# Biology Internal Assessment

Pages: 15 (3458 words) Published: November 28, 2010
IB Biology – Internal Assessment: Measuring Population Size A population is defined as a group of individuals of the same species, occupying a particular area at the same time. In all studies of quantitative ecology, it is essential to be able to estimate the number of organisms within a given area of ground or volume of water or air. In most cases, this is equivalent to estimating the population size; the methods employed are determined by the size and mode of life of organisms involved and also the size of the area under investigation. For species living in uniform and accessible habitats, given their sizes are large enough, the population can be estimated by marking and recapture methods, or by using square grids of known areas. In some cases, when one is dealing with relatively small areas, it is possible to isolate the entire population and take a complete census.

Although the methods of estimation are different, their outlying principles are simple and can be demonstrated in laboratory by using simple apparatuses.

Design
Experiment I
Question: Capture-recapture Method for Estimating Population Size Hypothesis: Population size can be estimated by capture-recapture method Materials: Big bowl, beans, quick drying marker, small spoon Procedure:

1. Filled the Petri dish with 500 beans.
2. 52 rice grains were taken out by random and marked with the marker. They were allowed to dry. 3. The marked beans were returned to the Petri dish and mixed thoroughly together with the unmarked beans. Here, all the beans represented individuals in a population, whereas the marked beans represented the first captured and then released individuals. 4. A sampled of beans was removed by using a small spoon. The numbers of marked and unmarked beans were counted and recorded. 5. Step 4 was repeated 9 times and the results were averaged and tabulated below.

Diagram of Setup

Data Collection and Processing
Raw data table:
Table 1: Number of marked and unmarked beans in 10 attempts Attempt Number| Beans|
| Unmarked| Marked (m)| Total (n)|
1| 13| 2| 15|
2| 11| 0| 11|
3| 34| 6| 40|
4| 71| 9| 80|
5| 39| 5| 44|
6| 32| 5| 37|
7| 25| 2| 27|
8| 45| 8| 53|
9| 38| 7| 45|
10| 43| 7| 50|

Data Processing
Finding the population size
Let N = Total Population
M = Total number marked
n = Number of recaptured individuals
m = Number of recaptured, marked individuals

We have P(1) = the proportion of marked to total individuals = MN
P(2) = the proportion of recaptured, marked to total recaptured individuals = mn Theoretically, P(1) = P(2)

MN = mn

Then N = M × nm

For this experiment, M = 52.
Using this value and the data listed in Table 1, the total population in each attempt could be calculated, as shown in Table 2. Sample Calculation (1st attempt): N = 52 × 152

Table 2: Total number of beans calculated in every attempt
Attempt number| Beans removed| Total number of beans|
| Unmarked| Marked| |
1| 13| 2| 390|
2| 11| 0| Invalid|
3| 34| 6| 347|
4| 71| 9| 462|
5| 39| 5| 457|
6| 32| 5| 385|
7| 25| 2| 702|
8| 45| 8| 345|
9| 38| 7| 334|
10| 43| 7| 372|
Averaged total: 442|

The result obtained in the second attempt was invalid and therefore was discarded. This invalid result was mainly due to a small number of beans being removed in the recapture step. It suggested that a higher percentage of beans should be removed during the recapture step in order to get an accurate result. Furthermore, the percentage error could be calculated by the following procedure. The total number of beans being used in this experiment was 500. Error = Actual no. – Calculated no.

= 500 – 422
= 72
Percentage error = 78500 × 100%
= 15.60%

Conclusion and Evaluation
Conclusion:
The results obtains from this experiment suggested that capture-recapture...