POPULATION DYNAMICS OF THE CRAYFISH PROCAMBARUS SPICULIFER OBSERVED IN DIFFERENT-SIZED STREAMS IN RESPONSE TO TWO DROUGHTS

Abstract

ABSTRACT Crayfish (Procambarus spiculifer) were studied for 8 years in 3 different study sites. During this period 2 droughts occurred. Consistent changes were observed in response to both droughts and in all study sites. The changes included reductions in both mean body size and abundance and an increase in the juvenile to adult ratio. In response to the first drought, one of the subpopulations changed to a smaller mean body size that was maintained for 5 years (nearly 2 generations) until the second drought caused a second reduction in body size. It is postulated that the reduced size can be maintained by a continued loss of the largest size classes coupled to an increased recruitment of small adults. Two other subpopulations became extinct, one following the 1981 drought and the other during the 1985 drought. The population changes appear related to habitat differences between study sites, differences between reference years and drought years, and the time since the last drought.