There are many species of Woodlice found around the world and because of their abundance they provide good material for an ecological investigation into their preferred habitat. Woodlice are of the order Isopoda which means, "The legs are alike". Different species prefer different dwellings however the Common Rough Woodlouse (Porcellio scaber), which has been used for this investigation, is commonly found around residential properties. They can be found under rocks or around compost heaps where the soil is moist and a humid atmosphere is maintained. One abiotic factor that affects the habitat of Woodlice includes damp or moist soil. Compost heaps also provide a continuous source of dead plants, which is part of the diet of Woodlice. This is another abiotic factor. Woodlice are believed to provide a vital role in the decomposition process as their eating habits return essential nutrients to the soil.
Closer examination of the anatomy of the Porcellio scaber may give more understanding of why they may be found in damp conditions. The external structure (fig.1) shows a hard exoskeleton, which is shed at intervals throughout their lives in order that they can grow longer. The exoskeleton consists of segments and the first section has a fusion of the thorax and the head. The uropod at the rear of the Woodlouse is used for the uptake of water and this is achieved when they are pressed against moist surfaces. Woodlice cannot retain water for long periods of time and because they have a large surface area to volume ratio they loose water quickly by diffusion. Their exoskeleton is not waterproof which means that they will also loose water through this.
Fig 1. Dorsal View of Porcellio scaber
The ventral view of the anatomy of Woodlice (fig. 2) shows that they have simple pseudo-lungs as their respiratory surface and this is also towards the rear. There is a pore opening that allows the exchange of gases in and out of the lungs and this does not close allowing the continual diffusion of water into and out of the inner surfaces of the pseudo-lung.
Fig.2 Ventral view of Porcellio scaber
This investigation aims to analyse habitat preference of the Porcellio scaber and in particular ascertain whether a dry or humid atmosphere is preferred as this may play a essential role in the choice of habitat of this particular species.
The Porcellio scaber will not show preference to either a humid or a adry atmosphere.
The Porcellio scaber will prefer a humid atmosphere.
It was expected that a woodlice would prefer damp, dark, but moderately warm surroundings. Normally one would expect to find slaters under logs or concrete slabs in one's garden. Under these large objects, the sun cannot reach directly; therefore it is darker, damper and colder than the surroundings. Nevertheless, in winter we do not see woodlice crawling around very often, and, also at night, it may actually be warmer under such objects, because it looses heat more slowly, so I predict that the woodlice would prefer a dark, damp and a temperature of around 15oC. (The ground temperature of a typical Scottish day). This preference to dark and damp surroundings is mainly due to woodlouse's inefficient water-storage system. A woodlouse, if exposed to heat or light for too long, can die due to the dramatic loss of water. They prefer a moderate temperature, because they are so small, and can be damaged by frost if they are exposed to the extreme of cold, but they don't want such a high temperature, either, because they would start loosing too much water. I would also expect the woodlouse to prefer a surrounding of slightly higher pressure (1.05 ~ 1.1 atmosphere), because water evaporates more slowly under a high pressure. However, this is not investigated in this experiment due...