Population Structure and Fluctuation

Abstract

Our present knowledge on the population dynamics of isopods is based on studies of a limited number of isopod species (15), which represent only a few families (see Table X in Warburg et al. 1984). A typical characteristic of population structure is the large number of young within a population. At times they comprise the bulk of the isopod population in any single location (Sutton 1968; Sunderland et al. 1976). However, there is a large variation in the number of juveniles produced per year (Al-Dabbagh and Block 1981). The population structure changes from a bimodal pattern when the mancas leave the marsupium to a unimodal one when they grow and mature. The lowest densities are observed just before recruitment of the young (Kheirallah and Omran 1986). This change may last for a few months or up to a year and was observed in several species: Cylisticus convexus (Hatchett 1947), Armadillidium vulgare (Paris and Pitelka 1962; Al-Dabbagh and Block 1981), Ligidium japonicum (Saito 1965), Trichoniscus rathkei (Breymeyer and Brozozowska 1967), T. pusillus (Sutton 1968; Phillipson 1983) and Hemilepistus reaumuri (Shachak et al. 1979).