Measuring Populations

1. Measuring Populations Direct Observation, Indirect Observation, Sampling, and Mark and Recapture!

2. Direct Observation • The most obvious way to figure out the size of a population. All you have to do is count every organism that is in the population. • Example: I went home and counted the gerbils that were in my cage. 2 1

3. Indirect Observation • It may be easier sometimes to not count all the organisms that are in an area. All this observation is, is that you observe the signs of organisms instead of the organisms themselves. • Example: I was walking down a street and I noticed a lot of bird nests in the trees on the side of the road, I counted 3 bird nests and I remembered that an average of 3 birds live in each nest so I can assume that there is 9 birds that live around that street 3 6 9

4. Sampling • Sampling is counting in a small area and then multiplying to get and estimate of who many organisms in that area • Example: I went to Donner Lake and counted trees in a small area and then multiplied by how big the area was and got an estimate of how many trees are in the big area.

5. Mark and Recapture • Mark and Recapture is marking animals counting how many there are and releasing them. Then coming back later and counting all the animals with and without marks. • Example: I marked ten turtles and let them go and then I came back a couple days later and counted them all and noticed that there was more than I had marked. . .