Landscape Influences on Cues and Spatial Scales of Fish Dispersal in Response to Drought Disturbance

A great deal of empirical work remains to be done on the cues and spatial scales of dispersal responses to changing environmental conditions.  Landscape structure can influence patterns of dispersal by affecting the strength of dispersal cues, distance between habitat patches, and resistance to movement during transit between patches.  To survive seasonal droughts in the Florida Everglades, large predatory fishes must disperse to deep-water refuges.  Underlying topographic relief and human-caused alterations to the landscape create spatial-temporal variability in the spatial extent and severity of droughts.  To investigate the spatial scale of fish response to fluctuating water levels, we used radio telemetry to quantify dispersal patterns of Florida gar, an important Everglades piscivore.  We were interested in determining the environmental cues of dispersal and factors influencing the spatial scale of dispersal responses.  Individuals were tagged with radio transmitters and released across a variety of locations in the Everglades landscape that varied in hydrology and distance to refuge habitats.  Patterns of dispersal initiation varied among individuals and were related to influence of landscape position on local hydrologic conditions.  Individuals in habitat patches that experienced relatively rapid rates of environmental change and underwent large drops in water level tended to disperse earlier in the dry season than individuals in patches where water level changed less and more slowly.  The spatial scale of the dispersal response increased somewhat with fish size, but was more strongly affected by spatial positioning of individuals on the landscape.  Dispersal distance increased with rate of decline in water level, severity of dry-down, and distance to refuge habitats.  The landscape exhibited greater resistance to fish movement (i.e., slower movement rates) when individuals dispersed against the grain of the landscape.  Florida gar selected a variety of refuge habitats, with individuals settling in canals, coastal rivers, airboat trails, and marsh sloughs.  Resolution of how relationships between landscape features and disturbance patterns influence dispersal responses is critical for understanding spatial scales of ecological interactions and predicting responses of aquatic organisms to environmental change brought about by water management and climate change.