Population Characteristics I. Population Density II. Natality

1. PEOPLE AND EARTH'S
ECOSYSTEM

2. TOPICS:
POPULATION CHARACTERISTICS
I. POPULATION DENSITY
-TYPES OF DENSITIES
-DETERMINING POPULATION SIZE
II. NATALITY

3. A POPULATION HAS SEVERAL CHARACTERISTICS OR
ATTRIBUTES WHICH ARE A FUNCTION OF THE WHOLE
GROUP AND NOT OF THE INDIVIDUAL. DIFFERENT
POPULATIONS CAN BE COMPARED BY MEASURING THESE
ATTRIBUTES. THESE ATTRIBUTES ARE POPULATION
DENSITY, NATALITY, MORTALITY, DISTRIBUTIONS, ETC.
THE STUDY OF THE GROUP CHARACTERISTICS OF A
POPULATION, THEIR CHANGES OVER TIME AND
PREDICTION OF FUTURE CHANGES IS KNOWN AS
DEMOGRAPHY.
POPULATION CHARACTERISTICS

4. THE SIZE OF THE POPULATION IS REPRESENTED BY ITS
FUNDAMENTAL PROPERTY CALLED DENSITY. IT IS
GENERALLY EXPRESSED AS THE NUMBER OF INDIVIDUALS
OR THE POPULATION BIOMASS PER UNIT AREA OR VOLUME.
I. POPULATION DENSITY
TWO TYPES OF DENSITIES:
1. CRUDE DENSITY
- IS THE DENSITY PER UNIT OF TOTAL SPACE. GENERALLY, POPULATIONS
DO NOT OCCUPY ALL THE SPACE AS WHOLE BECAUSE ALL AREA MAY NOT
BE HABITABLE.
2. SPECIFIC (OR ECOLOGICAL) DENSITY
- IS THE DENSITY PER UNIT OF HABITABLE SPACE. IT INCLUDES ONLY THAT
PORTION OF TOTAL SPACE THAT CAN ACTUALLY BE COLONIZED BY THE
POPULATION.

5. DETERMINING POPULATION
SIZE
ABUNDANCE
POPULATION SIZE CAN BE MEASURED BY SEVERAL
METHODS:
1.
- ABSOLUTE NUMBER OF INDIVIDUALS IN POPULATION.
2. NUMERICAL DENSITY
- NUMBER OF INDIVIDUALS PER UNIT AREA OR VOLUME. IT
IS EXPRESSED WHEN THE SIZE OF
INDIVIDUALS IN THE POPULATION IS RELATIVELY UNIFORM,
AS IN MAMMALS, INSECTS AND BIRDS.
3. BIOMASS DENSITY
- BIOMASS DENSITY IS EXPRESSED IN TERMS OF WET
WEIGHT, DRY WEIGHT, VOLUME, AND CARBON
AND NITROGEN WEIGHT PER UNIT AREA OR VOLUME.

6. POPULATION DENSITY CAN BE CALCULATED BY THE
FOLLOWING EQUATION:
IN THIS EQUATION, DP IS THE DENSITY OF POPULATION, N IS THE
TOTAL POPULATION AS A NUMBER OF PEOPLE, AND A IS THE
LAND AREA COVERED BY THAT POPULATION. A IS USUALLY
EXPRESSED IN TERMS OF EITHER SQUARE MILES OR SQUARE
KILOMETERS, ESPECIALLY WHEN LOOKING AT HUMAN
POPULATION. HOWEVER, WE COULD USE SMALLER UNITS AS
WELL.

7. FOR EXAMPLE, IF WE'RE LOOKING AT THE POPULATION DENSITY
OF A TYPE OF INSECT ON A TREE, WE WOULD USE SQUARE FEET
OR SQUARE METERS, BECAUSE KILOMETERS WOULD BE FAR
TOO LARGE. WE MIGHT ALSO USE ACRES IF WE'RE LOOKING AT
THE POPULATION DENSITY OF CATTLE ON A RANCH. THE SAME
POPULATION DENSITY FORMULA APPLIES TO BOTH HUMAN AND
NON-HUMAN POPULATIONS.

8. NATALITY REFERS TO THE RATE OF REPRODUCTION OR
BIRTH PER UNIT TIME. IT IS AN EXPRESSION OF THE
PRODUCTION OF NEW INDIVIDUALS IN THE POPULATION
BY BIRTH, HATCHING, GERMINATION OR FISSION.
II. NATALITY
THE MAXIMUM NUMBER OF BIRTHS PRODUCED PER INDIVIDUAL
UNDER IDEAL CONDITIONS OF
ENVIRONMENT IS CALLED POTENTIAL NATALITY. IT IS ALSO
CALLED REPRODUCTIVE OR BIOTIC POTENTIAL,
ABSOLUTE NATALITY OR MAXIMUM NATALITY.

9. NATALITY VARIES FROM ORGANISM TO ORGANISM. IT DEPENDS
NATALITY VARIES FROM ORGANISM TO ORGANISM. IT DEPENDS
UPON THE POPULATION DENSITY AND ENVIRONMENTAL
UPON THE POPULATION DENSITY AND ENVIRONMENTAL
FACTORS. IT IS A GENERAL RULE THAT IF THE POPULATION
FACTORS. IT IS A GENERAL RULE THAT IF THE POPULATION
DENSITY IS USUALLY LOW, THE BIRTH RATE IS ALSO LOW. THIS IS
DENSITY IS USUALLY LOW, THE BIRTH RATE IS ALSO LOW. THIS IS
SO BECAUSE THE CHANCES OF MATING BETWEEN MALES AND
SO BECAUSE THE CHANCES OF MATING BETWEEN MALES AND
FEMALES ARE LOW. IF POPULATION DENSITY IS UNUSUALLY HIGH,
FEMALES ARE LOW. IF POPULATION DENSITY IS UNUSUALLY HIGH,
THE BIRTH RATE MAY ALSO BELOW DUE TO POOR NUTRITION OR
THE BIRTH RATE MAY ALSO BELOW DUE TO POOR NUTRITION OR
PHYSIOLOGICAL OR PSYCHOLOGICAL PROBLEMS RELATED TO
PHYSIOLOGICAL OR PSYCHOLOGICAL PROBLEMS RELATED TO
CROWDING. THE MAXIMUM OR ABSOLUTE NATALITY IS
CROWDING. THE MAXIMUM OR ABSOLUTE NATALITY IS
OBSERVED WHEN THE SPECIES EXISTS UNDER IDEAL
OBSERVED WHEN THE SPECIES EXISTS UNDER IDEAL
ECOLOGICAL AND GENETIC CONDITIONS. THE ACTUAL NUMBER
ECOLOGICAL AND GENETIC CONDITIONS. THE ACTUAL NUMBER
OF BIRTHS OCCURRING UNDER THE EXISTING ENVIRONMENTAL
OF BIRTHS OCCURRING UNDER THE EXISTING ENVIRONMENTAL
CONDITIONS IS MUCH LESS AS COMPARED TO ABSOLUTE
CONDITIONS IS MUCH LESS AS COMPARED TO ABSOLUTE
NATALITY. IT IS REFERRED TO AS ECOLOGICAL NATALITY OR
NATALITY. IT IS REFERRED TO AS ECOLOGICAL NATALITY OR
REALIZED NATALITY. IT IS NOT CONSTANT FOR POPULATION AND
REALIZED NATALITY. IT IS NOT CONSTANT FOR POPULATION AND
MAY VARY WITH THE SIZE OF POPULATION AS WELL AS WITH THE
MAY VARY WITH THE SIZE OF POPULATION AS WELL AS WITH THE
TIME.
TIME.