The Effect of Light and Moisture on Distribution of Woodlice - Research Paper Example

An Investigation into the Effect of Light and Moisture on the Distribution of Woodlice Introduction Woodlice is the collective for a wide number of terrestrial isopods that fall within the subphylum Crustacea (Capinera, 2008). The different species of woodlice share many features in common. Among these is the need to have either a moist substrate or saturated air in the habitat in which they permanently inhabit (Edney, 1954). Woodlice primarily breathe through the use of gills, although they do have surfaces that act to absorb oxygen (Nardi, 2007). In their natural habitat, woodlice as generally observed as being restricted to dark and damp locations. Their sensory organs help them detect moisture (Burton and Burton, 2002). Woodlice show an innate behavioral response in moving towards sources of moisture and away from light sources (Allott, 2001). This indicates that both of these factors are important in the decisions that woodlice make concerning their habitats. This study focuses on two aspects of the environment in which woodlice inhabit, these are light and moisture level. These two effects work in combination with one another, as the dampness help woodlice to breathe, while the darkness prevents them from drying out. It was hoped that it could be determined which of these effects was predominant or whether they were both equally important. The aim of this study is to investigate the way in which light and moisture effect the way that woodlice distribute themselves and their preferences for environments. To do this, the variables of moisture and light intensity were modified independently to produce a total of four distinct environments. These environments were damp-dark, damp-light, dry-dark and dry-light. It was hypothesized that woodlice would preferentially move towards areas that were dark and moist, and away from those that were light and dry. This would result in an increased concentration of woodlice in the former areas, and few in the latter. Methods For this study, the dependent variable was the location of the woodlice following the five-minute adjustment period. The independent variable was the condition of the environment, which was determined by the modification of two separate variables, light and heat. Each of these variables was present in a dichotomy, light or dark and damp or dry, there were no intermediate variables. Eight woodlice were placed in an experimental container that contained an intermediate level of moisture and light. The light and moisture levels in the container were then modified to produce four quadrants each with different environmental conditions (Figure 1). After five minutes, the number of woodlice present in each quadrant was counted and noted. If a woodlouse settled on the boundary between two quadrants, it was scored as being in the area where its head was. The experiment was repeated four times, each time using a different set of woodlice to reduce the effect of preferences specific to individual woodlice. Results The results were similar across trials, with an average of 4.8 woodlice (59%) preferring the damp and dark habitat, and an average of 2.3 woodlice (28%) preferring the dry and dark habitat (Table 1). The differences between each environment type were substantial which can be seen by the error bars (Figure 2). Table 1: Woodlice distribution across the four environmental types after the five-minute adjustment period. Trial 1 Trial 2 Trial 3 Trial 4 Total Average Damp/Dark 4 4 6 5 19 4.8 Damp/Light 1 1 1 1 4 1 Dry/Dark 3 3 1 2 9 2.3 Dry/Light 0 0 0 0 0 0 Figure 2: Differences in woodlice preferences to the four environmental types. Error bars represent the standard error of the mean. If the results are broken down into the four individual types of environments, it can be seen that the strongest preference of woodlice was whether the environment was dark or light. A total of seven (88%) woodlice chose the dark environment in each trial, while only one chose the light environment. In contrast, selection was more variable concerning whether the woodlice chose the dry or damp environment, with an average of 5.8 (73%) choosing the damp environment per trial and while an average of 2.3 (29%) chose the dry environment. Note that all calculations are rounded to two significant figures. Table 2: Distribution of woodlice across each of the environmental variables. Note that each woodlouse was present in two environmental categories simultaneously. Number of Woodlice Trial 1 Trial 2 Trial 3 Trial 4 Average Dark 7 7 7 7 7 Light 1 1 1 1 1 Damp 5 5 7 6 5.8 Dry 3 3 1 2 2.3 Figure 3: Differences in woodlice density across each of the four environmental types. Note that each woodlouse was present in two environmental types simultaneously. Error bars represent the standard error of the mean. Because each of the variables considered in this study were discrete, rather than a continuum, the results are presented in a bar graph and there is no calculable gradient. Conclusion and Evaluation The study found that woodlice preferred the dark and damp environment, with the light intensity of the environment being the primary driving factor for which environment the woodlice chose. This resulted in 19 woodlice choosing the moist and dark environment (for all trails combined), and nine choosing the dry and dark environment. It was interesting to note that across all trials, no woodlice choose the dry and light environment, indicating that they needed their environment to be either damp or dark to survive and preferably both. This confirms the hypothesis for the study, which predicted that woodlice would be prevalent in the dark and moist environment and not in the light and dry environment. This agrees with scientific literature, which states that woodlice require a moist environment for survival, suggesting that the insects themselves need to remain moist. Even though the dry and dark environment was not moist, it was still chosen by a portion of woodlice in each trial (an average of 2.3, ranging from 1 to 3). This may be because the darkness of the environment prevents the woodlice from drying out. This conclusion is also supported by the fact that only one woodlouse per trial chose the damp and light environment, suggesting that while the drying out effect was countered by the dampness of the environment in this case, it was still not a highly desirable environment. One limitation of this study was that it considered only a small sample size (32 across four replicates). This makes it difficult to determine whether effects that were observed were genuine, or the result of random variation. However, the use of four replicates was an advantages and helps to reduce some of the chance for error, as the same pattern was seen in each trial. Although different woodlice were used for each of the four trials, each was conducted in the same experimental container. This is another limitation; as it is possible that woodlice were responding to an environmental gradient that the researchers were unaware of, such as one corner of the container being lower than the others are, changing the likelihood of the woodlice approaching this corner. The first type of error is random error, while the second is systematic. However, despite the potential for error within this study, the consistency across the different trials suggests that the results are likely to be reliable. Suggestions for improvements to this experiment would be to use a different experimental container for each replicate, and to have a larger number of woodlice in each replicate. This would reduce the possibility both for random and systematic error. References Allott, A. (2001). Biology for the Ib Diploma: Standard and Higher Levels, 136-137. Burton, M. & Burton, R. (2002). The International Wildlife Encyclopedia, 2973-2976. Capinera, J. L. (2008). Encyclopedia of Entomology, Springer, 2890-2892. Edney, E. (1954). Woodlice and the Land Habitat. Biological Reviews, 29, 185-219. Nardi, J. B. (2007). Life in the Soil: A Guide for Naturalists and Gardeners, University of Chicago Press, 114-115. Read More