Interspecific shelter competition between the sympatric crayfish species Procambarus clarkii (Girard) and Procambarus zonangulus (Hobbs and Hobbs)

Aggressive interactions and shelter possession were used to examine interspecific competition between Form I males of the sympatric crayfish species Procambarus clarkii and Procambarus zonangulus. Paired encounters were staged between heterospecifics, using a type of shelter shown to be equally preferred by both species. On Day 1, each heterospecific intruder encountered a resident P. clarkii or P. zonangulus, which had been occupying the shelter for the previous 24 h. Each pair remained in the resident's tank for 48 h after the initial encounter was settled, in order to determine subsequent shelter possession. Results indicated a significant prior residence advantage on Day 1 for resident P. clarkii, but not for resident P. zonangulus. Furthermore, on Days 2 and 3, resident and intruder P. clarkii were in possession of the shelters in a significantly higher proportion of cases than opponent P. zonangulus, reflecting an eventual species dominance advantage by P. clarkii. The influence of this competitive advantage on the differential prevalence of these species in the natural environment remains to be explored.