# 45.1 Population demography  (Page 3/17)

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## Demography

While population size and density describe a population at one particular point in time, scientists must use demography to study the dynamics of a population. Demography is the statistical study of population changes over time: birth rates, death rates, and life expectancies. Each of these measures, especially birth rates, may be affected by the population characteristics described above. For example, a large population size results in a higher birth rate because more potentially reproductive individuals are present. In contrast, a large population size can also result in a higher death rate because of competition, disease, and the accumulation of waste. Similarly, a higher population density or a clumped dispersion pattern results in more potential reproductive encounters between individuals, which can increase birth rate. Lastly, a female-biased sex ratio (the ratio of males to females) or age structure (the proportion of population members at specific age ranges) composed of many individuals of reproductive age can increase birth rates.

In addition, the demographic characteristics of a population can influence how the population grows or declines over time. If birth and death rates are equal, the population remains stable. However, the population size will increase if birth rates exceed death rates; the population will decrease if birth rates are less than death rates. Life expectancy is another important factor; the length of time individuals remain in the population impacts local resources, reproduction, and the overall health of the population. These demographic characteristics are often displayed in the form of a life table.

## Life tables

Life tables provide important information about the life history of an organism. Life tables divide the population into age groups and often sexes, and show how long a member of that group is likely to live. They are modeled after actuarial tables used by the insurance industry for estimating human life expectancy. Life tables may include the probability of individuals dying before their next birthday (i.e., their mortality rate    ), the percentage of surviving individuals dying at a particular age interval, and their life expectancy at each interval. An example of a life table is shown in [link] from a study of Dall mountain sheep, a species native to northwestern North America. Notice that the population is divided into age intervals (column A). The mortality rate (per 1000), shown in column D, is based on the number of individuals dying during the age interval (column B) divided by the number of individuals surviving at the beginning of the interval (Column C), multiplied by 1000.

what is endocytosis
what is the meaning of adrenocorticotropic
Belinda
ok thanks
Abigail
What is science of biology
The study 📓 of leaving things
John
how does a parasite benefit from its mode of living?
why are the images n diagrams unable to be seen?
Abuk
where are the illustrations
Simon
a parasite gets protection, food, shelter
Anguson
what is Alimentary canal?
what is commenialism
Do you mean commensalism?,it is a feeding relationship that has to do with two different species feeding, that is one is benefiting and the other is unaffected.
hamidat
commensalism is a feeding relationship that has to do with different species feeding, one is gaining and the other is unaffected.
hamidat
what is the work of phloem tissue
What is osmoregulation?
Jacklin
osmoregulation is the maintenance of internal body through the aid of water
favour
mention four characteristics of enzymes
Leah
mention four characteristics of enzymes
Agorong
The phloem tissue is responsible for the distribution of manufactured food in the shoot.
hamidat
Enzymes speed up the rate of chemical reactions,they are catalytic protein.
hamidat
to transport the manufactured food
Ronald
A skeleton is any film structure that gives mechanical support to the body and provides protection to the softer parts of the body.
nice
Kabir
A skeleton is a frame or bony part of a body that aid in the movement of different parts of the body.
hamidat
What is a skeleton?
is a bone without meat
Stanley
is a frame work of d body that provide support nd rigidity 4 d body
tunz
is a structure of the body without the organs and the skin
Rose
what is an electron microscope?
is a microscope that is used to study small organisms in the cell.
Rose
is a microscope which uses electricity to magnify
jamex
okay
Rose
what is commenialism
jamex
what is an antigen?
Luyando
an antigen is any thing that reduces the action of a gene
hamidat
what is biochemist
biochemistry:-is the study of chemical reaction with living organisms
Kabir
HOW MANY DNA STRANDS DOES CORONA VIRUS HAVE?
Baramox
hamidat
what are the scientific method
scientific method is the step by step approach use for solving problems
Stephen
describe the functioning of the Golgi body in animal cells
used to package minerals in the cell
Rose
what features does red blood have that allows it to effectively move through the blood and transport oxygen? list at least four features and explain how they help RBC's carry out their functions.
has nucleus, haemoglobin
favour
what is biology
it's the study of living organisms and their interactions with one another and the environment
Precious
Biology is the study of life.
hamidat
is the study of living organisms and there structure
Rose