Cooperative Fish and Wildlife Research Units Program: Arkansas
Education, Research and Technical Assistance for Managing Our Natural Resources

The crayfish Orconectes eupunctus is endemic to the Spring and Elevent Point rivers of Arkansas and Missouri, and appears to have been displaced from a portion of its range by the recently introduced crayfish Orconectes neglectus. Understanding the mechanisms behind this apparent displacement are important to the conservation and management of O. eupunctus. I investigated the role of life history and juvenile competition in the apparent displacement of O. eupunctus by O. neglectus using a combination of sampling, field experiments and laboratory experiments. Life history sampling from July 2005 through December 2006 revealed similar timing of reproductive events and growth rates between these species. Orconectes neglectus females carried significantly more eggs than O. eupunctus females, but a greater proportion of O. eupunctus females were ovigerous. Orconectes eupunctus juveniles survived and grew in stream cages in their former range, implicating biotic interactions rather than habitat degradation in the displacement. In laboratory experiments, O. neglectus juveniles were dominant over O. eupunctus juveniles in the presence of limited food, whereas size rather than species determined dominance in the presence of limited shelter. Orconectes neglectus juveniles did not inhibit growth or reduce survival of O. eupunctus juveniles in a field competition experiment using stream cages. These studies suggest that a mechanism other than competition at the juvenile life history stage is responsible for this crayfish species displacement, and alternate mechanisms, such as differential predation or reproductive interference, should be investigated. Results of my life history sampling should complement and inform these efforts.