Effect of Length on the Survival Rate of Woodlice - Essay Example

Effect of Length on the Survival Rate of Woodlice The woodlouse is a crustacean but not an insect; it has 14 parts on its body, this makes it more flexible to curl into a ball in order to protect itself from danger. Hence it’s hard outer shell is exposed (Freemann, 34). They are mostly found in damp and dark places. Generally, they are about 1 cm in length but several tropical species are more than 3 times this length. Their average lifespan is about two years but some can live up to 4 years. Woodlouse is the only crustacean species that inhabit land instead of watery habitats. It is believed that there are over 3,000 various woodlouse species around the world. Because of woodlouse small size and inspite of the fact that it has the capacity to protect itself by curling up into a ball, It can be preyed upon by several animals that include, spiders, millipedes centipedes, Toads, and sometimes by wasp (Schmalfuss ,187) .Some of the characteristics have emerged with time because of natural selection. This makes the organism to be able to protect itself and survive in the environment. With regards to the theory of Darwin, he thought that most of his concepts on evolution by natural selection were easy to understand but this is not the case, they are normally misunderstood most of the time. Darwin's evolution theory by natural selection is one of the best fundamental theories in the science history; it is supported by evidence from various scientific disciplines that include developmental biology, geology, paleontology and genetics. According to Darwin theory, a species can be changed in small ways by natural selection, resulting to a population changing in size or color over several generations course and it is referred to as "microevolution." Natural selection is a process where organisms do change over time following changes in heritable behavioral or physical traits. This change enables an organism to better adapt to its environment, hence assisting it to survive as well as have more offspring. To ascertain how the theory of Darwin works, a number of woodlice were included in the experiment and certain traits that seemed to be linked to evolution were considered, they include weight, size, sprint time and the number of dorsal plate. Conspicuous variation existed in some of the traits such as weight and sprint time. The length of the woodlice was slightly similar but within the required range, the dorsal plate number was same among the woodlice. With regards to the experiment, the length was chosen as the preferred variable. The length of these woodlice was related with sprint time in the presence of spider as the predator (forceps were used as simulator). The aim was to see how the change of length can affect the survival of these woodlice and in biological perspective when related to evolution for example, the length varied or changed in order for these woodlice to be able to evade there predators. The design of this experiment was to see how the woodlice with different lengths could respond to the spider which was the predator. The experiment hypothesis was, the higher the woodlouse length the higher the possibility that it will die. Hence the null hypothesis was, woodlice are not able to respond to predators. Method In the experiment, the basis on how to control a woodlice population was fundamental. With regards to this, forty woodlice were put on a tray with soil. Then the spider as the predator was included on the tray. The forceps were used to simulate the spider. After all these were set, it was left for some time to enable the woodlice to interact with the spiders. Later after sometime, observations were made on the tray; the number of dead and survived woodlice was recorded with their corresponding length. Woodlice were first killed in order to obtain their length. 20 individuals of the woodlice population were measured without performing any replications, and were taken as an experimental control. The other 20 was measured as well. Basically, these processes were done in order to ascertain whether the length has a significant effect to the survival. The experiment was ran alongside the control, whereby the forceps were used as a simulator to the spider. The control results indicated that almost 100% of the woodlice never died. Therefore the experiment was valid at 95% confident. Results Basing on the 20 samples selected randomly from the population, the average values of the four traits was calculated and recorded as shown in the table 1.The standard deviation which indicated the amount of variation among the proportions was also calculated. Besides standard error was as well calculated to determine the accuracy related to average values that represent the whole population. According to the observations made on the tray some of the woodlice had died and it was indicated that the woodlice proportion with longer length had the highest number of dead as compared to those ones with shorter length. The woodlice at length range between 0.6-0.7cm had the surviving population percentage that was much higher as compared to the original population. But this was seen to be lower than that at the length range of 0.7-0.8cm which had both its surviving population and original population percentage higher despite the difference between the surviving and original population was less as compared to the one at the range of 0.6-0.7cm.At the length range of 1.0-1.1 cm, the surviving population percentage is much lower than the original population. Similarly, at the length range of 1.2-1.3, the surviving population is much lower than the original population as shown in figure 1 Trait Mean Standard Deviation Standard Error Length (cm) 1.031 ± 0.179 ± 0.034 Speed (cm/sec) 1.173 ± 0.76 ± 0.1658 # Dorsal Plates 7 ± 0.59 ± 0.139 Weight (g) 0.067 ± 0.03 ± 0.068 Table 1: Statistical Analysis of 23 randomly selected Woodlice. For each of the four traits, the standard deviation, mean and standard error were calculated (for speed, length, dorsal plates number and weight) The woodlice post-predation surviving population was described using a histogram as shown in figure 1.Here this population was compared to the pre-predation original population so that to measure the way the woodlouse length would impact its survival when attacked by a predator. Figure1: A histogram showing Woodlice percentage against the length in cm. The original population is indicated in red while the surviving population is indicated in blue Discussion According to the findings of the experiment it is clearly evident that woodlice rate of survival is affected by its length. Hence, I reject the null hypothesis at 95% confidence interval that woodlice are not able to respond to predators. Thus, the survival rate is inversely proportional to the length. This results supports the hypothesis that the higher the woodlouse length the higher the possibility that it will die, because in the experiment, the woodlice population survival rate significantly decreased with the increase in the length. Implying that, shorter woodlice are able to survive longer than the longer ones. From the biological perspective, in relation to evolution, it is believed that long time ago may be there were so many woodlice which were longer, but with time they evolved to shorter ones due to natural selection. Hence there are fewer longer woodlice than the shorter ones which are able to evade the predators. All measurements taken for the four traits were not 100% accurate as it might be expected. This could be due to human error that include, there could be some bias when measuring the woodlice because this is a tedious process prone to more errors and the measurements are just the estimates of which its accuracy depends on the person taking the measurements. To avoid such errors, it is needed to be so keen, conscious and include calibrated equipment when taking these small measurements. Another human error could occur when handling this woodlice, poor handling such as straining and stressing them might result to wrong outcome because they may not behave normally during the experiment. To avoid such the protocol of the experiment needs to be carefully read and be understood appropriately before starting the experiment and always the experiment condition is needed to be kept normal. Hence the human error was supposed to be put into consideration for more accurate results. However, despite this, other errors were expected while conducting the experiment. This includes the nature of the environment in which the woodlice population was placed. This was not their usual environment and factors like temperature may affect their attitude hence compromising the outcome. It should be tried as much as possible to make sure that the experiment conditions are relatively closer to the normal conditions of the woodlice. If all this confounding factors are not put into consideration then there could be some bias in the result and this was not considered in this experiment that was carried out. Therefore it is recommended that in the future experiment; all the confounding factors should be identified and included in the experiment for accurate results that are more reliable. The standard error is able to estimate accuracy of the means’ values because it shows how close the new mean value is to the previous one. The length standard error in the experiment indicates that new mean will be within the standard error of ± 0.036 cm that is equal to 1.031cm. The standard deviation of the 23 randomly sampled woodlice is small for each weight and length, implying that most of these values were extremely closer to the average. The experiment was not done to the standard because first the sample size was not big enough to make a comprehensive conclusion. Inference statistics was not done in the experiment to really prove the hypothesis and ascertain whether the data was statistically significant. Therefore for this experiment to be up to the standard and reliable, in future such statistics need to be included. Besides the P value was not calculated as well which is so relevant in such experiment. The normal condition in the experiment was not relatively well controlled and this could have resulted to some errors in the experiment, hence affecting the outcome. It is recommended that more accurate and complex devices to be employed in future experiments such as experimental control or considering other traits. The human errors and other related errors should be included while conducting the experiment to avoid confounding factors which mostly do affect the outcome of the experiment. In the future studies, other traits which are more peculiar need to be identified and then be used in running experiment to understand various aspects of natural selection. Works Cited Schmalfuss, Helmut. World Catalog of Terrestrial Isopods (Isopoda:Oniscidea). Stuttgart: Staatliches Museum FürNaturkunde, 2003. Print Freeman, Scott. Biological Science. 4th ed. San Francisco, California: Pearson Benjamin Cummings, 2011. Print. Read More