<< Chapter < Page Chapter >> Page >
Photo (a) shows penguins, which maintain a defined territory and therefore have a uniform distribution. Photo (b) shows a field of dandelions whose seeds are dispersed by wind, resulting in a random distribution patter. Photo (c) shows elephants, which travel in herds resulting in a clumped distribution pattern.
Species may have uniform, random, or clumped distribution. Territorial birds such as penguins tend to have uniform distribution. Plants such as dandelions with wind-dispersed seeds tend to be randomly distributed. Animals such as elephants that travel in groups exhibit clumped distribution. (credit a: modification of work by Ben Tubby; credit b: modification of work by Rosendahl; credit c: modification of work by Rebecca Wood)

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.

Questions & Answers

hie guys please send questions
Monkey Reply
According to Charles Darwin theory, what character do human beings have and does a monkey?
Arcan Reply
What are macro-molecules?
Arcan
they are responsible for other life processes
Benjamin
a person with blood group A can not donate blood to a person with blood group B
KHUNGA Reply
differentiate between cytoplasm and protoplasm
Annet Reply
cell as a unit of life
Bhrah Reply
differentiate between cytoplasm and protoplasm
Annet
forms which cell exist
Zainab Reply
Wats a molecules in terms of biology?
Ayomide Reply
Important of kreb's cycle
yeboah
what conversation
Sally Reply
is agurment btn two or more people
Okello
what is biology?
KINEI Reply
the scientific study of the life and structure of plants and animals.
Boame
when is the right time to play sex in order to prevent pregnancy?
Guor
After finishing school
Hellen
study of living things n non living things
Benjamin
sex is sweet at anytime
Okello
study of living organsm
Hellen Reply
which element is the largest
Haja Reply
francium
Izzati
francium
Paul
how many groups do we have in the periodic table
Theola Reply
seven groups
Moses
the one that makes eight is the noble gases
Moses
okay thank you
Theola
we have eight groups in the periodic table
Ramsey
there are actually 18 groups or numbered columns
Izzati
so it will be like the s- p-and d block elements of the periodic table
Izzati
8 groups
Boame
how many times can a man release before the lady get pregnant
Smart Reply
nearly a hundred million
Izzati
one
Moses
what do you by one?
Izzati
two times
Theola
just only one time
Okello
what is a function of cell sap
Martin
it repair worn out tissue
Moses
when is the right time for playing sex to prevent pregnancy?
Guor
at anytime
Okello
what is biology
Darkoa Reply
it's study of all living organisms and their characteristics
Ice
study of living organism
Hellen
by what proces do ameaba reproduce?
Okello Reply
hi dear
Janet
hi my sist gudmorning
Okello
Hi
Muah
hello
Bob
yes
Mathew
hi
promise
what is biology
promise
amoeba reproduce asexually
Chidi
gudevening member
Okello
good chidi
Okello
hello
Felix
hello
Felix

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play




Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Biology' conversation and receive update notifications?

Ask