Aggressive interactions between the crayfishes Cambarus bartonii bartonii and C-robustus (Decapoda, Cambaridae): Interspecific and intraspecific contests

In the Province of Ontario, Canada, the two closely related crayfish specie s, Camburus bartonii bartonii and Cambarus robustus, appear to have similar habitat requirements and similar, asynchronous life cycles, but largely no noverlapping distributions. The analysis of the interspecific agonistic con tests between size-matched males of these two species showed that C. robust us were clearly dominant over C. b. bartonii of similar size. At the same t ime, C. robustus performed significantly more Lunge and Claws Raised initia tion behaviors than C. b. bartonii, during these contests. These two initia tion behaviors were strongly indicative of dominant status during intraspec ific contests of C. robustus. Cambarus robustus behaved more aggressively t oward C. b. bartonii than toward other conspecifics. Cambarus b. bartonii p erformed significantly more tail-flip escape behaviors than C. robustus. Ju venile C. robustus were dominant over adult C. b. bartonii in a majority of these contests. The clear dominance of C. robustus over C. b. bartonii dur ing agonistic contests, and the apparent recent expansion of the range of C . robustus in Ontario, sometimes at the expense of C. b. bartonii, suggest that C. robustus has the potential to competitively exclude C. b. bartonii, if the two species are in competition for limited resources such as shelte rs.