Diploma Thesis

Invasions and competition in freshwater crayfish communities: Lessons from chiliped injuries

Abstract

Reports of sympatric, feral populations of native European and introduced North American freshwater crayfish species become more and more frequent. These situations may result in the competitive replacement of the European species and interference competition by direct, agonistic behaviour, has been suggested as an important process in this displacement. The frequency of chiliped injuries has been proposed as an indicator of competition intensity. I observed sympatric populations of the European noble crayfish, Astacus astacus (Linnaeus) and the North American signal crayfish Pacifastacus leniusculus (Dana) at different creeks, to test two hypotheses. (i) There is competition between A. astacus and P. leniusculus in sympatric populations. (ii) Interspecific, agonistic interactions in sympatric, feral populations lead to a higher proportion of A. astacus with injured chilipeds depending on the abundance of P. leniusculus. To test these hypotheses I asked two questions: (i) Is abundance of A. astacus negatively correlated with the abundance of P. leniusculus? (ii) Are proportions of chiliped injuries in A. astacus positively correlated with the abundance of P. leniusculus? A negative correlation of the abundances of the two species was found, while no correlations between frequencies of chiliped injuries and species abundances were indicated. The results of this study indicate competition between A. astacus and P. leniusculus under different environmental conditions. But they challenge the importance of agonistic, interspecific behaviour in these competitive situations. At least my findings suggest, that the frequency of chiliped injuries is a doubtful indicator for intensity of competition in crayfish communities.

Publications

Schmidt,T.: Ist die Häufigkeit von Extremitätenverletzungen ein Hinweis auf die Verdrängung von Astacus astacus (L.) durch Pacifastacus leniusculus (Dana.)?, in proceedings 4. Internationales Symposium Flusskrebsforum 2009: 79 - 83, ed. forum flusskrebse, 2009.

Schmidt, T., Hösler, C., Siewert, W.: Kampf um die Höhle - Konkurrenzmechanismen in der Verdrängung des Edelkrebses durch den Signalkrebs: Ein Modellansatz, in proceedings 4. Internationales Symposium Flusskrebsforum 2009: 75 - 78, ed. forum flusskrebse, 2009.

Links

gecologic - Geoökologisches Büro [www.gecologic.de]

Advanced Studies on Ecological Modeling [www.asoem.org]

forum flusskrebse [www.forum-flusskrebse.org]

Unexpected voluntary assistance with my field protocols (young male signal crayfish).