Exposure, body size, and zooplankton overland dispersal capacity

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AbstractThe dormant life stages of freshwater zooplankton are generally resistant to environmental exposure, and this facilitates their overland dispersal. However, environmental exposure and overland dispersal are less well studied for the active life stages of freshwater zooplankton. To characterize empirically the longevity of active life stages out of water, survival time to air exposure was measured in the laboratory for seven cladoceran species using heartbeat cessation to signify survival time. Survival time increased with body dry weight with an allometric scaling exponent near 2/3 in both a single‐species model with Daphnia mendotae and a multispecies model with five bivalved species that included Bosmina longirostris, Acroperus harpae, Ceriodaphnia dubia, D. mendotae, and Daphnia magna. The 2/3 scaling exponent is consistent with Euclidean geometry and points to water loss across the surface of a spherical body as the cause. Survival time of a 6th species, Holopedium gibberum, was 618% longer than predictions based on the multispecies model, likely due to its gelatinous mantle. Survival time of a 7th species, Bythotrephes cederströmii, was 58–83% shorter than predictions based on the multispecies model, likely due to its lack of a bivalve carapace. The longest survival time of an individual was 225.4 min (H. gibberum). Results suggest that at landscape scales, body size could be a proxy for the geographic extent of overland dispersal capacity of the active life stage.