Mark-Release-Recapture of Woodlice.

Aim: -

To measure density of population of woodlice or any changes in its population

Limitations to the method ‘Mark-Release-Recapture’ method: -

There are many limitations to this method. Some of these are as follows: -

• The animal usually needs to be captured to be marked, which may injure it, or alter its behaviour pattern.
• The mark used may harm the animal - for example a dot of a particular paint may turn out to be toxic to the animal. Trials therefore need to be done to ensure that the animal is not harmed in any way.
• Marks may be removed in between release and recapture.
• Marks may make individual animals more, or less attractive to predators than non-marked individuals.
• The method assumes that all animals in the population are equally ‘catchable.’ However, 'catchability' of animals may vary with different life stages, seasons, times of day etc. It is therefore better to sampling under as similar conditions as possible and with the same amount of effort.
• Trapping responses of animals may vary. Some may become 'trap-shy' and avoid the traps after the first capture. This can be reduced as far as possible by choosing a method which will not distress the animal unduly. Some animals may become 'trap-happy', particularly if the traps are baited. This can be overcome by setting out the baited traps, without actually trapping, for some time before the first sample is taken. This allows all animals in the population to become equally trap-happy before you start
• Trap-shyness results in population overestimates, while trap-happiness results in population underestimation.
• The actual method used to investigate population size depends on whether you are measuring an open or closed population. A closed population means one in which you assume there is no immigration or emigration and no births or deaths. In practice, there are very few completely closed populations. This problem can be partially overcome by conducting the study over as short a period as possible and at a time when there are likely to be few changes in population size for any of the above reasons.
• Closed population methods applied to an open population will produce biased results.
• Open population methods produce less precise estimates of population size. (The Lincoln Index is a method which is used to estimate the size of closed populations)

Results: -

Below I have created a graph of all of the results recorded, this is basically to make the information easier to break down and analyse.

Data Analysis: -

The results show that 64 woodlice were caught painted and released back into the wilderness. On the second day 58 woodlice were recaptured and of those, 9 were painted. This meant that out of the 58 woodlice recaptured, 49 were not captured previously (therefore ‘new’), as only 9 were found painted.

Evaluation: -

There was a minor problem encountered when reviewing and analysing the results accumulated. This was basically that the results calculated about how many ‘new’ woodlice were captured could have been inaccurate as the paint used to mark the woodlice could have been washed off etc. deeming the results collected incorrect or inaccurate.

Many improvements could be made to improve this experiment, and to develop the results collected further making them more accurate and much more precise. One improvement could be to carry out the experiment at the same time. For example, the experiment was conducted at separate times. An improvement would be to conduct the actual experiment at the same time of the day. This could be due certain characteristics in the animal/insect studied, such as the woodlice maybe prone to be nocturnal etc.

Another improvement could be to carry out the whole of the experiment over a course of a few days, making the results of the ‘population density’ more accurate than if it were carried out in two days.

There are many important ways that this technique could be used in ecological research, for example it could be used to keep very important tabs on the population of certain species, or of a certain area. This could result in introducing predators if need be, to keep the population under control. The mark-release-recapture could also be used to basically investigate a certain species or an area, certain animals could be used as biological indicator but would show what sort of environment and atmosphere the species are living in.

Conclusion: -        

The results show that 64 woodlice were caught painted and released back into the wilderness. On the second day 58 woodlice were recaptured and of those, 9 were painted. This meant that out of the 58 woodlice recaptured, 49 were not captured previously as only 9 were found painted. This meant that 55 of the woodlice first captured have dispersed amongst themselves, died or the paint could have washed off their backs, making them indifferent to the newly caught woodlice.