|What method do scientists use to count the number
of species within a population?
|Question Date: 2006-05-26|
It can be a difficult task to count the amount of
individuals in a population and there are many
ways to do it depending on what you are counting.
Say you are counting the number of squirrels,
there is an experiment and equation that you can
use. You attract squirrels with food and tag them
somehow. You count how many you tag. You release
them again and wait awhile. Then you put out the
food again and then count the number of squirrels
comes and the number that is tagged. The equation
you use is: number of squirrels in the population
= (number caught the 2nd time x number of
squirrels you marked the first time) / the number
of tagged squirrels you caught the 2nd
Another way you can do it is to
"quadrant" off a small section of land where the
population lives and count how many are in that
small section. Then multiply the number of
sections there are total. So if you have a piece
of land that is 25 square miles and divide that
into five 5X5 quadrants/plots and find out that
there are 100 oaks in one 5X5 quadrant, then you
multiply 100 by 5 (because you assume that there
are 100 oaks in each quadrant and there are 5
quadrants.)This works well if the population you
are counting is fairly stationary (like a plant or
As I said before there are
lots of ways of counting, each with its
disadvantages and advantages. You just need to
choose the best method for the population that you
are interested in counting.
A population is all of the individuals of one
species in a particular area, like gray whales in
the Pacific Ocean or eucalyptus trees on a
campus.How we count the number of individuals
depends a lot on what we're counting. Counting
the number of trees in an area isn't too
difficult, especially if you have a map, but
things that move are harder to count. To count
whales, one method used is called mark/recapture.
Whales are tagged and then researchers capture
whales another day. Scientists then use a formula
to estimate how many whales there are.
Communities are collections of
populations, such as all of the living things in
the Pacific Ocean, or all of the living things on
a campus. Again, scientists have to use lots of
different methods to try to identify as many of
the species as they can because different species
have different habits.
There are a lot
more species in one area than you might think.
Use a piece of string to mark off an area that's
about one meter per side, then carefully try to
find as many species as possible in it. It
doesn't matter if you don't know their names. I
think you'll be surprised at the number. I
guarantee that you will also miss several species.
Thanks for asking.
Scientists are trying to figure out how to count
the number of species within a population. They're
also arguing about what are different species of
bacteria and what are just normal variations
between bacteria. Now days scientists use DNA
sequences a lot to identify the number of
different species in a population. They can dig
up some muck with bacteria and other
microorganisms in it and find all the different
DNA sequences for some gene and compare the DNA
sequences to see how many different categories the
DNA sequences seem to group into. Then they
compare them to the DNA sequences for known
microorganisms to try to count the number of
species and see if there are new species. I heard
talks about that research this week.
A population, by definition, is one
A community can have multiple
species, and the way that it is counted is by
simply going to the field, setting borders, and
counting everything found in the area. Naturally,
things get missed, because they're transient.
Estimating the true species number from a count in
the field is easier said than done.
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