Seasonal Abundance and Pattern of Chydorid, Caldocera in Mud and Vegetative Habitats

Pattern sampling (Whiteside and Williams 1975) was employed to study the population changes, habitats, and spatial arrangements (pattern) of littoral cladocera in Lake Itasca, Minnesota during 1974. Population dynamics of the 19 most abundant species of chydorids had changes similar to other populations studied in north-temperate lakes. All species had either spring or fall maxima, or both, a mid-summer low in numbers. Population trends were the same for vegetative and mud habitats. In a comparison of Chara vs. mud habitat we found Chydorus piger, Leydigia leydigi, Alona quadrangularis, Pleuroxus aduncus, and Alona circumfibriata to live mainly in littoral mud. Kruzia latissima, Camptocercus rectirostris and Chydorus faviformis were most restricted to the vegetative habitat, while other species were more ubiquitous. Pielou's (1974) terms describing pattern, phase, mosaic, grain, and intensity are discussed. We redefined intensity as describing the visual effect of density. The changes of intensity accompanying changes in density typified 1974 patterns, while no changes in the other parameters were evident. Preliminary experiments exploring the behavior of chydorids suggest that visual stimuli are very important in directing movements, followed by tactile and chemical clues.