Temperature Tolerances and Geographic Distribution of Three Species of Caridina (Decapoda,Atyidae) in Sri Lanka

The biokinetic zones of C. fernandoi, C. simoni and C. pristis were found to be 15–29 °C, 15–27 °C and 13–27 °C respectively, while their respective ranges of distribution were found to be in altitudes of 0–700, 0–700 and 450–850 m. Their responses to low temperatures indicate that all three species are unlikely to occur above 1,000 m. The lower limit of distribution of C. fernandoi and C. simoni extends to altitudes in which the temperature rises above their ultimate upper incipient lethal temperatures (UILT). They appear to avoid high temperatures by moving into cooler waters. C. pristis cannot do so since it lives in very shallow streams; the lower level of its distribution appears therefore to be limited by its UILT.