# 45.1 Population demography  (Page 2/17)

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For mobile organisms, such as mammals, birds, or fish, a technique called mark and recapture    is often used. This method involves marking a sample of captured animals in some way (such as tags, bands, paint, or other body markings), and then releasing them back into the environment to allow them to mix with the rest of the population; later, a new sample is collected, including some individuals that are marked (recaptures) and some individuals that are unmarked ( [link] ).

Using the ratio of marked and unmarked individuals, scientists determine how many individuals are in the sample. From this, calculations are used to estimate the total population size. This method assumes that the larger the population, the lower the percentage of tagged organisms that will be recaptured since they will have mixed with more untagged individuals. For example, if 80 deer are captured, tagged, and released into the forest, and later 100 deer are captured and 20 of them are already marked, we can determine the population size ( N ) using the following equation:

Using our example, the population size would be estimated at 400.

Therefore, there are an estimated 400 total individuals in the original population.

There are some limitations to the mark and recapture method. Some animals from the first catch may learn to avoid capture in the second round, thus inflating population estimates. Alternatively, animals may preferentially be retrapped (especially if a food reward is offered), resulting in an underestimate of population size. Also, some species may be harmed by the marking technique, reducing their survival. A variety of other techniques have been developed, including the electronic tracking of animals tagged with radio transmitters and the use of data from commercial fishing and trapping operations to estimate the size and health of populations and communities.

## Species distribution

In addition to measuring simple density, further information about a population can be obtained by looking at the distribution of the individuals. Species dispersion patterns (or distribution patterns) show the spatial relationship between members of a population within a habitat at a particular point in time. In other words, they show whether members of the species live close together or far apart, and what patterns are evident when they are spaced apart.

Individuals in a population can be more or less equally spaced apart, dispersed randomly with no predictable pattern, or clustered in groups. These are known as uniform, random, and clumped dispersion patterns, respectively ( [link] ). Uniform dispersion is observed in plants that secrete substances inhibiting the growth of nearby individuals (such as the release of toxic chemicals by the sage plant Salvia leucophylla, a phenomenon called allelopathy) and in animals like the penguin that maintain a defined territory. An example of random dispersion occurs with dandelion and other plants that have wind-dispersed seeds that germinate wherever they happen to fall in a favorable environment. A clumped dispersion may be seen in plants that drop their seeds straight to the ground, such as oak trees, or animals that live in groups (schools of fish or herds of elephants). Clumped dispersions may also be a function of habitat heterogeneity. Thus, the dispersion of the individuals within a population provides more information about how they interact with each other than does a simple density measurement. Just as lower density species might have more difficulty finding a mate, solitary species with a random distribution might have a similar difficulty when compared to social species clumped together in groups.

how can a human being die by drinking too much of water
Scientific name of a dog in canis familiarise?
what's biology?
Jaymez
Biology is the study of living organism and their interaction with one another and their environment
Sharon
Elsabet
what is biosphere.
Chinyi
where are pollen grains produced pls.
Chinyi
And what are emphatic factors.
Chinyi
@Chinyi Bahiyah -pollen grains are produced in the anther of plants. the anther is one part of the male part of the plant the other being filament and they together form the stamen. hoped that helped :) !!
xjuicy_editzz
what is science?
Science is the method of acquiring skills and knowledge through experimentation and observation in the World Series
Richmond
what is ecology
Bitwell
is the study that deals with the interaction between living things and their environment
Alexander
what is the main fuction of root hair cells?
Liteboho
the main function is to uptake of water and nutrients from the rhizosphere.
Benedict
State the genius to where the dog belong.
Jaymez
where does meiosis occur in male plant reproductive organ
plant cell is plasmolysed as a result of the
of the plant losing water
Esnart
"Head of a pin" means what?
types of genotype and types of blood group
what is biology
is the study of cell and structure of an organism
Atem
is the study of characteristics,life processes and phenomana of living organism
Atem
What is Monomer of protein?
What's nutrition and types of nutrition
Why is cheetah d fastest animal
because they are capable of reaching speeds of up to 70mph
Abu
Thanks
Jessica
what is a cell
what is an enzymes
Reuben
a cell is a biological catalyst that speeds up the rate of a chemical reaction without itself been changed
Israel
a cell is smallest unit of life
Francis
an Enzyme helps speed up a chemical reaction
Francis
is the basic structural and functional unit of all organism
Atem
what is deamination
Is the removal of amino radical from amino acid or any other amino compound.
Esnart
what is metabolism
metabolism is the the combination of all the reaction that occur within your body
xjuicy_editzz
These reaction can be either anabolic (which is the building up of molecules) or can be catabolism (breaking of molecules) but these processes occur simultaneously to maintain homeostasis(internal body environment) within the body.
xjuicy_editzz
hope that helps :D !!
xjuicy_editzz
list 20 element in their order
hydrogen helium lithium beryllium boron carbon nitrogen oxygen fluorine neon sodium Magnesium aluminium silicon phosphorus sulfur chlorine Aaron potassium calcium -Also if anyone is having trouble remembering the elements I recommend watching "The Periodic Table of elements song" :)
xjuicy_editzz