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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

what will happen if cytokenesis did not occurs during meiosi
Senamile Reply
hi
Samuel
what is the function of a nucleus
Japheth Reply
The different between animal cells and plant cells
Bridget Reply
plant cells have a cell wall and chloroplast but animal cells don't. vacuoles of plant cells are much larger than that of an animal cell.
Yazi
explain pyramids of numbers
Saanui Reply
a structure of the nerve cell
Ntale Reply
how many types of viruses do we have
amofa Reply
12
angelina
we Ave 21 families rna and dna viruses
Opeyemi
14 virus
Peter
what is the difference between gems and virus?🙄
Peter
What is nucleoprotein particles
Zanga Reply
nucleoprotein particles could be , tiny micro organizims regenerated and conducted matter.? 'is the least scary idea.'
Heidi
state the factors that determine energy requirements in human body?
Samson Reply
Name and explain 2 nutrients that do not require digestion before they are absorbed
Samson
Name and explain 2 nutrients that do not require digestion before they are absorbed
Samson
Name and explain 2 nutrients that do not require digestion before they are absorbed
Samson
Name and explain 2 nutrients that do not require digestion before they are absorbed
Samson
Name and explain 2 nutrients that do not require digestion before they are absorbed
Samson
Name and explain 2 nutrients that do not require digestion before they are absorbed
Samson
Name and explain 2 nutrients that do not require digestion before they are absorbed
Samson
water : it's a nutrient which helps in d proper digestion of nutrients, it doesn't require digestion because it's not affected by any factor in d mouth, and digestion start from the buccal cavity.
aweda
What are the relationship between Biology and Agriculture
Chisco Reply
what are the relationship between biology and chemistry
Abel
Hooliganism the study of living things(plants and animals) and chemistry focuses on chemical composition of matter.😊
Ronke
biology is the study of all life whereas agriculture is the science of cultivating the land including harvesting of crops, rearing and management of animals and tillage
angelina
biology is the study of life
Elizabeth
biology is the study of livingthing and non livingthing
Fahamia
boilogy is the study of life whilst agriculture is the study of crops etc...
Amoah
which cell organelle is found in abundance in skeletal tissue
Samson Reply
What are the functions of the cell membrane?
Samson Reply
Detects self cells and foreign cells during invasion by pathogens in the cell Protects the cell content Makes the cell very flexible in its function To regulate the entry n exit of substances in and out of the cell(selective permeability)
Agyei
controls the movement of substance in and out of the cell
Queen
cell membrane control movement in the cell
Amoah
what is the four chambers of the human heart and their functions.
Ismile Reply
right and left auricles right and left ventricles
Faith
In which group of the periodic table is beryllium?
Stuart Reply
2
Agyei
are we dealing with biology or chemistry
Samuel
We are dealing with biology
Godfred
what are the terminology in genetic
Odinaka Reply
I want to know if the following stated is be 1.increase, 2. decrease, 3. steady. 1. blood pressure 2. Blood volume 3. ECF volume 4. ICF volume 5. HCT volume 6. Blood protein concentration 7. ECF protein concentration 8. ICF protein concentration 9. Oxygen supply to the brain cells
Rinda Reply
increase
Favour
What are the types of cells?
Akuoch-magol
the two main type of cells are prokaryotic cell and eukaryotic cell but there are also other cells in the human body such as:the nerve cell,skin cell ,blood cell,bone cell etc
angelina
eukaryote cell prokaryotic cell erkayortic cell
Elizabeth

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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