LIFE-HISTORY PLASTICITY OF NEMOURA-TRISPINOSA (PLECOPTERA, NEMOURIDAE) ALONG A PERMANENT-TEMPORARY WATER HABITAT GRADIENT

1. The life history of the small herbivorous stonefly Nemoura trispino sa Claassen was studied in a variety of small springs in southern Onta rio, Canada. Nymphs generally were able to tolerate a wide range of en vironmental conditions and were found in 78% of habitats sampled, alth ough population densities differed markedly. 2. Life-cycle patterns va ried from a univoltine, slow seasonal type to a univoltine, fast seaso nal type with extended egg development. In one, highly stable, spring the life cycle was semivoltine. Inter-year variation was studied for 5 years in one spring and was found to be low relative to among-spring variation. 3. Differences in the life history traits of N. trispinosa populations from our spring series were most probably an expression of phenotypic plasticity rather than of genetic differentiation. 4. Maxi mum annual water temperature was the factor most influential on nympha l growth rate (non-linear relationship), whereas range in generation t ime was related to the degree of habitat permanence.