capture – mark – recapture method
DESCRIPTION
The Lincoln Index Used to estimate the size of an animal population. Capture animals Mark them with a tag Release them and wait a period of time Capture animals againTRANSCRIPT
CAPTURE MARK RECAPTURE METHOD
The Lincoln Index CAPTURE MARK RECAPTURE METHOD The Lincoln Index
Used to estimate the size of an animal population.
Capture animals Mark them with a tag Release them and wait a period
of time Capture animals again Assumptions The population of
organisms must be closed, no immigration or emigration. The time
between samples must be small compared to the life span of the
organism The marked organisms must mix completely with the rest of
the population during the time between sampling. Assumption: The
proportion of animals caught to the whole population is the same as
the marked animals in the second sample. First Capture =Marked
animals, second capture Whole populationsecond capture Equation n1=
m2 N n2 n1 = number of animals first marked and released. n2 =
number of animals captured in the second sample m2 = number of
marked animals in the second sample Solve for N = n1 . n2 to find
the total population m2 Limitations Marking or capturing the animal
might change its behavior to avoid recapture The mark might be
toxic or cause predators to see it Marks might cause the animal to
be rejected by its own population Trapping might cause the animal
to avoid the traps in the future or to choose to be trapped to get
food! Assumptions: No animals are born or die during the period
tested
No animals immigrate or emigrate in the period tested. Animals do
not die because of the markings. The tags do not fall off. What is
the estimated snail population in a woodland?
In a woodland, the undergrowth was sampled for snails and 430 were
found and marked. They were then released and the population
similarly sampled after a two-week period. This second sampling
produced 410 snails, 100 of which were marked. Answer n1 = 430 n2 =
410 m2 = 100 N = 430 x 410 = 1763 snails 100 Woodlice Woodlice are
terrestrial crustaceans that live under logs and stones in damp
soil. To assess the population of woodlice in an area, students
collected as many of the animals as they could find, and marked
each with a drop of fluorescent paint. A total of 303 were marked.
24 hours later, woodlice were collected again in the same place.
This time 297 were found, of which 99 were marked from the first
time. What is the estimated population of woodlice in this area?
Population estimate N = 303 x 297 = 909 99 Voles While studying
field voles, an ecologist caught 500 and ringed a foot of each
before releasing them.Every day for the next two weeks he examined
the waste material found in the nests of their predators.He
collected a total of 300 field vole skulls and 15 rings. How many
field voles were probably in the area examined? Population estimate
N = 300 x 500= 15 A harder problem from the 2009 IB exam
A population of meadow voles in an area of woodland was sampled
using small mammal traps over a period of four days. On each
occasion any unmarked individuals were marked and all the voles
from the capture were then released. The following table represents
the data obtained on each of the four days. Estimate the population
size Vole population calculation
n1 = number in the first sample and marked = 35 You need to know
how many animals were marked! n2 = number in the second sample 23
m2 = number in the second sample with a mark 8 N = 35x23 = The size
of the population is 101 as voles is impossible! Estimate the size
of a turtle population:
yearCapturedMarked pond turtles1992:18 1993: (12) 1994: (18)
Results 1992: :34 (12) :30 (18) :N = 18(34)= 51 turtles 12
____________________________________ The total number marked is 12
= 40 :N = 40(30)= 67 turtles 18 This assumes that none of the paint
came off of the turtles over the course of two years. Mini
experiment: Does the size of the first capture, n1, while the size
of the second capture is held constant, affect the accuracy of the
population estimate, N? Does the size of the second capture, n2,
while the size of the first capture is held constant, affect the
accuracy of the population estimate, N? Hypothesis? Do you think
that the Lincoln Index is more reliable if many animals are
captured and marked in the first capture? Do you think that the
Lincoln Index is more reliable if many animals are captured in the
second capture? Mini experiment with beans
You will use beans instead of animals to study the accuracy of the
Lincoln index. Independent variable: Vary either the size of the
first capture OR the second capture while holding the other
variable constant Dependent variable: The value for m2 will change,
so the value for N will change. maybe Minilab: Investigation with
beans:
Separate black and white beans Count 150 white beans into a cup
Capture some white beans, n1 Mark the captured beans. Release the
marked beans into the cup and mix. Capture a second sample, n2
Count the number of marked beans in the second sample, m2 Repeat
for a second and third trial, using the same size captures. ( Three
trials of the same experiment should improve your accuracy.) Change
the size of the first or second capture while keeping the same
value for the other capture.Repeat Change the number of beans in
one of the captures.. Five times total. Data table: Numbers of
beans + 1
Trial n1 n2 m2 1 2 3 1 Data Processing: Calculate N
Calculate the population estimate for N Mean value Estimated
population N Percent error Graph the results Do the population
estimates improve with increasing first or second captures? The
independent variable is on the x axis The dependent variable is on
the y axis Rubric for grading