Porcellio Scaber (Slater, Woodlouse)
The crustacean Porcellio Scaber, or more commonly known as the woodlouse, is a species usually found in leaf litter or in fallen trees and bark. It feeds on detritus like many other isopods of its type, and is generally predated on by small mammals, lizards and some insects. The woodlouse habitat reflects its need to avoid warm and dry areas. The woodlouse is prone to desiccation (drying out) due to its body’s large surface area to volume ratio. This results in a variety of behavioural adaptations that help it conserve moisture and avoid desiccation.
The woodlouse exhibits negative phototaxes behaviour, this results in them moving away from brighter areas in order to find a darker one. This is because darker areas are usually damper and will be better for moisture conservation. In terms of humidity they show a kinetic reaction to dry conditions. Their rate of movement will increase in dry areas along with their rate of turning in order to quickly find a damper area. They will also move slower in humid conditions in order to conserve energy. They show a similar response in regards to an increase in temperature. A warmer environment promotes desiccation, while a cooler environment will help conserve moisture. Other responses shown include a positive thigmokinetic behavioural reaction. A woodlouse’s rate of movement will decrease in regards to how much of its body is in contact with another object. This results in a ‘clumping’ behaviour with groups of woodlice. They will group together in order to stave off both desiccation and risk of predation.
As well as behavioural adaptations the woodlouse also has several physiological adaptations that increase its chances of survival and subsequently reproduction. Its respiration system consists of a pore on the outside of its body that lets air in to a pseudo-lung that will absorb oxygen directly from the air. This pore is permanently open however and is a major reason why desiccation is a danger to woodlice. The pore is the reason for a lot of the woodlouse’s water loss. Woodlice also exhibit an adaptation that allows them to absorb moisture from their surroundings through their exo-skeleton when in areas of high humidity. This can lead to an excess of water in the woodlouse and it will subsequently move to an area with lower humidity. In summary the Porcellio Scaber’s ecological niche consists of; a diet of detritus and other decomposing organisms, a damp and dark habitat, various predators, and a range of behavioural and physiological adaptations designed to combat the risk of desiccation and predation.
The aim of this investigation is to find the relationship, if one exists, between the rate of movement of woodlice and light intensity. The hypothesis indicates that the brighter an area is lit, the faster the woodlouse will move.
The aspect of the woodlouse’s ecological niche covered in this investigation is its behaviour in regards to changes in light intensity. The woodlouse has a negative phototaxes behaviour and if the hypothesis is correct then when the voltage, and therefore light intensity, is higher then an increase in the woodlouse’s rate of movement should occur. The woodlice have this reaction due to the risk of desiccation that comes with brightly lit areas. The woodlouse is prone to desiccation due to its high surface area to volume ration, as well as the permanently open respiratory pore that contributes heavily to moisture loss.
-Bucket (Moderately sized, the one used in this investigation was 4L) -12V24W Light bulb (Cannot be overly large. The one used in this investigation was 6cm in height attached to a wooden base 5.3cmx4.5cmx2cm. The base is not necessary) -DC adjustable power supply (Must be able to accurately produce light at the voltages specified in the test range (10,11,12,13,14,15V) -2...