties
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INTRODUCTION
� Population ± a collection of organisms of
the same species occupying a particular
space at a particular time. The ultimateconstituents of the population are
individual organisms that can potentially
__________.
e.g. Deer population
Narra trees in a forest
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INTRODUCTION
� Population Properties ± statistical
measures that cannot be applied to
individuals such as density, dispersion,natality, mortality, dispersal, age structure
and sex r atio.
- interpreted to be
the summation of individual properties or
char acteristics
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1. POPULATION DENSITY
Abundance ± number of individuals in a given
area
Density ± number of individuals expressed per
unit area or volume.e.g. There are 100 birds in a 2.5 ha of land
Abundance = 100 birds
Density = 100/2.5 = 40 birds/hectare
- number of trees per acre of land
- number of humans per square km
- number of diatoms per cu m of water
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2. DISPERSION
- how individuals are distributed in
space
- r andom, uniform, clumped
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� Random Dispersion
(a) the environment is uniform
(b) resources equally availablethrough the years
(c) no patterns of attr action or avoidance
� Uniform Dispersion(a) more even spacing than would occur by chance
(b) Autotoxicity
� Clumped Dispersion
(a) due to habitat differences(b) reproductive patterns and social behaviors
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3. Natality- production of new individuals in a populationthrough birth, germination, hatching, budding or fission.
e.g. bacteria by cell division
plants by production of seeds
animals by production of offspring
Birth rate ± number of individuals born per 1000 individuals per year.
e.g. a popn of 2000 individuals produced
20 offspring per year BR = 10 per thousand
per year
M ost organisms produce many offspring than are needed to replace
themselves.
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Related Terms:
� FERTILITY ± a physiological term which
refers to the ability of the organism to
breed and to produce offspring.
� FECUNDITY ± an ecological term which
gr ades an organism based on the number
of offspring it can produce in a given
period of time.
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4. Mortality
- loss of individuals in a population as a result of death.
e.g. seed mortality is very high
immature animals die before theyhave the chance to reproduce
Death Rate ± number of people who died
per 1000 individuals per year
³For population to grow, BR>DR´
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SURVIVORSHIP CURVE
- gr aphical representation of death schedules
I ± heavy mortality at the ___ of
the species life span.
e.g. humans, sheeps,
mammals, and some
plants
II ± constant age-specific mortality
rate; constant exponential decrease
in the population with time
e.g. hydr as, rodents, birds
perennial plants
III ± high mortality rates in early life
e.g. oysters, fishes, invertebr ates
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5. AGE STRUCTURE
� - refers to the relative proportion of individualsbelonging to different age classes in a population.
Ecological Ages (Bodenheimer, 1939)1. Prereproductive Age (1-14)
2. Reproductive Age (15-54)
3. Postreproductive Age (55- )
e.g. insects (long pre, short rep and no post)
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Significance of Age Distribution
� (1) influences both natality and mortality
� (2) determines the current reproductive
status of the population and indicateswhat may be expected in the ______
� (3) helps global agencies and government
future population trends and needs
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Age Pyramid
� Is constructed by getting the % of
population at different age classes. The %
is reflected on the lengths of horizontal
bars.
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6. SEX RATIO
� Compares the number of male members
to the number of female members in the
population.
S.R. = number of males x 100
number of females
e.g. 1995 SR for Philippines
SR = 34,584,170 x 100 = 101.62
34,032, 300
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2003 Census (PHILIPPINES)
Total Population (84,619,974)
Sex Ratioat birth: 1.05 male(s)/female
under 15 years: 1.04 male(s)/female
15-64 years: 0.99 male(s)/female
65 years and over: 0.77 male(s)/female
total population: 1 male(s)/female (2003 est.)
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7. DEPENDENCY RATIO
� Relates the size of the dependent segment
of the population to the economically
productive segment of the population
(applicable for human population)
Dependency Ratio ± 0-14 yrs old + 60 yrs and over x 100
15 -64 yrs old
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8. DISPERSAL (MIGRATION)
� The mass directional movement of large
numbers of individuals of a population from
one location to another
Immigration ± migr ation into a population
Emigration ± movement out of a population
Net Migr ation Rate = I - E
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Why migr ate?
1. Food2. Space
3. Competition
4. Seasonal changes
Effects of migration
1. Population Size
2. Age Distribution3. Genetic Pool
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End of Lecture