The existence of an Allee effect in populations of Porcellio scaber (Isopoda: Oniscidea)

Below densities of 70 m-2 relative growth rates increased as a function of density, above 70 m-2 growth rate decreased with increasing density. Time spent walking and searching increased at lower densities. These behavioural observations, together with the original observations on water loss and oxygen consumption made by Allee [1], are used to interpret the curvilinear growth rate response to density as an example of a component Allee effect, which is discussed in relation to the importance of aggregation as an adaptation to the terrestrial environment in the Oniscidea.