Endurance tests explain recolonization patterns following hydrological disturbance

Background/Question/Methods

Inundation of floodplain ecosystems makes habitat available and creates pulses in primary production.  Immigration to newly inundated habitats is well documented, but the mechanisms that influence a species’ ability to recolonize successfully are poorly understood.  Recent studies focus on the behavioral changes and directionality of fish movement caused by changing hydrology.  However, recolonization may be limited by physiological performance.  We focus on how intraspecific differences in critical swimming speed (U_CRIT) can explain recolonization patterns following a drying event.  We documented U_CRIT for 20 juveniles and 20 adults of six coexisting species from the Florida Everglades.  Individuals were placed in a Blazka-style swim chamber and allowed to acclimate at a low flow velocity (1-3 BLS) for 30 minutes.  Following acclimation, the flow velocity was increased 2 cm/s every 5 minutes until the fish could no longer maintain station in the tunnel; U_CRIT of each individual was calculated using the time until fatigue.  We tested the full size range of each species to determine any effect of body size.  We then compared the rank order of estimated U_CRIT to the observed recolonization patterns over the past 17 years in the Florida Everglades. 

Results/Conclusions

Spatial-temporal patterns of recolonization were correlated with interspecific differences in sustained swimming ability.  Early colonizers were associated with higher estimates of U_CRIT suggesting high swimming endurance; whereas, species that appear later following a drought had lower estimates suggesting low swimming endurance.  Intraspecific variation in swimming ability was best explained by differences in body size.  Interspecific differences were not explained by differences in body size.  For example, a 26-mm Lucania goodei had an estimated U_CRIT of 15.3 cm/s, while a similar sized Gambusia holbrooki had a U_CRIT of 36.1 cm/s.  A 46-mm Fundulus chrysotus had an estimated U_CRIT of 33.32 cm/s, less than that of a smaller G. holbrooki.  Although the ecological relevance of the critical swimming speed is often disputed, these estimates can provide insight into a species’ ability to respond to a changing environment.  We demonstrate that U_CRIT not only describes a species’ ability to maintain station at certain flow velocities, but may be a metric of dispersal potential.  Our results suggest that endurance tests can be a helpful tool in explaining certain ecological processes.