HABITAT HETEROGENEITY, ENVIRONMENTAL-CHANGE, AND THE CLONAL STRUCTUREOF DAPHNIA POPULATIONS

1. Organisms capable of asexual reproduction often maintain substantia l clonal diversity within their populations. We ask whether such diver sity in Daphnia pulicaria populations is maintained by temporal and sp atial variation in selection. 2. We monitored temporal and spatial var iation in the relative abundance of electrophoretically determined clo nal groups in three lake populations of D. pulicaria from April to Oct ober 1991. 3. Clonal composition differed among lakes, but within each population we observed strong temporal changes in the relative abunda nce of different clonal groups. The timing and rate of this clonal suc cession was associated with the rate of loss of deep water habitat fro m seasonal anoxia. 4. Within each lake, clonal groups also segregated vertically into shallow and deep water assemblages. The magnitude of t his habitat segregation varied temporally and was associated with the abundance of a shallow water competitor species, D. galeata. 5. We sug gest that strong associations of clonal succession and clonal habitat segregation with environmental changes (habitat availability and compe titor abundance) indicate selection operating on the clonal compositio n of these populations.