Drought-induced Changes in Crayfish Populations along a Stream Continuum

Abstract

Crayfish populations in 2ndand 5th-order streams in NE Georgia varied significantly between sites within 1 year and between years. The 1st year had normal rainfall and the second a severe drought. Of two crayfish species that inhabit the drainage the burrowing species (Cambarus latimanus) showed no significant changes, whereas the nonburrower (Procambarus spiculifer) exhibited large drought-induced population changes, including reductions in adult population densities, resident densities and body size, an alteration in the reproductive timing and an increase in the number of juveniles in the population. I hypothesize that many of the changes in P. spiculifer resulted from their size-dependent preference for deep water sites, and that the reduction of these sites during the drought led to adult emigration and increased predation on larger adults. The distribution of population variables between study sites exhibited the same depth-dependent distribution, the shallower reaches having small populations of small adults and large numbers of juveniles. As the habitat depth decreased during the drought, the above subpopulation properties adjusted spatially, apparently following the physical conditions to which they were adapted. These results agree with the stream continuum concept.