Lecture 8 Population Properties

8/7/2019 Lecture 8 Population Properties

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ECOLOGY OF POPULATIONS

Population Properties

LECTURE 8



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



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



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



2. DISPERSION

- how individuals are distributed in

space

- r andom, uniform, clumped



� 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



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.



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.



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´



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



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)



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



Age Pyramid

� Is constructed by getting the % of

population at different age classes. The %

is reflected on the lengths of horizontal

bars.



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



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.)



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



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



Why migr ate?

1. Food2. Space

3. Competition

4. Seasonal changes

Effects of migration

1. Population Size

2. Age Distribution3. Genetic Pool



End of Lecture

Lecture 8 Population Properties

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