Lab 3 Mark and Recapture PDF

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Summary

An important step in an ecosystem study is determining population size of the species present. This laboratory includes an exercise in estimating the population size of animals using the "mark-recapture" method...

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Josiah Takang Biology 3370L Mark-Recapture Lab This lab was to perform a mark-recapture experiment on the isopods living in a given habitat at Kennesaw State University. The table below shows how many isopods were marked with a special paint across lab sections. It also shows how many isopods lab sections captured, and how many of those displayed a mark (recaptured).

By using the following equation: N=M(C+1)/(R+1), an estimated population size of 131.25 was calculated for the isopods. Certain assumptions had to be met in order for this experiment to be valid. 1. All individuals in the population have an equal chance of being captured. - This assumption was met, because the area used for capturing was fairly reasonable in terms of accessibility, and each group scattered throughout the area captured roughly the same amount of isopods. 2. There is no change in the ratio of marked to unmarked animals between capture times. This means that there have been no significant additions of unmarked individuals to the population and that decreases in the population have affected marked and unmarked individuals proportionally. - Death of ispods between capture times seemed implausible, because the ratio between marked and unmarked individuals was significant. This assumption was met. 3. Marked individuals distribute themselves in the population homogeneously after being released. - This assumption was met in that enough time passed before a recapture event had occurred. All isopods were distributed evenly back into their habitat when released after being captured by each lab section. 4. Capturing and marking an organism does not affect its chances of being recaptured. - By marking the isopods with paint, we made sure to mark them on a discrete part of their back in a dull paint color, making sure the mark wouldn’t attract predators causing death, thus not being able to be recaptured, therefore this assumption was met.

5. Marks are not lost or overlooked. - The paint marks on the isopods seemed to hold up after days of being marked. The paint had faded slightly but it was clear which individuals had been marked previously, and which had not. This assumption was also met. If the fifth assumption was not met, whereas the marks placed on the isopods washed off in the rain, or were not seen by observers, then the calculated population size estimate would be over-estimated. This being because the recaptured value would be lower than how many isopods actually did have a mark on them at one point, causing a higher estimate for population size....